Susceptibility of European cultivars of Italian and perennial ryegrass to crown and stem rust

Susceptibility of European cultivars of Italian and perennialryegrass to crown and stem rust

F. X. Schubiger • J. Baert • B. Bayle • P. Bourdon • B. Cagas • V. Cernoch •

E. Czembor • F. Eickmeyer • U. Feuerstein • S. Hartmann • H. Jakesova •

D. Johnston • B. Krautzer • H. Leenheer • H. Lellbach • C. Persson • W. Pietraszek •

U. K. Posselt • M. Romani • L. Russi • S. Schulze • M. C. Tardin • F. VanHee •

L. van Kruijssen • P. Wilkins • E. Willner • L. Wolters • B. Boller

Received: 24 July 2009 / Accepted: 20 May 2010 / Published online: 8 June 2010

� Springer Science+Business Media B.V. 2010

Abstract A set of 15 Italian (Lolium multiflorum),

three hybrid (L. boucheanum) and 33 perennial

ryegrass (L. perenne) cultivars were evaluated for

their rust susceptibility in the field. The cultivars were

grown in 2001, 2004 and 2007 at 29, 32 and 27

European sites, respectively. Rust incidence was

scored during different growth cycles using a scale

from one (no rust) to nine (susceptible). Crown rust

(Puccinia coronata f. sp. lolii) was the most

frequently observed rust species on Italian, hybrid

and perennial ryegrass during all three experimental

years. There was a highly significant difference in

mean crown rust scores among Italian and perennial

ryegrass cultivars, respectively, in each of the

F. X. Schubiger (&) � B. Boller

Agroscope Reckenholz-Tanikon, Research Station ART,

Reckenholzstrasse 191, 8046 Zurich, Switzerland

e-mail: [email protected]

J. Baert

ILVO-Eenheid Plant, 9090 Melle, Belgium

B. Bayle

DLF Trifolium, 49320 Les Alleuds, France

P. Bourdon

S.A. Carneau, 59310 Orchies, France

B. Cagas

OSEVA PRO Ltd., Grassland Research Station Roznov

Zubri, 75654 Zubri, Czech Republic

V. Cernoch

Plant Breeding Station, 74247 Hladke Zivotice,

Czech Republic

E. Czembor

IHAR Radzikow, 05-870 Blonie, Poland

F. Eickmeyer

Saatzucht Steinach, 94377 Steinach, Germany

U. Feuerstein

Euro Grass Breeding GmbH, 27330 Asendorf, Germany

S. Hartmann

Institut fur Pflanzenbau u. Pflanzenzuchtung der

Bayerischen Landesanstalt fur Landwirtschaft,

85354 Freising, Germany

H. Jakesova

Plant Breeding, 74247 Hladke Zivotice,

Czech Republic

D. Johnston

N.I. Horticulture and Plant Breeding Station, Loughall,

Armagh BT 618 JB, Northern Ireland, UK

B. Krautzer

Bundesanstalt fur alpenlandische Landwirtschaft

Gumpenstein, 8952 Irdning, Austria

H. Leenheer

DLF Trifolium Netherlands B.V., 4727 ST Moerstraten,

The Netherlands

H. Lellbach

BAZ Institut fur Landwirtschaft und Kulturen,

18190 Gross Luesewitz, Germany

123

Euphytica (2010) 176:167–181

DOI 10.1007/s10681-010-0200-5

3 years. The ranking of the cultivars was very

consistent across the different sites within each year

(with some exceptions), despite a significant inter-

action of cultivar response with sites. Moreover, the

rank order correlations of mean cultivar rust scores

were highly significant (r [ 0.9) between the years.

Stem rust (P. graminis f. sp. graminicola) occurred

almost exclusively on perennial ryegrass. The culti-

vars showed significant variation in stem rust sus-

ceptibility. Rank order correlations of mean cultivar

stem rust scores were mostly significant between sites

within each year and highly significant between the

years. The ranking of perennial ryegrass cultivars was

different depending on whether crown or stem rust

was scored. However, the rank order correlation

between the mean disease scores of the cultivars for

the two pathogens was low but still significant. At a

particular site the assessment of crown or stem rust

was in most cases very consistent over the period of

experimentation. Therefore there was no evidence

that rust resistance of an individual cultivar was

overcome by the rust pathogen at a particular site over

the 7 years of experimentation.

Keywords Lolium multiflorum � Lolium perenne �Puccinia coronata � Puccinia graminis �Resistance � Rust � Ryegrass

Introduction

Perennial ryegrass (Lolium perenne L.), Italian

ryegrass (L. multiflorum Lam.) and hybrid ryegrass

(L. boucheanum Kunth) are important forage grass

species in Europe. Ryegrasses are prevalent in most

pastures and meadows in temperate Europe. Rye-

grasses are often used in seed mixture together with a

legume (white or red clover) and a more permanent

cool season grass (cocksfoot, timothy) to support

meat and milk production. Overall, ryegrasses

account for over 60% of all agricultural grass seed

used in Europe (Abberton et al. 2008). They have

numerous desirable agronomic characteristics. They

establish rapidly, are high yielding under favourable

environments and can be grazed and used for hay or

silage. Ryegrasses are among the highest quality

forage grasses, possessing high nutrient contents and,

in addition, their high digestibility makes them

suitable for all types of ruminants.

Ryegrasses are attacked by several rust fungi of

the genus Puccinia. Two or more rust species may

attack the same grass plant at the same time. The two

most serious rust diseases are considered to be crown

rust, caused by Puccinia coronata f. sp. lolii Corda,

and stem rust, caused by P. graminis f. sp. gramini-

cola Pers. (Kimbeng 1999; Potter et al. 1990;

Roderick and Thomas 1997). Furthermore, brown

rust (P. hordei G.H. Otth., synonym P. loliina

Sydow.) has been reported on ryegrass (Gaumann

C. Persson

Weibull AB, 26881 Svalov, Sweden

W. Pietraszek

RAGT 2n Ferme experimentale La Boucaudiere,

Montours, 35460 St. Brice en Cogles, France

U. K. Posselt

Universitat Hohenheim, 70593 Stuttgart, Germany

M. Romani

CRA-FLC, 26900 Lodi, Italy

L. Russi

Universita degli Studi, 06121 Perugia, Italy

S. Schulze

Saatzucht Steinach Bornhof, 17219 Bocksee, Germany

M. C. Tardin

RAGT 2n Centre de recherche de Druelle,

12510 Druelle, France

F. VanHee

Innoseeds, 4421 AJ Kapelle,

The Netherlands

L. van Kruijssen

Barenbrug Research, 6874 BX Wolfheze,

The Netherlands

P. Wilkins

IBERS, Aberystwyth University,

Aberystwyth SY23 3EB, UK

E. Willner

IPK Genbank, 23999 Malchow, Germany

L. Wolters

Euro Grass Breeding GmbH, 6590 AA Gennep,

The Netherlands

168 Euphytica (2010) 176:167–181

123

1959; Swertz 1994). According to Gaumann (1959)

and Cummins (1971) the species complex of

P. recondita Dietel & Holw. (syn. P. triticina Eriks.)

and P. striiformis var. striiformis Westend. (syn.

