Current Virulence of Pyrenophora teres on Barley in Western Australia

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1 Current Virulence of Pyrenophor teres on Brley in Western Austrli Snjiv Gupt, Stte Agriculturl Biotechnology Centre, Division of Science nd Engineering, Murdoch University, Murdoch, Western Austrli 6150, Austrli; nd Robert Loughmn, Plnt Pthology, Agriculture Western Austrli, Bron-Hy Court, South Perth, Western Austrli 6151, Austrli ABSTRACT Gupt, S., nd Loughmn, R Current virulence of Pyrenophor teres on brley in Western Austrli. Plnt Dis. 85: Studies on vrition, occurrence, nd distribution of virulence in Pyrenophor teres re helpful to identify effective sources of resistnce tht cn be used for brley breeding in Western Austrli. Seventy-nine isoltes of Pyrenophor teres were collected from different brley fields of Western Austrli in Seventy-four induced net type symptoms (P. teres f. teres) nd five induced spot type symptoms (P. teres f. mcult). Net type isolte responses on 47 brley lines were similr to the rnge of responses induced by nine historicl isoltes collected in the region between 1975 nd These net type isoltes were clssified into two distinct groups bsed on virulence to the cultivr Beecher. Isoltes were further clssified into eight groups bsed on minor pthogenic vrition mong the popultion. The virulence phenotype present in n estern Austrlin isolte ws not observed in ny isoltes collected from Western Austrli. An nlysis of vrince on subset of 12 net type isoltes indicted significnt line isolte interction (P < 0.001), with the interction term vrince component four times lrger thn the error vrince. Bsed on these studies, the virulence mong net type isoltes hs remined stble in Western Austrli for the lst 19 yers. Spot type isoltes were collected from wider geogrphic re thn previously reported nd vried in virulence bsed on response to brley line Hert. Vrition in spot-type isoltes is reported for the first time from the region. The results from this study re being used in the development of resistnt vrieties. Additionl keywords: brley differentil set, hierrchicl clssifiction Net blotch, cused by Pyrenophor teres Drechs. (nmorph: Drechsler teres (Scc.) Shoemker), is prominent folir disese of brley (Hordeum vulgre L. emend. Bowden) in Western Austrli (19,46), s well s elsewhere in the world (13,28,31,34,39,41). Two types of lef symptoms re ssocited with the net blotch disese: the net type, cused by P. teres f. teres, which cuses horizontl nd verticl crisscrossed drk brown vention tht sometimes turns chlorotic; nd the spot type, cused by P. teres f. mcult, which cuses drk brown circulr or ellipticl spots ccompnied by chlorosis of the surrounding lef tissue (20,32). Both pthogens reduce yield (7,11,22,23,27,35,36), minly through reduced grin size, which my impir the brewing qulity of mlting brley. Yield loss experiments conducted in Western Austrli demonstrted 17% yield decrese in brley cultivr Beecher due to net type net blotch (30). In more detiled study, cultivr Dmpier hd men yield reduction of 21% with mximum loss of 37% (16). For spot type, yield losses Corresponding uthor: Snjiv Gupt E-mil: snjiv@centrl.murdoch.edu.u Accepted for publiction 22 My Publiction no. D R 2001 The Americn Phytopthologicl Society vried from 3 to 22% in cultivrs Beecher nd O Conner in Western Austrli (17). Studies on the occurrence nd distribution of different virulence types of P. teres re essentil to identify useful forms of resistnce nd ssist in the development of future brley breeding strtegies. Pon (26) first reported the vrition in virulence in P. teres f. teres isoltes in the United Sttes. Since then, vrious studies hve been conducted to understnd the pthogenic vrition nd prevlence of pthotypes of P. teres round the globe using rnge of differentil brley lines (1 3,9,10,12 15,20,25,29,34,39,40) nd lso restriction frgment length polymorphism (RFLP) nd rndom mplified polymorphic DNA (RAPD) mrkers (21,24,45). In Western Austrli where net blotch is endemic, three pthotypes of P. teres f. teres were reported by Khn nd Boyd (18). The occurrence nd virulence of P. teres f. mcult ws reported by Khn nd Tekuz (20). A chnge in virulence ws observed with the introduction of new brley cultivrs in Western Austrli. The incidence of net type