Plant Pathology (\990) 39, 424-433

Genes for race-specific resistance to yellow rust{Puccinia striiformis) in Indian wheat cultivars

H. SINGH,* R. JOHNSON and D. SETHfCambridge Laboratory, AFRC Institute of Plant Science Research, Colney Lane,Norwich NR4 7UJ, UK

Seedlings of Indian wheat cultivars (Kalyansona, Sonalika, WL71I and eight others releasedcommercially) were tested with 13 British and four alien races of Puccinia striiformis. The data indicatedthe probable presence of the resistance gene Yr2 in the three cultivars named above and in six of theothers. Reactions of the remaining two cultivars, PWB12 and WL2265, were consistent with the presenceof the gene Yr7. The presence of Yr2 in Kalyansona, Sonalika and WL711 was supported by evidencefrom crosses between them and with Heines VII, which is known to carry Yr2. In crosses of Sonalika witha susceptible cultivar, Kharchia Local and also with WL711, tests of F1, F2 and F3 generations indicatedthat, in addition to Yr2, Sonalika possesses at least two other genes. Both these genes were difScult todetect but the F3 data supported the hypothesis that there is a single partially recessive gene givingresistance to alien race 6E16 and a different, possibly complementary, gene system effective againstanother alien race, 39E134. The presence of resistance in addition to Yr2 was also detected in WL711 andHD2329.

INTRODUCTION

Yellow rust of wheat, caused by Puceinia striifor-mis. is an important disease in the wheat growingarea of northern India (Sharma et ai, 1972) andbreeding for resistance is an important objectiveof wheat breeders in this zone. However, there arefew reports that can be interpreted internation-ally describing the genetic basis of resistance toyellow rust in the wheat cultivars developed inIndia in the last two decades. Such informationcould provide a more rational basis for breedingresistant cultivars in the future and for under-standing the variation in the pathogen occurringin India. Singh & Johnson (1988) indicated thatthe widely grown cultivar Kalyansona possessesthe gene Yr2 first reported by Lupton and Macer(1962) in the differential cultivar Heines VII

In the present study, genes for resistance in 11Indian wheat cultivars were postulated by com-parison of their reactions to 17 races of P.striiformis with the reactions of cultivars possess-ing known genes, and in relation to their pedi-

• Present address: Plant Breeder, Dryland AgriculturalResearch Project, IX-partmcnt of Soils. Punjab Agrieul-tur<il Universily, Ludhiana 141004, Indiu.t Present address: School of Biological Sciences.University of East Anglia. Norwich NR4 7TJ, UK.

grees. in Kalyansona, Sonalika and WL7Ii thepresence of genes postulated by this method wastested by genetic analysis.

MATERIALS AND METHODS

The 11 wheat cultivars examined, with theirpedigrees and dates of introduction, are shown inTable 1. The cultivars were tested with 17 races ofP. striiformis but to reduce the quantity of datapresented the results of tests with only 10 of theraces are given fully. The data from the otherseven races are given in part to show that theysupported the gene postulations presented. The10 races, classified with an international set ofdifferential cultivars (Johnson et ai, 1972) plusthe cultivar Clement, are shown in Table 2. Six ofthe races were of British origin; the remainingfour were of alien origin and comprised race 6E16(isolate WYR 85/23) from Lebanon, races 6E0(WYR 85/22) and 66E0 (WYR 85/26) fromEcuador, and race 39E134 (WYR 68/2) from TheNetherlands. These four races were supplied byR. W. Stubbs, Research Institute for Plant Pro-tection, Wageningen, The Netherlands, and wereimported and used under the conditions specifiedin UK Ministry of Agriculture. Fisheries andFood Licence No. PF48A/116(87),

Resistance to yellow rust in Indian wheat cultivars

Table I. Pedigrees and year of release of Indian wheat cultivars

425

Cultivar

KalyansonaSonalikaWL7IIHD2329PBW54PBW120WG377WHI47WL1562PBWI2WL2265

Pedigree

Penjamo 62'S7Gabo55"II53-388/An/3/Yt54/N10B//LR64S308/Chris//KalyansonaHD1962/E4870//K65/3/HD1553/UP262HD216O/WG377WG377/HD2I60WGI43/USA255//KalyansonaE4870/C303//S339/PV18Kalyansona/Justin//VP301Ciano/Gallo//WL71INapo/Tob's'//1856/3/KaIyansona/Bb

Year of release

19671967197619851983198419731975197919821984

"Symbols: /first cross,//second cross, /3/ third cross.