P. glumarum Erikss. & Henning) may infect Lolium

species as well. In addition, Gaumann (1959) men-

tioned a P. loliicola Vienne.-Bourg. on Lolium

species.

First uredia of crown rust appear in summer

releasing several hundred thousand uredospores

which can re-infect ryegrass plants and produce new

uredia and more uredospores. Within one growing

season many successive infections of ryegrass plants

by uredospores may take place. In autumn teliospores

instead of uredospores are produced. Teliospores do

not infect ryegrass but are the overwintering stage of

the fungus. Therefore, the epidemic of crown rust

disease often breaks down during the last growth in

autumn. Rust infection reduces foliage, rate of

photosynthesis, water-soluble carbohydrate concen-

tration (Potter 1987) and increases the rate of respi-

ration. These effects result in severe losses in dry

matter yield (Lancashire and Latch 1970), in lower

forage quality and palatability (Carr 1975). Damages

due to crown rust attack may be alleviated by growing

multispecies swards, an increasing practice in Europe.

However, crown rust reduces the competitive ability

of infected plants to the advantage of other plants.

Lancashire and Latch (1970) reported a more severe

yield loss of a susceptible perennial ryegrass cultivar

when planted in a mixed ryegrass-clover sward,

leading to clover dominance. In consideration of the

damaging potential of a crown rust infection, resis-

tance to crown rust is an important criterion in variety

registration and is a major goal in ryegrass breeding

(Humphreys et al. 2010).

Stem rust is predominantly a disease of seed crops

of perennial ryegrass attacking stems and reducing

seed yield (Pfender 2001). However, ryegrass is not

only attacked during the reproductive development;

severe infections have been observed also on leaves

and sheaths (Latch 1966; Smiley et al. 2005; Smith

et al. 1989).

The most effective means of control of crown and

stem rust is through the use of ryegrass varieties

resistant to infection by the pathogen. Specific host

genes for resistance provide the basis for this control

(Hayward 1977; Muylle et al. 2005; Studer et al.

2007). However, changes in virulence may occur in

the existing rust population, causing a previously

resistant cultivar to become susceptible.

There is evidence of different physiological races

of crown rust which differ in their virulence on

particular perennial ryegrass genotypes (Aldaoud

et al. 2004; Potter et al. 1990; Wilkins 1978a, b).

The occurrence of individual races appears to vary

from region to region (Potter et al. 1990). Moreover,

a rust population at a given site contains more than

one physiological race (Schubiger et al. 2007b).

However, information on occurrence and distribution

of races in the European population of crown and

stem rust on ryegrass is largely lacking. Physiological

races have yet to be identified and described in terms

of virulence on ryegrass plants with specific rust

resistance genes.

The present paper reports on a co-ordinated

European study to determine the susceptibility of

different Italian, hybrid and perennial ryegrass culti-

vars to the most important rust species throughout

Europe. This multisite rust evaluation trial was

conducted three times over a period of 7 years in

order to find out if rust resistance of individual

cultivars breaks down and is overcome by the rust

pathogen over the course of time. In addition, this

study may provide an assessment of the virulence of

different European rust populations.

Materials and methods

The study was initiated in 2000 by the EUCARPIA

(European Association for Research on Plant Breed-

ing) Fodder crops and Amenity grasses section and

was called EUCARPIA multisite rust evaluation trial.

The trial was started 2001 and was repeated in 2004

and 2007. The number of sites varied from year to

year (Table 1): in 2001 the trials were sown at 29

sites in 10 European countries, in 2004 at 32 sites in

12 countries and in 2007 at 27 sites in 12 countries

(Fig. 1). At 21 sites the trials were established in all

3 years.

Each participant, who was responsible for at least

one site, was asked to select two cultivars for inclusion

in the trial, either one of his own or a cultivar which

is widely used in the region. The definitive list of

ryegrass cultivars therefore comprised a wide range of

cultivars from highly rust resistant to susceptible

coming from different European ryegrass breeding

Euphytica (2010) 176:167–181 169

123

Table 1 Sites where crown (Puccinia coronata) and stem rust

(P. graminis) susceptibility of Italian (Lolium multiflorum) and

perennial ryegrass (L. perenne) cultivars were assessed;