net blotch declined in the 1970s, nd by the erly 1980s, 73% of P. teres f. teres isoltes were virulent on the previously susceptible cultivrs Beecher nd Atls (15). The modertely resistnt cultivrs Stirling nd O Connor becme susceptible decde fter their relese in Western Austrli, indicting the bility of the pthogen popultion to chnge with cultivrs. The chnge in virulence, doption of high-yield production methods, nd wide use of conservtion tillge prctices hve contributed to the reemergence of net blotch s thret to brley production. The objective of this study ws to determine the virulence spectrum of current popultions nd ssess possible chnges in P. teres over the 19 yers since it ws lst ssessed by Khn (15) in Western Austrli. MATERIALS AND METHODS Collection of P. teres isoltes. In spring of 1995 nd 1996, 79 net blotch infected lef smples were collected from brley fields distributed cross ll brley growing regions of Western Austrli (Fig. 1). The infected leves from ech loction were plced in pper envelopes, dried, nd stored t room temperture (20 to 25 C). Nine historicl isoltes of P. teres f. teres collected nd lyophilized between 1975 nd 1985 were supplied by the Plnt Pthology culture collection, Agriculture Western Austrli, South Perth. These nine isoltes of P. teres f. teres were used to compre the vrition in virulence with current isoltes (Fig. 1). One P. teres f. teres isolte from estern Austrli ws supplied by the Queenslnd Deprtment of Primry Industries, Toowoomb, Queenslnd, Austrli. Single-spore isoltion nd inoculum production. Lef tissue with net blotch lesions ws cut into 5- to 10-mm-dimeter frgments, surfce-sterilized in 0.5% sodium hypochlorite solution for 2 min, nd then double rinsed in sterile deionized wter for 1 min. Frgments were blotted dry nd septiclly trnsferred to 2% wter gr pltes. Isoltion pltes were incubted t 15 to 18 C with 12 h ner-uv light/12 h drk. For the historicl reference isoltes, lyophilized culture frgments were trnsferred to 2% wter gr pltes nd incubted s bove. After 3 to 5 dys, single conidium representing ech collection ws trnsferred, using the needle under the microscope, to penut otmel gr (POA) medium pltes (33) nd incubted for 2 weeks to induce sporultion. Differentil brley set. A set of 47 brley lines ws used. The set comprised 22 lines used by Steffenson nd Webster (34) nd eight by Tekuz (39); the remining 17 were cultivrs from different regions of Austrli. Most lines were supplied by Queenslnd Deprtment of Primry Industries, Toowoomb, Queenslnd, Austrli. 960 Plnt Disese / Vol. 85 No. 9

2 Lines were sown in 10-cm-dimeter plstic pots in clumps of 10 seeds per line nd two lines per pot using psteurized soil mix (2 prts river snd nd 1 prt pet moss with nutrients nd trce elements, ph 6.8 to 7). The plnts were grown in the glsshouse t 18 to 22 C for 2 weeks with n verge dy length of 12 h or until the second lef ws fully opened. Inoculum nd inocultion of host plnts. Conidi were hrvested from POA pltes by dding sterile distilled wter nd rubbing with rubber sptul. The spore suspension ws filtered through guze nd djusted to conidi per milliliter. Two milliliters of this suspension ws pplied per pot of 20 seedlings (pproximtely conidi per plnt) using n irbrush spryer. The plnts were plced in mist chmber, nd lef wetness ws mintined t 16 to 18 C for 24 h. Then the plnts were returned to the glsshouse for symptom development. Thirteen (12 P. teres f. teres nd one P. teres f. mcult) out of 89 (79 current + 9 historicl + 1 Queenslnd) isoltes were repeted to determine reproducibility of the infection types. Scoring infection types. Infection types on the second leves were scored 9 dys postinocultion for net type net blotch nd 11 dys postinocultion for spot type net blotch using the scles of Tekuz (37). Assessment of differentil lines for net blotch rection t the dult plnt stge. For net type net blotch, ll lines were sown in rndomized block design with two replictes t South Perth. Ech plot comprised 10 to 15 plnts s single 1-m rows. Brley strw infested with net type net blotch ws pplied t 50 g/m 2 t the seedling (four- to five-lef) stge. Plnts in ech plot were ssessed ccording to Tekuz (37) by ssessing leves on which infection hd dvnced by nthesis (flg-1 nd flg-2 leves). Sttisticl nlysis. In this study, seedling