Abstracts of papers presented at the first Israeli-Italian phytopathological symposium

M E E T I N G

ABSTRACTS OF PAPERS PRESENTED AT

T H E F I R S T I S R A E L I - I T A L I A N P H Y T O P A T H O L O G I C A L S Y M P O S I U M

February 13-15, 1989 Bet Dagan, Israel

INVITED LECTURES

PLANT PATHOLOGY IN THE MEDITERRANEAN REGION A. GRANITI

CURRENT AND FUTURE RESEARCH AND EXTENSION TRENDS IN PHYTOPATHOLOGY IN ISRAEL

J. KATAN

A: RUSTS AND DOWNY MILDEWS

UP-DATED REGIONAL HOST-DOWNY MILDEW CHECKLISTS: A NECESSITY

R. G. KENNETH Dept. of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem,

Rehovot, Israel

Through examination of national host-pathogen checklists and monographs of Peronosporaceae (the Downy Mildews = dm), we found that Mediterranean semi-arid countries may be surprisingly well represented. This is on the basis of number of dm genera present (Israel: seven out of eight accepted genera), number of plant families in which dm was recorded (Israel: 28 for Peronospora), and number of plant genera with dm within a family (Israel: 15 out of the 31 known host genera of Leguminosae with Peronospora). For Italy, a Mediterranean country, the figures are 6, 30 and 11, respectively, using Berlese's Ieonographia (1898) and Ciferri 's List (1961). These figures compare well with those of temperate-climate countries: highest for families with Peronospora (Rumania: 34) and for legumes with Peronospora (Germany: 22).

Phytoparasitica 17:2, 1989 131

The data are incomplete, as many countries have checklists that do not include dms, ignore wild plants, or else, however excellent, are very old, e.g. Japan (1936). Only last year, for instance, an update of the British list of 1959 changed from 17 to 32 the number of host families with Peronospora.

One finding, with Plasmopara, points to the need to update and include more details in checklists. Ciferri listed plants from ten genera of Umbelliferae as hosts in Italy, yet Israel, Jordan, Turkey and even neighboring Greece have none reported, in spite of the known presence of long-lived oospores that could have facilitated transfer. As Ciferri did not mention localities within Italy, could it be that Pl. nivea attacked plants only in a non- Mediterranean region of Italy, and that it is incapable of surviving in semi-arid lands? We hope to clarify this through cooperation with Italian colleagues. We furthermore suggest an international effort to collate data on world-wide dm distribution to establish potential climatic limits of the pathogens; a terminal and repository for information should be chosen; and analyses revealing interesting findings and correlations could be made available by publication of results.

EVOLUTION OF HOST-PARASITE SYSTEMS IN BARLEY LEAF RUSTS

Y. ANIKSTER, J. MANISTERSKI and I. WAHL Dept. of Botany, Faculty of Life Sciences, Tel.Aviv University, Ramat Aviv 69978, Israel

In Israel the indigenous wild Hordeum spp. are parasitized by Puccinia hordei and several Uromyces spp. All rusts are heteroecious and alternate with indigenous Liliacieae plants. The results have co-evolved from antiquity with the main and alternate hosts in the center of their origin and have reached the stage of balanced polymorphism. The sporophytic stage is limited to the genus Hordeum, while P. hordei alternates with Ornithogalurn spp., Dipcadi erythraeum and Leopoldia eburnea The Uromyces rusts alternate with Bellevalia spp., Scilla spp., Muscari parviflorum and L. eburnea. Apparently, unlike P. graminis and P. coronata, the barley rusts have biogenetically radiated from the main to the alternate hosts. In the process of long regressive evolution, Uromyces spp. developed on the alternate hosts microcyclic correlated species and are phylogenetically more ancient than P. hordei lacking microcyclic descendents.

The assumed plurivorous nature of ancient rusts is retained in L. eburnea, which is compatible with all barley leaf rusts and their microcyclic descendents.

Only rust organisms developing on H. spontaneum are congenial with cultivated barley and important in leaf rust epidemics on H. vulgare, and only resistance from H. spontaneum can be utilized in barley breeding.

RESEARCH ON PUCCINIA RECONDITA IN ISRAEL

J. MANISTERSKI, Y. ANIKSTER and I. WAHL Dept. of Botany, Faculty of Life Sciences, Tel-Aviv University, Rarnat Aviv 69978, l~rael

Israel serves as a.center of origin and diversification for wheat, several of its close relatives and some of its obligate parasites. Assuming a co-evolution process of hosts mad

132 Phytoparasitica 17:2, 1989

parasites, there is special interest in studying this system in ~ country. Leaf rust e .aut~ by Puccinia recondita, a world-wide problem, attacks manually cultivated wheat, the wild r Trit&um turgidum var. dicoccoides and Aegilops spp.

Studies in Israel have shown virulence of P. recondita tritici on numerous reahttane~ genes of the Lr series. Only genes Lr 2a, Lr 9 and I i 24 have shown resistance to all isolates. The parasite population is composed of many biotypes, Recent studies have shown an enlarged range of pathogenicity, i.e., virulence on resistance genes lar 2at and I I 26 that originate from rye, as found lately in Mediterranean countries and in other parts of the world.

Intensive research on the P. recondita complex has led to the conclusion that Itar~ organisms exist, with the following life cycles: (i) A cycle from cultivated wheats, Triticum aestivum and T. durum, or wild cromer, T.

dicoccoides, to the European Thalictrum speciosissimum. (ii) From Aegilops longissima and A. variabilis to Anchusa aggregata. (iii) From Aegilops ovata to Echium glomeratum.

Several Anchusa spp. and Echium spp. carry pycnia and aecia annually in nature. A new major host, Hordeum marinum, was found infected by leaf rust. Under controlled

conditions, teliospores from it were compatible with Thalictrum, aeciospores formed, and infected T. aestivum as well as H. marinum. H. marinum was resistant to aeciospores from Anchusa and Echium or urediospores from Aegilops spp.

The wide dispersal of genes for virulence and eompatability of Thalictrum with isolates from different parts of the world attests to the universality of the leaf rust disease.

BIOLOGY AND EPIDEMIOLOGY OF PINE RUSTS IN ITALY

A. RAGAZZ[, E MORIONDO ~d B. NALD/NI LONGO Istituto di Patologia e Zoologia Forestale e Agraria, and Centre di Studio per la Patologia delle Specie

Legnose Montane, Firenze, Italy

In Italy there are three macrocyclic and heteroecious rusts on Mediterranean pines: (i) Cronartium flaccidum (Alb. et Schw.) Wint. (= blister rust), with the pycnio-aecial

stage on Pinus pinea L., P. pinaster Ait. and P. halepensis Mill., and the uredial- telial stage on Vincetoxicum hirundinaria Med. and Paeonia spp. Other pine species infected by the fungus are: P. nigra Am., P. laricio Poir., and sporadically P. sylvestris L.

(ii) Melarnpsora pinitorqua (Rostr.) (= twist rust), with the pycnio-aecial stage on P. pinea, P. pinaster and P. halepensis; and the uredial-telial stage on Populus tremula L., P. canescens Sm. and P. alba L. Other pine species infected by the fungus are: P. sylvestris and P. nigra, the latter only on herbaceous seedlings.

(iii) Coleosporium spp. (= needle blister rust), with the pycnio-aecial stage on P . halepensis, P. pinea and P. pin, aster; and the uredial-telial stage mostly on Senecio spp. and Inula spp. Pycnia and aecia are produced on branches and stems of C. flaccidum, on shoots of M.

pimtorqua, and on needles of Coleosporium spp. Uredia and telia appear on the lower surface of the leaves of the alternative hosts. The infections of C. flaccidum on pine needles occur in summer, following an incubation period which can vary from 2 to 5 years. Aecia appear on branches during the spring. The systemic infections are perennial on pines. The infections of


M. pinitorqua occur during spring, after an incubation period which varies from 10 to 15 days. The rust overwinters as telia on leaves of Populus spp., and as systemic myoelium on young poplar shoots. C. flaccidum is very aggressive both for young and old plants. The susceptibility of pines to twist rust is very high on young plants up to 3 m tall.

THE LIFE CYCLE OF PUCCINIA ALLH, THE CAUSAL AGENT OF GARLIC RUST IN ISRAEL

Y. ANIKSTER

Dept. of Botany, Faculty of Life Sciences, Tel-Aviv University, Ramat Aviv 69978, Israel

Cultivated garlic, Allium sativum L., is attacked annually by the autoecious rust fungus Puccinia allii Rud. In Israel only the uredial and the telial stages appear in cultivated garlic fields. Uredia can be found from the end of January, followed by a later appearance of telia. In the absence of fungicide treatments, almost all leaves are covered with the rust by the end of the growing season, in the spring.

Wild leek, Allium ampeloprasum, which grows in nature in Israel and other Mediterranean countries, was found to sustain all stages of P. allii. In reciprocal inoculation experiments under controlled and natural conditions, with basidiospores, aeciospores and urediospores secured from A. ampeloprasum and cultivated garlic, both hosts were infected. Cultivated leek was also infected readily by rust from both sources.

In Israel the annual start of the rust life cycle occurs in A. ampeloprasum 6-8 weeks before the start of epidemics in cultivated garlic fields. It appears that aeciospores and urediospores produced on the wild species are the primary source for infections of cultivated garlic.

B: BIOCONTROL AGENTS: PHYSIOLOGICAL ASPECTS AND ACTIVITY

MECHANISMS INVOLVED IN BIOLOGICAL CONTROL BY TRICHODERMA SPP.