x = the corresponding rust species occurred and mean rust

score was higher than 2 at this specific site, 0 = the

corresponding rust species was not present or mean rust score

was lower than 2, – = no trial was established during the

corresponding year

Site (country) Italian ryegrass Perennial ryegrass

Crown rust Stem rust Crown rust Stem rust

2001 2004 2007 2001 2004 2007 2001 2004 2007 2001 2004 2007

Aberystwyth (UK) x 0 – 0 0 – x 0 – 0 0 –

Asendorf (D) – x x – 0 0 x x x 0 0 0

Aston Le Walls (UK) – x – – 0 – – x – – 0 –

Boelshoj (DK) x 0 0 0 0 0 0 0 0 x 0 0

Bornhof (D) x x x 0 0 0 x x x 0 0 0

Druelle (F) x – x 0 – 0 0 – x x – 0

Flaujaques (F) x – – 0 – – x – – 0 – –

Gross Luesewitz (D) x x x 0 0 0 x x x 0 0 0

Gumpenstein (A) 0 x x 0 0 0 0 x 0 0 0 x

Hladke Zivotice (CZ) x 0 0 0 x x x 0 0 x x x

Hohenheim (D) x x x 0 0 0 0 x 0 x 0 x

Jevicko (CZ) – x 0 – 0 0 – 0 0 – x x

Lelystad B. (NL) x x – 0 0 – x x – 0 0 –

Lelystad C. (NL) x x x 0 0 0 x x x 0 0 0

Les Alleuds (F) x x – 0 0 – x x – 0 0 –

Les Rosiers (F) – x x – 0 0 – 0 x – 0 0

Lodi (I) x x x 0 0 x 0 x x x x x

Loughgall (UK) x x 0 0 0 0 0 x 0 x 0 0

Malchow (D) x x x 0 x x x x x x x x

Merelbeke (B) x x x 0 0 0 x x x 0 0 0

Montours (F) x x x 0 0 0 x x x x x x

Neuhof (D) x 0 – 0 0 – 0 0 – x 0 –

Nort s. Erdre (F) x – – 0 – – x – – 0 – –

Orchies (F) x x x 0 0 0 x x x x 0 0

Ottersum (NL) x x x 0 0 0 x x x 0 0 0

Perugia (I) x x x 0 0 0 0 0 0 x x x

Pulling (D) x 0 x 0 0 0 0 0 x 0 0 0

Radzikow (PL) – x x – 0 0 – x 0 – x x

Rennes (F) – 0 x – 0 0 – 0 x – 0 0

Swifterband (NL) – – – – – – 0 x – x 0 –

Roznov Zubri (CZ) – 0 x – 0 0 – 0 0 – x x

Spitalhof (D) 0 0 x 0 0 0 0 0 0 0 0 x

Steinach (D) x x x 0 0 0 x x x 0 x 0

Svalov (S) 0 – – 0 – – 0 x 0 0 0 0

Zurich (CH) x x x 0 0 0 x x x 0 x x

Total sitesa 24 22 22 0 2 3 17 21 16 12 10 12

a With an average score of at least two

170 Euphytica (2010) 176:167–181

123

companies. The germplasm evaluated in this study

consisted of 15 Italian, three hybrid and 33 perennial

ryegrass cultivars (Tables 2, 3). Ten Italian, one

hybrid and 14 perennial ryegrass cultivars were

tetraploid, the other cultivars were diploid. Once

selected, 2� kg of seed of each cultivar was stored at

4�C at the Research Station of Agroscope ART

Reckenholz in Zurich. This stock was used to provide

the participants with seed for each trial.

Twelve grams of seed of each cultivar were

forwarded to each participant in the form of encoded

seed lots. At each site the seed was sown in spring in

a completely randomized block design with four

replicates.

The cultivars were grown as rows (3 m long and

0.5 m apart). Seed density was 1 g seed per running

meter, corresponding to 20 kg per hectare. The

perennial and Italian ryegrass cultivars were sown

in separate trials. The hybrid ryegrass cultivars were

included in the Italian ryegrass trial, because two of

the three cultivars (Pirol and Gumpensteiner) were of

purely Italian type and only Aberexcel was of

intermediate type. The trials were cut at least once

before the first rust scoring was done. The rows were

fertilized as was customary at each site.

The method used to test cultivars for rust resis-

tance was based on an estimation of the percentage of

leaf area affected. A scale of 1–9 was used, with

1 = no rust disease, 2 = trace of rust, 3 = 5%,

4 = 10%, 5 = 25%, 6 = 40%, 7 = 60%, 8 = 75%

and 9 = more than 75% of the foliage covered with

rust. The rating values represented a relative estimate

of leaf area occupied by rust pustules, and not

reaction type. However, this evaluation procedure did

not differentiate between the proportion of suscepti-

ble individuals within a cultivar and the disease

severity of infected plants, which are impossible to

carry out in a dense sward.

Participants scored the trials for rust incidence in

the year of seeding between July and the beginning of

November one to five times during different growth

cycles and periods of abundant rust development.

Scoring data with an average score of at least two at a

particular site and date were included in the analysis.

Fig. 1 Geographical location of

the experimental sites

Euphytica (2010) 176:167–181 171

123

If there were sites with more than one valid scoring

per year, means of the scorings (per row) were

calculated and used in further analysis.

Participants were asked to score the cultivars for

each rust species occurring in the field separately. In

order to verify these indications, uredo- and teliospores

of leaf samples with typical disease symptoms were

sent to Agroscope ART and analysed with a micro-

scope. This procedure allowed assigning the scorings

to the corresponding rust species. In case of doubt the

scoring was eliminated.

Data of each ryegrass and rust species were

analyzed separately by analysis of variance (ANOVA)

using STATISTICA software. Individual ANOVAs

were carried out testing the main factors cultivar and

site and the interaction for each year. The data from

those sites, where a significant rust infection was

observed during 3 years, was subjected to a separate

ANOVA to test the main factors cultivar, site and year

and the respective interactions.

A two-step procedure as suggested by Boller et al.

(2009) was used to determine the contribution of each

cultivar to the corresponding interaction. The contri-

bution of a specific cultivar to the cultivar 9 site and

cultivar 9 year interaction was estimated by omitting

the cultivar from the dataset and comparing the

interaction terms of the complete and the reduced

dataset. F-statistics was applied to determine the

significance.

The temporal and spatial variation of crown rust

assessment was estimated by computing Spearman

rank order correlations. Rank order correlations were

used to avoid overestimates of correlation due to

consistent high disease scores of extremely resistant

and susceptible cultivars. Correlations were calcu-

lated between the data of each year at a particular site

Table 2 Mean crown rust (Puccinia coronata) disease scores

(1 = resistant; 9 = susceptible) of 16 Italian ryegrass (Loliummultiflorum) and three hybrid ryegrass (L. boucheanum)

cultivars; the ranking order of cultivars in respect of crown

rust resistance is indicated in parentheses for each year and for

the mean value

Cultivar (ploidy) Breeder/owner First listed Evaluation year Mean

2001 2004 2007

Tarandus (4n) ART/DSP 2000 2.3 (1) 2.7 (2) 2.5 (1) 2.5 (1)

Domino (4n) DLF 1995 2.5 (2) 2.6 (1) 2.9 (4) 2.7 (2)

Caballo (4n) Limagrain/DLF 1995 2.5 (3) 2.8 (3) 2.8 (3) 2.7 (3)

Zorro (4n) DLF 1996 2.5 (4) 2.9 (4) 2.7 (2) 2.7 (4)

Tonyl (4n) RAGT SA 1992 2.6 (5) 3.0 (6) 3.0 (5) 2.9 (5)

Bolero (4n) Zelder/Euro Grass 2000 2.7 (6) 3.0 (5) 3.1 (6) 2.9 (6)

Aberexcela (4n) IBERS 1997 2.7 (7) 3.1 (7) 3.5 (9) 3.1 (7)

Barprisma (2n) Barenbrug 1990 3.1 (8) 3.5 (8) 3.2 (7) 3.3 (8)

Ellire (4n) ART/DSP 1985 3.1 (9) 3.5 (9) 3.9 (10) 3.5 (9)

Fastyl (2n) RAGT SA 1989 3.3 (10) 3.9 (10) 3.4 (8) 3.5 (10)