responses to P. teres isoltes were clssified using the pckge GEBEI (University of Queenslnd) by pplying n gglomertive hierrchicl clssifiction procedure (43) with squred Eucliden distnce s the mesure of similrity mong entries for the 47 brley lines nd incrementl sum of squres (ISS) s the grouping strtegy (4,5,42,44). To determine the optiml trunction points for use with the hierrchicl clssifiction method, we considered the effectiveness of the prtition of sums of squres mong groups nd the mgnitude of the vrition within groups (8). These were determined using the pproprite prtition of the sums of squres for one-wy clssifiction of the dt mtrix (6). The brley differentil lines lso were clssified in this wy. Duplicte seedling infection responses were subject to nlysis of vrince using the pckge GENSTAT. Fig. 1. Collection sites of Pyrenophor teres isoltes nd distribution of its pthotypes in Western Austrli. Plnt Disese / September

3 RESULTS Net type nd spot type net blotch were widely distributed in the brley growing regions of Western Austrli. The distribution of the obtined isoltes ccording to their min distinguishing virulence chrcteristics (bsed on cv. Beecher for net type net blotch nd cv. Hert for spot type net blotch) is shown in Figure 1. P. teres f. teres isolte clssifiction. The number of groups used for detiled exmintion ws determined from the prtitions of the sums of squres mong the groups, the men squres for the vrition within groups, nd the number of members within groups. The eight group level ws chosen for further nlysis. At this level of trunction, reltively high proportions of the vrition due to differences in isolte mens cross brley lines (57%) nd differences in ptterns cross the brley lines (62%) were prtitioned mong groups. Isolte groups (IGs) hd 2 to 45 isoltes, which were reltively homogenous within ech group (Fig. 2). The nodes of the dendrogrm nd the eight terminl groups were lbeled using the fusion point tht they represented in the sequence of clssifiction. In the dendrogrm, groups tht were more similr fused erlier. Ninety-six (84+12 repet) isolte responses were considered s two mjor isolte groups (IGs) tht differed strongly for cluster t node 89 specificlly in line groups LG8 nd LG31 (Fig. 2) for infection types in lines Beecher, Hzer, Atls, nd Kombr (Fig. 3). Isoltes comprising cluster 94 induced low infection types verging from 2.0 to 3.6 on these line groups, while those comprising cluster 89 induced high infection types verging 6.4 to 7.8. Cluster 89 isoltes lso induced low verge infection type on Clipper nd more on members of LG10 (Prto nd Steptoe, Fig. 3) compred to cluster 94 isoltes. The cluster t node 89 ws comprised of two smll IGs, 48 nd 78. These two IGs were similr to ech other except group 48 isoltes induced 0.7 to 1.0 unit higher disese on brley line groups LG31, LG8, LG10, nd LG30. IG48 isoltes were ll collected from Wongn Hills Reserch Sttion during the current survey nd induced high infection type (men = 8) on line Dmpier, universl susceptible (rw Fig. 2. The tbulted men responses of 47 lines s 13 line groups (LG) on the bsis of seedling net type Pyrenophor teres response from 96 tests using 84 isoltes (including 12 repets) clustered into eight isolte groups (IG). Numbers in bold indicte mjor contributions to the different groupings. The dendrogrm depicts the reltionship mong groups of isoltes. The number of isoltes in ech group is indicted in brckets. dt not shown). IG78 isoltes were ll historic isoltes collected from rnge of environments nd induced modertely high (men = 6) infection type on line Dmpier (rw dt not shown). The second min cluster, fusing t node 94, contined members with low disese response on LGs 8 nd 31 (Fig. 2). These six groups (including the estern Austrlin isolte QNB85i) hd ptterns of response tht differed in vrious degrees from ech other. Cluster 91 comprised the mjority of isoltes (63, of which 8 were repet tests), which fell into two similr groups, 88 nd 84, differing minly in their response on Cmeo ( men infection type difference of only 1.2, rw dt not shown). The responses of other line groups to these two isolte groups were mostly similr. Duplicte responses of QNB85i grouped together, nd the reltion of this smll group to other groups cn be seen in the dendrogrm (Fig. 