A pluralistic approach in the study of Pleurotus species with emphasis on compatibility and physiology of the European morphotaxa

Mycol. Res. 100 (6): 717-731 (1996) Printed in Great Britain 717

A pluralistic approach in the study of Pleurotus species with emphasis on compatibility and physiology of the European morphotaxa

GEORGIOS ZERVAKISY A N D CONSTANTINOS BALIS Laboratory of General and Agricultural Microbiology, Agricultural University of Athens, lera Odos 75, 11855 Athens, Greece

The anatomical, physiological, ecological and cultural characters of 11 Pleurotus morphotaxa reported to occur in Europe are described in detail and compared with the outcome of a pairing-analysis performed among monokaryons of 101 dikaryotic strains (including collections from other continents). The results revealed eight intersterility groups in Europe: P. ostreatw, P. pulmonariw, P. cornucopiae, P. eyngii, P. cystidiosus, P. dy inw , P. calyptratus and P. opuntiae. In addition, strains formerly identified as 'P. sajor-caju' were found to be intercompatible with P. pulrnonarius, while the speciation process currently under way for P. columbinw, P. citrinopileatus and the ecotypes of P. eryngii is discussed. A synthesis of the data obtained so far on Pleurotw systematics is evaluated in the light of recent evidence together with the world distribution of the recognized biological species of the genus.

Species of Pleurotus (Fr.) P. Kumm. are widely known as efficient decomposers of a large range of agricultural wastes and for producing edible basidiomata of high organoleptic qualities. These properties favoured significantly the spread of their commercial cultivation which recently accounted for about a quarter of the total world mushroom production (Chang & Miles, 1991). Further progress on the breeding strategies and the optimization of cultivation techniques for certain representatives of this fungal group could be achieved by clarifying the perplexed state of taxonomy within the genus.

The biological species concept (Dobzhansky, 1970; Mayr, 1970) has been applied to various groups of Basidiomycotina for species delimitation, for establishing systematic relationships among different taxa and for drawing more accurate conclusions about speciation processes (Hallenberg, 1984; Boidin, 1986; Vilgalys, 1991; Petersen, 1995 b), although its generalized use in fungi has proved to be problematic in certain cases (Parmasto, 1985 ; Brasier, 1987). The importance of adopting such a concept is obvious, as the ability of individuals to interbreed provides information on the type of reproductive system and the structure of mating factors, reveals the degree of gene flow between populations and the existence of genetic and/or sterility barriers. Thus, studies on mating behaviour, apart from contributing to phylogeny, are valuable for confirming the validity of existing morpho- logically based taxa. -

In the case of Pleurotus systematics there has been controversy in the past, especially regarding taxa such as P. osfreatus (Jacq.: Fr.) P. Kumm., P. columbinus (Quil.) QuCl., P. pulmonarius (Fr.) Quil. and P. sapidus (Schulzer) Sacc.

* Present address: Institute of Kalamata, National Agricultural Research Foundation, Lakonikis 85, 24100 Kalamata, Greece.

(Anderson, Wang & Schwandt, 1973; Eger, Li & Leal-Lara, 1979; Hilber, 1982); P.salmoneostramineusVassil jeva, P. osfreatoroseus Singer and P. djamor (Fr.) Boedijn (Pegler, 1977a, b ; Comer, 1981; Neda, Furukawa & Migayi, 1988; Guzmhn et al., 1993; Petersen & Hughes, 1993); P. citrinopileafus Singer and P. cornucopiae (Paulet) Rolland (Hilber, 1982; Ohira, 1990); P. cystidiosus 0 . K. Mill., P. abalonus Y. H. Han, K. M. Chen & S. Cheng and P. srnifhii Guzmin (Han, Chen & Cheng, 1974; Jong & Peng, 1975; Guzmin, Bandala & Montoya, 1991). These taxonomic ambiguities are due to initial misidenti- fications, absence of species typification, significant influence exercised by the environment and substratum on the morphology of most taxa, the limited existence of sound physiological characters and the lack of suitable compatibility studies (Anderson et al., 1973; Eger el a]., 1979; HiIber, 1982; Bresinsky et al., 1987; Zervakis, 1992). Except for Hilber's (1982) comprehensive monograph, it was not until recently that generic systematics were addressed either by mating experiments (Petersen & Hughes, 1993; Vilgalys et al., 1993, Petersen, 1995 a), or by modem biochemical (May & Royse, 1988; Zervakis & Labarkre, 1992; Zervalus, Sourdis & Balis, 1994) and molecular (Vilgalys & Sun, 1994; Ira~abal, Zervakis & Labarkre, 1995) approaches.

The work reported below forms part of a multifaceted study and includes a thorough analysis of matings performed among the homokaryotic isolates from more than 100 Pleurofus dikaryons, originally assigned to 13 different taxa. Particular emphasis is being placed on taxa found in Europe, for each of which a detailed morphological, physiological and ecological description is provided based on data from collection sites, and comparative cultivation and culture trials. The evaluation of the results in conjunction with the outcome of other relative investigations aims at defining the genetic relationships between Pleurotus species and establishing the intersterility groups that exist within the genus.

The pluralistic species concept in Pleurotus 718

Table 1. Details of Pleurotus dikaryons used in this study: strain numbers, species to whlch they were originally assigned, host or substrate, geographical origin and acquisition source

Strain Host/ no. Species substrate

Geographic Acqu~sition origin sourcet

01 P. calyptratus 02 P. calyptratus 03 P. calyptratus 04 P. ritrinopi/eatus 05 P. citrinopiieatus 06 P. columbinus 07 P. columbinus 08 P. columbinus 09 P. cornuropiae 10 P. cornuropiae 11 P. cornuropiae 12 P. cornucopiae 13 P. cornucoptae 14 P. cornucopiae 15 P. cornucopiae 16 P. cystidiosus 17 P. dryinus 18 P. dryrnus 19 P. dryinus 20 P. dryinus 21 P. dryinus 22 P. dryinus 23 P. eryngri 24 P. eryngii 25 P. eryngrr 26 P. eryngii 27 P. eryngri 28 P. eryngrt 29 P. eryngtt 30 P. eryngii 31 P. eryngii 32 P. eryngrr 33 P. eryngii 34 P. eryngii 35 P. eryngrr 36 P. eryngri 37 P. eryngii 38 P. flabellatus 39 P. flabellatus 40 P.flabellatw 41 P. flabellatus 42 P. opuntrae 43 P. ostreatus 44 P. ostreatus 45 P. ostreatus 46 P. osfreatus 47 P. osfreatus 48 P. osfreatus 49 P. ostreatus 50 P. ostreatus 5 1 P. ostreatus 52 P. ostreatus 53 P. ostreatus 54 P. ostreatus 55 P. ostreatus 56 P. ostreatus 57 P. ostreatus 58 P. ostreatus 59 P. ostreatus 60 P. ostreatus 61 P. ostreatus 62 P. ostreatus 63 P. ostreatus 64 P. ostreatus 65 P. ostreatus

Populus alba Populus alba

Ulmus sp. Ulmus sp.

Ficw carica Hardwood Populus tremula Juglans regia Malus sylvestrrs M . sylvestris Hardwood Eryngium s p Eryngium sp Ferulu sp. Ferula sp. Field

Eryngium sp. Ferula sp. Erynghm sp. Ferula sp. Laserpitium latifolium Laserpitium latifolium Eryngium sp. Ferula sp. Rotting log Oil palm waste Coconut

Agave sp. Fagus sylvatica F. sylvatica F. sylvafrca Castanen sutiva Abies sp. Populus sp. Populus sp. Populus sp. Populus sp. Abies sp. Abies sp. Saltx sp. Abies sp.

Quercw sp. Populus nigra Populw sp. Abies sp.

ex-Czechoslovakia China Malaysia France Italy France Germany Great Britain Netherlands ex-Czechoslovakia Belgium France France Piraeus, Greece Germany Norway N o w a y ex-Czechoslovakia Netherlands Netherlands Crete, Greece Crete, Greece Evros, Greece Evros, Greece ex-Czechoslovakia Italy

France France Hungary Italy France France France France

Malaysia Indonesia Singapore Crete, Greece Vardoussia, Greece Vardoussia, Greece Vardoussia, Greece Arcadia, Greece Attica. Greece Evros, Greece Fthiotida, Greece Evros, Greece Evros, Greece Attica, Greece Attica, Greece Corinthia, Greece Evea, Greece Germany Germany

Netherlands Italy France Hungary France Hungary France

ATCC 52209 MUCL 28909 MUCL 28910 ATCC 60892 MUCL 28684 ATCC 36498"' CBS 3 735 1 MUCL 28154 ATCC 38547'" CBS 27633 CBS 38380 ATCC 42045 MUCL 28732 LGM 15 LGM 50 LGAM P50' ATCC 36502 ATCC 48595 ATCC 48603 CBS 44977 CBS 80485 CBS 72483 LGAM P63' LGAM P64 LGAM P65 LGAM P66' ATCC 36047 CBS 13021 CBS 10082 LGM 851101 LGM 81 LGM 850404' LGM 841043 LGM 831101" LGM 831102 LGM 820301 LGM 80' ATCC 38138 CBS 66585 MUCL 28913 F 1 LGAM P51 LGAM PIS* LGAM P35" LGAM P38 LGAM P57 LGAM P58 LGAM P59 LGAM P60" LGAM P61' LGAM P62 LGAM P67 LGAM P68 LGAM P69 LGAM P71 ATCC 32783 ATCC 34675"' ATCC 38538" CBS 12513 CBS 37551 CBS 29147 LGM 850401 LGM 24 LGM 59 LGM 841101

G. Zervakis and C. Balis 719

Table 1 (cont.)

Strain Host/ no. Species substrate

Geographic Acquisition origin sourcet

P. ostreatw P. ostreatus P. ostreatw P. ostreatw P. ostreatw P. ostreatw P. ostreatw P. ostreatus P. ostreatus P. ostreatus P. pulmonarius P. pulmonarius P. pulmonariw P. pulmonarius P. pulmonariw P. pulmonariw P. pulmonariw P. pulmonariw P. pulmonariw P. pulmonarius P. pulmonarius P. pulmonarius P. pulmonariw P. pulmonariw P. pulmonarius P. pulmonariw P. pulmonariw P. pulmonarius P. sajor-caju P. sajor-caju P. sajor-caju P. sajor-caju P. sajor-caju P. sajor-caju P. sajor-caju P. sapidw

Salix sp. Fagw sylvatica Quercw sp.

Fagw sylvatica F. sylvatica F. sylvatica F. sylvatica F. sylvatica F. sylvatica F. sylvatica Unidentified stump Fagw sp. Abies alba Populw tremula

Euphorbia royleana

Hardwood

Hungary France ex-Czechoslovakia Belgium U.S.A. U.S.A. U.S.A. lndia lndia Brazil Vardoussia. Greece Vardoussia, Greece Vardoussia. Greece Vardoussia. Greece Vardoussia, Greece Vardoussia. Greece Rodopi, Greece ex-Czechoslovakia Germany Germany Sweden Netherlands France France Belgium U.S.A. U.S.A. U.S.A. India India India India India Malaysia Hong Kong U.S.A.