Pirola (2n) SZ Steinach 1994 4.1 (11) 4.6 (11) 4.5 (11) 4.4 (11)

Meryl (2n) ILVO 1996 4.4 (12) 4.8 (12) 4.8 (12) 4.6 (12)

Danergo (4n) DLF 1989 4.7 (13) 5.1 (13) 5.4 (13) 5.1 (13)

Lolita (4n) Zivotice/DLF 1975 5.1 (14) 5.5 (14) 5.7 (14) 5.4 (14)

Ligrande (2n) DSV/Euro Grass 1994 5.9 (15) 6.1 (15) 6.2 (16) 6.1 (15)

Lema (2n) NPZ 1955 6.2 (16) 6.4 (16) 6.1 (15) 6.2 (16)

Gordo (2n) Zelder/Euro Grass 1987 6.4 (18) 6.6 (18) 6.3 (17) 6.4 (17)

Gumpensteinera (2n) BAL 1992 6.3 (17) 6.5 (17) 6.6 (18) 6.5 (18)

Mean 3.9 4.3 4.3 4.1

LSD (P = 0.05) 0.39 0.43 0.47

Number of sites with crown rust incidence 24 22 22

a Hybrid ryegrass

172 Euphytica (2010) 176:167–181

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(1), between the data of the different sites within a

year of experimentation (2), between mean rust

susceptibility over years at each site (3) and among

mean rust disease scores of each year (4).

Results

Crown rust caused severe infections on Italian, hybrid

and perennial ryegrass throughout the region where

Table 3 Mean crown rust (Puccinia coronata) disease scores

(1 = resistant; 9 = susceptible) of 33 cultivars of perennial

ryegrass (Lolium perenne); the ranking order of cultivars in

respect of crown rust resistance is indicated in parentheses for

each year and for the mean value

Cultivar (ploidy) Breeder/owner First listed Evaluation year Mean

2001 2004 2007

Gwendal (4n) RAGT SA 1998 2.4 (1) 2.7 (1) 2.6 (2) 2.6 (1)

Bocage (4n) Carneau 1997 2.7 (2) 2.8 (2) 2.5 (1) 2.7 (2)

Lacerta (4n) ART/DSP 1996 2.8 (3) 3.2 (5) 2.6 (3) 2.9 (3)

Pastoral (4n) RAGT SA 1997 3.2 (5) 3.0 (3) 2.8 (4) 3.0 (4)

Carrera (2n) Carneau 2000 3.1 (4) 3.1 (4) 2.8 (5) 3.0 (5)

Vincent (2n) Zelder/Euro Grass 1993 3.6 (8) 3.5 (8) 3.2 (7) 3.4 (6)

Aubisque (4n) Advanta/DLF 1992 3.6 (9) 3.5 (7) 3.2 (8) 3.4 (7)

Option (2n) Cebeco/DLF 1997 3.5 (7) 3.8 (10) 3.1 (6) 3.5 (8)

Orval (2n) GIE REGA 2000 3.3 (6) 3.2 (6) 3.9 (20) 3.5 (9)

Heraut (2n) Zelder/Euro Grass 1987 3.7 (10) 3.9 (12) 3.3 (9) 3.6 (10)

Elgon (4n) Advanta/DLF 1992 4.0 (12) 3.6 (9) 3.5 (10) 3.7 (11)

Barnhem (2n) Barenbrug 1999 4.0 (11) 4.0 (13) 3.6 (11) 3.9 (12)

Roy (4n) ILVO 1997 4.1 (14) 3.8 (11) 3.7 (13) 3.9 (13)

Kells (2n) afbi 1999 4.1 (13) 4.1 (14) 3.8 (15) 4.0 (14)

Kentaur (4n) Zivotice/DLF 1997 4.3 (15) 4.1 (15) 3.9 (18) 4.1 (15)

Weigra (2n) SZ Steinach 1993 4.5 (16) 4.2 (17) 3.8 (16) 4.2 (16)

Fennema (2n) NPZ 1987 4.6 (19) 4.4 (23) 3.7 (12) 4.3 (17)

Terry (4n) Svalof Weibull 1996 4.8 (22) 4.2 (16) 3.8 (14) 4.3 (18)

Arabella (2n) SZ Steinach 1994 4.5 (17) 4.6 (24) 3.8 (17) 4.3 (19)

Sponsor (2n) Cebeco/DLF 1997 4.7 (21) 4.4 (21) 3.9 (19) 4.3 (20)

Corbet (2n) afbi 1997 4.7 (20) 4.3 (18) 4.0 (21) 4.3 (21)

Aberdart (2n) IBERS 1998 4.6 (18) 4.4 (19) 4.2 (22) 4.4 (22)

Litempo (4n) DSV/Euro Grass 2000 4.8 (23) 4.4 (20) 4.5 (24) 4.6 (23)

Gladio (2n) Zelder/Euro Grass 1995 5.0 (25) 4.8 (28) 4.6 (26) 4.8 (24)

Guru (2n) BAL 1999 4.9 (24) 4.4 (22) 5.2 (31) 4.9 (25)

Tivoli (4n) DLF 1988 5.4 (26) 4.7 (25) 4.6 (27) 4.9 (26)

Aristo (2n) Limagrain/DLF 1999 5.6 (30) 4.8 (26) 4.5 (23) 5.0 (27)

Foxtrot (2n) Limagrain/DLF 1996 5.4 (29) 5.0 (30) 4.5 (25) 5.0 (28)

Sirocco (4n) Zelder/Euro Grass 1999 5.4 (28) 4.8 (27) 5.1 (28) 5.1 (29)

Helmer (4n) Svalof Weibull 1991 5.4 (27) 4.9 (29) 5.1 (29) 5.1 (30)

Lipresso (2n) DSV/Euro Grass 1999 5.9 (31) 5.2 (31) 5.3 (32) 5.5 (31)

Condesa (4n) Advanta/DLF 1982 6.4 (32) 5.3 (32) 5.2 (30) 5.6 (32)

Aurora (2n) IBERS 1987 8.1 (33) 6.9 (33) 6.5 (33) 7.2 (33)

Mean 4.5 4.2 4.0 4.2

LSD (P = 0.05) 0.53 0.46 0.56

Number of sites with crown rust incidence 17 21 16

Euphytica (2010) 176:167–181 173

123

field trials were established (Table 1). On the

contrary, stem rust occurred mainly on perennial

ryegrass and was uncommon on Italian and hybrid

ryegrass.