I. CHET 1 , A. ORDENTLICH 1, Q. MIGItELI 2 and A. SIVAN 1 I Dept. of Plant Pathology and Microbiology, The Itebrew University of Jerusalem, Faculty of Agriculture,

Rehovot, Israel; and 2lstituto di Patologia Vegetale, Universitd degli Studi, Torino, Italy

Isolates of Trichoderma harzianum antagonistic to Sclerotium rolfsii, Rhizoctonia solani and Pythium spp. were isolated and selected from field soils. The isolates producing effective results in the greenhouse were grown by a semi-solid fermentation technique on wheat bran:peat (1:1 w/w) and applied to the seedling's potting mixture or as a seed coating. Significant reduction in disease incidence was observed. Studying the mechanism involved in disease reduction revealed that Trichoderma acts as a mycoparasite. Apparently it detects its host from a distance and chemotropic growth can be observed. It "recognizes" and attaches to the pathogenic fungus by sugar-lectin linkage and begins to excrete extracellular lytic


enzymes such as 13-1,3-glucanase, chitinase, protease and lipase. However, T-35 did not show antagonism in dual culture even though it was effective in soil against Fusarium in melon, cotton and tomato. It appears that the mechanism there is competition rather than mycoparasitism. Recently more than 80 strains of Trichoderma spp. were isolated from soil samples of different geographical origin and tested for their antagonistic ability against Fusarium spp. in dual culture. Two of the most active isolates were tested for their mycolytic activity in comparison with the T-35. Indeed the differences in [:~-l,3-glucanase and chitinase production among the isolates were significant, thus indicating that several mechanisms may be involved in the biological control of Fusarium.

STUDIES OF THE MECHANISM OF SUPPRESSIVENESS OF A SOIL AGAINST FUSARIUM OXYSPORUM F. SP. DIANTH1

A. GARIBALDI lstituto di Patologia Vegetale, Universitd degli Studi, Torino, Italy

Fusarium-suppressive soils were found in different regions of Italy and the microbial nature of suppressiveness was demonstrated. Suppressiveness involves the role of nonpathogenic strains of Fusaria. Carnation plants grown in soil infested with antagonistic Fusaria and F. oxysporum f. sp. dianthi had less infection than plants grown in the .presence of the pathogen alone. The number of propagules of F. dianthi isolated from soil contaminated with the pathogen alone or with the pathogen and the antagonistic Fusaria was similar. However, in the rhizosphere of carnation plants, the number of propagules of the pathogen obtained from plants grown in the presence of the antagonists was 10% of the number obtained from roots of plants inoculated with F. dianthi only. The observations carried out on root colonization in steamed soil indicate that F. dianthi is much more likely to form a colony at the surface of the carnation root in the absence of antagonistic Fusarium. The antagonistic Fusaria applied to melon and tomato seeds were able to colonize the rhizosphere more than 10 cm from treated seeds in untreated soil. The addition of benomyl enhanced the growth of antagonistic BCM-resistant Fusaria on the roots of different plants. These antagonistic organisms evinced a high root-colonizing ability.

ENZYMES INVOLVED IN GERMINATION OF TRICHODERMA HAMATUM SPORES

LEA NOL and Y. HENIS Dept. of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture,

Rehovot, Israel

Germination of Trichoderma hamatum phialospores, expressed as germ tube emergence, did not occur when the spores were incubated in a synthetic medium at 30~ for 22 h at a concentration of >2"108/ml. On the other hand, 100% germination was obtained when spore concentration was reduced to <2"107/mi, The possible role of trehalase, 13-1,3 glucanase

and I$-glucosidase in the germination of T. hamatum spores was studied. Trehalase was detected in cell-free extracts of both dormant and germinating T. hamatum spores. The optimum conditions for its activity were pH 3 and 50-60~ In high-density spore


suspensions incubated in synthetic medium, trehalase activity remained unchanged for 5 h of incubation, as compared with dormant spores. On the other hand, at low spore concentrations, enzyme activity increased during the first hour of incubation, remained at a high level for 2 h, and then returned to the initial level. [3-1,3-glucanase and [3-glucosidase activities were detected in beth cell-free extracts and walls of T. hamatum spores, being most active at pH 5 and 50-60~ In cell-free extracts of spores incubated at high density in synthetic medium for 5 h, the activity of both enzymes remained unchanged as compared with the dormant spores. At the lower spore density, activities of both glucanases declined during the incubation period, but starting from the third hour 13-glucanase activity increased, and returned to the initial level toward the end of the incubation period. On the other hand, the activity of both enzymes in cell-wall preparations of T. hamatum spores remained unchanged during incubation at low densities in synthetic medium. However, upon incubation with cell- free extracts or with Novozyme, these cell-wall preparations released substantially more sugars than did the walls of the unincubated control.

It is suggested that during incubation at the lower densities germ tube emergence is initiated by increased trehalase activity, and that prior to germ tube emergence the spore wall enzymes and/or polysaccharides undergo changes in activity and/or availability, resulting in enhanced enzymatic degradation of the spore wall.

PROTOPLAST FUSION: A USEFUL TOOL FOR IMPROVEMENT OF TRICHODERMA AS A BIOCONTROL AGENT

SARA PE'ER and I. CHET Dept. of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture,

Rehovot, Israel

Trichoderma harzianum serves as a biocontrol agent against soilborne plant pathogenic fungi. Individual strains of Trichoderma obtained through selection or mutation possess one or a few desirable traits, but none has several of the attributes required to realize the full potential of these beneficial fungi. Since our Trichoderma has no sexual stages, protoplast fusion techniques were used.

Auxotrophic mutants of T. harzianum Rifai (ATCC) 32173 were combined by protoplast fusion, and fusion progeny were isolated by forced nutritional complementation. Conidia from four prototrophic colonies showed a high frequency of nonparental type colonies. Conidia from the other prototrophic colonies were nearly all auxotrophic. The antagonistic ability of prototrophic strains and parental strains against the soilborne pathogenic fungi Rhizoctonia solani, Sclerotium rolfsii and Pythium aphanidermatum was evaluated by testing their ability to overgrgw the pathogenic fungi colonies in dual culture. The prototrophic strains varied in their antagonistic abilities against a number of pathogenic fungi. The prototrophic strain A2 overgrew all the pathogenic fungi more rapidly than did the parental strains. In the greenhouse, prototrophic strain A2, applied to the R solani-infested soil, effectively controlled damping-off of cotton seedlings as compared with the parental strains. It appears that protoplast fusion can serve as a useful tool to combine desirable traits from parental strains to produce better biocontrol agents.

136 Phytoparasitica 17:2. 1989

AMPELOMYCES QUISQUALIS: A BIOCONTROL AGENT OF POWDERY MILDEWS UNDER FIELD CONDITIONS

A. SZTEJNBERG Dept. of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture,

Rehovot, lsrael

Effective biocontrol of cucumber, zucchini, carrot, mango and apple powdery mildew (PM) was obtained through hyperparasitism by Ampelomyces quisqualis (AQ) applied as a bio-fungicide suspension of 1 • 106 spores/ml, in greenhouse and field experiments. In one greenhouse trial, treating PM of cucumber with AQ alone significantly decreased disease severity and also increased cucumber yield by 50%. A greater increase in yield was obtained by applying the fungicide pyrazophos alone or in combination with AQ. In a second trial all chemical and biocontrol treatments increased the yield over the untreated control, which did not produce fruits. In a field experiment where PM on carrot was treated wiih AQ, plants with hyperparasitized PM remained more vital than those with unparasitized PM, although both had similar PM coverage. In a field trial treating zucchini PM with AQ or with any one of five recommended fungicides, the yield obtained from the AQ treatment was similar to that obtained from all but one of the fungicide treatments. The yield increase was 39%, significantly higher than the untreated control. In an organically farmed mango orchard, the experiments were done in two consecutive years and PM of mango was treated with AQ or sulfur. Yield and number of mango fruits per tree were higher in the AQ treatments than in the sulfur treatments and significantly higher than in the untreated control: by 54--62% in the first year and by 35% in the second year. High hyperparasitism and reduction of PM by AQ were achieved in an apple orchard trial. It is concluded that AQ might be an effective biocontrol agent for PM under field conditions.

C: DIAGNOSTICS OF PLANT PATHOGENS

APPLICATIONS OF SCANNING ELECTRON MICROSCOPY IN PLANT PATHOLOGY

1L I.X~CI Chair of Mycology, University of Udine, Udine, Italy

Although developed at the same time as transmission electron microscopy (TEM), scanning electron microscopy (SEM) initially developed rather slowly until the late 1960s, when it enjoyed an unexpected boom and thereafter increasing popularity, even in biology. Applications of the technique in plant pathology and related fields in Italy during the last 20 years were reviewed and considered. In particular, we covered the evaluation of microbial growth on plant surfaces, effects of saprophytes and pathogens on the outer aerial surfaces, dynamics of phytopathogenic processes by fungi and bacteria, investigations on the devdopmental cycle of pathogenic and saprophytic fungi, generic identification of filamentous fungi, evaluation of seed contamination, detection of the dormant or active status

of some microorganisms in soil, phenomena of mycoparasitism, etc. Examples of utilization


of signals, other than secondary electrons, deriving from the electron beam - - sample interaction (X-ray, cathodoluminescence, etc.), were drawn up. The advantages and disadvantages of SEM in respect to light microscopy and to TEM were considered. Although SEM has contributed notably to advancements in plant pathology, best results are obtained by using a combination of various observation techniques

RECOGNITION OF BACTERIA BY PLANTS: THE LOCALIZED CELLULAR REACTION

PAOLA MINARDI, E. STEFANI and U. M~UCCHI lstituto di Patologia Vegetale, Universitd di Bologna, Bologna, Italy

Pretreatment of tobacco leaves with protein-lipopolysaccharide complexes (pr-LPS) prevents the hypersensitive reaction (HR) and prevents or delays the susceptible reaction (SR) towards challenging phytopathogenic bacteria. A localized cellular reaction (LCR) is induced following pr-LPS injections. Ultrastructurally, the LCR becomes visible 4 h after infiltration at points opposite the intercellular structured deposits on the plant cell wails, reaches a peak at~ h and disappears by 48 h. At 12, 24 and 48 h the plasmalemma of treated cells was locally separated from the wall and convoluted. The distance from the cell was maximal at 24 h, whereas the convolution was more obvious at 24 h and disappeared at 48 h. The cytoplasmic and periplasmic vesiculation can be interpreted as an expression of the exocytosis process induced by pr-LPS injection. Moreover, the increase in conductivity, calcium ions, sugar, uronic acids and protein in the intercellular fluids of the pr-LPS-injected tissue was interpreted as a direct or indirect effect of the LCR. Furthermore, in the treated tissue at 48 h, the intercellular fluid peroxidase activity was doubled compared with the control. At 48 h after infiltration with pr-LPS, the intercellular fluid SDS-polyacrylamide gel electrophoresis revealed a new protein absent in the control fluid and in the pr-LPS complexes at 0 and 48 h. At the same time the duroquinone-dependent NAD(P)H dehydrogenase activity of tobacco mesophyll microsomes was assayed at 0, 24 and 48 h after infiltration with pr-LPS complexes (treated tissue) and with water (control tissue). This activity occurred in different membranes but it appeared to be located mainly in particles with the properties of the plasmalemma. Moreover, at 48 h it was three times higher than in the control microsomes. These phenomena can be correlated, directly or indirectly, to the LCR.