Seedlings of the wheat cultivars were grown ina glasshouse with filtered air. When the first leafwas fully expanded, and the second leaf abouthalf the length of the first, the plants wereinoculated with urediospores of single isolates ofP. striiformis dispersed in talc. After inoculationthe seedlings were placed in the dark at IOC with100% r,h. for 24 h to encourage infection andthen returned to the glasshouse. After about 14days they were scored for infection type, using thefollowing scale: ; (small chlorotic flecks with nosporulation), 0 (larger chlorotic areas with nosporulation) and 1-4 (increasing sporulationwith decreasing chlorosis). When reactions wereslightly higher or lower than the mean infectiontype for the class plus (-H) or minus (—) signs,respectively, were added to the score. To savespace, the range of infection types produced ondifferent plants of a cultivar by a given race ispresented as the extremes observed withoutspaces or dashes between them. Severe necrosis isdesignated by N. Thus, an infection type ;2-fNindicates that a range of reactions was observedbetween ; at one extreme to 2 -)- N at the other.

For genetic analysis, cultivars were crossed andFI, F2 and F3 generations were produced. Self-fertilization of the Fl and F2 plants was assuredby bagging the ears with transparent bags prior toanthesis, Seedlitigs of the crossed lines were testedfor resistance in the same way as the cultivars. Insome tests two different races of the pathogenwere used. Spores of the first race were appliedwhen the first leaf was fully expanded and the«econd leaf beginning to emerge; the second racewas applied about a week later when the secondleaf was fully emerged and the third leaf about

half emerged. Scoring the reactions of the plantswas carried out on the first leaf and tip of thesecond leaf for the first race. and. about a weeklater, on the base of the second leaf and distal halfof the third leaf for the second race. The followinggenerations were produced from the crosses andtested with the races indicated:

I HeinesVlIX Kalyansona Fl. F2X Sonalika FI. F2X WL711 Fl. F2

2. SonalikaxWL711 F1.F2

3. SonalikaXWL711 F1.F2. F3

4. SonalikaxKharchia Local Fl. F2.

RESULTS

Race 108E9(WYR 81/20)Race 108E9(WYR 81 20)Race 108E9 (WYR 81/20)

Race 108E9(WYR 81/20)

Race 39E134 (WYR 68/2)

F3 Race 6E16 (WYR 85 23)Race 39E134 (WYR 68/2)

The cultivars shown in Table 1 that were releasedbefore 1980 were all extensively cultivated. Ofthose introduced after 1980. WL2265 andHD2329 were released nationally, the latter hav-ing been very successful. PBWl 2, 54 and 120 werereleased in the Punjab only. The pedigrees of thecultivars indicate the frequent use of the highlysuccessful cultivar Kalyansona and its sister linePVI8 as parents. Also. HDI553 in the pedigree ofHD2329 is a synonym for Sonalika,

The reactions of an internationally used set ofdifferential cultivars to ten races of P. striiformisarc shown in Table 2 Three of the races of Britishorigin, namely I04E9. 108E9 and I09E9 lackpathogenicity for Heines VII and for the geneYr2. The four races on the right side of the tableare all of European origin (British or Dutch) and

426 H. Singh et al.

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Resistance to yellow rust in Indian wheat cultivars 427

possess pathogenicity for Heines VII and for Yr2.The three alien races on the left of Table 2. namely6E16, 6E0 and 66E0 also lack pathogenicity forHeines VII but are, nevertheless, believed topossess pathogenicity for Yr2. The low infectiontypes these three races induce on Heines VII aredue to its possession of another gene or genes notdetected by the European races (Sitigh & John-son, 1988),

The reactions of the Indian cultivars, plus asusceptible control, Kharchia Local, to the sameset of 10 pathogen races are given in Table 3. Thesimilarity between the reaction types of the firstnine cultivars in Table 3 to these races is clear;they were resistant to the races lacking pathogen-icity for Yr2 and more susceptible to thosepossessing pathogenicity for Yr2. These ninecultivars may therefore be postulated to carryYr2. The intermediate resistance of WL711.HD2329 and Sonalika to races with pathogen-icity for Yr2 is considered below.

Compared with the nine cultivars discussedabove, PW12 and WL2265 showed a differentpattern of reactions with the set of 10 races, whtchcorresponded closely to the pattern displayed bythe differential cultivar Lee which possesses Yr7.