Crown rust incidence on Italian and hybrid

ryegrass

The incidence of crown rust on Italian ryegrass was

very consistent during the 3 years of evaluation: Out

of 83 sown trials a crown rust disease was observed in

68 trials (82%). The disease was observed from

Perugia (Italy) in the south of Europe to Boelshoj

(Denmark) in the north, from Loughgall (Northern

Ireland) and western France to Poland and Czech

Republic in the eastern part of Europe.

Significant crown rust incidence was reported from

July to early November. The first observations of the

disease were done each year in Italy and in western

France. In August and September crown rust infec-

tions were most severe: nearly 80% of all the scoring

was done in this period of time. Often two consec-

utive growth cycles were attacked. In October and

early November a crown rust incidence was reported

only sporadically.

The overall infection pressure was comparable in

all 3 years when data were collected: mean rust

scoring differed only slightly and the number of sites

with a significant rust disease was comparable

(Table 2).

There were highly significant differences in mean

crown rust scores among Italian ryegrass cultivars

(P \ 0.001) in each of the three experimental years

(Table 4). Overall, cultivars differed greatly in their

susceptibility to crown rust. Cultivars Tarandus,

Domino, Caballo and Zorro were the most resistant

and Gordo and Gumpensteiner the most susceptible

(Table 2). On average the most resistant cultivar was

scored four points better than the most susceptible

one.

Analysis of variance for crown rust disease scores

on Italian ryegrass revealed a significant difference

for mean crown rust susceptibility between sites and

for the cultivar 9 site interaction in each year

(Table 4). In addition, the ANOVA, carried out with

the data of only those sites where a rust infection was

observed in all the 3 years, showed a significant

difference between years and significance for all the

respective interactions. All cultivars, except for

Domino, contributed significantly to the culti-

var 9 site interaction, but only three cultivars to the

cultivar 9 year interaction (P = 0.05).

At 22 sites a significant crown rust infection on

Italian ryegrass was observed at least during two

different years (Table 1). The variability in crown

rust susceptibility between years within each site,

with respect to cultivar ranking, was very low. The

Spearman rank order correlations were significant

(P \ 0.05) between the years at each of these 22 sites

(0.97 [ r [ 0.52) (Table 5).

In order to estimate the consistency of cultivar

ranking between the different sites, Spearman rank

order correlations between mean crown rust suscep-

tibility of each site within each year was calculated.

In 2004 only the data of Loughgall showed no

significant correlation with those of three other sites.

In 2007 the data of Lodi showed a low correlation

with the scores of 3 sites and those of Roznov Zubri

did not correlate with the data of nearly all other sites.

All other possible correlations (714 out of 738) were

significant (P \ 0.05), showing a highly consistent

ranking of the cultivars over a wide range of different

sites (Table 5).

The rank order correlations between mean crown

rust susceptibility over the years of evaluation at each

site were significant (P \ 0.05) in nearly all cases

(Table 5). Only the cultivar ranking of Loughgall and

Roznov Zubri did not correlate with the ranking of

three and 29 sites, respectively.

The Spearman rank order correlations of mean

cultivar disease scores between the years were

highly significant (Table 6). The ranking of 14 out

of 18 cultivars tested differed by no more than one

rank between any 2 years. Only the cultivar Dom-

ino differed by three ranks in one comparison

(Table 2).

Stem rust on Italian and hybrid ryegrass

Stem rust on Italian ryegrass was reported in 2004 at

only two sites and in 2007 at three sites (Table 1). In

2001 no stem rust was observed at all. The few

records of stem rust were coming from sites in the

eastern part of Europe and from one site in North

Italy.

Mean stem rust scores were significantly different

among cultivars in both years (data not shown). In

addition the ranking of the cultivars were comparable

174 Euphytica (2010) 176:167–181

123

between 2004 and 2007, with a Spearman correlation

coefficient of r = 0.87 (P \ 0.05).

Crown rust incidence on perennial ryegrass

Crown rust was the most serious rust disease on

perennial ryegrass. It was observed in 61% of the

trials established (Table 1). In each country crown

rust occurred at least at one site in one of the 3 years.

However, the most frequent incidence of crown rust

was in France, Belgium, The Netherlands, Germany

and Switzerland.

The first crown rust observations were reported

already in July. The highest number of observations

were recorded during August and September with

40% of the scorings done during each of these

2 months. It was common to have two consecutive

cycles of infection in the same year. In October and

early November much less crown rust incidence was

recorded.

The absolute number as well as the percentage of

sites with a significant crown rust disease was highest

in 2004 (Table 1). However, mean crown rust scores

were highest in 2001 (Table 3).

Significant variation for crown rust resistance

between cultivars and sites was found in each year

of evaluation (Table 4). The cultivar 9 site interac-

tion was significant (P \ 0.001) in each year. The

ANOVA, based only on data of sites where a rust

infection was observed during the 3 years, showed

significant differences between years and significance

for all the respective interactions. Nearly all cultivars

(with the exception of Foxtrot, Gladio and Option)

contributed significantly to the cultivar 9 site inter-

action, but only 15 out of 33 cultivars to the

cultivar 9 year interaction (P = 0.05).

Table 4 Degree of freedom (df) and F-values from analysis of variance of crown (Puccinia coronata) and stem rust (P. graminis)

disease scores of Italian (Lolium multiflorum) and perennial ryegrass (L. perenne)

Source of variation Italian ryegrass Perennial ryegrass

Crown rust Crown rust Stem rust

df F-values df F-values df F-values

2001

Cultivars 17 375.6 32 129.9 32 65.6

Sites 23 129.5 16 261.5 11 272.1

Cultivar 9 site interaction 391 3.5 512 3.9 352 3.3

2004

Cultivars 17 261.4 32 107.7 32 51.4

Sites 21 111.3 20 284.0 9 265.5

Cultivar 9 site interaction 357 3.0 640 5.4 288 6.1

2007

Cultivars 17 310.9 32 80.4 32 58.2

Sites 21 195.5 15 286.3 11 203.2

Cultivar 9 site interaction 357 4.6 480 4.4 352 3.2

All 3 yearsa

Cultivars 17 571.7 32 217.3 32 66.3

Sites 12 100.0 10 566.3 4 501.4

Years 2 277.3 2 145.8 2 148.1

Cultivar 9 site interaction 204 4.3 320 6.2 128 5.3

Cultivar 9 year interaction 34 2.1 64 5.2 64 6.8

Site 9 year interaction 24 86.4 20 125.2 8 127.0

Cultivar 9 site 9 year interaction 408 2.1 640 3.2 256 3.2

All F-values were significant at P \ 0.001a F-values were calculated with the data of those sites which had a significant rust infection during all of the 3 years of evaluation

(see Table 1)

Euphytica (2010) 176:167–181 175

123

Overall mean crown rust susceptibility scores of

individual cultivars in each year of evaluation are

presented in Table 3. In each year the cultivars

Gwendal and Bocage were the most resistant among

the cultivars screened. In contrast, Lipresso, Condesa

and Aurora were always highly susceptible to crown

rust. On average, the score of the most resistant

cultivar was 4.6 points lower than the score of the

most susceptible one.