MOLECULAR BASIS OF PATHOGENICITY IN ERWINIA HERBICOLA PV. GYPSOPHILA

SHULAMIT MANULIS 1 , ELLEN CLARK 2, Y. OPtlIR 2 and Y. GAFNI 2 1Dept. of Plant Pathology and 2Dept. of Plant Genetics, ARO, The Volcani Center, Bet Dagan, Israel

Erwinia herbicola pv. gypsophila (E..h.g.) is a bactorial phytopathogen which generates galls on its host, and has had a serious impact on propagation of the flowering ornamental Gypsophila paniculata in Israel. We are examining the role of indoleacetic acid (IAA) biosynthesis by this pathogen in generating disease symptoms. Pathogenic strains of E.h.g. produce IAA when cultured in minimal media supplemented with L-tryptophan, while no IAA could be detected in a nonpathogenic strain used as a control in these experiments.

In DNA hybridization experiments it was found that E.h.g., like both Agrobacterium tumefaciens and Pseudomonas savastanoi, possesses sequences directing IAA biosynthesis


which are located on a plasmid. However, infection of Gypsophila paniculata by E.h.g. does not result in neoplastic transformation of the host cells, as is the case of infection by A. tumefaciens.

A DNA fragment that exhibits homology to the A A genes of P. savastanoi was cloned from a larnbda library of E.h.g. plasmid DNA. A 7.5 kb fragment was further subcloned into pUCl l8 plasmid in both orientations. Both plasmids direct IAA biosynthesis in transformed E. coli cells. Further work will determine the relationships between IAA production and Pathogenicity of E.h.g.

THE USE OF MONOCLONAL ANTIBODIES FOR THE DIAGNOSIS OF PLANT VIRUSES

MARINA BARBA Istituto Sperimentale per la Patologia Vegetale, Roma, Italy

Monoclonal antibodies (MCAbs) have been used recently for the diagnosis of plant viruses in Italy. In our laboratory monoclonal antibodies have been produced against Cucumber mosaic (CMV) and Grapevine clostero type III viruses. Production of grapevine fanleaf virus (GFV), apple mosaic virus (ApMV), grapevine virus A (GVA) and Grapevine clostero type I MCAbs is in process. The results obtained until now show that CMV MCAbs were able to differentiate two groups of the following virus isolates: anemone, daisy, tomato, pepper, bean, eggplant. When compared with polyclonal antibodies, the closterovirus type III MCAbs showed a higher sensitivity in the detection of the virus directly in grapes collected in the field.

EPIDEMIOLOGICAL STUDIES OF MAL SECCO DISEASE OF CITRUS THROUGH CLONED PROBES AND POLYMERASE CHAIN REACTION

F. ROLLO 1 , A. CATARA 2, A. AMICI 3 and I. DI SILVESTRO 3 1Dept. of Cellular Biology , Camerino," 2Institute of Plant Pathology, University of Catania, Catania; and

3AID Research Center, Catania, Italy

A virulent strain of Phoma tracheiphila was used to obtain DNA probes for the detection of the fungus. Total fungal DNA was EcoR1, and shot-gun cloned into a pBR322 vector. In order to select P. tracheiphila-specific clones, the resulting library was repeatedly screened against homologous and heterologous DNAs. In this way a recombinant clone (pPhoB25) was singled out. The selected probe was thoroughly tested against the DNAs isolated from 62 fungi belonging to 21 genera, among which there were eight species of Phoma, and against plant DNA extracted from 16 species and varieties of citrus. The probe enabled us to detect approximately 20 pg fungal DNA and was used successfully to recognize 54 different isolates of the pathogen. It was employed to test hundreds of samples collected from the greenhouse and field. In order to increase the sensitivity of the test, a derivative of pPhoB25, capable of generating a riboprobe, was produced. However, only minor improvements of the test were obtained by this artifice.

Eventually, a polymerase chain reaction (PCR) system was employed to detect and characterize P. tracheiphila DNA. The PCR system was designed on the basis of a 102 bp

Phytoparasitica l 7.'2, 1989 13 9

nucleotide sequence derived from the pPhoB25 fungal insert. With the PCR we were able to detect elusive (0.01 pg) amounts of P. tracheiphila DNA iv plant and soil samples.

SEROLOGICAL DIFFERENTIATION OF PHYSIOLOGICAL RACES OF FUSARIUM

OXYSPORUM SCHLECHT F. SP. DIANTHI (PRILL ET DEL.) SNYD. ET HANSEN

E SCALA, 1L CAPPARELLL D. IANNELLI and C. NOVIELLO Institute of Plant Pathology, University of Naples, Portici (NA), Italy

During the last few years our laboratory has attempted to develop serological tests useful for the classification and differentiation of isolates belonging to the genus Fusarium. Monoclonal antibodies raised against spores of Fusaria enabled us to detect differences at the level of species and formae speciales. Monoclonal antibodies displayed extensive cross- reactions toward closely related target cells. The above differences were therefore only quantitative. To overcome this limitation two different approaches were used: one based on the immunization of mice with a purified protein, and the other based on the tolerance of mice with one cell type followed by immunization with another cell type.

The electrophoretic patterns of extracts from eight different pathotypes of F . oxysporum f.sp. dianthi were analyzed. Pathotype 2 displayed a unique band; this band was recovered from the gel and used to immunize one mouse. Monoclonal antibodies raised against this single protein reacted with pathotype 2 much more strongly than with other pathotypes.

To increase the fraction of antibodies that differentiate selectively among pathotypes, ten newborn mice were rendered tolerant with pathotype 1 and, at the age of 4 weeks, immunized with pathotype 2. Five mice were immunized by the intraperitoneal route and five by the intrasplenic route. All five of the mice of the former group reacted the same against the tolerance-inducing as well as the immunizing pathotype; two of the five mice of the latter group reacted against the immunizing pathotype much more strongly than against the tolerance-inducing one.

THE ROLE OF EPICUTICULAR WAX OF AVOCADO FRUIT IN APPRESSORIA FORMATION OF COLLETOTRICHUM GLOEOSPORIOIDES

D. PRUSKY and H. SAKA Dept. of Fruit and Vegetable Storage, ARO, The Volcani Center, Bet Dagan, Israel

Twelve hours after Colletotrichum gloeosporioides inoculation of the peel of freshly harvested avocado fruits, 97% of the conidia had germinated and most had formed appressoria. Seventy-two hours after inoculation, appressoria had germinated, penetrated the cuticle and reached the epidermal cells. Symptoms of disease were observed 10 days after harvest.

Inoculation of the flesh of freshly harvested avocado fruits showed a germination timing similar to that in intact peel, but no appressoria were formed. Symptoms of disease were observed 2 days after harvest.

The role of epicuticular wax in intact fruit was considered in relation to quiescence of C. gloeosporioides and the changes of the antifungal diene.


D: PHYSIOLOGY AND BIOCHEMISTRY IN PLANT PATHOLOGY

PHYSIOLOGY OF SCLEROTINIA SCLEROTIORUM: THE ROLE OF FUNGAL METABOLITES IN PATHOGENESIS AND IN HOST RESPONSE TO INFECTION

P. MAGRO 1, P. MARCIANO 2 and F. FAVARON 2 llstituto di DO~esa delle Piante, Universitd della Tuscia, Viterbo and 21stituto di Patologia Vegetale,

Universitd di Padova, Padova, Italy

Sclerotinia sclerotiorum (Lib.) de Bary, like many other pathogenic micro-organisms, produces oxalic acid (OxA), and a number of cell wall-degrading enzymes, both in vitro and in vivo. The results of a 5-year research project on the role of these fungal metabolites in S. sclerotiorum pathogenesis and in host response to infection have shown a positive correlation between in vivo production of OxA and virulence. The different levels of OxA produced by the virulent and hypovirulent isolates do not seem to derive from different capabilities of oxalate decarboxylation. In fact, the mycelia of both isolates contain equivalent amounts of oxalate decarboxylase. The presence of high levels of OxA in host tissues lowers their pH. These low values of pH are optimal for the activity of polyphenoloxidases, enzymes which are involved in the plant's defense system.

Polygalacturonase (PG) and the complete set of cellulolytic enzymes are secreted in vivo as several molecular forms, each of them acting as a random or terminal type enzyme. Cellulolytic enzymes enable the pathogen completely to degrade insoluble and soluble forms of cellulose. OxA and some molecular forms of PG produced by S. sclerotiorum during soybean infection elicit synthesis of the phytoalexin glyceollin I. Maximum accumulation of glyceollin was achieved with a 5 mM treatment, while higher concentrations of OxA decreased phytoalexin accumulation. Elicitor activity was exhibited in the range of concentrations assayed (0.15-1.2 reducing units/ml), by PG II and PG IV, two endo-PG isoenzymes present in soybean hypocotyls colonized by S. sclerotiorum.

In conclusion, PG and OxA may play an important role in pathogenesis, but also may be involved in resistance against plant pathogens behaving as a trigger for phytoalexin production.

FUSARIUM SPECIES AND THEIR MYCOTOXINS IN CEREALS

A. BO'ITAL1CO 1, A. VISCONTI 2 and A. LOGRIECO 2 IDipartimento di Patologia Vegetale dell' Universit& degli Studi," and 2lstituto Tossine e Micotossine da

Parassiti Vegetali del Consiglio Nazionale delle Ricerche, Bari, Italy

Surveys of cereals (infected plants and stored grains) for Fusarium species and their mycotoxins were carried out on samples collected from various countries.