LGM 850402 LGM 22 LGM 851001 MUCL 19000 ATCC 52946 ATCC 52952 ATCC 52965 LGM 23 LGM 40 ZA 02 LGAM PI* LGAM PZ" LGAM PI3 LGAM PI6 LGAM P26' LGAM P46** LGAM P47 ATCC 36050" ATCC 42046 ATCC 42047 ATCC 42048 CBS 50785 CBS 65487 LGM 850403 MUCL 29418 ATCC 52968 ATCC 52969 CBS 13285 ATCC 32078 LGM 13145 LGM 35 LGM 37- LGM 851003 MUCL 28683 MUCL 29757 ATCC 24986**

Dikaryotic strains deposited in ATCC and/or MUCL. '* Monokaryotic tester-strains deposited in ATCC. t The Pleurotw isolates used were obtained from the following fungal culture collections: ATCC: American Type Culture Collection, Rockville, MD, U.S.A.

CBS: Centraalbureau voor Schimmelcultures, Baam, The Netherlands. MUCL: Mycotheque de I'Universite Catholique de Louvain, Belgium. LGM: Laboratoire de GCnCtique Moleculaire et d'AmClioration des Champignons CultivCs, UniversitC de Bordeaux 11, France. ZA: Instituto de BotPnica, SPo Paulo, Brazil. LGAM: Laboratory of General and Agricultural Microbiology, Agricultural University of Athens, Greece.

MATERIALS AND METHODS

Organisms

For the needs of this study, 101 wild dikaryotic strains of Pleurotus (Basidiomycotina) were examined. Details on each strain's initial identity (taxonomic assignment they carried when they were obtained), geographic origin, host/substrate and acquisition source, appear in Table 1.

Culture media and establishment of monokaryotic cultures

The culture media used were: (i) complete yeast medium (CYM) for routine cultures and storage purposes (Raper, Raper & Miller, 1972); (ii) potato dextrose agar (PDA, Difco) for growth rate measurements; (iii) cellulose medium (CM) for

growth rate measurements and estimation of cellulose degradation efficacy (Eggins & Pugh, 1962).

Fruit bodies were produced, under precisely controlled environmental conditions, 40-90 d (depending on the Pleurotus species cultivated, see below) after inoculation of a comcobs- based substrate (Zervakis & Balis, 1992). Following harvest, single basidiospore isolation was performed as described elsewhere (Zervakis ef nl., 1994), and more than 20 individual germlings per dikaryon were picked up under microscope observation and placed one by one in separate Petri dishes. When resultant monokaryotic colonies reached 6-8 mm diam. they were transferred to slants with CYM for storage at 4 OC.

Pairing experiments

Pairings were performed in 90 mm Petri dishes with CYM. Agar plugs (3 mm diam.) from 12 monokaryotic isolates for

The pluralistic species concept in Pleurofus

each Pleurotus dikaryon were placed in pairs, about 15 mrn apart, in all possible combinations. Then they were left until resultant colonies overgrew the space between the inocula and developed a contact zone (usually after 3-6 d). However, pairings were not interpreted until 1-2 wk after inoculation, in order to have an established nuclear migration and a well- formed confrontation zone. Additional pairings were carried out when these self-crosses failed to reveal all four mating types for a given dikaryon. For pairings among homokaryons from different dikaryons, two tester strains were selected out of each one of the four incompatibility groups from every dikaryon, and then were paired in all combinations and in the same way as in the case of the self-crosses. Pairings were scored as compatible if clamp-connexions could be observed on the hyphae, both in the contact zone and away from it, under the microscope (400 x ).

Dikaryon-monokaryon matings were also performed among two compatible tester strains (obtained from each dikaryon as described above) and the rest of the dikaryons studied. For this purpose, agar plugs from the monokaryon and the dikaryon were placed 30 mm apart (so that the latter could not overgrow the former in a short time) in Petri dishes. As soon as the two resultant colonies established a contact zone, the converse side of the monokaryon donor block was examined for clamp-connexions (through nuclear migration, 'Buller phenomenon'). Furthermore, hyphae from the same part of this colony were transferred to another Petri dish, left to grow and then examined again for clamp-connexions.

Morphological and physiological feahrres

Spore prints were obtained by fixing pieces of pilei over sterile white paper. Spores, basidia, hyphae and cystidia were measured with the aid of a micrometer in a Leitz microscope. Colour description and encoding terminology are from Maerz & Paul (1930).

Mycelium growth rates were estimated in 90 mm Petri dishes, containing 15 ml of medium (PDA and CM), with four replicates of each dikaryon. Inocula of 3 mm diam. taken from the periphery of 5-d-old colonies, were placed in the centre of the dishes and measurements were taken every 24 h for 6 d (at 23').

Cellulose degradation efficacy (CDE) was defined as: (Rtr- Rcl)/Rcl, where Rcl is the colony radius, and Rtr is the radius of the zone of transparency which was formed (due to cellulose degradation by the fungus) after flooding 5-d-old colonies growing on CM in Petri dishes with KI-HCl reagent (1% I and 2% KI in 0.1 M HCl). Four replicates of each dikaryon were used.

Earliness was defined as the time period between substrate inoculation and appearance of the first basidiomata, while temperature optima for fructification were established as the temperature range mostly preferred by the various taxa to produce fruit bodies within the quoted earliness values.

In all experiments, at least five dikaryons under each name were examined; except when only fewer isolates for a particular morphotaxon were available, in which case all were used.

RESULTS A N D DISCUSSION

This work forms the concluding part of an integrated study carried out by the authors on the taxonomic infrastructure of Pleurofus. Previously, special emphasis had been placed in the application of biochemical (isozyrnes: use of isoelectric focusing and starch gel electrophoresis) and molecular (RFLPs) techniques (Zervakis & Labarere, 1992; Zervakis ef al., 1994; Iracabal, Zervakis & Labarere, 1995). After analysing morphological, physiological and cultural characteristics of numerous Pleurofus strains and extensive matings among them, an up-to-date account of the systematics in this genus is presented here.

Self-crosses revealed a bifactorial heterothallic mode of sexual reproduction for all Pleurottis taxa examined. This tetrapolar system with multiple alleles was also clearly demonstrated in all previous compatibility studies on Pleurofus species (e.g. Anderson ef al., 1973; Eger ef a/., 1979; Hilber, 1982; Vilgalys ef al., 1993; Petersen, 1995~) . The results of the matings performed, in the frame of the present work, among monokaryotic isolates (mon-mon) and monokaryotic and dikaryotic strains (di-mon) of Pleurotus are outlined in Table 2.

The physiologicai features of the European morphotaxa studied are also furnished. Strains from each particular taxon (constituent dikaryons listed under 'material examined' in the respective morphological descriptions) were analysed; the mean values and the variation were calculated and the results are illustrated in Figs 1 and 2.

A detailed morphological description for each Pleurofus taxon follows, supplemented with compatibility and physiological data, and a commentary on the taxonomic status and the genetic relationships of each biological entity is provided as well.

Pleurotus calyptratus (Lindblad) Sacc.

Matings. All three P. calypfrafw isolates examined were not found to be interbreedable with any one of the other Pleurotus

Table 2. Outline of the results obtained from the crosses among rnonokaryotic tester-strains of the 101 Pleurotw dikaryons examined, originally assigned to 13 rnorphotoxa

+ = compatible matings; - = incompatible matings. Abbreviations used: cp: P. calyptratw, ci: P. citrinopileatus, cl: P. columbinw,

cr: P. cornucopiae, cs: P. cystidiosw, dr: P. d y i n w , er: P. eryngii, fl: P. flabellatus, op: P. opuntiae, 0s: P. ostreatw, pl: P. pulmonariw, sc: P. sajor-caju, sp: P. sapidw.

G. Zervakis and C. Balis

6 orange to warm brown (12/5E to 11/3E to 9/41 to 15/11E), with broad, inrolled to sinuate margin. Lamellae thin, dense, decurrent to the top of the stipe, entire, without anastomoses

4 but with numerous lamellulae, cream to light beige (10/3C to - - I u 11/3E). Stipe absent. Presence of veil extending from the

2 pileal margin to the base of pileus, white to cream (to 10/3C). - 2 0

Odour neutral or honey-like. Taste mild. Flesh solid and thick, E white to cream (to 10/3C). 9 Basidiospores 8.5-1 17.0 x 3.0-6-5 pm (average 12.20 f e 0 9 1.73 x 4.75 f0 -93 pm), cylindric to elliptic, thin-walled, with

e a small and broad apiculus, containing yellow oily drops and granules. Spore print (dry) white to cream (to 10/3C). Basidia

2 35-45 x 8.0-11.0 pm, cylindric, thin-walled; sterigmata 4, 5 pm long. Cheilocystidia and pleurocystidia absent. Hyphal

4 system dimitic. Pileipellis 120-140 pm thick, with irregular cp cl cr cs dr er op os pl interwoven, thin-walled generative hyphae. Pileus trarna

PIeurotus morphotaxa composed of tightly interwoven, thin-walled and sclerified Fig. 1. Cellulose degradation efficacy (I, CDE) and growth rates on generative hyphae 3'8-6.8 pm dim. and PDA (0) and CM (8) of nine pleurotw morphotaxa (cp: p, hyphae 4.0-6.6 pm diam. Lamellar trama irregular with thin- calyptratus, cl.: P. columbinw, cr: P. cornucopiae, cs: P. cystidiosw, dr: P. walled generative hyphae 5'2-6.2 I J ~ diam., sclerified thick- dryinw, er: P. eryngii, op: P. opuntiae, 0s: P. ostreatw, pl: P. walled generative hyphae, 6.4-9.8 pm diam. and thick-walled pulmonariw). The bar for each taxon represents the mean of the skeletal hyphae 4.0-6.0 pm diam. Stipe context irregular, values of its constituent strains, while the line extending from top composed of i n t e ~ o v e n , thin-walled generative hyphae: and bottom indicates the average variation. 3.6-5.0 diam. and sclerified thick-walled generative hyphae

8-2-10.2 pm diam., and numerous thick-walled hyphae 4.6-

loo 0 6-2 pm d i m . All generative hyphae with clamp-connexions.

9n Subhymenium formed of tightly packed thin-walled short cells

Pleurotus morphotaxa

Fig. 2. Earliness (d) and optimal temperature (OC) for production of basidiomata for nine Pleurotw morphotaxa (cp: P. calyptratus, cl: P. columbinw, cr: P. cornucopiae, cs: P. cysfidiosus, dr: P. dryinw, er: P. eryngii, op: P. opuntiae, 0s: P. ostreatus, pl: P. pulmonarius). ., Earliness; H, temperature.

strains, while they were perfectly compatible in the crosses among them.

Habit, habitat and distribution. A relatively rare fungus, usually appearing in small groups from late spring until autumn chiefly on poplar (Populus alba, P. tremula, etc.). It presents a limited distribution in countries of central and eastern Europe, i.e. Germany, Hungary, Croatia, Slovakia and Russia (Pilat, 1935; Tortic & Hocevar, 1977; Hilber, 1981; D. Samgina, pers. comm.).