Table 4 shows the reactions of Heines VII andLee plus the Indian cultivars to the other sevenraces, Kharchia Local was susceptible to all theraces with which it was tested. The reactions ofPWI2 and WL2265 were similar to those of Leeand those of the other nine cultivars were similarto the reactions of Heines VII. supporting thegene postulations given above.

Table 5 shows the results of inoculation withrace I08E9 (WYR 81/20) (lacking pathogenicityfor Yr2) of the Fl and F2 generations fromcrosses between Heines VII and Kalyansona.Sonalika and WL711 and between Sonalika andWL711, There was some variation in the reactionof the first leaves of some plants of Kalyansona.Sonalika and WL711 in this test, and this varia-tion was slightly greater than that observed in thedata presented in Tables 3 and 4. However, thereactions of the second leaves of WL711 andSonalika tended to be more consistent. The Flplants from the crosses were less variable andgave consistent low infection types on both firstand second leaves. A range of reactions wasobserved on the first leaves in the F2 populationsand a few plants were classified as type 3 in all thecrosses. There was a similar range of reactions onthe tips of the second leaves (data not shown).However, there was no fully susceptible plant andthe data therefore support the hypothesis that all

these cultivars possess a gene in common, prob-ably Yr2.

The data in Table 3 indicate that Sonalika.WL71I and HD2329 all gave moderately lowinfection types with race 6EI6. despite its pre-sumed pathogenicity for Yr2 and the evidence forthe presence of Yr2 in each of these cultivars. Thisindicates the presence of resistance in addition toYr2. For Sonalika the data given in Tables 3 and 4also show its intermediate resistance to the racesof European origin that possess pathogenicity forYr2. It is. however, more resistant to the Britishraces lacking pathogenicity for ";>2. namely.104E9, 108E9. 109E9 and 40E8.

The resistance in Fl . F2 and F3 generationsfrom crosses of Sonalika with the susceptiblecultivar Kharchia Local was tested with tworaces, 6E16 and 39E134. both possessing patho-genicity for Yr2 (Table 6). The data indicate thatSonalika was resistant on the first and secondleaves to both races, with more necrosis in the testwith race 39E134 than with race 6E16. KharchiaLocal was susceptible to both races, apart from asingle plant that gave a lower infection type withrace 6E16. The Fl plants were less resistant thanSonalika with a variable reaction on the first leafwith race 6EI6 but a susceptible reaction on thesecond leaf, and both leaves showing only slightresistance to race 39E134. There was muchvariation in the reactions of F2 plants to bothraces, but no clear discontinuity in the data topermit a division into resistant and susceptibleclasses. There were plants resistant to race 6EI6but susceptible to race 39E134 and vice versa,suggesting that resistance to the two races wasdue to different genes. Because two races wereused, the classification of F3 families was compli-cated. The usual criteria were that families inwhich no plant was scored higher than 2+ wereclassified as honnozygously resistant, and familieswith no plants scoring below 3 were classified ashomozygously susceptible. The remainder wereclassified as segregating. Using these criteria theevidence for resistance to races 6E16 and 39E134being controlled by different genes was supportedby the data of the F3 families where there werefamilies uniformly resistant to race 6E16 and fullysusceptible to race 39E134. No family was fullysusceptible to race 6E16 and fully resistant to race39E134 but four families classified as fully suscep-tible to race 6EI6 segregated for reaction to race39E134. Contingency x" tests were applied to theF2 plant and F3 family distributions given inTable 6. For the F2, r was 32 97 ( P < 0 01 for 16d,l,) and lor the F3 x- was 15 65 (P<01M)5 for 4

428 H. Singh et al.

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Resistance to yellow rust in Indian wheat cultivars 429

Table 4. Reactions (;-4 scale) of seedlings of two differential wheat cultivars and 12 Indian cultivars to sevenBritish races of Puccinia striiformis

Cultivars

DifferentialLeeHeines VII

IndianKalyansonaSonalikaWL7nHD2329PBW54PBWI20WG377WH147WL1562PBW12WL2265Kharchia Local