At 14 sites a significant crown rust disease was

observed at least during 2 years of evaluation

(Table 1) and a cross computation of a rank order

correlation between the data of 2–3 years at each site

was possible. In all but two cases the correlations

were significant at P \ 0.05 (Table 5). The excep-

tions were the non-significant correlations of the data

in 2001 and 2007 in Malchow and in 2001 and 2004

in Steinach, respectively. The assessment of crown

rust resistance was therefore very consistent over the

3 years of evaluation at a particular site.

Despite the occurrence of significant culti-

var 9 site interactions (Table 4), the cultivars did

display a consistent behaviour across the different

locations within a certain year of evaluation. Out of

466 possible rank order correlations 392 were

significant at P \ 0.05 (Table 5). Apart from these

significant correlations, the data from Hladke Zivo-

tice did not correlate in 2001 with those of Bornhof

and Lelystad B., respectively. In 2004 the ranking of

the cultivars of five sites (Gumpenstein, Hohenheim,

Lodi, Loughgall, and Steinach) did not correlate with

the ranking of 8–18 other sites. In 2007 there were six

sites (Bornhof, Orchies, Lelystad C., Lodi, Gross

Luesewitz and Malchow) with a cultivar ranking

which did not correlate with 4–7 other sites each.

The rank order correlations between mean crown

rust susceptibility over the 3 years of evaluation at

each site were significant in most cases (P \ 0.05)

(Table 5). Only the cultivar ranking of Gumpenstein,

Hohenheim, Lodi and Loughgall did not correlate

with the ranking of 13, 14, 10 and 24 sites,

respectively.

The most remarkable finding was the close Spear-

man rank order correlation of mean cultivar disease

scores between the years (Table 6). Despite the high

number of sites, representing different environments,

and the large number of cultivars tested, the ranking

of most cultivars in terms of crown rust resistance

was very consistent over the years. However, the

correlations were less close than those observed in

Italian ryegrass. For 23 out of 33 cultivars tested, the

ranking differed by a maximum of three ranks

between any 2 years (Table 3). The six cultivars

Arabella, Aristo, Fennema, Guru, Orval and Terry

differed by seven or more ranks in the most extreme

comparisons.

Table 6 Coefficients of Spearman rank order correlations

among mean crown (Puccinia coronata) and stem rust (P.graminis) disease scores of Italian (Lolium multiflorum) and

perennial ryegrass (L. perenne) in 3 years of evaluation

Italian ryegrass Perennial ryegrass

Crown rust Crown rust Stem rust

2001 vs. 2004 0.99* 0.97* 0.95*

2001 vs. 2007 0.98* 0.92* 0.94*

2004 vs. 2007 0.97* 0.90* 0.98*

* Significant at P \ 0.01

Table 5 Number of significant rank order correlations (P \ 0.05) in respect of rust susceptibility as a percentage of all possible

combinations

Between the data of each year

at a particular site (%)

Between the data of different sites

within a year of experimentation (%)

Between the data of mean rust

susceptibility over years at each site (%)

Italian ryegrass

crown rust

100 97 94

Perennial

ryegrass

crown rust

94 84 87

Perennial

ryegrass stem

rust

75 84 96

176 Euphytica (2010) 176:167–181

123

Stem rust incidence on perennial ryegrass

Stem rust on perennial ryegrass occurred frequently

in the eastern part of Europe and in the two locations

in Italy (Table 1). In addition, this disease was

observed sporadically in other sites, mainly in

Germany, France and Switzerland. In 39% of the

sites established, the overall cultivar mean score for

stem rust was above 2.0.

The first observations were done as early as in

June, but the most frequent occurrence of stem rust

was in August with one half of the scoring being

recorded in this month.

There were highly significant differences in mean

stem rust scores among perennial ryegrass cultivars and

sites (Table 4). The interactions showed significant

variations as well. For 23 out of 33 cultivars a significant

contribution to the cultivar 9 site interaction was

observed. The contribution to the cultivar 9 year

interaction was significant for 20 cultivars (P = 0.05).

Table 7 shows the mean stem rust scores of each

cultivar. Gwendal and Pastoral were the top ranking

and Lipresso and Aurora the bottom ranking cultivars

in each year of evaluation.

At 10 sites a significant stem rust disease was

observed at least during 2 years of evaluation

(Table 1) and a cross computation of a rank order

correlation between the data of 2–3 years at each

site was possible. In all but two cases the Spearman

rank order correlations were significant (P \ 0.05)

(Table 5), with the exception that the ranking of

Lodi did not correlate significantly in two of three

possible comparisons and in Montours in all three

comparisons, respectively. The assessment of stem

rust resistance was therefore quite consistent over

the 3 years of evaluation at a particular site.

The ranking of cultivars in terms of stem rust

resistance between the different sites within each year

correlated significantly (P \ 0.05) in 149 out of 177

possible combinations (Table 5). In 2001 the cultivar

ranking of Boelshoj and Loughgall, in 2004 of Lodi,

Radzikov and Montours and in 2007 of Montours

showed no significant correlations with those of

between one and 10 other sites.

The relationships between the rankings of cultivars

at each site, in respect to mean stem rust values over

years, were very close. Only Loughgall, Montours

and Boelshoj did not correlate significantly between

one and five other sites (Table 5).

Moreover, most cultivars displayed a consistent

response to stem rust infection over time. The

Spearman rank order correlations of mean cultivar

disease scores were highly significant between the

years (Table 6). The ranking of 17 out of 33 cultivars

differed by a maximum of three ranks between any

2 years (Table 7). The cultivars Barnhem, Heraut,

Orval and Roy differed by 7–9 ranks in the most

extreme comparisons.

Correlation of crown and stem rust scores

The ranking of perennial ryegrass cultivars was

different depending on whether crown or stem rust

was scored (Fig. 2). Although the Spearman rank

order correlation between the mean disease scores of

the cultivars for the two pathogens was low, it was still

significant (r = 0.48, P \ 0.05). Cultivars Option,

Vincent, Heraut, Barnhem, Kells, Weigra, Fennema,

Arabella and Corbet were relatively more resistant

against crown rust than against stem rust. The contrary

was true for the cultivars Tivoli, Helmer, Sirocco and

Condesa. The three cultivars Gwendal, Bocage and

Pastoral were among the most crown and stem rust

resistant cultivars.