Pileus at first flat, smooth, semicircular to mussel-shaped, colour beige-brown to warm brown to brown (13/6E to 15/11E to 15/7C); at maturity, size 4.0-11-0 cm, circular to oyster-like, mostly flat, beige-buff to light beige to beige-

3.5-5.0 pm d i m . Basidiospores, basidia and trama hyaline in KOH and Melzer's reagent.

Pigments absent on mycelial cultures. Dikaryotic colonies with dense and flat aerial, and submerged mycelium, more or less radial; margin even, colour white to cream (to 10/3C); hyphae irregularly interwoven with abundant clamp-connexions.

Myceliumgrowth rates. 1.0 mm d-' on PDA and 1.2 mm d-' on CM. Cellulose degradation efficacy was high (#le82). Basidiomata produced in vitro after 70-80 d at a preferred temperature of 20°.

Material examined. ex-Czechoslovakia, coll. A. Ginterova (ATCC 52209); ex-Czechoslovakia, 1958, coll. A. Czemy, on a dead tree of Populus alba (MUCL 28909); ex-Czechoslovakia, 1958, coll. A. Czemy, on roots of Populus alba (MUCL 28910).

The only species assigned to the section Calypfrafi by Singer (1986) is P. calyptratus. Although it shares many morphological similarities with P. d y i n u s , it can be distinguished thanks to -

the absence of stipe and chlamydospores and the formation of a pellicular veil. Furthermore, its mycelium grows faster and in vifro fructification is realized earlier. Hilber (1982) also referred to the presence of arboriform skeletal hyphae in P. calyptratus trama, the period of the year they produce their basidiomata (P. calyptratus from summer to October, P. d y i n u s from September to spring) and the substrate-specificity for P. calyptratus (growing only on Populus spp.). The latter, however, does not seem to hold true as there are reports on the existence of other P. calyptratus hosts, e.g. Tremula spp. (D. Samgina, pers. comm.; mentioning its occurrence in Kazakh- stan, Siberia and eastern Russia, too). In addition, all crossing


experiments performed among isolates of the two species in the frame of this study showed complete incompatibility, confirming therefore their distinct taxonomic status.

Pleurotus cornucopiae (Paulet) Rolland

Matings. The outcome of the crosses among monokaryons from P. cornucopiae and P. citrinopileatus was positive in the vast majority of confrontations (81-loo%, with the 50% of the individual crosses producing 100% dikaryons), while di- mon matings between them were all successful.

Habit, habitat and distribution. Appears from late spring . .

until autumn on various host (Quercus, Alnus, Fagus, Fraxinus, Acer, Prunus, more usually Ulmus trees). It is widely dis- tributed throughout Europe, from England, Spain, France and Germany to Italy, Croatia and Greece to Slovakia, Poland and Russia (Romagnesi, 1969; Hilber, 1982; Zervakis, 1992; M. Garcia-Rollan, pers. comm., D. Samgina, pers. comm.).

Pileus at first flat, smooth to velvet-like, circular to mussel- shaped, colour yellow to bright yellow to light warm yellow (9/3L to 17/1L to 9/2J); at maturity, size 3.5-8.0 cm, circular, flat around the periphery and becoming infundibular towards the centre, smooth, cream to orange-beige to light yellow to lemon yellow to yellow (10/3C to 10/51 to 9/11 to 9/1L to 9/3L), with even margin. Lamellae thin, wide, dense, decurrent up to the base of the stipe, entire edges, with frequent anastomoses, cream to light beige to light yellow (10/3C to 11/3C to 9/11), Stipe size 1.0-3.5 cm; central-subcentral, seldom lateral, cylindric to fistulose, solid, smooth, colour same as lamellae. Flesh compact but relatively thin and fragile, cream in colour (10/3C). Odour anise-like. Taste mild and occasionally spicy.

Basidiospores 6.5-13.5 x 3.0-5.0 ym (average 9.08 f 1.12 x 3.98,0-43 ym) subcylindric to ellipsoid, thin-walled, with

a distinct broad apiculus. Spore-print (dry) dark purple to purple (7/4E to 7/6E). Basidia 25-36 x 5.6-6.8 ym, cylindric, thin-walled; sterigmata 4, 2 Vm long. Caulocystidia as long sterile hymenial elements, 16-20 x 2.8-5.4 ym size. Cheilo- cystidia and pleurocystidia absent. Hyphal system dimitic. Pileipellis 70-120 ym broad, with regular interwoven, thin- walled generative hyphae and clamp-connexions. Pileus trama composed of tightly interwoven, thin-walled and sclerified generative hyphae, 5.5-12 Vm diam.; and thick-walled skeletal hyphae, without clamp-connexions, 4.0-7.0 ym diam. Lamellar trama irregular with thin-walled generative hyphae 3.9- 9.4 vm diam., sclerified, thick-walled generative hyphae 1-5-2.8 diam. and skeletal hyphae thick-walled, 2.8-4.1 ym diam. Stipe context irregular, composed of interwoven thin- walled generative hyphae 6.0-13.2 ym diam., sclerified thick- walled generative hyphae 7.9-10.0 ym diam.; and numerous thick-walled skeletal hyphae 3.5-4.9 ym diam. All generative hyphae with clamp connexions. Subhymenium formed of thin- walled short cells 3.0-5.0 ym diam. Basidiospores, basidia and trama hyaline in KOH and Melzer's reagent.

Pigments absent on mycelial cultures. Dikaryotic colonies with submerged and a mostly flat and dense aerial mycelium, mostly radial with even margin, colour white to cream to

ivory (to 10/3C to 10/2B); thin-walled hyphae with clamp- connexions.

Myceliumgrowth rates. 2.8 mm d-' on PDA and 1.2 mm d-' on CM. Cellulose degradation efficacy- of the fungus was very high (#2.78). Basidiomata produced in vitro after 45-55 d at a preferred temperature of l5O.

Material examined. Germany, coll. F . Zadrazil (ATCC 38547); ex- Czechoslovakia, coll. 0. Hilber, on Ulmus sp. (ATCC 42045); United Kingdom, coll. K. Cartwright (CBS 27633); The Netherlands, on Ulmus sp. (CBS 38380); Belgium (MUCL 28732).

Pleurotus cornucopiae is a well-known species of the European mycobiota. It is mainly distinguished from the other taxa of the section Pleurotus, thanks to the convex to infundibuliform whitish to yellow pilei, the fistulose-dichotomic subcentral stipe, the dimitic hyphal system and the distinctive purple spore-print colour. All the examined P. cornucopiae strains demonstrated also an increased efficacy in metabolizing cellulose. Until recently, P. citrinopileatus was thought to be a separate species (Singer, 1986) occurring in the eastern part of the Asiatic continent (Japan, China, far-eastem Russia). In spite of its close morphological resemblance to P. cornucopiae, it was reported to differ in the bright yellow colour of the pilei, smaller basidiospores, lighter spore-print colour, abundance of cheilocystidia, monomitic trama and the habitat (Hilber, 1982). However, comparative in vitro cultivation trials yielded pilei of the same colour for both P. cornucopiae and P. citrinopileatus strains examined. In addition, the hyphal system of P. citrinopileatus isolates was in all cases dimitic and differences in spore-print colour and basidiospore size were rather minute. Still more important, crosses among monokaryons of the two taxa presented 81-100% compatibility (for half of the pairings the compatibility was 100%). Thus, the mating studies of Ohira (1990) and Petersen & Hughes (1993) are confirmed, and P. citrinopileatus should be considered as a morphovariety of P. cornucopiae. The relatively high percentages of intercompatibility noted here suggest that although their occurrence is recorded at distant regions, the gene flow between them is not hindered, probably because they show a more or less uniform geographical distribution throughout Eurasia. A similar situation with increased genetic information exchange was evidenced (through the use of enzyme patterns) among P. pulmonarius collections originating from the same greater area (Petersen, 1995 b).

Pleurotus cystidiosus 0. K. Mill.

Only one strain of this species has been so far isolated and described from Europe (Zervakis, Dimou & Balis, 1992).

Maferial examined. Basidiomata (together with the imperfect state of the fungus, a synnematoid anamorph) were recovered from the island of Salamina, near Piraeus, Greece from the trunk of a fig-tree (Ficus carica L.) in May 1990, coll. D. Dimou & G. Zervakis (LGAM P50).

The subgenus Coremiopleurotus 0. Hilber includes isolates with the distinct character of forming asexual synnematoid anamorphs (assigned to Anfromycopsis); but also possesses several other taxonomic characteristics such as the oblong- elliptical basidiospores, the abundance of clavate pileocystidia and cheilocystidia, very slow growth rates, increased cellulo-


lytic activity, etc. Among the taxa placed within this subgenus, P. cystidiosus is considered to be the type species. It presents a wide distribution being already reported from the United States, South Africa, Europe and Asia (Miller, 1969; Moore, 1985; Zervakis et al., 1992). On the latter continent, many recorded strains were assigned the name P. abalonus Han, Chen & Cheng (1974), while another closely related taxonomic entity is P. smithii detected in Latin America (Guzmin, Valenzuela & Canale, 1980; A. Arambarri, pers. comm.); and a fourth coremia-producing taxon has been described from New Zealand, P. purpureo-olivaceus [=P. mttenbuyi Segedin (1984)] Segedin, Buchanan & Wilkie (1995). It is obvious that the relationships within the P. cystidiosus species complex remain ambiguous, and it is yet far from clear whether the taxa mentioned above form distinct biological species or not. Preliminary investigations of the authors have so far demonstrated a pairing incompatibility among P. cystidiosus, P. smithii and P. purpureo-olivaceus isolates, as well as a very restricted ability to interbreed between P. abalonus and P. cystidiosus (G. Zervakis, unpublished results). Initial speculation for gradual genetic divergence and endemism should hold true for several populations of this species complex, due to their non-continuous geographical distribution and existence of physical barriers obstructing gene flow among them.

Pleurotus dryinus (Pers. : Fr.) P. Kumm.

Habit, habitat and distribution. Grows by forming single basidiomata, in autumn and winter, on a variety of hosts such as Picea, Iuglans, Malus, Alnus, Fagus and Ulmus trees. This species is reported to occur throughout Europe (Norway, The Netherlands, Germany, Spain, Italy, Austria, Croatia, Slovakia, Russia) (Tortic & Hocevar, 1977; Hilber, 1981; Venturella, 1991; M. Garcia-Rollan, pers. comm.).

Pileus at first flat, smooth, semicircular to mussel-shaped, beige-buff to beige-brown to warm brown to brown (12/5E to 13/6E to 15/ I IE to 16/7C); at maturity, size 7.0-11.0 cm, mussel-shaped to oyster-like, flat to convex, coarse-looking, beige-brown to beige-buff to light beige to beige-orange (13/6E to 12/5E to 11/3E to 9/41), with broad to sinuate margin. Lamellae thin, dense, decurrent to the top of the stipe, entire edges, with frequent anastomoses particularly close to the stipe where they often form a net, cream to light warm yellow to light beige-orange (10/3C to 9/21 to 10171). Stipe size 3-0-5.5 cm, lateral to central, cylindric to subcylindric to fistulose, solid, smooth, white to cream (to 10/3C). Presence of veil extending from the pileus rim to the upper part of the stipe, coloured cream to ivory (10/3C to 10/2B). Odour sometimes distinct and unpleasant. Taste mild. Flesh firm and solid, white to cream (to 10/3C).