2). QNB85i ws similr to other non-beecher ttcking isoltes except tht it produced high rection scores in LG22 on lines Corvette (infection type 9), Gilbert (infection type 8), nd Grimmett (infection type 7) (individul dt not tbulted). QNB85i ws less virulent on Betzes compred with other similr IGs, nmely 86, 75, nd 87, which hd 6, 3, nd 12 isoltes, respectively. These groups remined seprte until fusion t the 4 group level (cluster 92). IG87, which included duplicte isolte, induced slightly higher men rections on Tifng (3.4 versus 1.5), CI4922 (3.9 versus 2.5), nd Ming (3.8 versus 2.6) members of LG34 thn on IGs 75 nd 86 (rw dt not shown). Isoltes in group 86 differed slightly from those in group 75, inducing intermedite rection scores compred with more resistnt scores in Cmeo, Betzes, LG31, LG22, nd LG33. Twelve of the 84 isoltes were screened in duplicte on seprte dtes to guge the rndom vrition in response of brley lines to isoltes. For the purpose of clssifiction, the duplicte responses were clssified s individul responses. Ten of the duplicte isoltes grouped with their corresponding replicte. One isolte hd its replictes in the similr groups 88 nd 84, nd the other hd its replictes in groups 87 nd 84. Significnt line isolte effects (P < 0.001) were observed mong the 12 isoltes tested in duplicte (Tble 1). The vrince component for line ws lrge (σ L 2 = 2.369) compred with effects of isolte (σ I 2 = 0.003) or interction (σ IL 2 = 0.493). Isolte 95NB100, which occurred in IG48, showed significntly (P < 0.001) higher rection score thn other isoltes on cvs. Atls, Beecher, Hzer, Kombr, Prto, nd Steptoe while it induced lower rections thn the mjority of other isoltes on cvs. Cmeo nd Clipper. Another isolte, QNB85i, induced significntly (P < 0.001) higher disese on lines Corvette, Gilbert, 962 Plnt Disese / Vol. 85 No. 9

4 Golf, nd Grimmett compred with other isoltes. Six IG84 isoltes (95NB66, 95NB74, 95NB82, 95NB87, 95NB90, nd 95NB119) induced little vrition in response pttern mong the brley lines, responses mostly being within 1 unit of score mong ech line for ech isolte. These six isoltes were generlly similr to 95NB129 (IG88), except for higher response on Cmeo nd Cndin Lke Shore (P < 0.001) (Tble 1). P. teres f. mcult isolte clssifiction. Only five of 79 isoltes induced spot type symptoms. These isoltes originted from Bdgingrr nd Wongn Hills (centrl griculturl res) nd Mt. Ridley nd Plinup River (southern griculturl res) (Fig. 1). Seedling infection types for these isoltes re shown in Tble 2. Isolte 95NB117 showed higher (intermedite) rection scores on brley lines Atls, Clipper, Hrbin, Moondyne, Rojo, nd Steptoe compred with other isoltes. This isolte lso induced resistnt rection on Betzes nd Hert compred with intermedite or susceptible rection scores for the other isoltes. Rection to P. teres f. teres t dult plnt stge. Net type expression in the field showed virulence on line Beecher (Tble 3). In field grown dult plnts, net type net blotch rections were similr to those in seedlings with Beecher virulent isoltes (dult plnt responses shown in brckets in Figure 3). The rection of Betzes ws intermedite on dult plnts compred with intermedite to susceptible rection s seedlings. Brley differentil set clssifiction. The grouping of brley lines ws truncted t the 13 group level for further nlysis. At this level of trunction, reltively high proportions of the vrition due to differences in brley line mens cross isoltes (99%) nd differences in ptterns cross the isoltes (61%) were prtitioned mong groups. Line groups (LGs) hd from 1 to 10 members nd were reltively homogenous within ech group. The responses of the 47 brley lines were considered s two mjor clusters in the dendrogrm (Fig. 3). Moderte to high seedling rection scores were common mong lines tht formed cluster 42 (Fig. 2). This cluster consisted of LG30, group of universlly susceptible lines, the single member group Betzes, which ws similr to LG30 but hd lower rection scores to most isoltes (prticulrly Fig. 3. The reltionships nd members of 13 groups of 47 lines clssified from seedling net type net blotch response. The numbers in brckets re men dult plnt responses to Beecher virulent isolte. QNB85i), nd two single member groups, Clipper nd Cmeo. Clipper nd Cmeo were modertely susceptible to mny