Discussion

Crown rust was the most serious and the most

frequently observed rust disease of Italian and

perennial ryegrass in most parts of Europe where

ryegrass is cultivated. However, in the eastern part of

Europe and in Italy stem rust was the predominant

rust species on perennial ryegrass. Previous studies

also revealed the importance of crown rust in Europe

(Potter et al. 1990; Roderick and Thomas 1997). In

Australia, crown rust is considered to be the most

serious disease of perennial ryegrass (Kimbeng 1999;

Aldaoud et al. 2004). Stem rust is present on

perennial ryegrass in many areas including New

Zealand, USA and UK (Latch 1966; Roderick and

Thomas 1997; Rose-Fricker et al. 1986) and is

considered less important than crown rust but as a

major disease in seed production (Pfender 2001).

Analysis of variance showed highly significant

differences between the cultivars of Italian and

perennial ryegrass, between sites and years in terms

of crown and stem rust susceptibility, respectively.

Euphytica (2010) 176:167–181 177

123

The detailed results of all the experimental sites in

each year where a rust disease occurred, are already

published in the Proceedings of the ‘‘Eucarpia Fodder

Crops and Amenity Grasses’’ meetings in Braun-

schweig 2002, Perugia 2006 and La Rochelle 2009,

respectively (Boller et al. 2003; Schubiger et al.

2007a, 2010). It is generally known that ryegrass

cultivars show a wide range of susceptibility (Kopec

et al. 1983; Potter et al. 1990; Reheul and Ghesquiere

1996; Wilkins 1978a, b).

The most striking finding was the consistent

ranking of the Italian as well as the perennial

ryegrass cultivars in terms of crown and stem rust

resistance not only over a large number of sites but

Table 7 Mean stem rust

(Puccinia graminis) disease

scores (1 = resistant;

9 = susceptible) of 33

cultivars of perennial

ryegrass (Lolium perenne);

the ranking order of

cultivars in respect of stem

rust resistance is indicated

in parentheses for each year

and for the mean value

Cultivar (ploidy) Evaluation year Mean

2001 2004 2007

Gwendal (4n) 2.2 (1) 2.6 (2) 1.9 (1) 2.2 (1)

Pastoral (4n) 2.2 (2) 2.6 (1) 2.0 (3) 2.3 (2)

Bocage (4n) 2.5 (3) 2.7 (3) 2.0 (2) 2.4 (3)

Elgon (4n) 2.7 (5) 2.9 (4) 2.4 (8) 2.7 (4)

Aubisque (4n) 2.6 (4) 3.0 (6) 2.5 (10) 2.7 (5)

Orval (2n) 3.1 (12) 2.9 (5) 2.4 (5) 2.8 (6)

Roy (4n) 3.0 (10) 3.4 (11) 2.2 (4) 2.8 (7)

Kentaur (4n) 2.7 (6) 3.3 (9) 2.6 (11) 2.9 (8)

Lacerta (4n) 3.0 (9) 3.2 (8) 2.4 (6) 2.9 (9)

Tivoli (4n) 2.8 (8) 3.4 (10) 2.4 (7) 2.9 (10)

Terry (4n) 2.7 (7) 3.5 (12) 2.5 (9) 2.9 (11)

Carrera (2n) 3.0 (11) 3.2 (7) 2.6 (12) 2.9 (12)

Helmer (4n) 3.2 (15) 3.7 (14) 2.8 (15) 3.2 (13)

Litempo (4n) 3.1 (13) 4.1 (19) 2.7 (13) 3.3 (14)

Aberdart (2n) 3.1 (14) 3.8 (16) 3.1 (17) 3.4 (15)

Sirocco (4n) 3.4 (16) 3.8 (15) 3.0 (16) 3.4 (16)

Condesa (4n) 3.5 (17) 4.1 (18) 2.7 (14) 3.4 (17)

Foxtrot (2n) 3.6 (19) 3.7 (13) 3.1 (19) 3.5 (18)

Aristo (2n) 3.5 (18) 3.9 (17) 3.1 (18) 3.5 (19)

Option (2n) 3.8 (21) 4.1 (21) 3.3 (21) 3.8 (20)

Gladio (2n) 3.9 (22) 4.3 (23) 3.2 (20) 3.8 (21)

Barnhem (2n) 3.7 (20) 4.1 (20) 3.8 (29) 3.9 (22)

Guru (2n) 4.2 (27) 4.2 (22) 3.3 (22) 3.9 (23)

Kells (2n) 4.1 (25) 4.4 (26) 3.5 (25) 4.0 (24)

Sponsor (2n) 4.1 (24) 4.3 (24) 3.6 (26) 4.0 (25)

Vincent (2n) 4.0 (23) 4.7 (27) 3.6 (27) 4.1 (26)

Heraut (2n) 4.2 (26) 4.8 (30) 3.4 (23) 4.1 (27)

Weigra (2n) 4.5 (29) 4.3 (25) 3.7 (28) 4.1 (28)

Fennema (2n) 4.6 (30) 4.7 (28) 3.4 (24) 4.2 (29)

Arabella (2n) 4.6 (31) 4.7 (29) 3.9 (31) 4.4 (30)

Corbet (2n) 4.5 (28) 5.0 (31) 3.8 (30) 4.4 (31)

Lipresso (2n) 5.0 (32) 5.7 (32) 4.1 (32) 4.9 (32)

Aurora (2n) 5.7 (33) 6.1 (33) 4.9 (33) 5.6 (33)

Mean 3.5 3.9 3.0 3.5

LSD (P = 0.05) 0.54 0.65 0.44

Number of sites with stem rust incidence 12 10 12

178 Euphytica (2010) 176:167–181

123

also over a period of 6 years. The most resistant

cultivars showed a very consistent reaction to a rust

infection in all environments (sites per year). The

Italian ryegrass cultivars Tarandus and Domino were

among the significantly most resistant cultivars to

crown rust in 53 out of 68 environments, and the

perennial ryegrass cultivars Gwendal and Bocage in

45 out of 54 environments, respectively. Gwendal

and Pastoral, top ranking in stem rust resistance, were

within the significantly most resistant cultivars in 29

out of 34 environments. This clearly indicates that the

high level of resistance of these cultivars was

effective across Europe. The European rust popula-

tions were not virulent to the majority of the plants of

these cultivars. The sites from the border of the grass

growing regions of Europe (Loughgall, Lodi and sites

from the eastern part of Europe) were mostly

responsible for an aberrant ranking of the cultivars.