Samples of corn stalk and ear rot standing in the field and collected mainly in southern Italy, proved to be contaminated with zearalenone (ZON), zearalenol (ZOL), and deoxynivalenol (DON). The Fusarium species most frequently isolated were: F. miniliforme, C. culmorum, F. equiseti, F. proliferatum and F. graminearum. Samples of corn kernels from F. graminearum -infected ears in Auslxia were found to be contaminated with ZON, DON,


fusarenone, nivalenol, and 3-acetyldeoxynivalenol (3-AcDON). Samples of corn ears from Poland, heavily infected by F. sporotrichioides, were contaminated with several type A trichothecene derivatives, namely, T-2 toxin, HT-2 toxin, T-2 tetraol, neosolaniol, and T-2 triol. In addition, samples of Polish wheat infected in the field by F. culmorum and F. graminearum were contaminated with DON and 3-AcDON, and a high correlation was found between the concentration of these two toxins and the severity of wheat head fusariosis.

A survey was carried out on a total of 102 samples of stored cereal grains (wheat, barley, rice, oat, rye and corn) originating from various Mediterranean countries (Egypt, France, Greece, Italy, Lebanon, Portugal, Turkey and Yugoslavia). The Fusarium species most frequently isolated were: F. culmorum and F. graminearurn from wheat; F. moniliforrne and F. proliferatum from corn; and F. semitectum from rice. The analyses of some visibly colonized samples showed the occurrence of DON in barley, wheat and corn, and of ZON in barley and c o r n .

These findings suggest that the occurrence of Fusarium mycotoxins in infected plants, as well as in stored and commercial grains, is a real problem both in central European and in Mediterranean countries.

SCREENING FOR VERTICILLIUM TOLERANCE IN POTATO

A. NACHMiAS, JANNETE ORENSTEIN and L. LIVESCU Dept. of Plant Pathology, ARO, Gilat Experiment Station, Negev, Israel

Verticillium wilt, caused by Verticillium dahliae Kleb., is a major disease of economic importance in numerous crops, including tomato, potato, cotton, hops, alfalfa, tobacco and eggplant, causing yield losses of up to 50%. Chlorosis, followed by necrosis of leaf laminar tissue, occurs at a relatively large distance from the pathogen, suggesting that all or part of the wilt syndrome may be caused by a translocatable phytotoxin. Verticillium spp. elaborate in culture numerous high- and low-molecular-weight non-enzymic phytotoxie substances that have been implicated in the Verticillium wilt syndrome. Such phytotoxic compounds have a potential for selection of plants both for resistance in the field and to the toxin in controlled tissue culture conditions. Breeding for resistance to Verticillium wilt is a useful means of controlling the disease in most crops.

Verticillium toxin has been successfully used to screen plants for disease resistance. It is important to differentiate between susceptibility to the fungus and susceptibility to the disease. From our work it seems that phytotoxins cannot adequately screen for all types of resistance, but rather only for tolerance to the toxin.

In this study toxin was purified from a fungal liquid medium. There are several steps in the purification process, including acetone precipitate, molecular weight separation, column dialysis and HPLC means. The screening procedure in the lab is based on exposure of potato tissue culture (protoplasts, cell suspension, callus and sterile plantlets) to highly purified Verticillium toxin. Parallel to the work in ,the lab, the plant material was exposed to Verticillium dahliae in the field.

The results showed that toxin sensitivity was correlated with reduction of tuber yield in infected potato lines, rather than with severity of symptoms. On the basis of these results, a potato variety was considered disease-tolerant if, despite penetration and colonization by the fungus and late expression of foliar symptoms, there was a less than 15% reduction in tuber yield. One explanation for this phenomenon is that this type of disease resistance,


which we have termed 'Alpha-type tolerance', may be due to immunity to the effects of the Verticillium toxin. With this screening procedure, the toxin showed a remarkable host specificity when used to screen new potato germplasm for tolerance to disease.

SPECIES OF SEIRIDIUM ASSOCIATED WITH CYPRESS CANKER DISEASES IN THE MEDITERRANEAN AREA, AND THEIR TOXIC ACTIVITIES

A. GRANITI Dipartimento di Patologia Vegetale, Universit?~, Bari, Italy

Three canker diseases affect wild and cultivated species of Cupressus and related conifers in the Mediterranean area. They are associated with microscopic fungi having a conidial state in the same genus (Seiridium Nees ex Fr.). 1. Seiridium cardinale (Wag.) Sutton et Gibson

The canker disease caused by S. cardinale, first reported in Europe (southern France) in 1944, is the major disease of cypress in the Mediterranean area. Heavy losses have been caused to the nursery industry, to plantations used for forestation and windbreaks, and to ornamental trees in gardens and parks, especially in Italy and in Greece. 2. Lepteutypa cupressi (Nattrass et al.) Swart. Anamorph: Seiridium cupressi ((Guba) Boesew.

The disease caused by L. cupressi, previously referred to as Monochaetia unicornis, was responsible for serious losses in East Africa in the 1940s and later spread to other parts of the world. In 1984 a strain of S. cupressi was recorded from Greece, and it is now slowly spreading on the island of Kos. 3. Seiridium unicorne (Cooke et Ellis) Sutton

The cypress canker caused by S. unicorne, a widespread and plurivorous fungus, seems to be a minor disease in the Mediterranean area, particularly in Portugal.

Besides the cankers, yellowing and reddening of the foliage and dieback of branches frequently occur in plant parts distal from where the pathogens can be isolated, thus suggesting that phytotoxins may be involved in the development of these symptoms. This possibility has been investigated in Italy by a group of plant pathologists (A. Graniti, L. Sparapano and S. Frisullo, University of Bari) and biochemists (A. Ballio, Univ. of Rome, A. Evidente and G. Randazzo, Univ. of Naples).

Isolates of the three species of Seiridium were grown in liquid media. Several non host-selective phytotoxic substances were extracted from culture filtrates and subsequently purified and characterized.

Two toxic butenolides, seiridin and iso-seiridin, were found to be produced by all the species of Seiridium, together with small amounts of a third structurally related compound. A new'phytotoxic macrolide, seiricuprolide, and a new trisubstituted resorcinol, seiricuprine, were produced by the Greek strain of S. cupressi. Another four metabolites, named seidcardins, the structures of which are still under investigation, were isolated from cultures of S. cupressi and S. unicorne.


VARIABILITY OF SEIRIDIUM CARDINALE PATHOGENICITY AND BREEDING STRATEGY FOR CYPRESS CANKER RESISTANCE

P. RADDI and A. PANCONESI C.N.R., Centro di Studio per la Patologia delle Spec& Legnose Montane, Firenze, Italy

Since its first appearance in Europe, cypress canker incited by Seiridium cardinale has spread gradually through almost all the countries of the Mediterranean basin, where it causes serious damage to many Cupressaceae growing both spontaneously and in cultivation, especially to Cupressus sempervirens (Italian cypress), a species which is indigenous or has been naturalized in this area. The dispersal of the disease, in connection with climate and edaphic conditions, was considered.

Because of the continuous deterioration in the cypress's health, research has been directed towards finding effective control measures, with special emphasis on chemical control and on the genetic improvement of the cypress for canker resistance. Particular attention has been devoted to procedures for determining variability in pathogenicity of S. cardinale isolates and between the Seiridium species. Our findings show that variability in susceptibility occurs within the Italian cypresses and between various cypress species; immune reactions are not known among the Cupressus species; and the recovery mechanism identified in C. sempervirens seems to be due to a system resembling horizontal resistance.

Our breeding program is based on the identification of a large base of resistant Italian cypress and the manipulation of resistance genes through intra- and interspecific crosses. A breeding strategy for "durable" cypress canker resistance was developed in relation to the various problems and difficulties.

As a result of this research, three clones were patented for cypress canker resistance in Italy and France.

COMPARATIVE ANALYSIS OF BIOTIC AND ABIOTIC STRESS IN RELATION TO INDUCED RESISTANCE TO FUSARIUM WILT OF TOMATO

A. MATI'A, I. ABBATYISTA GEN'IqLE and L FERRARIS Istituto di Patologia Vegetale dell' Universitd , V .P. Giuria 15, Torino, Italy

Symptoms of Fusarium wilt (F. oxysporum f. sp. lycopersici) in tomato were reduced by different abiotic stresses applied to the roots of the plants before inoculation. The induced protection was similar to that induced by formae speciales of F. oxysporurn avirulent on tomato.

The variations over 7-12 days of phenols concentration, peroxidase (PO),

polyphenoloxidase (PPO), 1,3-[3-glucanase, chitinase activity and ethylene emission were determined for roots, stem and leaves of tomato plants (cv. 'Bonny Best'), the roots of which were treated with heat or chloroform, or inoculated with F. oxysporum f. sp. melonis and then left uninoculated or challenged with f. lycopersici. All treatments induced an increase in phenols, PO and PPO activity which reached a maximum 3--4 days after the treatments in all the plant parts and then decreased to the levels in the control plants after 8-12 days. Heat and

chloroform also caused a systemic increase of 1,3-~-glucanase and chitinase activity, with the same general trend (max. after 5 days) but more marked than that caused by f. melonis.


PO, PPO, 1,3-[3-glucanase and chitinase were further stimulated and the phenol content increased by challenge inoculation with f. lycopersici in previously stressed plants. Heat, chloroform and f. melonis also caused an increase in ethylene emission 3--4 days after treatment. However, the variation in ethylene production in the plants subjected to biotic and abiotic stresses were not related in a simple way with changes of phenol concentration and tested enzyme activities: enzymes and phenols were induced in leaves and further stimulated by challenge inoculation, whereas ethylene was not.

The results suggest that a similar physiological syndrome, probably triggered by irreversible injuries to part of the roots, is evoked in tomato plants by inoculation of avirulent forms of F. oxysporum and by abiotic stresses. The stress seems to activate general defense mechanisms that are responsible for the reduced Fusarium wilt symptoms in tomato plants. Treated plants appear also to be sensitized to respond more promptly to the pathogen.

EXPRESSION OF RESISTANCE OR SUSCEPTIBILITY-RELATED EVENTS IN PLANT TISSUE CULTURES

A. SCALA Istituto di Patologia e Zoologia Forestale e Agraria, Universitd, P.le delle Cascine 28, Firenze, Italy

Many workers have shown how in vitro plant tissue cultures assist in constructing model systems for analyzing physiological and molecular pathogenesis-related events, and in selecting resistant plant material. Experiments were carried out by us recently using two systems: Fusarium oxysporum-carnation and Phytophthora infestans-tomato, in which the induction of phenylalanine ammonia lyase activity, the synthesis of new organic-soluble compounds and phytoalexins were studied. The elicitation of hypersensitive cell death in callus cultures derived from resistant carnation cultivars, after an eliciting treatment with a Fusarium mycelium derived complex, was investigated. A hypersensitive-deficient cell line of a resistant cultivar was also selected. In inoculating callus cultures with conidia of F . oxysporum f. sp. dianthi race 2, there was a delay in the hyphal development on the resistant calli; it seems to be related to these elicited resistance-related events.