isoltes but were modertely resistnt to the Beecher ttcking isoltes in IGs 48 nd 78. In cluster 45, low to intermedite infection types were most common, but some high infection types occurred (Fig. 2). This cluster consisted of LGs 16 nd 32, universlly resistnt lines; LG10, similr to LG16 but produced intermedite infection types with Beecher ttcking isoltes (IG48 nd IG78); LGs 31 nd 8, susceptible to Beecher virulent isoltes but resistnt to other isoltes; LGs 17, 22, nd 33, which generlly hd intermedite rection scores (but Grimmett, Corvette, nd Gilbert of LG22 were susceptible to the isolte QNB85i from Queenslnd); nd LG34, resistnt to intermedite to ll isoltes. DISCUSSION Both forms of P. teres were widely distributed cross brley growing res of Western Austrli in 1995 nd 1996, with P. teres f. teres isoltes being more frequently recovered from surveyed crops. Among P. teres f. teres isoltes, two distinct virulence groups were detected. A smll number of isoltes ws differentited by their virulence on lines Atls, Beecher, Hzer, nd Kombr. The virulence represented by these isoltes ws reported in Western Austrli by Khn nd Boyd (18) s Beecher virulent. Beecher previously occupied more thn 75% of the stte s brley producing re then declined rpidly in populrity in 1970s (15). It is now rrely grown (less thn 0.3%) in Western Austrli, nd the present distribution of isoltes virulent on this cultivr is limited to Wongn Hills (Fig. 1). Wongn Hills isoltes were collected t the Agriculture Western Austrli Reserch Sttion, where mix of Atls nd Dmpier brley hs been cultivted nnully since 1980 to mintin supply of net blotch infested residues for disese screening inoculum. Thus, the Atls/Beecher virulence hs been mintined in the P. teres f. teres popultion. Throughout other res, this virulence ws undetectble nd isoltes with greter virulence on cultivr Clipper occurred in ssocition with the commercil cultivtion of Clipper in the 1980s. The mjority of contemporry P. teres f. teres isoltes were Beecher virulent, nd comprtively little vrition existed mong these. Further virulence previously identified in Western Austrli by Khn nd Boyd (18) on cultivr Algerin (CI1179) ws not detected mong the contemporry popultion of the pthogen. The vrition in rection of the brley lines to infection with the rnge of isoltes rose from both genetic nd rndom effects. When the size of these components ws estimted from subset of isoltes, the component of vrince for the isolte Plnt Disese / September

5 line interction ws four times lrger thn the error vrince component. While some brley lines gve very distinctive responses to different P. teres f. teres isoltes, the degree of vrition of other isoltes ws smll nd similr to the vrition induced by rndom effects. Among the 12 isoltes tested s duplictes, 10 hd responses grouped together following clssifiction. The nlysis of vrince for these isoltes confirms the mjor differences observed mong the groups of Beecher virulent, Beecher virulent, nd Queenslnd types. The two remining duplicted isoltes, 95NB69 nd 95NB70, hd replicte responses llocted to different groups upon clssifiction. For 95NB70, the duplicte responses were llocted to the very similr IGs 88 nd 84, while the 95NB69 duplicte responses were llocted to the generlly less similr IG87 nd IG84. However, the response dt for these isoltes indicted tht the duplictes differed by not more thn rection score of 1.0 for 16 to 18 of the 47 lines. It is possible tht by chnce, this ws sufficient to give these pttern of response more like tht of other isoltes thn like their own. While smll repetble differences were observed between isoltes in groups 88 nd 84 of cluster 94 (Tble 1), it ppers tht some of the vrition observed within this cluster hs little biologicl significnce except for QNB85i, which however is not relevnt to Western Austrli. This nlysis on isoltes in duplicte suggested tht the rection scores of different P. teres f. teres isoltes re repetble with gret relibility. Pthotypes of P. teres f. teres prevlent in Western Austrli cn be differentited using cvs. Beecher, CI 9214, nd Dmpier or Stirling or Prior (Tble 3). On this bsis, two pthotypes of P. teres f. teres re differentited. Beecher virulence (depicted by the clusters of isoltes t node 94, Fig. 2) is common in the popultion. Minor