Basidiospores 8.5-15.0 x 3.0-5.5 pm (average 11.92 & 1.61 x 4.15 +0-66 pm), cylindric, thin-walled, with a small and broad apiculus, containing yellow oily drops and granules. Spore print (dry) white to cream to light yellow (to 10/3C to 9/11). Basidia 45-60 x 8.0-10-0 pm, cylindric, thin-walled; sterigmata 4, 5 pm long. Cheilocystidia and pleur~c~stidia absent. Hyphal system dimitic. Pileipellis 110-130 pm broad, with irregular interwoven, thin-walled generative hyphae.

Pileus trama composed of tightly interwoven, thin-walled and sclerified thick-walled generative hyphae 5.2-11.4 pm diam. and thick-walled skeletal hyphae (without clamp-comexions) 6.2-9-0 ~ l m diam. Lamellar trama irregular with thin-walled generative hyphae 4.C-6.2 ~ l m diam., sclerified thick-walled generative hyphae 7-0-10-8 pm diam.; and skeletal hyphae thick-walled 4.0-5.6 pm d i m . Stipe context irregular, composed of interwoven, thin-walled generative hyphae 4.0- 5.4 diam. , sclerified thick-walled generative hyphae 7.0- 11-2 pm diam. and numerous thick-walled skeletal hyphae 5.0- 5.8 pm diam. All generative hyphae with clamp-connexions. Subhymenium formed of tightly packed thin-walled short cells 3.0-40 diam. Frequent presence of oleiferous hyphae and basidia with yellow contents. Basidiospores and basidia hyaline in KOH and Melzer's reagent; trama yellowish in KOH.

Pigments absent, but present brown chlamydospores (average size: 14-0-25.0 v) present on mycelial cultures. Dikaryotic colonies with flat and dense aerial, and submerged mycelium, margin even to more or less fringed, colour dark green to olive green to brown to warm brown (18/4E to 18/9B to 15/7C to 15/11E) and white only at the periphery; hyphae irregularly interwoven with abundant clamp-connexions.

Mycelium growth rates. 0.4 mm d-' on PDA and 0.3 mm d-' on CM. Cellulose degradation efficacy was very high (#2.44).

Basidiomata produced in vitro after 75-85 d at a preferred temperature of 20'. Material examined. Germany, coll. H. Lyr (ATCC 36502); Norway, Vennesla, Vest-Adger, October 1982, coll. F. Roll-Hansen, on stored timber of Populw tremula (ATCC 48595); Norway, Kristiansand, Vest-Adger, October 1956, coll. F. Roll-Hansen, on ftrglans regia (ATCC 48603); ex-Czechoslovakia (CBS 44977); The Netherlands (CBS 72483); The Netherlands (CBS 80485). Among the well-distinguished Pleurotus species is P. dyinus , placed in the section Lepiotarii (Fr.) Pilit (Singer, 1986). It produces light beige to light brown pilei, chlamydospores in culture, has a distinct veil and dimitic hyphal system, very slow growth rates and high cellulase production. Although it was previously reported that P. dy inus cannot fruit under laboratory conditions (Hilber, 1982), we obtained basidiomata after a cultivation period of about 80 d at 20°, but germination of basidiospores was very limited. Thus it appears that the chlamydospores play an essential role in the biological cycle of this fungus (they germinate quite easily). O n the other hand, the crosses ~erformed did not yield any evidence for the existence of more than one subspecies ('Kleinarten') of P. dy inus as Hilber (1982) had assumed because of the variability he observed in basidiospore dimensions. The occurrence of P. dyinus is reported from Europe, Africa (Alexandria, Egypt; Pilit, 1936), Asia (Siberia and far-eastem Russia; D. Samgina, pers. comm.) and N. America (Vilgalys & Sun, 1994). There are also records of other related Pleurotus taxa bearing a distinct veil: P. vehfus Segedin, Buchanan & Wilkie (1995) in New Zealand, P. pomefi (Fr.) QuPI. (Pilit, 1935) with elongated spores and host-specific on Malus spp., P. rickii Bres. and P. lindquistii Singer (Singer, 1986). With the exception of P.


porneti which is possibly a form of P. dryinus, the rest require further examination and more importantly mating with European P. dryinus strains before any definite conclusions can be drawn on their exact taxonomic identity.

Pleurotus eryngii (DC. : Fr.) Qud.

Matings. Pairings among single-spore isolates (mon-rnon) of P. eyngii deriving from Eryngiurn hosts demonstrated an intercompatibility of loo%, and the same percentage was obtained out of strains isolated from Laserpitiurn plants, while a slightly lower value was scored among strains from Ferula spp. (94%). As regards crosses among these three host-based groups, there was 25-88 % compatibility between isolates grown on Eryngiurn and Laserpitiurn plants, 38-75% between strains from Eyngiurn and Ferula, and 31-63% between individuals from Ferula and Laserpitiurn. Crosses among dikaryons and monokaryons (di-mon) of P. eyngii were almost always compatible (95-100% dikaryotization of monokaryons by the mating dikaryons).

Habit, habitat and distribution. A fungus of the northern hemisphere, a weak parasite on the roots of Umbelliferae (Eyngiurn carnpesfre, E. rnaritirnurn, E. alpinurn, E. planurn, E. maroccanurn, Ferula cornmunis, Ferulago galbanifera, Cachrys ferulacea, Laserpitiurn latifoliurn, L. siler, L. gallicurn, Diplotaenia cachrydifolia, 0. darnavandica, Elaeoselinurn asclepiurn, Opopanax chironiurn, Prangos ferulacea) and Compositae (Peucedanum spp., Scorzonera uillosa, Tragopogon porrifolius), appearing mostly in groups from autumn until late spring. The geographical distribution lies within a rather well-defined area between about 30-50° N (between N. France, S. Germany, Poland, S. Russia, and the Mediterranean coastal belt of Africa, Iran, Afghanistan), westwards to the Atlantic coasts of France and Morocco, and eastwards to the western borders of India and China. Particularly for Europe present, in France: the Cher, Loire, Sa6ne and Rhbne valleys, the Alps, on the southwest coast and in Corsica (Cailleux & Diop, 1976; Cailleux, Diop & Joly, 1981; Joly, Cailleux & Cerceau, 1990); in continental Italy: from the Alps along the Apennines till the Etna and Nebrodi mountains, as well as in Sicily and Sardinia (Bresadola, 1928; Ferri, 1985; Venturella, 1991); in continental Greece, Crete and on the islands of the Aegean sea (Zervakis, 1992); in Spain, Croatia, Slovakia, Hungary and Russia (Hilber, 1982; M. Garcia-Rollan, pers. comm.).

Pileus at first flat to slightly convex, smooth, circular to mussel-shaped, colour warm grey to beige-buff to light beige (I5/11E to 12/5E to 11/3C) with a few scattered light brown spots (15/9C); at maturity, size 4.0-12.5 cm, mostly flat and circular, smooth, dry, warm brown to light beige to beige brown (15/11E to 11/3C to 13/6E), covered with numerous beige brown to light brown squammules (13/6E to 15/9C), with even or slightly sinuate and inrolled margin. Larnellae thin, broad, not particularly dense, decurrent to the top of the stipe, entire, without anastomoses, cream to ivory to light beige-orange (10/3C to 10/2B to 10/71). Stipe size 1.5-3.5 x 0.5-2.5 cm, central and seldom subcentral, mostly cylindric, solid, with floccule mainly around its base, cream to ivory (10/3C to 10/2B). Flesh firm but sometimes elastic,

solid, white to cream. Odour mild to anise-like. Taste mild and distinctively pleasant.

Basidiospores 8-0-13.0 x 3.5-6.0 pm (average 10.43 + 1.54 x 4.70 k0.68 pm), cylindric, thin-walled, with a small and broad apiculus, usually with yellow contents. Spore print (dry) cream to light yellow to light brown (10/3C to 9/11 to 15/9C). Basidia 30-52 x 7-1-8.8 pm cylindric, thin-walled; sterigmata 4, 4 pm long. Caulocystidia infrequent, mostly on the upper half of the stipe, as pubescence. Cheilocystidia rare, same as before. Pleurocystidia absent. Hyphal system monomitic. Pileipellis 260-420 pm broad, with irregular interwoven generative hyphae. Pileus trama composed of tightly arranged hyphae 4.1-5.5 pm. Lamellar trama with irregular, branched hyphae 3.9-5.4 pm diam. Stipe context composed of irregular interwoven hyphae 4-6-8.5 um diam. All generative hyphae thin-walled, with clamp-connexions. Subhyrnenium formed of tightly packed thin-walled short and broad cells. Basidiospores, basidia and trama (with occasional presence of oleiferous hyphae) hyaline in KOH and Melzer's reagent.

Pigments absent on mycelial cultures. Dikaryotic colonies mostly presenting a loose submerged and suppressed aerial mycelium, more or less zonate and radial, even margin, colour white to cream (to IO/SC); thin-walled hyphae with abundant clamp-connexions; occasional production of microdroplets, singly on short secretory sterigmata on aerial hyphae (for nematode trapping).

Myceliumgrowth rates. 3.7 mm d-' on PDA and 2.8 mm d-' on CM. Cellulose degradation efficacy was low (#0.18). Basidiomata produced in uitro after 75-85 d at a preferred temperature of 20°.

Material examined. Greece, Crete, Croustas, January 1989, coll. E. Vasilakis & G. Zervakis, on Eyngiurn campestre (LGAM P63); same location, date and substrate (LGAM P64); Greece, Evros, Orestiada, March 1989, coll. J. Franzeskakis & G. Zervakis, on Ferula sp. (LGAM P65); same location and substrate, April 1989 (LGAM P66); ex- Czechoslovakia, coll. A. Ginterova, from field (ATCC 36047); Italy (CBS 13021); France, donated by J. Labarere, on Eryngium sp. (LGM 851101); same location and substrate (LGM 820301); France, donated by J. Labarere, on Ferula sp. (LGM 80); same location and substrate (LGM 81); France, donated by J. Labarere, on Laserpitiurn latifolium (LGM 831101); same location and substrate (LGM 831102); Hungary, donated by J. Labarere, on Eyngium sp. (LGM 850404); Italy, donated by J. Labarere, on Ferula sp. (LGM 841043).