In the P. infestans-tomato system, we observed hypersensitive-browning, host cell death and rishitin synthesis (in callus cultures and cotyledons) in a susceptible cultivar following an eliciting preparation from sporangia-free mycelium of P. infestans race lB. The growth of the pathogen was restricted on both elicited differentiated and undifferentiated tissues. Substance(s) released by germinating sporangia suppressed the defense reaction. Moreover, a low molecular weight fraction from the culture illtrate of the pathogen showed cultivar selectivity in causing damage to susceptible tomato cultivars (inhibition of callus growth and ion leakage from leaves). No damage occurred in resistant near-isogenic cultivars carrying the gene Ph-2; this gene confers partial resistance to race lB.


SUPPRESSION OF VERTICILLIUM WILT IN PEANUTS BY IRON, AND MECHANISMS FOR IRON SEQUESTRATION BY THE PATHOGEN

I. BARASH 1,2, N. B1TAN 2, I. KORDOVA 2, J. KRIKUN 1 and A. NACHMIAS 1 IDept. of Plant Pathology, ARO, The Volcani Center, Bet Dagan; and 2Dept. of Botany, Tel-Aviv

University, Ramat Aviv, Israel

Soil application of FeEDDHA suppressed virulence of Verticillium dahliae in peanuts cultivated in calcareous soils. Reduction in virulence was expressed by inhibition of characteristic disease symptoms such as plant stunting, reduced leaf size and chlorosis. The levels of phenols and peroxidase activity were significantly higher in infected plants than in noninfeeted. However, addition of iron decreased the content of phenols but increased peroxidase activity in infected plants. The phytoalexins medicarpin, demethylrnedicarpin, vestiton and formononetin were detected in stems of infected as well as of noninfected peanuts. However, the total amount of these phytoalexins in infected plants was approximately 3.6 times higher than in noninfected plants which were supplied with iron. Iron deficiency in healthy plants induced the increase in phytoalexins by 2.8-fold, whereas only a slight elevation in phytoalexins was observed in infected plants due to iron deficiency. Since iron application did not influence the advancement and distribution of the pathogen within the plant, it was concluded that in the present system, phytoalexins may not be involved in the suppression of virulence by iron.

Coprogen B and dimerum acid were identified as the predominant siderophores produced by V. dahliae. The siderophore-mediated iron transport systems of this pathogen were characterized. The fungus was also capable of utilizing effectively exogenous siderophores which are produced naturally by other fungi. Peanut plants were found to be capable of utilizing iron from iron-bound siderophores produced by V. dahliae.

BIOCHEMICAL REACTION OF SUSCEPTIBLE AND RESISTANT PLANTS TO NEMATODE INVASION

G. ZACHEO Istituto di Nematologia Agraria, CNR, Via Amendola 165/A, Bari, Italy

Several and varied biochemical responses have been considered in studying the biological mechanism of plant resistance and susceptibility to nematodes. It is currently accepted that at the beginning of nematode infection the root cells respond with an increase in synthesis of DNA, RNA and proteins. Resistant tomato roots attacked by root-knot nematodes showed a rapid and pronounced increase in the rate of respiration. The increased respiration of infested tomato roots, linked to the hypersensitive reaction, is associated with the increased activity of oxidases and peroxidases. No changes in respiration, oxidase or peroxidase activity were found in infested susceptible roots. Activation of NADPH-dependent 0a generation also started in resistant tomato roots infested with the root-knot nematode Meloidogyne incognita. It has been suggested that superoxides produced by plants after infection may be directly or indirectly responsible for the hypersensitive reaction. Infestation of M. incognita on susceptible tomato plants induced galls on the roots and scarcely generated 02 �9 The activity of superoxide dismutase (SOD) increased in galled tissue


and protected plants against free radicals of oxygen. The SOD protection declined in resistant plants.

There is evidence that the activation of the 0~ generating system in plant tissue is elicited by nematode infestation. In resistant plants free radicals are not scavenged, because of the decline in the activity of SOD; the tissues are damaged as a consequence of several events, including lipid peroxidation, production of rigid membrane lipids, and loss of enzymatic activity. In susceptible plants the maintenance of high SOD activity removes superoxide free radicals, thus preventing extensive damage to the various biological structures of the cells.

E: EPIDEMIOLOGY AND CONTROL OF PLANT PATHOGENS BY NONCONVENTIONAL MEANS AND SOLARIZATION

EFFECT OF FILM-FORMING POLYMERS ON POWDERY MILDEW AND GRAY MOLD OF CUCUMBER IN GREENHOUSES

Y. ELAD 1, N. AYISH 1 and O. Z1V 2 1Dept. of Plant Pathology and 2Dept. of Field Crops, ARO, The Volcani Center, Bet Dagan, Israel

Several coating polymers which are originally film-forming antitxanspirants were tested for their ability to control powdery mildew and gray mold of cucumber. In one greenhouse experiment 'Safe Pack' significantly (P = 0.05) reduced severity of powdery mildew by 100 and 20% and the number of infected leaves by 71 and 15%, 37 and 72 days after planting, respectively. Gray mold was not seen in the greenhouse and downy mildew was not reduced by the polymer. In a second greenhouse experiment, powdery mildew was reduced by 'Vapor Gard' throughout the growth season (153 days), and 'Folicote' was effective until 146 days after planting. In a third greenhouse experiment, gray mold incidence on senescing female flowers of cucumber and on the stem nodes was reduced by ca 50% by 'Biofiim', 'Vapor Gard', and the fungicide Bravo (chlorothalonil). The fungicide mixture of carbendazim with diethofencarb was significantly more effective than the other treatments.

The polymers were tested on various crops in dew and mist chambers. Gray mold disease was significantly reduced on tomato leaves by 'Safe Pack', 'Wilt Pruf', 'Vapor Gard', 'Colfix' and 'Biofilm'. Those polymers and 'Folicote' , but not 'Vapor Gard', effectively reduced gray mold on bean and on cucumber. All the polymers reduced disease on popper leaves. Severity of powdery mildew of cucumber grown in a growth chamber was reduced by 84 and 18% by 'Vapor Gard' and 'Wilt Pruf', respectively, as compared with the untreated control (which was rated 3.2 out of a maximum grade of 5.0).

In a study of the effect of polymers on mycelial growth and on conidial germination in culture and on leaves, only some of the polymers were found to affect the pathogen.


H O T - W A T E R T R E A T M E N T AS A MEANS FOR R E D U C I N G P O S T H A R V E S T DECAY IN 'GALIA' MELONS

D.C. TEITEL, Y. AHARONI and R. BARKAI-GOLAN Dept. of Fruit and Vegetable Storage, ARO, The Volcani Center, Bet Dagan, Israel

In accordance with the trend to reduce the use of chemical treatments for the control of postharvest diseases of fruits and vegetables, the present study examined the efficiency of heat treatments and plastic wraps as alternative techniques for melons.

Immersion of harvested 'Galia' melons for 2 min in a 52~ hot-water bath conferred effective antifungal protection for up to 8 days at 20~ Oven heating of melons to a surface temperature of 52~ did not afford similar protection. PVC wrap (10 ~tm) prevented dehydration of the fruits but stimulated fungal decay in all but the hot-water-dipped treatment. The hot-water dip also proved effective for prewrapped melons when the exposure time was prolonge'd.

No injury was caused by the heat treatments and no changes in the TSS, firmness, percent dry weight, or respiration rates were recorded. In organoleptic tests, heated fruits pretreated with 10% CO 2 were preferred over control fruits.

R E S I S T A N C E TO DIETHOFENCARB (NPC) IN BENOMYL-RESISTANT FIELD ISOLATES OF BOTRYTIS CINEREA IN ISRAEL

Y. ELAD and TAIAIA KATAN Dept. of Plant Pathology, ARO, The Volcani Center, Bet Dagan, Israel

The control of gray mold on table grapes and various protected crops in Israel has relied heavily on fungicides, mainly benzimidazoles and dicarboximides. However, the spread of Botrytis cinerea strains resistant to either one or both groups of fungicides greatly reduced the latter's effectiveness. Benomyl-resistant (Ben-R) strains of B. cinerea and some other fungi showed sensitivity to methyl N-(3,5-dichlorophenyl) carbamate and isopropyl N-(3,4- diethoxyphenyl) carbamate (diethofencarb; NPC). This raised the possibility of using such N- phenylcarbamates as fungicides against Ben-R strains. However, benomyl-sensitive (Ben-S) wild-type strains remain resistant to the N-phenylcarbamates. Based on this 'negative cross resistance' between N-phenylcarbamates and benzimidazole fungicides, the fungicidal mixture of carbendazim + diethofencarb (MBC+NPC) was introduced, to control B. cinerea phenotypes which are either sensitive to benzimidazoles and resistant to NPC (wild-type: Ben-S NPC-R), or resistant to benzimidazoles and sensitive to NPC (Ben-R NPC-S). The mixture gave good control in 1986/87 in experiments in cucumber greenhouses, where resistance of B. cinerea to benomyl had been stable at 100%, and resistance to dicarboximides varied.

In 1988, unsatisfactory control of gray mold was reported from one site where cucumber greenhouses had been treated five times with MBC+NPC. Samples of B. cinerea from this site were tested for germination and growth on media amended with benomyl, MBC, NPC, MBC+NPC, or iprodione. Many of the isolates were able to germinate and grow normally in the presence of MBC+NPC (10 + 10 ~tg/ml), as well as on unamended medium and on media amended with 10 [.tg/ml of benomyl, MBC or NPC. These isolates therefore show a


new phenotype, designated Ben-R NPC-R, which is resistant to both benzimidazoles and diethofencarb. Most of the isolates of the new phenotype tested so far were sensitive to dicarboximides.

The appearance of such strains during the first year of limited use indicates that the mixture should be incorporated in control programs rather than used exclusively.