biologicl vrition in vrietl response observed mong Beecher virulent groups of Western Austrlin isoltes is of limited immedite ppliction for resistnce breeding. Western Austrlin pthotypes re different from those found in Queenslnd (G. Pltz, personl communiction) nd other prts of the world. Preliminry virulence studies on limited set of 18 isoltes indicted tht there is wide rnge of pthotypes of P. teres f. teres in Queenslnd (25). The reference isolte from Queenslnd (QNB85i) ws virulent on Grimmett, Corvette, Golf, nd Gilbert, which clerly differentited this isolte from Western Austrlin isoltes. It ppers this is biologicl response on Grimmett likely to hve risen in Queenslnd in response to the commercil cultivtion of this cultivr. In the bsence of commercil plntings of this nd the other three cultivrs in Western Austrli, there ppers to hve been no opportunity for virulence to hve incresed in the Western Austrli P. teres f. teres popultion. Twenty-two brley lines in this study were the sme s those used by Steffenson nd Webster (34). Seven of the 22 lines were found to be resistnt to ll Western Austrlin isoltes compred with 10 out of 22 in the studies of Steffenson nd Webster (34) with Cliforni P. teres f. teres isoltes. None of these 22 lines ws susceptible to ll Western Austrlin isoltes, lthough this ws the cse for three other lines (Dmpier, Stirling, nd Prior) Tble 2. Rection scores (1 to 9 scle) of Hert virulent isolte (95NB117) nd four Hert virulent isoltes of Pyrenophor teres f. mcult on brley differentil lines Isolte Brley line 95NB117 b 95NB97 95NB104 95NB106 95NB155 Atls Betzes Hrbin Hert Steptoe Only lines contributing to significnt interction of line isolte effects re shown (min contributing scores in bold). b Isolte 95NB117 men of 2 replictes, other isoltes unreplicted. Tble 1. Rection scores (1 to 10 scle) of Beecher virulent isolte (95NB100), 10 Beecher virulent isoltes, nd one Queenslnd isolte (QNB85i) of Pyrenophor teres f. teres tested in duplicte on brley differentil lines Isolte IG48 IG84 IG88/ IG84 b IG88 IG87/ IG84 b IG87 Brley line 95NB NB NB 66 95NB 74 95NB 82 95NB 87 95NB 90 95NB 70 95NB NB 69 95NB 95 QNB 85i Algerin Atls Beecher Betzes Cmeo CI Clipper Corvette Gilbert Golf Grimmett Hzer Hert Kombr Ming Moondyne Prto Rik Steptoe Tllon Yerong P (line.isol) <0.001 LSD 5% 0.7 CV% 9 Only lines contributing to significnt interction of line isolte effects re shown (min contributing scores in bold). b One replicte occurred in both groups. 964 Plnt Disese / Vol. 85 No. 9

6 from Austrli. Steffenson nd Webster (34) found Prto, Kombr, nd Atls to be susceptible to the mjority of their isoltes, wheres we found intermedite to susceptible rection for these lines only to minority of our isoltes (those being Beecher virulent). The 13 pthotypes identified from Cliforni nd elsewhere were different from Western Austrlin virulences. Tekuz in 1990 (39) reported the occurrence of 65 pthotypes out of 219 P. teres isoltes using 12 brley differentil lines. Eight out of 12 lines were included in our study. The differentil virulence in these eight lines in Cnd provides sufficient evidence tht the Cndin virulence spectrum of P. teres is different from Western Austrli. Jonsson et l. (13) identified 14 pthotypes of P. teres f. teres using 18 brley lines in Sweden. Nine of the 18 lines were the sme s used in our study. Golf ws susceptible to ll the pthotypes in Sweden, wheres it ws intermedite in our study, indicting virulence types in Sweden re different from Western Austrli. Afnsenko nd Levitin (2) reported s mny s 80 pthotypes of P. teres f. teres from Russi using seven differentils. More recently, Afnsenko et l. (1) reported wide rnge of pthotype diversity for P. teres f. teres from Russi, Germny, Czech Republic, nd Slovki using 38 brley lines. P. teres f. teres virulence in Western Austrli is unique nd hs been reltively stble in recent decdes. This is likely due to lck of selection pressure for pthogen virulence becuse highly resistnt cultivrs hve not been grown in this region. The brley lines used to differentite isolte responses were identified from sets used previously (15,25,34), but lso included lines which re widely grown in Western Austrli nd elsewhere in Austrli. The brod rnge of resistnces ws more thn required to discriminte mong