The P. eryngii species-complex includes isolates which are weak parasites on the roots and stems of Umbelliferae plants. The white to brown pileus colours scattered with numerous beige squamules, the well-developed central to subcentral stipe, the relatively large basidiospores, the morphology of the mycelial colony and the long incubation period before fructification in uitro were assessed as the principal distinctive features of P. eyngii. This species was in the past extensively studied by Hilber (1982), who concluded that it could be divided into three host-specific varieties: P. eyngii var. eryngii, P. eryngii var. ferube Lanzi and P. eyngii var. nebrodensis (Inzenga) Sacc. The results of the present work limitedly confirm his data; in this case the three ecotypes appear to be already quite distant, especially var. nebrodensis from the other two (percentages of compatible matings around 45% in


confrontations including nebrodensis, in contrast to about 60% between vars eryngii and ferulae). The morphological distinc- tions are rather minute, and related with pileus colour and basidiospore dimensions, tending to collapse when the fungi are grown in vitro. On the other hand, previous biochemical and molecular studies, which included some of the strains used here, demonstrated high levels of phenetic similarities within the P. eyngii group (Zervakis et al., 1994; Iracabal et al., 1995). A genetic isolation is apparently under way, however, based on ecological (not only host, but also climate dependent) specialization; the three taxa are still compatible (at least in the laboratory) and therefore cannot be considered to belong to independent species; in spite of other views supporting such a separation, especially regarding 'P. nebrodensis sensu lato' (var. nebrodensis and var. hadamardii Costantin) (Joly et al., 1990). This Pleurotus group could be rather divided into subspecies, each presenting a distinct habitat specialization - resembling the 'microevolutionary units' (Duncan, 1972) - within a common area. In the past, similar speciation processes were noted in Heferobasidion annosum (Fr.) Bref. (Worrall, Parmeter & Cobb, 1983), Puxillus involutus (Batsch: Fr.) Fr. (Fries, 1985) and Peniophora cinerea (Pers: Fr.) Cooke (Chamuris, 1991). Recently, Vilgalys & Sun (1994) reported that some isolates assigned to P. eryngii from Europe and P. fossulatus (Cooke) Sacc. from India were found to be intercompatible. Although no further details were fumished (e.g. percentages of successful matings), a comparison of the anatomical features of P. eryngii studied here with a description of P. fossulatus fumished by Pegler (1977 a), reveals a morphological resemblance indicating their possible taxonomic affinity.

Pleurotus opuntiae (Durieu 6 Lev.) Sacc.

Matings. Only one P. opuntiae strain was examined and was found to be incompatible with all other Pleurotus strains.

Habit, habitat and distribution. Rare fungus of the Mediterranean region, already reported from Spain, Italy, Greece and the north coast of Africa. It appears in autumn and winter, mostly in small groups on residues of Opuntia, Agave, Yucca and Pky tolacca plants (Bresadola, 1928 ; Hilber, 1982 ; Ferri, 1985 ; Venturella, 1991).

Pileus at first flat to slightly convex, smooth, semicircular to oyster-shaped, colour white to cream (to 10/3C); at maturity, size 4.0-12.0 cm, flat and often concave towards the centre, spathulate to circular, smooth, dry, cream to ivory or light yellow (10/3C to 10/2B or 9/11), with slightly inrolled and lobed margin. Lamellae thin, broad, dense, decurrent to the base of the stipe, with 3-4 tiers of lamellulae, entire, without anastomoses, white to cream (to 10/3C). Stipe short (0.8-1-5 x 0.3-1.2 cm), lateral to subcentral, cylindric, solid, fibrous, cream to ivory (10/3C to 10/2B). Flesh soft to firm, whitish. Odour neutral. Taste mild.

Basidiospores 7-5-12.0 x 3.0-5.0 ym (average 923 f 1.14

in size. Hyphal system dimitic. Pileipellis 210-380 pm broad, with irregular interwoven generative hyphae. Pileus trarna formed by tightly arranged generative hyphae 5.2-76 ~ u n in size; towards the subhynenium interwoven with skeletal hyphae. Lamellar trama irregular and branched, mostly composed of thick-walled skeletal hyphae, with clamp- connexions 3.9-5.0 pm diam.; generative hyphae 4.5-6.5 pm diam. Stipe context formed of irregular and interwoven generative hyphae 49-7.8 ~ u n diarn. All generative hyphae thin-walled with clamp-connexions. Subhymenium with thin- walled short and broad cells 4 . 0 4 0 size. Basidiospores, basidia and trama (occasional appearance of oleiferous hyphae) hyaline in KOH and Melzer's reagent.

Pigments absent on mycelial cultures. Dikaryotic colonies with submerged and a mostly flat and dense aerial mycelium, even margin, colour white to cream (to 10/3C); thin-walled hyphae with abundant clamp-connexions.

Mycelium growth rates. 3 mm d-' on PDA and 2.4 mm d-' on CM. Cellulose degradation efficacy was low (#Oe31). Basidiomata produced in vitro after 60-70 d at a preferred temperature of 20'. Material examined. Greece, Crete, Kalo Horio, November 1993, coll. E. Papadakis, on Agave sp. (LGAM P51).

The Pleurotus morphotaxa with white to tan to pink basidiomata present a wide distribution throughout the world, being frequently reported from tropical and subtropical regions (Pegler, 1977a, 1983 a, Comer, 1981). Previous mating studies demonstrated the intercompatibility among strains originally assigned to P. djamor (Fr.) Boedijn, P. salmoneostrarninew Vassilieva and P. ostreatoroseus Singer from Asia and America (Neda et al., 1988; Arias, Soto-Velazco & Guzmln-Davalos, 1991; Petersen & Hughes, 1993). Another related and widely occurring taxon is P. opuntiae; its presence being recorded in Mediterranean Europe, South America, Africa (Pegler, 1977 b), Asia (Comer, 1981) and New Zealand (Segedin et al., 1995). However, Petersen (1995a) showed (by examining strains from North and South America and New Zealand) that 'P. opuntiae' represents just a colour variant within the P. djamor intersterility group. The sole P. opuntiae isolate examined in the present study proved to be intersterile with all the other Pleurotus isolates tested, including some P. flabellatus (synonym of P. djamor) strains. Such type of mating behaviour could possibly be explained by heterogenic incompatibility caused by geographical separation and host specificity phenomena among these particular populations, without excluding the possibility of being presented with a distinct biological species, interincompatible with the P. djamor group. Therefore, definite conclusions regarding the taxonomic status of P. opuntiae (especially as this is represented in the European continent) cannot be drawn until a larger number of cultures are analysed by a combination of approaches (including crosses, isozyme and molecular techniques).

x 4.05 f 0.49 ym), subcylindric to elliptical, thin-walled, with Pleurotus ostreatus uacq. : Fr.) P. Kumm. a broad apiculus and yellow contents. Spore print (dry) white. . .

Basidia 25-44 x 5.9-8.0 ym, cylindric, thin-walled; sterigmata Matings. High percentages of positive results were fumished 4, 3 pm long. Pleurocystidia absent. Cheilocystidia rather by crossing the monokaryons of P. ostreatus and P. columbinus; frequent, cylindric to ovoid, thin-walled, 20-38 x 2.2-3.2 ym they were found to interbreed with frequencies of 56-100%


(67% of the individual crosses, between a given pair of sets of tester strains, yielded 100% dikaryons). Furthermore, isolates of P. colurnbinus induced dikaryotization to P. osfreafus monokaryons. On the other hand, crosses among these two morphotaxa and the rest of the Pleurotus species examined were incompatible.

Habit, habitat and distribution. It appears from early autumn until winter, usually in large clusters on a wide range of host- plants (Abies, Fagw, Populus, Quercus, Betula, Picea, Ulmus, Salix, A l n w , Iuglans, etc.). It presents a wide distribution throughout Europe.

Pileus at first flat to slightly convex, semicircular to mussel- shaped, smooth to velvet-like, moist, colour warm grey to gunmetal to steel, or orange-brown to beige-orange to brown (47/4A to 39/2A to 48/2C, or 9/41 to 10151 to 15/7C); at maturity, size 4.0-16.0 crn, flat to slightly convex, mussel- shaped to spathulate to oyster-shaped, smooth, beige-buff to light brown to warm brown or light blue-grey to light warm grey to light grey to warm grey to nickel to grey to platinum (12/5E to 15/9C to 15/11E or 42/5A to 35/1A to 45/3A to 47/4A to 36/1A to 9/2A to 45/3A), with even to slightly inrolled margin. Lamellae thin and broad, dense, decurrent to the upper part of the stipe, entire, with anastomoses and lamellulae, white to cream to light beige or to ivory to light warm grey (to 10/3C to 11/3C or to 10/2B to 35/1A). Stipe size 0.5-4 cm, sometimes also absent; lateral to eccentric, cylindric to strigose near its base, solid, smooth or villous or with floccules, white to cream to ivory (to 10/3C to 10/2B). Flesh firm, usually thin, elastic and sometimes fragile, white to cream in colour. Odour mostly neutral. Taste mild and pleasant.

Basidiospores 6.5-13.5 x 3.0-5.0 Vm (average 9.54 0.86 x 3.54 & 0.42 pm), subcylindric to cylindric, thin-walled, with

a small apiculus, hyaline in KOH and Melzer's reagent, sometimes with yellow oily contents. Spore-print (dry) white to cream to ivory to light rose to light warm grey to light blue grey (to 10/3C to 10/2B to 2/9B to 35/1A to 42/5A). Basidia 20-45 x 4.0-8.5 pm, cylindric to clavate, hyaline, thin-walled; sterigmata 4, 4 pm long. Cheilocystidia and pleurocystidia absent. Hyphal system monomitic. Pileipellis 100-150 yrn broad, formed of generative hyphae. Pileus trama composed of oleiferous hyphae 6.2-13.0 ym diam. Lamellar trama with interwoven oleiferous hyphae 4.4- 8.6 pm diam. Stipe context composed of thin-walled and of sclerified thick-walled hyphae 5.2-10.8 Dm diam. All generative hyphae irregular, thin-walled, with clamp-connexions. Subhymenium formed of short thin-walled hyphae 2.5- 4.5 ym diam.

Presence of yellow to orange (I7/1L to 9/3K) pigments on mycelial cultures. Dikaryotic colonies with dense and cottony aerial, and submerged mycelium, more or less radial, even margin, coloured white to cream to ivory (to 10/3C to 10/2B); thin-walled hyphae with abundant clamp-connexions; occasional production of microdroplets, singly on short secretory sterigmata on aerial hyphae (for nematode trapping).

Myceliumgrowth rates. 4.6 mm d-' on PDA and 2.2 mrn d-' on CM. Cellulose degradation eficacy was low ($0.12).

Basidiomata produced in vitro after 40-50 d at a preferred temperature of 15'.

Material examined. Greece, Vardoussia, Grameni Oxia, October 1988, ~011. D. Dimou & G. Zervakis, on a fallen trunk of Fagus syluatica (LGAM P15); same location and substrate, October 1984 (LGAM P35, P38); Greece, Arcadia, Tripolis, November 1992, coll. G. Zervakis, on a stump of Castanea satiua (LGAM P57); Greece, Fthiotida, Fteri, October 1989, coll. D. Dimou & G. Zervakis, on a log of Populw sp. (LGAM P60); Greece, Evros, Orestiada, November 1989, toll. J. Franzeskakis & G. Zemakis, on Populus sp. (LGAM P61, P62); Greece, Attica, Pamitha, November 1993, coll. E. Lahouvaris & G. Zervakis, on Abies sp. (LGAM P70, P72); Germany, coll. Inst. Forst. Mycol. Holzsch. Hannoversch-Munden (ATCC 32783); Germany, coil. K. Esser (ATCC 34675); location, date and substrate unknown (ATCC 38538); France, coll. R. Kiihner (CBS 29147); France, donated by J. Labarhre, on Populus nigra (LGM 254); France, donated by J. Labarhre, on Abies sp. (LGM 841101); Hungary, donated by J.Labarhre, on Quercw sp. (LGM 850401); Hungary, donated by J. Labarhre, on Salir sp. (LGM 850402); ex- Czechoslovakia, donated by J. Labarhre, on Quercus sp. (LGM 851001); Belgium, Holsbeek, December 1972, coll. G. Hennebert (MUCL 19000).