DYNAMICS OF POPULATIONS OF BOTRYTIS CINEREA AS A CONSEQUENCE OF DIFFERENT SPRAY REGIMES

M.L. GULLINO, C. ALOI and A. GARIBALDI Istituto di Patologia Vegetale, Universitd degli Studi, Via Giuria 15, Torino, Italy

Dicarboximide fungicides have been used successfully to control gray mold, caused by Botrytis cinerea Pets., on a range of crops until resistance developed. Practical resistance problems first occurred in protected crops and later on grapevines, as a consequence of repeated applications of dicarboximides. Resistance often developed in strains of B. cinerea already resistant to benzimidazoles (double resistance), thus complicating control of gray mold. The evolution of natural and artificial mixed populations of B. cinerea, under different spray regimes, was evaluated in a 3-year study with strawberry, tomato and grape.

Tomato and strawberry plants, grown in a greenhouse, were artificially inoculated with mixed populations of B. cinerea (90% sensitive, 10% double resistant). The evolution of naturally occurring populations of the pathogen in grape was evaluated in vineyards where fungicide resistance was constant. On tomato and strawberry, a rapid increase in the resistant fraction of the crop was observed under the selection pressure exerted by dicarboximides. Related fungicides (chlorothalonil, thiram) sprayed alternately or in mixture with dicarboximides, reduced to a certain extent the increase of the resistant population. The mixture of benzimidazole with diethofencarb, a fungicide causing plant cross resistance with benzimidazoles, effectively inhibited the strains of B. cinerea resistant to benzimidazoles and doubly resistant to benzimidazole and dicarboximides under all the tested conditions.

FEASIBILITY OF SOIL SOLARIZATION FOR CONTROLLING SOILBORNE PATHOGENS

OF SOLANACEOUS PLANTS IN SICILY

G. CARTIA and N. GRECX) lstituto di Patologia Vegetale, Universitd degli Studi, Via Valdisavoia 5, Catania, Italy

Because of the danger of environmental pollution caused by chemicals, efforts are being made to limit the use of soil sterilants in agriculture. Recently it was demonstrated that polyethylene mulching of soil is effective in controlling pathogens occurring in the top soil profile. Investigations undertaken in a plastic-house in Sicily since 1982 have shown that this method is very effective against Pyrenochaeta lycopersici, Verticillium dahliae, pcp i~ stem base necrosis and root-knot nematodes (Meloidogyne spp.) affecting solanaecous plants. Yields in solarized soils were similar to those obtained in plots treated with the suggested rate (60 g/m) of methyl bromide, but significantly higher than in the controls. I n general, control of these pathogens in the solarized plots was satisfactory and a substantial


increase in the pathogen populations occurred only at the end of the crop season, thus requiring that solarization be repeated every year. The combination of solarization with reduced rates (30 g/m) of methyl bromide resulted in a greater yield increase and protected the plants throughout the growing season. In the latter case, soil treatments are required only every 2 years. It is envisaged that soil solarization, along with the adoption of other methods of control, will be useful to maintain population densities of the above pathogens below damaging levels.

SOIL SOLARIZATION AGAINST SCLEROTINIA MINOR AND RHIZOCTONIA SOLANI IN ITALY

G. VANNACCI and E. TRIOLO Dipartimento di Coltivazione e Difesa delle Specie Legnose, Sez. Patologia Vegetale, 56010 S. Piero a

Grado, Pisa, Italy

Soil solarization has been tested in northern and central Italy since 1983 to evaluate its efficacy against soilborne Sclerotinia minor and Rhizoctonia solani, both in the open field and in greenhouses, using as hosts, respectively, lettuce (Lactuca sativa L.) and radish (Raphanus sativus L.). Naturally or artificially infected soil was generally covered with a 50- ~tm-thick polyethylene tarp for a period of about 40 days during July - August and temperatures were recorded at 0-2, 4-6, and 14-16 cm depths.

Both pathogens were controlled by the treatments. The findings obtained in the trials against S. minor allow us to suggest the introduction of solarization as a cultural practice for lettuce crops in Italy. Investigations on the influence of solarization on buried sclerotia revealed that the treatment affects both the recovery and the viability of these structures and modifies the microflora-infecting sclerotia. The treatment promotes the growth of lettuce roots and does not adversely affect their mycorrhizal colonization.

BIOLOGICAL CONTROL IN SOLARIZED SOILS

A. GREENBERGER t, S. FREEMAN 2, A. GAMLIEL 2, A. YOGEV 2 and J. KATAN 2 1Dept. of Vegetable Crops, ARO, The Volcani Center, Bet Dagan; and 2Dept. of Plant Pathology and

Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel

Biological control mechanisms which operate in the soil during and after solarization are frequently involved in the mechanisms of pathogen control, in addition to the direct heating effects. Mechanisms of biological control are: increased sensitivity of resting structures to antagonists due to a weakening effect, stimulation of antagonists (e.g. Trichoderma, Talaromyces, fluorescent pseudomonads), diminished fungistasis, enhanced lytic activity and accumulation of volatiles. The weakening effect may be expressed in a delay in germination and growth of mycelium, reduced survival and disease incidence, and changes in protein synthesis. Frequently, the solarized soils become less receptive to pathogen reinfestation, i.e., induced suppressiveness. The incidence of disease caused by Fusarium, Sclerotium rolfsii, and Verticillium was lower in solarized and subsequently inoculated soils than in nontreated inoculated ones, while populations of lytic and antibiotic-producing


microorganisms were higher. The suppression of ctdamydospore formation was frequently observed. Methods for intensifying biological control in solarized soils, e.g. by combining mhriz~tion and biocontrol agents, were considered.

MICROBIAL CHANGES IN SOLARIZED SOILS AS RELATED TO PLANT GROWTH

A. GAMI JRI. and J. KATAN Dept. of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture,

Rehovot, Israel

Plant growth in solarized soils is frequently enhanced even in the absence of known pathogens, as shown with many soils. Sn numerous experiments the following findings were obtained. Dry weight of bioassayed plants was increased in the solarized soils by 20-200%. Possible biotic mechanisms include stimulation of beneficial microorganisms and control of deleterious ones. Populations of fluorescent pseudomonads (FP) were increased in the rhizosphere and roots of plants in solarized soils, although these bacteria are heat sensitive. Isolates of these bacteria increased the growth of tomato plants in greenhouse tests. Solarization has strongly reduced populations of total fungi, Pythium spp., and of fungi causing plant stunting. Decreased growth and yield of plants occurs in monoculture systems. In such soils populations of FP decrease while those of deleterious microorganisms increase in the rhizosphere and root of cotton, tomato and gypsophila plants. Solarization of monocultured soil improved plant growth and yield in the greenhouse and open field. A shift in microbial populations similar to that described above was observed. Populations of deleterious fungi remained very low in the roots of the solarized plots, throughout the growth period.

F: EPIDEMIOLOGY AND CONTROL OF PLANT VIRUSES

NATURAL SPREAD OF CORKY-BARK DISEASE IN VINEYARDS IN ISRAEL

EDNA TANNE 1, B. RACCAH 1 and RUTH MARCUS 2 1Dept. of Virology and 2 Dept. of Statistics and Experiment Design, ARO, The Volcani Center, Bet

Dagan, Israel

Corky-bark was first identified in Israel in the 'Thompson Seedless' variety of grape, in the Lakhish region, in 1982. A field survey was carried out for 5 years in one of the infected vineyards in order to obtain information on the natural spread of the disease. All plants in the vineyard were visually inspected twice yearly, in the spring and autumn, for leaf symptoms, stem pitting or grooving and the appearance of thick, spongy and soft bark. Budwood from symptom-showing plants was grafted on indicator vines, and the LN/33 indicator reacted with typical symptoms. The spatial pattern of infected vines at each assessment time was studied. The results showed that the spatial pattern of infection varied over time. The temporal spread of infection was also analyzed.


EPIDEMIOLOGICAL STUDIES OF BARLEY YELLOW DWARF VIRUS IN THE CENTRAL PO VALLEY (NORTHERN ITALY)

G. BELLI and S. PRATI Istituto di Patologia Vegetale, Universitd di Milano, Milano, Italy

Research on barley yellow dwarf virus (BYDV) was initiated at our Institute about 20 years ago, with the study of rice "giallume" (yellows), a severe disease that had previously been unknown there. Detection and identification of BYDV were done initially on the basis of symptoms and of aphid transmission tests. Subsequently, enzyme-linked immunosorbent assay (ELISA) serological tests were carried out with different antisera. The two methods of detection (aphid transmission and ELISA) gave similar results.

BYDV was detected throughout the growing season in barley (from November to April), wheat (from February to May), rice (June and July), corn (from June to October) and oats (from October to April). Most of the isolates which were obtained belong to the 'PAV - strain' (sensu Rochow, 1969) of BYDV. This strain was found to infect all the cereal crops that have been tested by us.

PLUM POX VIRUS EPIDEMIOLOGY IN NORTHWEST ITALY

M. CONTI and A. EYNARD Istituto di Fitovirologia Applicata, CNR, Torino, Italy

Since 1984, plum pox virus (PPV) has been found infecting apricots and, in some limited areas, also peaches and plums in several Italian regions. In Piedmont, NW Italy, the virus has occurred epidemically only in apricots and is diagnosed routinely by symptoms, DAS-ELISA, and ISEM. By serological means the virus distribution and concentration were shown to be quite variable in both naturally and experimentally infected stone-fruit plants.

In most cases primary infection foci in orchards formed due to the use of infected mirabolan rootstocks that had not been screened for PPV. Secondary virus spread occurred by aphids, becoming evident 2-4 years later. Of eight stone-fruit-infesting aphid species tested as PPV vectors, Brachycaudus helichrysi, Hyalopterus pruni, Myzus persicae, Myzus varians and Phorodon pruni transmitted the virus. Their ability and efficiency to transmit, however, depended greatly on the virus source/virus indicator plant combination adopted in the experimental tests. The susceptibility of apricots to aphid-inoculated PPV also seemed to vary considerably, depending on the age at which plants were inoculated. Young apricot seedlings, for example, could become infected 2-3 weeks after the inoculation, while 50 two- year-old plants inoculated in 1984 still do not show evidence of infection. M. persicae was found to be the most efficient experimental vector, and to transmit most activity at 18~ with short (< 60 sec) acquisition and inoculation feeding periods.