the simple rnge of virulences present in Western Austrli. Cultivr Beecher discriminted mong the P. teres f. teres isoltes. CI 9214 represents universlly resistnt line, while Dmpier, Stirling, nd Prior represent universlly susceptible lines (Tble 3). Corvette nd Grimmett differentited the Queenslnd isolte QNB85i from ll others used in this study. Betzes cn lso be used s differentil line for distinguishing Beecher virulent (modertely susceptible to susceptible rections) nd Beecher virulent (intermedite rection) isoltes. While there my be scope for simplifiction of the full differentil set, it is pprent tht the Western Austrlin P. teres f. teres popultion does not provide frmework for selecting the fewest genotypiclly distinct lines becuse of lck of diversity. Khn nd Boyd (18) used Algerin (CI 1179) s brley differentil. This line did not detect ny differentil responses mong the current isoltes but could possibly detect rre virulence bsed on previous ssessments of the popultion (15). P. teres f. mcult ws much less prevlent thn P. teres f. teres in this survey of the Western Austrli P. teres popultion. Vrition in P. teres f. mcult isoltes is reported for the first time from this region. Differences in virulence of P. teres f. mcult were differentited on brley line Hert despite being limited to smll proportion of the popultion (Tble 4). Skiff/Norbert nd Cost/Cpe were universlly resistnt nd susceptible, respectively. Khn nd Tekuz (20) reported Hert virulence from the northern griculturl regions of Western Austrli, previously considered to be the recognized rnge for this disese. The identifiction of spot type net blotch outside this rnge in southern griculturl res nd the occurrence of Hert virulence suggest tht further work on the extent nd diversity of P. teres f. mcult in Western Austrli is wrrnted. This is prticulrly pertinent in light of epidemics of this disese in southern res of Western Austrli in 1997 nd 1998, which occurred fter the current survey. A more comprehensive survey to Tble 3. Lines tht distinguish net type Pyrenophor teres isoltes tested on seedlings or dult plnts, nd their rections Isolte Dmpier or Stirling or Prior CI 9214 Beecher Corvette or Grimmett Betzes Beecher virulent S R R I MS-S Beecher virulent S R S I I QNB85i S R R S I Beecher virulent (dult) S R R I I S = infection types 7, MS = infection type 6, I = infection types 4 to 5, R = infection types 1 to 3. Tble 4. Lines tht distinguish spot type Pyrenophor teres isoltes tested on seedlings, nd their rections Isolte Cost or Cpe Skiff or Norbert Hert Hert virulent S R R Hert virulent S R S S = infection types 7, MS = infection type 6, I = infection types 4 to 5, R = infection types 1 to 3. delimit the extent of vrition mong the P. teres f. mcult popultion would be n importnt prelude to breeding for resistnce to this pthogen. The differentil responses of brley lines t the seedling nd dult plnt stge were studied by Tekuz (38) nd Douiyssi et l. (9). Expression of low infection types on seedlings cn pper s high infection types on dult plnts, nd vice vers, nd is pthotype specific. Seedling glsshouse nd dult field responses to P. teres observed in the current study were very similr, with only minor vrition in disese rection observed s lower dult infection types in Betzes nd Clipper. The current sitution suggests tht selection for resistnce to the common forms of P. teres f. teres using seedling tests will lrgely reflect dult plnt responses when those resistnces re deployed in the field. In conclusion, the current virulence spectrum of P. teres hs remined stble in Western Austrli in the lst two decdes, except tht P. teres f. mcult hs been found to be more widely distributed within the region thn previously reported. Work is in progress to pyrmid diverse resistnces in breeding progrms. ACKNOWLEDGMENTS We thnk In Goss nd Chris King for their technicl support. We lso thnk Grins Reserch nd Development Corportion, Grin Pool of Western Austrli, Joe White, nd Kirin Mltings for finncil support. LITERATURE CITED 1. Afnsenko, O. S., Hrtleb, H., Gusev, N. N., Minrikov, V., nd Jnoshev, M A set of differentils to chrcterize popultions of Pyrenophor teres Drechs. for interntionl use. J. Phytopthol. 143: Afnsenko, O. S., nd Levitin, M. 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