Pleurotus columbinus (QueZ) QQu.

Habit, habitat and distribution. Grows in groups on a variety of substrates (trees of Abies, Picea, Fagus, Acer and U l m w ) , in autumn and winter. Specimens assigned to this rare taxon were isolated from areas of central and western Europe (Bresadola, 1928; Romagnesi, 1969; Eger ef al., 1979; Hilber, 1982).

Pileus at first flat to slightly convex, semicircular to mussel- shaped, smooth, colour warm grey to steel to brown (47/4A to 48/2C to 15/7C); at maturity, size 39-10.0 cm; mostly flat, mussel-shaped to oyster-shaped, smooth, nickel to light warm grey to light blue grey to platinum to warm brown (36/1A to 35/1A to 42/5A to 45/3A to 15/11E), with even margin. Lamellae thin, dense, decurrent to the top of the stipe, entire with frequent anastomoses, white to cream to ivory (to 10/3C to 11/3C). Stipe size: 0.5-2.5 cm, sometimes also absent; lateral to central, cylindric, solid, smooth or villous, white to cream to ivory (to 10/3C to 10/2B). Flesh usually thin, firm and elastic. Odour mostly neutral. Taste mild and pleasant.

Basidiospores 8.0-11.5 x 3.5-5.0 Vm (average 9.65 +0.78 x 3.90f 0.46 pm), cylindric to subcylindric, thin-walled, with

a small but distinct apiculus, with yellow oily contents. Spore- print (dry) white to cream (to 10/3C). Basidia 20-45 x 4.0-8.5 ym, cylindric, thin-walled, hyaline; sterigmata 4, 4 ym long. Cheilocystidia and pleurocystidia absent. Hyphal system monomitic. Pileipellis formed of irregular generative hyphae 120-140 pm broad. Pileus trama composed of hyphae 8.0-11.2 Urn diam. Lamellar trarna with irregular interwoven oleiferous hyphae 3.4-7.4 pm diam. Stipe trama composed mostly of sclerified hyphae 5.8-9.6 ym diam. All generative hyphae thin-walled, with clamp-connexions. Subhymenium formed of thin-walled short hyphae 4.0-5.5 ym in size. Basidiospores, basidia and trama hyaline in KOH and Melzer's reagent.

Pigments absent on mycelial cultures. Dikaryotic colonies


with dense and cottony aerial, and submerged mycelium with even margin, coloured white to cream to ivory (to 10/3C to 10/2B); thin-walled, interwoven hyphae with abundant clamp- connexions; occasional production of microdroplets, singly on short secretory sterigmata on aerial hyphae (for nematode trapping).

Myceliurngrozuth rates. 4.6 mm d-' on PDA and 1.9 mm d-' on CM. Cellulose degradation efficacy was low (#0.24). Basidiomata produced in vitro after 4&50 d at a preferred temperature of 15O.

Material examined. France, coll. R. Vandendries (ATCC 36498); Italy (CBS 37351); France, Langeais, 1983, coil. J. Poppe (MUCL 28154).

The P. ostreatus species complex includes the most thoroughly investigated taxa of Pleurotus, P. osfreatus being the type species. The complex presents a very wide distribution and a particularly large host-range. The fungus in Europe is characterized by the dark grey-brown imbricate pilei, the dense anastomizing lamellae, the rather lateral stipe, the monomitic hyphal system and the preference for fructification at low temperatures on a variety of substrates. Controversies arose in the past regarding the exact relationships of several putative taxa with P. osfreafus sensu sfricfo. For example, P. salignus (Pers.: Fr.) P. Kumm. and P. spodoleucus Imaz. & Toki were once described as distinct species but were later confirmed to be synonyms or variants of P. ostreatus (Hilber, 1982; Magae ef al., 1990). However, the most debated case within this complex concerned P. colurnbinus. At first it was regarded as a separate species mainly due to its distinctive blue-grey basidiomata, coniferous habitat and reported incompatibility with P. ostreafus (Romagnesi 1969; Hilber, 1977). Later on, other studies demonstrated that the two taxa were intercompatible, and P. colurnbinus was reduced to varietal status under P. osfreatus (Eger et al., 1979; Hilber, 1982). The present work revealed certain morphological differences between them and more importantly partial compatibility was observed in crosses performed among their monokaryons (56-100%). The outcome from earlier biochemical and molecular analysis (including some of the same strains studied here) showed that P. colurnbinus isolates were always placed in a separate cluster from the P. ostreatus group on resulting dendrograms (Zervakis & Labargre, 1992; Zervakis ef al., 1994; Ira~abal ef a]., 1995). The respective values of the genetic distances in relation with the degree of compatibility noted before, lead to the hypothesis of a sympatric speciation process that is currently under way for P. colurnbinus. Strains of this taxon, though still intercompatible with P. ostreafus (at least partially and in vitro), are rare, geographically confined in certain areas of central Europe and by possessing ecological peculiarities (growing only on coniferous wood and fruiting during the colder seasons of the year), might progressively evolve as distinct species. The habitat selection and the allochrony (different time periods for production of basidiomata and thus different mating periods) were reported by Maynard Smith (1966) to be essential factors for sympatric speciation. This type of speciation process gains in importance under the light of recent evidence (Fedder, Chilcote & Bush, 1988; Rice & Salt, 1990), although

here the succession of events seems to follow the opposite pattern from what was reported to occur in Coprinus where genetic isolation precedes any kind of differentiation (Kemp, 1975).

Pleurotus pulmonarius (Fr.) Qud.

Matings. The outcome of the crosses among the monokaryons of P. pulrnonarius and the rest of the Pleurotus taxa examined was negative, but with the following two exceptions. The pairings among P. pulmonarius and 'P. sajor-caju' yielded relatively high percentages of compatibility (50-loo%, with 40% of the individual crosses producing 100% dikaryons); and this was also the case for the confrontations among P. pulrnonarius and P. sapidus monokaryons (63-loo%, with 75 % of the individual crosses producing 100% dikaryons). Moreover, 'P. sajor-caju' and P. sapidus produced inferior values of intercompatibility when mated (3 1-100 %, with the 33% of the individual inter-strain crosses producing 100% dikaryons). The di-mon matings between P. pulrnonarius-'P. sajor-caju' and P. pulmonarius-P. sapidus were all positive, while the crosses of 'P . sajor-caju' and P. sapidus yielded some non-successful pairings (75 % dikaryotization).

Habit, habitat and distribution. Appears from summer to early winter, usually in clusters and groups, growing on a wide range of angiosperm wood belonging to Fagus, Populus, Sorbus, Aesculus, Fraxinus, Betuh, Quercus etc. It is reported to occur throughout Europe, extending from Spain and France to Russia and from the Scandinavian countries to Italy and Greece.

Pileus at first flat to slightly convex, spathulate to mussel- shaped, with a leathery appearance, colour light brown to beige brown to beige-buff to orange brown (15/9C to 13/6E to 12/5E to 9/41); at maturity, size 4-12 cm, circular to spathulate to lung-shaped, usually flat but sometimes concave towards the centre or slightly infundibular, smooth, light beige to beige-brown to warm brown to beige-buff to light brown to brown (11/3C to 13/6E to 15/11E to 12/5E to 15/9C to 15/7C), with numerous small darker coloured spots, with slightly to very sinuate and wavy margin as it gets older. Lamellae thin, dense, decurrent to the top of the stipe and often intervenose along its entire length, entire, with rare anastomoses, white to cream to ivory (to 10/3C to 10/2B). Stipe size 1.5-4-5 cm; central to sublateral, cylindric to tomentose near its base, solid, smooth to slightly villous, white to cream (to 10/3C). Flesh firm and elastic, solid, white to cream. Odour mild to anise-like. Taste distinct and pleasant.

Basidiospores 7.5-14.5 x 2.5-5.0 Dm (average 10.11 + 0-77 x 3.82 1 0 . 4 7 pm), subcylindric to cylindric, thin-walled, with a distinct apiculus. Spore-print (dry) cream to light beige to beige-buff (10/3C to 9/11 to 12/5E). Basidia 20-54 x 3.5-8.5 pm, cylindric to clavate, thin-walled; sterigmata 4, 4 yrn long. Cheilo~~stidia and pleurocystidia absent. Hyphal system monomitic. Pileipellis 5C!-70 pm broad, with thin- walled generative hyphae. Pileus trama composed of irregular, thin-walled and of sclerified thick-walled hyphae 2.4-6.2 pm diam. Lamellar trama irregular with interwoven thin-walled and with sclerified thick-walled hyphae 4.0-11.2 pm diam.

The pluralistic species concept in Pleurofw 728

Stipe context irregular, composed of thin-walled and of sclerified thick-walled hyphae 3.4-9.6 ym diam. All generative hyphae with clamp-connexions. Subhymenium with short, thin-walled hyphae 3.5-6.0 ym in size. Basidiospores, basidia and trama hyaline in KOH and Melzer's reagent.

Presence of yellow to orange coloured (17/1L to 9/3K) pigments on mycelial cultures. Dikaryotic colonies with dense and cottony aerial, and submerged mycelium, more or less radial, even margin, colour white to cream to ivory (to 10/3C to 10/2B); thin-walled hyphae with abundant clamp- connexions; occasional production of microdroplets, singly on short secretory sterigmata on aerial hyphae (for nematode trapping).

Mycelium growth rates. 4-9 mm d-' on PDA and 4.2 mm d-' on CM. Cellulose degradation efficacy became negative (# - 0.06). Basidiomata produced in vifro after 40-50 d at a preferred temperature of 15'.

Material examined. Greece, Vardoussia, Grameni Oxia, October 1984, coll. D. Dimou & G. Zervakis, on Fagus sylvatica (LGAM PI, P6, P26); same location and substrate, October 1988 (LGAM P16, P36); Greece, Rodopi, November 1993, coll. E. Lahouvaris & G. Zervakis, on Fagus sylvatica (LGAM P47); ex-Czechoslovakia, coll. A. Ginterova, on unidentified stump (ATCC 36050); Germany, coll. 0 . Hilber, on Fagw sp. (ATCC 42046); Germany, coll. 0 . Hilber, on Abies alba (ATCC 42047); Sweden, 0. Hilber, on Populus tremula (ATCC 42048); France, donated by J. Labarhre (LGM 850403); France (CBS 65487); Belgium, Rijkel, 1986, coll. F. Vandenhoven (MUCL 29418); The Netherlands (CBS 50785).