PPV was detected very occasionally in peaches and, in one case, in wild plums, but not in about 180 herbaceous plants of 16 different species growing in PPV-infected orchards. Several drupaceous species growing wild or in private gardens appeared to be the most important local sources of aphid vectors.

152 P hytoparasitica 17:2, 1989

Experimental studies over a period of 3 years failed to demonstrate seed or pollen transmissibility of PPV in apricot, although the virus could be detected in a high proportion (72-90%) of the seeds extracted from infected fruit showing typical, severe virus symptoms.

PLANT VIRUSES IN WATER ENVIRONMENTS IN ITALY

P. PIAZZOLLA Dipartimeato di Patologia Vegetale "and Centro di Studio sui Virus e le Virosi delle Colture Mediterrane,

Via Amendola 165/A, Bari, Italy

In recent years several researchers have been involved in studies concerning the recovery of plant viruses from water environments in different regions. Viruses belonging to different taxonomic groups, with elongated or isodiametric particles, have been found in Apulia, Basilicata, Campania, Emilia Romagna, Sicily and Veneto: e.g. cucumber mosaic virus (CMV), pelargonium zonate spot virus (PZSV), tobacco necrosis virus (TNV), a tombnsvirus, some tobamoviruses and some ungrouped ones. Among them should be noted the presence of CMV, a widespread plant virus, present in all temperate regions of the world. CMV has an extremely wide host range, which includes cereals, forages, woody and herbaceous ornamentals, vegetable and fruit crops, and its occurrence is enhanced by the relative ease of its natural transmission by aphids.

X-ray or IR spectroscopy analysis of the sediments present in waters where CMV was found revealed high percentages of clay minerals, suggesting the existence of stabilizing effects on the viral architecture conferred by these materials. The resistance of a CMV suspension to dissociation induced by 1 M LiC1 was determined after treatment with kaolinite, montmorillonite and vermiculite clays. Experiments carried out by analytical and/or sucrose density gradient centrifugation, along with infectivity assays, demonstrated that the clays have a protective effect on the virus suspension, probably due either to the adsorption of virus particles and salt ions or to changes in the quaternary structure of the viral protein subunits, or to both.

These results may have important epidemiological implications, as they suggest that water environments may constitute a reservoir of sediment stabilized viruses, with an unknown potential for infection.

CHARACTERISTIC OF ANTIVIRAL FACTORS FROM VIRUS-INFECTED CHENOPODIUM AMARANTICOLOR AND OTHER PLANT SPECIES

G. FACCIOLI and M. FORNI Istituto di Patologia Vegetale, Universit& di Bologna, Bologna, Italy

An antiviral factor(s) (AVF) present in tobacco necrosis virus (TNV) locally infected leaves of Chenopodium amaranticolor, partially purified with hydrated calcium phosphate and DEAE-colunm chromatography, was found active in different plants against various virus infections. Such a factor(s), probably a phosphorylated glycoprotein, has several features

similar to those of interferons (c~, [3): its formation is prevented in plants by AMD and vitamin C treatments, while it is elicited by polyacrylic acid and Poly(I:C). Extraction of

Phytoparasitica 17.'2, 1989 153

oligonucleotides from TNV-infected C. amaranticolor leaves yielded extracts having antiviral activity, and treatments with synthetic nucleotides [ppp2-5(A)3 or 2-5(A)3] also reduced TNV infection. It seems, therefore, that AVF may act, like interferons, by inducing the formation of oligoadenylates [ppp2-5(A)n] through ATP polymerization. AVF was also recovered from intercellular fluid of TNV-infected leaves, collected after vacuum infiltration with 0.1 M phosphate buffer (pH 7).

Comparative SDS-PAGE experiments showed that in calcium, phosphate and intercellular fluid extracts, there were visible two similar bands which were not present in extracts of the relative controls. PAGE experiments under non-denaturating conditions yielded similar results, and enabled demonstration that such bands have antiviral properties. Calcium phosphate extracts, recovered from other virus-infected plant species, also showed antiviral activity when absorbed through the petiole of TNV-inoculated leaves of C. amaranticolor. Among them were those obtained from potato virus x (PVX) locally infected leaves of Gomphrena globosa and from leaves of Nicotiana tabacum cv. 'White Burley', Nicotiana glutinosa, Chenopodium quinoa, and leaves and seeds of Phaseolus vulgaris cv. 'Taylor' systemically infected by PVX, potato virus Y (PVY), peanut mottle virus (PMV) and bean common mosaic virus (BCMV), respectively.

It thus appears that plant AVFs are highly nonspecific, with respect to both virus and plant host, and that their formation could be due to both local and systemic virus infections.

G: PHYTOBACTERIOLOGY

EFFECT OF METHAM SODIUM ON SEVERAL BACTERIAL DISEASES

G. KRITZMAN Dept. of Plant Pathology, ARO, The Volcani Center, Bet Dagan, Israel

Metham sodium (MS), a common fumigant, is widely used to control soilborne pathogens. The effects of MS on bacterial diseases were studied in various experiments. Growing potatoes in Verticillium dahliae - infested soil treated with MS resulted in the following effects: (i) significant reduction in the soilborne fungal pathogen V. dahliae and seedborne bacterial pathogen Erwinia spp. populations estimated on the daughter tubers and stems. (ii) Yield reduction by V. dahliae was 19.6%, by Erwinia spp. 24.6%, and by the combined pathogen 75%. (iii) MS prevented the interaction between these two pathogens but, on the other hand, there was a significant increase in the population of and damage by a new pathogen, Streptomyces spp. This pathogen caused deep pitted scab in potato tubers and warts on peanut pods and is probably different from Streptomyces scabies.


TRANSMISSION OF THE PEANUT SCAB AGENT STREPTOMFCR$ SP. BY PgANUT SEEDS, AND ITS PREVENTION

G. KR1TZMAN 1 , A. GRINSTEIN 2, YEHUD1TH RIVEN 2, S. W ARSHA VSKY 3 and H. FRANKEL 2 1Dept. of Plant Pathology and 2Dept. of Pesticide Application Research, ARO, The Voicani Ctntcr, B#t

Da&an; and 3Hevel Ma ' On Enterprises, Ne&ev, Israel

The bacterium Streptomyces sp. causes pod wart of peanut. Black, swollen calluses develop on the exterior surface of peanut shells, and Streptomyces sp. can be isolated from infected areas. No disease symptoms can be seen on the internal side of shells, and isolnlions from this part showed no pathogen presence. Seeds are not naturally infected inside the pods. However, they are contaminated during mechanical cracking and subsequently become carriers.

Surface disinfection of the pods by 3% iodine solution in glacial acetic acid, as well as by other chemicals applied by the reduced volume applications (RVA) technique in an aerosol chamber, resulted in complete pathogen control. Shelled seeds from mechanically cracked severely diseased pods were pathogen-free after prior disinfestation. These seeds were also less contaminated with other seedborne pathogens such as Aspergillus spp.

STUDIES OF GRAPEVINE CROWN GALL

C. BAZZI l, T.J. BURR 2 and E. STEFANI 1 l lstituto di Patologia Vegetale, Universitd degli Studi, Bologna, Italy; and 2Dept. of Plant Pathology,

Cornell University, Geneva, NY, USA

Crown gall is of increasing concern in many major grapevine production areas. The disease is primarily associated with Agrobacterium tumefaciens biovar 3, which survives systemically in the plant. A rapid sampling procedure, based on serological analysis of vascular fluids obtained by vacuum washing of 1-year-old dormant cuttings, has been developed for the selection of A. tumefaciens-free cuttings on a large scale. Detection of the pathogen in callus tissue is time-consuming but appears to be more sensitive than the flushing indexing method. Polyclonal and monoclonal antibodies for A. tumefaciens biovar 3 were tested in comparative studies of different biovars. Differences in antibody reactivity were observed according to the serological assay: using IFAS, no bacterial strains reacted with the monoclonal antibody which was, however, highly specific for all biovar 3's when indirect solid-phase ELISA was used.

For quarantine purposes, rapid and accurate testing is essential for tumorigenicity of agrobacteria, frequently associated with hyperplasias of uncertain origin. Preliminary tests (at the Cornell University Dept. of Plant Pathology)) using genetic probes, seem to offer interesting prospects.

The efficacy of the current indexing procedures could be improved with more information on the relative distribution of the pathogen in canes: an immunofluorescent staining procedure for in situ detection of bacterial antigens in serial sections of plant tissue looks promising.

Biovar 3 of A. tumefaciens and of A. radiobacter, causing root-specific decay of grape, may also play an important role in the replant disease syndrome. Propagation materials must


be free of this biovar. Results obtained at the Waite Agricultural Research Institute in Adelaide, South Australia, suggest the effectiveness of hot water dips (50~ for 30 min) for eradicating bacteria in dormant cuttings.

Spread of A. tumefaciens is being studied in an experimental vineyard, using a rifampicin-resistant mutant of the pathogen.

RECENT STUDIES OF THE BIOLOGY AND EPIDEMIOLOGY OF THE OLIVE AND OLEANDER KNOT ORGANISM

G. SURICO Istituto di Patologia e Zoologia Forestale e Agraria, Universitd degli Studi, Firenze, Italy

Infection of olive and oleander plants by Pseudomonas syringae pv. savastanoi results in the formation of knots on young stems and branches and, less frequently, on the leaves and fruits of olive trees. Symptoms are due largely to the bacterial production of 3- indoleacetic acid (IAA) and a battery of cytokinins which probably release cells in the host from normal morphogenetic influences, resulting in growth responses to the pathogen.

Definitive evidence has been obtained indicating that IAA production in oleander strains is plasmid-determined. However, a considerably different situation exists in the localization of IAA genes among strains of P.s. pv. savastanoi. In addition, the plasmid profiles show remarkable differences between oleander and olive strains. Generally, oleander strains have three or four plasmids while olive strains have six or seven. Some atypical P.s. pv. savastanoi strains were isolated from olive knots and healthy leaves. When cultured on nutrient-sucrose agar, they gave rise to levan-positive colonies, contrary to typical P.s. pv. savastanoi strains. Moreover, these strains did not produce any fluorescent pigment on King B agar. Rather, they released high amounts of IAA and cytokinins in culture and were able to induce outgrowth when inoculated on olive plants of different cultivars. Two of the strains, UF5 and UF3, harbor three plasmids, of 91, 56 and 39 Kb, respectively, while UF8 contains only two plasmids, of 39 and 100 Kb. All other physiological, biochemical and cultural characteristics corresponded to those typical of P.s. pv. savastanoi.