This suggests a uniformity of the European rust

population over a wide range of geographical regions.

While most cultivars showed a very consistent

rating over time, the perennial ryegrass cultivar Orval

was obviously inconsistent in terms of crown rust

resistance. In relation to the mean over site, Orval

was in 2007 more susceptible than in 2001 at 10 out

of 11 sites and compared with the rating of 2004 at

nine out of 12 sites, respectively. Already in 2004

Orval was, compared with the mean over sites, more

susceptible than in 2001. This was the case at seven

out of 12 sites. This increased rating could be an

indication of an erosion of the effectiveness of the

resistance genes in Orval. The European Multisite

Rust Evaluation Trial, which is newly repeated every

3 years, will demonstrate in the future whether

resistance of formerly resistant cultivars, such as

Orval, is overcome by the pathogen.

In all 3 years and with both rust species, signif-

icant cultivar 9 site interaction was found, indicating

differences among cultivars in their response to sites

and years. Many cultivars contributed significantly to

the cultivar by site and cultivar by year interaction,

respectively. In a disease screening situation the

explanation of such an interaction is complicated

because there are a host and a pathogen involved.

Whether this was caused by different environment or

by the incidence of different races still needs to be

examined. Temperature may have an influence on the

expression of resistance (Roderick et al. 2000). On

the other hand it has to be assumed that different

races at particular sites occur (Aldaoud et al. 2004;

Kopec et al. 1983; Potter et al. 1990). In addition,

Schubiger et al. (2007b) showed a high variability of

virulence and a high number of virulence combina-

tions in European isolates of crown rust. This

situation is found in other grass rust species as well

(Long et al. 2002; Singh et al. 2008; Xianming et al.

2002). Another reason for this significant interaction

could be the mixed infections of crown and stem rust

on the same cultivar making an appropriate scoring

very difficult. Nearly at all sites with a deviant rank

order of the cultivars in respect to rust susceptibility,

an incidence of crown and stem rust was recorded.

Vincent

Option

Herault

Barnhem

Kells

WeigraFennema

Arabella

Sponsor

Corbet

Gladio

Guru

AristoFoxtrot

LipressoAurora

20

25

30

35

Gwendal

Bocage

Lacerta

Pastoral

Carrera

AubisqueOrval

Elgon

RoyKentaur

Terry

AberdartLitempo

Tivoli

Sirocco

Helmer

Condesa

0

5

10

15

0 5 10 15 20 25 30 35

ran

kin

g o

rder

in r

esp

ect

of

stem

ru

st

ranking order in respect of crown rust

Fig. 2 Correlation between

the ranking orders in respect

of crown rust (Pucciniacoronata) and stem rust

(P. graminis) susceptibility

of 33 perennial ryegrass

(Lolium perenne) cultivars.

Spearman rank order

correlation r = 0.48

(P \ 0.05)

Euphytica (2010) 176:167–181 179

123

Several different physiologic rust races may occur

at a particular site. However, at least races with

virulence to the susceptible and avirulence to the

resistant cultivars under examination predominated

and were widespread in Europe. On the other hand,

ryegrass is a cross-pollinated species. Cultivars have

a broad genetic basis and comprise many genotypes

with different resistance genes and gene combina-

tions (Potter et al. 1990). Resistant cultivars may

have a higher number of different effective resistance

genes than susceptible cultivars. Moreover, these

effective resistance genes may occur more frequently

in individual genotypes of a resistant cultivar. Such a

cultivar is resistant to a wide range of rust races with

different virulence characteristics. Therefore, a con-

sistent cultivar ranking in different environments, in

terms of rust resistance, is possible even if the rust

population is highly variable.

There are perennial ryegrass cultivars with resis-

tance to crown as well as to stem rust. However, the

low correlation between crown and stem rust

resistance of the cultivars suggests different resis-

tance genes to be effective against the two rust

species. Breeding rust resistant ryegrass cultivars in

an environment where crown and stem rust naturally

occur may result in genetic material with resistance

to both species. There is not necessarily a genetic

linkage between the respective resistance. Based on

the present study, the best sites for breeding crown

and stem rust resistant cultivars in a field screening

without artificial inoculation are Lodi, Malchow,

Montours and Zurich. Here in at least two out of

3 years of evaluations both rust species occurred and

yielded significant differences among cultivars

(Table 1). In addition, rank order correlations with

the overall mean were consistently high for Mon-

tours and Zurich in terms of crown rust scores and

for Malchow and Zurich in terms of stem rust scores

(Boller et al. 2003; Schubiger et al. 2007a, 2010).

The results obtained from the present study allow

several conclusions to be made. There is evidence for

genetic differences for crown and stem rust reactions

among European cultivars of Italian and perennial

ryegrass. Resistant cultivars showed a quite stable

resistance in different environments as well as over

time. Therefore only a limited number of testing sites

is necessary to obtain a reliable ranking of cultivars in

terms of rust resistance in official cultivar testing. A

single site with regular crown and stem rust infections

over the years may be sufficient to successfully select

rust resistant breeding material. On the other hand a

resistant cultivar can be grown in a wide range of

geographical regions and over a certain period of

time without the risk of a breakdown of resistance.

However, since rust fungi have the capacity to

overcome host resistance by evolving new virulent

races, the durability of resistance is limited (Aldaoud

et al. 2004; Leach et al. 2001; Potter et al. 1990).

Therefore, improving rust resistance has to be one of

the major goals in ryegrass breeding. Genetically

diverse rust resistance sources and types of resis-

tance have to be identified, conserved and used in a

breeding program to get durable and effective

resistance (Kopec et al. 1983; Reheul and Ghesqui-

ere 1996; Wilkins and Humphreys 2003). The

objective is to increase the frequency of diverse

resistance genes or different allelic genes in a new

cultivar, which could lead to a conflict with the

distinctness and homogeneity criteria of cultivar

registration. The combined resistance genes should

be effective relative to the majority of physiological

races occurring in the environment in which the

cultivar is to be grown. Therefore, information on

the physiological races of P. coronata f. sp. lolii and

P. graminis f. sp. graminicola would undoubtedly

enhance the development of durable resistant culti-

vars. Since uredospores are blown from one area to

another, pathogen population has to be observed

over a wide range of geographical regions in order to

ensure a sustainable system. However, avirulence

genes in the crown and stem rust pathogen with the

corresponding resistance genes in the ryegrass have

yet to be characterised.

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