The taxonomic relationships of P. ostreafus with P. pulmonarius have also been questioned in the past mainly due to their morphological similarities and overlapping distribution (Hilber, 1977; Eger ef al., 1979). Consequently more attention was placed on their mating interactions, and Hilber (1982) working mainly with European collections, Vilgalys ef al. (1993) with North American isolates and Petersen & Hughes (1993) with intercontinental populations clearly demonstrated that P. pulmonarius and P. ostreafus are two different biological species. The crosses performed within the context of the present work (using strains previously unexamined from various parts of the world) confirmed these results, as all pairings yielded complete interincompatibility between monokaryons of the two species. Other reports supporting this conclusion by adopting other experimental approaches were provided by Zervakis & Labarkre (1992), Vilgalys & Sun (1994), Zervakis ef al. (1994)' and Iracabal ef al. (1995). On the other hand, comparative examination of their morphological and physiological characters shows that P. pulrnonarius could be distinguished from P. ostreafus (though still with difficulty) on the basis of its lighter pilei colour (for specimens collected from Europe), the slightly larger basidiospores, the thinner pileipellis and the faster growth rates. In addition, P. pulmonarius seems to be better adapted to withstand a broader range of climatic variation (as its distribution range suggests) and presents a distinct preference for angiospers as hosts (Eger et al., 1979; Hilber, 1982; Bresinsky ef al. 1987; Zervakis, 1992).

Until recently 'P . sajor-caju' was regarded as a separate Pleurotus species and its use under this name remains very

common. A report on the intercompatibility of some commercial 'P. sajor-caju' strains with P. pulmonarius was published by Hilber (1982); our work attempted to evaluate the mating behaviour of several wild isolates of ' P. sajor-caju' originating from southeastern Asia. The results demonstrated a partial compatibility among monokaryons of 'P. sajor-caju' and P. pulmonarius (in general it ranged from 50 to 100%; with 40% of the crosses between monokaryons from specific dikaryons yielding only positive results: 100 % compatibility), while all of the di-mon crosses performed yielded dikaryons. Comparative study of the morphology and physiology of isolates classified under these two names also presented extensive similarities. Furthermore, previous investigations examining their isozyme patterns and rDNA polymorphism demonstrated a very close affinity (Zervakis ef al., 1994; Iracabal ef al., 1995). Thus, ' P . sajor-caju' represents a group of strains of P. pulrnonarius, nowadays being widely cultivated for production of mushrooms in southern and eastern regions of Asia (D. Cha, pers. comm.). The intermediate degree of mating interincompatibility revealed among their strains might be attributed to the long-distance separation of the two populations and the appearance of heterogenic incompatibility phenomena (Esser & Blaich, 1973; Petersen, 1995 b); such cases are quite common among fungal species, i.e. Armillaria mellea (Anderson, Korhonen & Ullrich, 1980), Sfeccherinurn oreophilum (David & Boidin, 1984) and Suillus lufeus (Fries & Neumann, 1990). Here, special mention has to be made on the strain ATCC 32078 isolated from Euphorbia royleana in India (deposited by Rangaswami in 1975) serving for quite a long time as a representative specimen of 'P. sajor-caju' (Jandaick, 1974). This strain has been recently erroneously relabelled from Pleurotus to Lenfinus in the ATCC catalogue, while the present work determined that ATCC 32078 is perfectly compatible with European P. pulmonarius isolates. Perhaps, the confusion could be attributed to Lenfinus sajor-caju descriptions from palaeotropical areas (Comer, 1981; Pegler, 1983 b); the use of this species epithet for Lenfinus is certainly correct but it describes a completely different fungus from the ' P . sajor- caju' strains examined in this study (e.g. existence of annulus, different hyphal system and basidiospore size, etc.). Another controversial report was made in the past on the existence of an anamorphic state of 'P . sajor-caju' (Nair & Kaul, 1980). The teleomorph was apparently misidentified and the Anfro- mycopsis species described by Nair & Kaul should be related with the occurrence of a Corerniopleurofus taxon in India.

Another Pleurofus taxon, found only in North America and showing a certain affinity with the P. osfreafus species- complex, was recently established as a separate species: P. populinus 0 . Hilber & 0. K. Mill. (Vilgalys ef al., 1993). The authors discarded P. sapidus as nomen nudum for a taxon, as strains deposited in culture collections with this name were intercompatible with P. osfreafus, while the material used in the study of Anderson ef al. (1973) as P. sapidus seems to belong either to P. pulmonarius or to P. populinus. The only putative P. sapidw strain (ATCC 24986) examined here proved to be partially compatible with P. pulmonarius isolates from various parts of the world, confirming earlier results obtained with isozymes and RFLPs (Zervakis ef al., 1994; Iracabal ef al., 1995).


Table 3. Established biological species within Pleurotus, their corresponding synonyms and/or taxa at a subspecies level, and the respective intersterility groups

Intersterility Species Synonymrsubspecies taxa groupst

P. ostreatus P. columbinrrs, P. salignw', P. I spodoleucw'

P. pulmonariw P. sajor-caju, P. sapidw I1 P. populinus 111 P. cornucopiae P. citrinopileatw IV P. djamor P. flabellatw, P. V

osfreatoroseus". P. salmoneostraminew*, P. euosmw

P. eyngii P. ferube, P. nebrodensis, P. VI hadamardii, P. fossulatus

P. cystidiosw P. abalonw VII P. calyptratw VIIl P. d y i n w IX P. purpureo-oliuacerrs P. tuberregium

* Taxa not included in the present work; information derived from previous studies only.

t The numbering of Pleurotw intersterility groups follows the one proposed by Vilgalys & Sun (1994) for reasons of standardization.

Recent studies concerned with establishing the generic limits of Pleurofus, Panus and Lentinus seem to show that Pleurofus taxa can be distinguished from species of the other two genera in possessing a trama without ligative hyphae and hyphal pegs, and in most cases with mycelium bearing nematode-trapping structures (Molina, Shen & Jong, 1992; Hibbett & Vilgalys, 1993; Hibbett & Thorn, 1994). These characters contributed also to the placement of P. fuberregium (Fr.) Singer in Pleurotus, as opposed to Pegler's (1983 b) and Comer's (1981) classifications which had placed it in Lentintrs and Panus respectively because they adopted different concepts for discriminating among these three genera.

The established biological species of Pleurotus, derived from the matings analysed above and from literature data, are presented in Table 3, while information related to their so far reported world-distribution appears in Table 4. Recent reports on the occurrence of additional taxa such as P. bajocalifomica

Esteve-Rav. (Moreno, Esteve-Raventos & Ayala, 19931, P. australis Cooke & Massee and P. parsonsii G. Stev. (Segedin et al., 1995) furnish more work to be accomplished to define the intersterility groups to which they belong, while there remains much to be done towards assessing the exact distribution of each Pleurotus species, understanding the genetics of such fungal populations and elucidating their perplexed taxonomic relationships. For instance, taxa placed in the P. djamor, P. hirtus (Fr.) Singer and P. eyngii species complexes or belonging in the subgenus Coremiopleurotus are still poorly known. Likewise, the knowledge of Pleurofus fungi from tropical and subtropical regions (Central and South America, Africa, Australasia) is very limited.

Recent investigations on Pleurotus genetics and taxonomy contributed considerably to coping with problems related to the significant influence of the host-substrate and the environment on the phenotype of the fungus, and to the occurrence of hard to interpret nuclear phenomena which affect the already complexed mating behaviour of isolates from this genus (Zervakis, 1992; Petersen & Ridley, 1996). Lately, Petersen & Hughes (1993) proposed a representative specimen for P. pulmonarius and Petersen & Krisai-Greilhuber (1996) designated an ex fypus culture for P. ostreatus. In addition, R. Vilgalys (pers. comm.) and Petersen (1995a) have suggested the formation of standard sets of tester single-spore isolates representing established intersterility groups and/or morphotaxa. These efforts towards conducting fastidious morphological and compatibility studies in combination with the application of biochemical and molecular approaches based on a large number of individuals point in the right direction for obtaining answers on Pleurofus systematics.

Table 4. Established biological species of Pleurotw and their known world-distribution

We would like to thank the following colleagues for their kind collaboration, for providing information regarding Pleurofw distribution and biological material: P. Buchanan, G. Ventu- rella, D. Samgina, M. Saber, A. Arambam, M. Garcia-Rollan, V. Bononi, R. Shivas and D. Cha. We are particularly grateful to Professor J. Labarkre for donating several Pleurotus dikaryons. The first author (G.Z.) wishes also to thank Dr D. Moore for facilitating a literature search during his stay in the U.K. and Professors R. Petersen and R. Vilgalys for helpful discussions on Pleurofus systematics.

Europe Asia N. America S. America Africa Australasia

P. ostreatw P. pulmonarius P. populinw P. cornucopiae P. djamor P. eyngii P. cystidioswt P. dyinus P. calypfratus P. purpureo-olivacew P. tuberregium

* Y: recorded and confirmed existence of the species; Y?: recorded existence of the species; blanks denote occurrence not reported. t The distribution data do not include the Coremiopleurotw taxon of P. smithii.

The pluralistic species concept in Pleurofus 730

REFERENCES

Anderson, J. B., Korhonen, K. & Ullrich, R. C. (1980). Relationships between European and North American biological species of Armillaria mellea. Experimental Mycology 4, 97-95.

Anderson, N., Wang, S. S. & Schwandt, J. W. (1973). The Pleurotw ostreatw-sap~dus species complex. Mycologia 65, 28-35.

Arias, A., Soto-Velazco, C. & Guzmhn-Davalos, L. (1991). Obtenci6n de cepas de Pleurotw spp. por apareamiento dimonocari6n y su cultivo en bagazo de maguey tequilero. In Memoirs, IV Congreso Nacional de Micologia. Tlaxcala, Mexico.

Boidin, J. (1986). Intercompatibility and the species concept in the saprobic Basidiomycotina. Mycotaxon 26, 319336 .

Brasier, C. M. (1987). The dynamics of fungal speciation. In Evolutionary Biology of the Fungi (ed. A. D. M. Rayner, C. M. Brasier & D. Moore), pp. 231-238. Cambridge University Press: Cambridge, U.K.

Bresadola, G. (1928). Iconographia Mycologica. Band 6. Bresinsky, A., Fischer, M., Meixner, B. & Paulus, W. (1987). Speciation in

Pleurotw. Mycologia 79, 234-245. Cailleux, R. & Diop, A. (1976). Recherches prbliminaires sur la fructification en

culture du Pleurotw eyngii (Fr. ex DC.) QuClet. Revue de Mycologie 40, 365-388.

Cailleux, R., Diop, A. & Joly, P. (1981). Relations d'interfertilite entre quelques reprksentents des Pleurotes des Ombelliferes. Bulletin de la Socie'ti Mycologique de France 97, 97-124.

Chamuris, G. P. (1991). Speciation in the Peniophora cinerea complex. Mycologia 83, 736-742.

Chang, S. T. & Miles, P. G. (1991). Recent trends in world production of cultivated mushrooms. Mushroom Journal 504, 15-18.

Comer, E. I. H. (1981). The agaric genera Lentinus, Panus and Pleurofus with particular reference to Malaysian species. Beihefte zur Nova Hedwigia 69, 1-169.

David, A. & Boidin, J. (1984). Prhsence en Europe de Steccherinum oreophilum (Basidiomycetes) dCcrit d'ArnCrique du Nord. Mycotaxon 21, 427-430.

Dobzhansky, T. (1970). Genetics of the Evolutionary Process. Columbia University Press: New York.

Duncan, E. G. (1972). Microevolution in Auricularia polytricha. Mycologia 64, 394-404.