Epidemiological studies using a semi-selective medium, PVF-1, indicated that P.s. pv. savastanoi has an epiphytic growth phase not only on leaves but on the twigs and drupes of olive plants as well. Conditions for survival and multiplication of the bacterium appear better in the bark than on leaves. The bacterium also has an epiphytic growth phase on oleander leaves. By studying the bacterial populations which colonize the phylloplane of olive and oleander plants, we found that many saprophytic bacteria produce IAA. Those producing the highest amount of the phytohormone (-25 mg/l of culture medium) induced a visible outgrowth when inoculated on olive plants. Other epiphytic bacteria were able to produce antibacterial substances active against P.s. pv. savastanoi. These results indicate that great variability may exist among P.s. pv. savastanoi straihs and that important interactions may occur between epiphytic bacteria and the olive and oleander knot organism.

Finally, there is some evidence that, as in the ease of Agrobacteriurn turnefaciens, attachment of P.s. pv. savastanoi to a host wound site may be an essential early event in the knot initiation process.

156 Phytoparaaitica 17:2, 1989

H: EPID EMIOLOGICAL ASPECTS AND CHEMICAL CONTROL

VARIATIONS IN SENSITIVITY TO FOSETYL-AL AND PHOSPHOROUS ACID IN PHYTOPHTHORA INFESTAN$

BILHA BASHAN, Y. LEVY and Y. OOHEN Dept. of Life Sciences, Bar-llan University, Ramat Gan, Israel

Twenty-three field isolates of Phytophthora infestans (Mont.) de Bar), from America, Europe and Israel were tested for sensitivity to fosetyl-Al (aluminum t r i s -O-e thy l phosphonate) and phosphorous acid on rye seed agar and on leaf tissue of 12 potato (Solarium tuberosum L.) cultivars. EDs0 values on rye agar (pH 6.5) at 20"C in the dark ranged between 44 and 1037 mg a.i./ml for fosetyl-A1 and between 3 and 301 mg/ml for phosphorous acid, Sensitivity to fosetyl-A1 was closely correlated (R2=0.87) with sensitivity to phosphorous acid but poorly correlated with sensitivity to metalaxyl. ED50 values for the control of late blight on potato (cv. 'Alpha ') leaves ranged between 1 and 77 mg fosetyl-Al per ml, depending on the isolate of P. infestans. A poor correlation was observed between sensitivity to fosetyl-A1 on rye seed agar and sensitivity to fosetyl-A1 on potato leaves. The efficacy of fosetyl-A1 in controlling late blight was dependent on the potato cultivar. Among the 11 cultivars tested, the best control was achieved with 'Nicola' and 'Atica' and the poorest with 'D6sir6e'.

Analysis of variance showed a significant interaction between cultivar x isolate and fosetyl-A1 efficacy. Other experiments revealed that fosetyl-A1 performed better in older than in younger leaves of potato and in shorter than in longer photoperiods. These results explain the controversial reports on the efficacy of fosetyl-A1 in controlling P. infestans on potato.

THE PATHOLOGY AND CONTROL OF THE BLACK MOLD DISEASE CAUSED BY RHIZOPUS ON GRAPES

ZOHAR (KEREN) SHACHAM 1, N. LISKER I and RUTH BEN-ARIE 2 1Dept. of Seed Research and 2Dept. of Fruit and Vegetable Storage, ARO, The Volcani Center, Bet Dagan,

Israel

Rhizopus stolonifer (Ehrenb. ex Fr.) Lind causes severe losses to Israeli grapes for export. The fungus develops on mature berries in the field, during storage at temperatures above 0~ and during shelf life. It macerates the berries, leaving whole clusters unacceptable for marketing. The fungus can be isolated from naturally contaminated soils throughout the year. From the soil it appears to spread to the fruits, but the fungus was isolated from them only from the beginning of July onwards. Intact young berries were shown to be more resistant than mature ones to Rhizopus inoculations, both natural and artificial. Wounding or chloroform dips dramatically increased the susceptibility of young berries.

Young fruits had a high organic acid content which decreased with maturation. Malic acid decreased during the season from approximately 40% to 10% of the total acid content but tartaric acid remained within the range of 35-40%. During fruit growth and ripening, total


soluble solids increased from -6* to 20* Bx. Total soluble phenols decreased at the beginning of the harvest season and slightly increased near the end of the season.

In vitro studies showed that CGA-169374 was superior to iprodione and dichloro- mtro-aniline in inhibiting fungal growth. However, in field studies iprodione gave better control of storage decay than the other fungicides tested.

DEVELOPMENT OF CERCOSPORA BETICOLA EPIDEMICS ON SUSCEPTIBLE AND 'TOLERANT' GENOTYPES OF SUGARBEET

V. ROSSI 1 and P. BAT]IIANI 2 llstituto di Patoiogia Vegetale e Forestale, Universitd della Basilicata, Potenza; and 2lstituto di Patologia

Vegetale, Universitd Cattolica S. Cuore, Piaeenza, Italy

Ganotypes of sugarbeet 'tolerant' towards Cercospora beticola Sacc. are widespread in Italy. The aim of this study was to compare the development of Cercospora leaf spot on slasceptible and ' tolerant ' genotypes of sugarbeet, in order to obtain knowledge on the behavior of 'tolerant' cultivars in the field and the means to plan the protection of the crop.

The intensity of epidemics was assessed weekly as percentage of affected leaf area, during 3 years (1986--88), at ten sites in the western Po Valley. Two groups of cultivars were examined: the susceptible 'Extxamonosaros', 'Specialmono' and 'Zaffiro', and the 'tolerant' 'Crernona', 'Monodoro' and 'Ritmo'. Epidemiological data were interpolated by a logistic function, with time as the independent variable and intensity of disease as the dependent one. The interactions among year, site and cultivar were strong, but genotype was the most important variable.

Under the same epidemiological conditions, the primary infections appeared at the same time on all cultivars considered. The first phase of epidemics (where the infection rate and the intensity of disease are very low) was longer in the 'tolerant' genotypes (27 + 2 days) than in the susceptible ones (36 + 4 days). Subsequently the intensity of Cercospora leaf spot increased rapidly, but the infection rates were higher in the susceptible cultivars (1.02 + 0.05% affected leaf area/day) than in the 'tolerant' cultivars (0.73 • 0.07%). Therefore, the f'mal level of disease was lower in the 'tolerant' cultivars (35.9 + 4.2% affected leaf area) than in the susceptible ones (54.9 • 3.0%).

A different degree of 'tolerance' can be found in some genotypes, chiefly under epidemiological conditions that favor the development of disease. This ' tolerance' is expressed primarily by a delay in the development of disease during the epidemic. In these genotypes, when other epidemiological conditions are unfavorable for the fungus, the epidemic may not develop.

Chemical control of the disease in 'tolerant' cultivars can be started later than usual, thereby enabling a reduction in the number of chemical treatments.


EFFECTS OF SUBLETHAL CONCENTRATIONS OF TR1ADIMEFON ON REDUCING LEAF RUST IN BARLEY

U. BRODNY Faculty of Life Sciences, Inst. for Cereal Crops Improvement, Tel-Aviv University, Ramat Aviv, Israel

In studies of the control of leaf rust (Puccinia hordei Otth.) in barley with triadimefon WP 25 [ l-(4-chlorophenoxy)-3,3-dimethyl- 1-(1H- 1,2,4-triazol- 1-yl)-2-butanone], it was found that a fungal isolate inoculated onto plants treated with sublethal concentrations of this fungicide greatly reduced infection rates in the greenhouse as well as in the field. These fungicide applications at sublethal concentrations may affect the same components of disease development as slow rusting genetically carried by the host plant. Studies of disease management with such low dosages should be carried out in order to determine whether such procedures will reduce the risk of causing rapid selection of fungicide-tolerant isolates and increase the commercial life of both cultivars and fungicides.

EPIDEMIOLOGICAL ASPECTS OF PYRENOPIIORA GRAMINEA ON WINTER BARLEY IN ITALY

G. VANNACCI 1, A. PORTA-PUGLIA 2 and G. DELOGU 3 I Dipartimento di Coltivazione e Difesa delle Specie Legnose, Sezione di Patologia Vegetale, Universitd di

Pisa; 2lstituto Sperimentale per la Patologia Vegetale, Roma; and 31stituto Sperimenlale per la Cerealicoltura, Sezione di Fiorenzuola d'Arda, Italy

Barley leaf stripe, caused by the seedborne pathogen Pyrenophora graminea Ito et Kuribay., is one of the major diseases of winter barley in Italy. The increased acreage of this crop during the last decade and the ban on organomercury seed treatments which was not followed by efficient substitutes for some years, account for the increased presence of the pathogen both in the field and in commercial seed lots.

The effect of seed infection levels on disease incidence and yield losses was investigated in field experiments during 1982/83 and 1983/84 with the highly susceptible variety 'Perga', at three locations representative of major growing areas. Results showed a 0.3% and 0.9% yield reduction per 1% of infected seeds and 1% of infected tillers, respectively. The threshold of seed infection over which the production was significantly reduced compared with the healthy control, was 14%. The behavior of 30 barley varieties towards the pathogen was investigated in the field in 2 other years. In the first year, rows of varieties to be tested were sown within a grid of 'Perga' from a lot of seeds heavily infected by P. graminea. The harvested seeds were sown the following year. The results from seed analyses and field records showed a fair amount of variability in the reaction of different varieties to the fungus. The variability was particularly high as concerns the rate of P. graminea transmission from seeds to plants. Artificial inoculation through the seed with 14 isolates of the pathogen was performed in a controlled environment on 17 varieties. Large variability in the pathogenicity of the fungus was observed.

These studies contributed to the improvement of seed production schemes (including generalized chemical seed treatments) and to the identification of sources of resistance to P graminea suitable for Needing programs.


Abstracts of papers presented at the first Israeli-Italian phytopathological symposium

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