Eger, G., Li, S. F. & Leal-Lara, H. (1979). Contribution to the discussion on the species concept in the Pleurotus ostreatw complex. Mycologia 71, 577-588.

Eggins, H. 0. W. & Pugh, G. J. F. (1962). Isolation of cellulose decomposing fungi from the soil. Nature 193, 94-95.

Esser, K. & Blaich, R. (1973). Heterogenic incompatibility in plants and animals. Advances in Genetics 17, 107-152.

Fedder, J. L., Chilcote, C. A. & Bush, G. L. (1988). Genetic differentiation between sympatric host races of the apple maggot fly Rhagoletis pornonella. Nature 336, 6 1 4 4 .

Ferri, F. (1985). Un medesimo substrato per piu specie fungine. Mushroom Information 3, 24-30.

Fries, N. (1985). Intersterility groups in Paxillus involutw. Mycotaxon 24, 403-409.

Fries, N. & Neumann, W. (1990). Sexual incompatibility in Suillw luteus and S. granulatw. Mycological Research 94, 64-70.

Guzmin, G., Bandala, V. M. & Montoya, L. (1991). A comparative study of teleomorphs and anamorphs of Pleurotus cystidiosus and Pleurotw smithii. Mycological Research 95, 1264-1269.

GuzmAn, G., Montoya, L., Salmones, D. & Bandala, V. M. (1993). Studies of the genus Pleurotw (Basidiomycotina), 11. P, djamor in Mexico and in other Latin American countries, taxonomic confusions, distribution and semi- industrial culture. Cryptogamic Botany 3, 213-220.

Guzmin, G., Valenzuela, R. & Canale, A. (1980). Primer registro de Pleurotus smithii de AmCrica del Sur y obtencion da la fase asexual de la cepa mexicana. Boletin de la Sociedad Mexicana de Micologla 14, 17-26.

Hallenberg, N. (1984). Compatibility between species of Corticiaceae S. L. (Basidiomycotina) from Europe and North America. Mycotaxon 21, 335-338.

Han, Y. H., Chen, K. M. & Cheng, S. (1974). Characteristics and cultivation of a new PIeurotw in Taiwan. Mushroom Science 9, 167-174.

Hibbett, D. S. & Thorn, R. G. (1994). Nematode-trapping in Pleurotus tuberregium. Mycologia 86, 696499 .

Hibbett, D. S. & Vilgalys, R. (1993). Phylogenetic relationships of Lentinus (Basidiomycotina) inferred from molecular and morphological characters. Systematic Botany 18, 409433 .

Hilber, 0. (1977). Einige Aspekte aus der Pleurotw ostreatw Gruppe. &ski Mykologie 31, 142-154.

Hilber, 0. (1981). Biosystematische Untersuchungen zur Kenntnis von Pleurotus calyptratus (Lindbl. in Fr.) Sacc. und Pleurotus dyinus (Pers. ex Fr.) Kummer. Zeitung der Mykologie 47, 2 7 4 2 .

Hilber, 0. (1982). Die Gattung Pleurotus (Fr.) Kummer unter besonderer Beriicksichtigung des Pkurotw eyngir-F~rmenkom~lexes. In Bibliotheca Mycologica 87. J. Cramer: Vaduz.

Ira~abal, B., Zervakis, G. & Labarere, J. (1995). Molecular systematics of the genus Pleurotw: analysis of restriction length polymorphisms in ribosomal DNA. Microbiology 141, 1479-1490.

Jandaick, C. L. (1974). Artificial cultivation of Pleurotus sajor-caju. Mushroom Journal 22, 405.

Joly, P., Cailleux, R. & Cerceau, M.-T. (1990). La stCrilitC mile pathologique, ClCment de la co-adaptation entre populations de champignons et de plantes-h6tes: modkle des Pleurotes des Ombelliferes. Bulletin de la Socie'te' Bofanique de France 137, Actualitb botaniques 71-85.

Jong, S. C. & Peng, J. G. (1975). Identity and cultivation of a new commercial mushroom in Taiwan. Mycologia 67, 123551238,

Kemp, R. F. 0. (1975). Breeding biology of Coprinus species of the section Lanatuli. Transactions of the British Mycological Society 65, 375-388.

Maerz A. & Paul M. R. (1930). Dictionary of Color. McGraw Hill Book Company Inc.: New York.

Magai, Y., Haga, K., Taniguchi, H. & Sasaki, T. (1990). Enzymes of strains of Pleurotw species (Basidiomycetes) compared by electrophoresis. Journal of General and Applied Microbiology 36, 69-80.

May, B. & Royse, D. 1. (1988). Interspecific allozyme variation within the fungal genus Pleurotw. Transactions of the British Mycological Society 90, 29-36.

Maynard Smith, J. (1966). Sympatric speciation. American Naturalist 100, 637450.

Mayr, E. (1970). Populations, Species and evolution. Harvard University Press: Cambridge, MA.

Miller, 0. K. (1969). A new species of Pleurotus with a coremioid imperfect stage. Mycologia 61, 887-893.

Molina, F. I., Shen, P. & Jong, S.-C. (1992). Molecular evidence supports the separation of Lentinula edodes from Lentinus and related genera. Canadian Journal of Botany 70, 2446-2452.

Moore, R. T. (1985). Mating type factors in Pleurotw cystidiosus. Transactions of the British Mycvlogical Society 85, 354-358.

Moreno, G., Esteve-Raventos, F. & Ayala, N. (1993). A new species of Pleurotus from the San Felipe desert (Baja California, Mexico). Mycotaxon 48, 451-457.

Nair, L. N. & Kaul, V. P. (1980). The anamorphs of Pleurotw sajor-caju (Fr.) Singer and Pleurotus gemmellarii (Inzeng.) Sacc. Sydowia 33, 221-224.

Neda, H., Furukawa, H. & Migayi, T. (1988). Two Pleurotw species from Okinawa. Proceedings of the 32nd Annual Meeting of fhe Mycoiogicaf Society of Japan.

Ohira, I . (1990). A revision of the taxonomic status of Pleurotw citrinopileatus. Reports of the Tottori Mycological Institute 28, 143-150.

Parmasto, E. (1985). The species concept in Hymenochaetaceae (Fungi, Hymenomycetes). Proceedings of the Indian Academy of Sciences 94 ,369380 .

Pegler, D. N. (1977~) . Pleurotus (Agaricales) in India, Nepal and Pakistan. Kew Bulletin 31, 501-510.

Pegler, D. N. (1977 b). A preliminary agaric flora of East Africa. Kew Bulletin Additional Series 6, 615.

Pegler, D. N. (1983~) . Agaric flora of the Lesser Antilles. Kew Bulktin Additional Series 9, 1 4 6 8 .

Pegler, D. N. (1983 b). The genus Lentinus. Kew Bulktin Additional Series 10, 1-281.

Petersen, R. H. (1995~). Contributions of mating studies to mushroom systematics, Canadian Journal of Botany 7 3 (supplement 1). 831-842.

Petersen, R. H. (1995 b). There's more to a mushroom than meets the eye: mating studies in the Agaricales. Mycologia 87, 1-17.

Petersen, R. H. & Hughes. K. W. (1993). Intercontinental interbreeding

G. Zervakis and C. Balis

collections of Pleurotus pulmonarius, with notes on other species. Sydowia 45, 139-152.

Petersen, R. H. & Krisai-Greilhuber, 1. (1996). A neotype for Pleurotus ostreatw. Mycologicul Research 100, 229-235.

Petersen, R. H. & Ridley, G. W. (1996). A New Zealand Pleurotw with mult~ple-species sexual compatibility. Mycologia 88, 198-207.

Pildt, A. (1935). Pleurotus Fries. In Atlas des Champignons de I'Europe, Band 2. Prague.

Pildt, A. (1936). Revision der tropischen Lentinus Arten aus den Herber des Botanischen Museums in Berlin-Dahlem. Annuls der Mykologie 39, 71-103.

Raper, C. A., Raper, J. R. & Miller, R. E. (1972). Genetic analysis of the life cycle of Aguricw btsporccs. Mycologia 64, 1088-1117.

Rice. W. R. & Salt, G. W. (1990). The evolution of reproductive isolation as a correlated character under sympatric conditions: experimental evidence. Evolution 44, 1140-1152.

Romagnesi, H. (1969). Sur les Pleurotw du groupe ostreatus (Ostreomyces Pilit). Bulletin de la Socie'tPMycologique de France 85, 305-314.

Segedin, B. (1984). A new species of Pleurotus (Agaricales) in New Zealand. Tune 30, 235-238.

Segedin, B. P., Buchanan, P. K. & Wilkie, J. P. (1995). Studies in the Agaricales of New Zealand: new species, new records and renamed species of Pleurotus (Pleurotaceae). Australian Systematic Botany 8, 453-482.

Singer, R. (1986). The Agaricales in Modern Taxonomy, 4th ed. Koeltz Scientific Books: Koenigstein, Germany.

Tortic, M. & Hocevar, S. (1977). Some lignicolous Macromycetes from Krakovski Gozd, new or rare in Yugoslavia. Acta Botanica Croatica 36, 145-152.

Venturella, G. (1991). A check-list of Sicilian fungi. Bocconea 2, 1-221. Vilgalys, R. (1991). Speciation and species concepts in the Collybia dyophila

complex. Mycologia 83, 758-773. Vilgalys, R., Smith, A,, Sun, B. L. & Miller, 0. K. (1993). Intersterility groups

in the Pleurotw ostreatus complex from the continental United States and adjacent Canada. Canadian Journal of Botany 71, 113-128.

Vilgalys, R. & Sun, B. L. (1994). Ancient and recent patterns of geographic speciation in the oyster mushroom Pleurotus revealed by phylogenetic analysis of ribosomal DNA sequences. Proceedings of the National Academy of Sciences, U S A 91, 4599-4603.

Worrall, 1. J., Parmeter, 1. R. Jr & Cobb, F. W. Jr (1983). Host specialization of Heterobasidion annosum. Phytopathology 73, 304-307.

Zewakis, G. (1992). Genetic and taxonomic analysis of fungal isolates belonging to the genus Pleurotus. Ph.D. Dissertation, Agricultural University of Athens, Greece.

Zewakis, G. & Balis, C. (1992). Comparative study on the cultural characters of Pleurotw species under the influence of different substrates and fruiting temperatures. Micologia Neotropical Aplicada 5, 39-47.

Zervakis, G., Dimou, D. & Balis, C. (1992). First record of the natural occurrence in Europe of the basidiomycete Pleurotw cystidiosw on a new host. Mycological Research 96, 874-876.

Zervakis, G. & Labarkre, J. (1992). Taxonomic relationships within the fungal genus Pleurotw as determined by isoelectric focusing analysis of enzyme patterns. Journal of General Microbiology 138, 635445.

Zervakis, G., Sourdis, J. & Balis, C. (1994). Genetic variability and systematics of eleven Pleurotw species based on isozyme analysis. Mycological Research 98, 32F341.

(Accepted 13 December 1995)

A pluralistic approach in the study of Pleurotus species with emphasis on compatibility and physiology of the European morphotaxa

Documents

species of pleurotus

study of pleurotus species

species delimitation

different taxa

based taxa

recognized biological

pleurotus morphotaxa

case of pleurotus systematics