40E8WYR78/6

ONOON

l- l - l -l - l - l -2 - 3;0N

;o; 1 -I -1-22-3-ONOON

4

109E141WYR81/26

0N2-N4

4 -2N3-N

44 - 44 - 44 - 44 - 4

44 - 41N21N23 - 4

Races (IPSR WYR

169E136WYR82/4

ON4 - 4

4 - 42N3-N

43-t-

a

44———

4IE136WYR86/1

ONI-N2-(-3-

4 - 422 + N

43-3 +

3-t-4-(0)''4 - 44 - 44 - 44 - 4

ONl-NONl-

4

isolate)

45EI40WYR75/23

ONI-N4 - 4

42 + N

43 + 4 -3 + 44 - 4

44

4 - 4ONl-NONl-N

4 - 4

43E138WYR72/56

3 +3 + 4

42 + 3

43 + 4

444

4 - 444

3 + 44

106EI39WYR81/24

4 - 43 + 4

41 + N 3 - N

44———44———

'No data.•"Single plant with uncharacteristic action.

Table 5. Reactions to race 108E9 (WYR 81/20) of Puccinia striiformis(lacking pathogenicity for Yr2) in parents and progenies from crosses

between them

Parents orcross and progeny

Heines VII (H)Kalyansona (K)Sonalika (S)WL711 (W)

H/KFlF2

H/SFlF2

H/WFlF2

S/WFlF2

First leaf

01 3 -1-21 3 -

0 2 -

OON

; 2 -

ON

Second leaf

0 1 -0 3 -01

01 +

ONl-N

0

0N1 +

ON

;0

144

167

68

101

Plants in

1

100

26

55

78

F2

2

34

4

24

II

Class

3

1

1

24

2

4

0

0

0

0

430 H. Singh et al.

Table 6. Reactions (;-4 scale) to races 6E16 and 39E134 of Puccinia striiformis ofparents, Fl and F2 plants and F3 families from the cross between Sonalika and

Kharchia Local

Parents or progeny

Sonalika

Kharchia Local

Fl

F2 plantsRace 39E134(3rd leaOClass

;01234

Total

F3 familiesRace 39E134(2nd and 3rdleaOResistantSegregatingSusceptible

Total

Race

6E16

39E134

6E16

39E134

6E16

39E134

;0

47353

22

Resistant212

5

1

778

114

37

Leaf

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2nd0 N 3 -

1st4-4 4

2nd4

1stI - N 3 -

2nd3 4 - 3 -

2ndl-t-O-t-)"

3rd0N2N

2nd-4(3-)"

3rd4-4

2nd3-1-4

3rd

Race 6E16 (1st leaf)Class

2 3 4

11159

17

Race 6E16 (1st

Segregating7

2511

43

0 04 24 1

10 316 8

34 14

and 2n(l leaO

Susceptible04

12

16

Total

1221173440

124

Total9

302S

64

"Single plants with uncharacteristic infection type.

d.f), in both cases indicating a significant devia-tion from independent distribution. The numberof seedlings tested in each F3 family variedaccording to availability of seeds. In most families14 seedlings were tested and in a few there were 21seedlings, but for some families there were insuffi-cient seeds and as few as seven seedlings weretested.

Sixteen families, out of the 64 tested, wereclassified as uniformly susceptible to race 6E16.This provides a perfect fit to a 3 (resistant orsegregating): 1 (susceptible) ratio expected if asingle gene cot\\.ro\\c6 the resistance. However,the fit to the expected I (resistant): 2 (segregat-ing): I (susceptible) families is poor due to

insufficient uniformly resistant families( r = l l 34, / 'for 2 d.f.<0-005).

For race 39E134, ;f- for a 1:2:1 ratio expectedfor a single gene is 8 25 (P for 2 d.f. =001-0-025)indicating a significant deviation from the ratio.Because of a suggestion that Sonalika mightpossess complementary genes for resistance tosome races of P. striiformis (Wellings et al, 1988)the F3 families were also tested for fit to a 1(resistant):8 (segregating):7 (susceptible) ratio.Chi-squared (1:8:7) was 6-7 (/»for 2 d.f. =0025-0 05), which, although a better fit than for the 3:1ratio, is still a significant deviation from 1:8:7.

Additional data were obtained from the Fl, F2and F3 generations from the cross of Sonalika

Resistance to yellow rust in Indian wheat cultivars 431

Table 7. Reactions to race 39EI34 of Puccinia striiformis in parents, FI, F2 andF3 generations of the cross between Sonalika and WL711

Generation

SonalikaWL711

Fl

F2 (3rd leaf)

F3 families

ObservedExpected (1:8:

X^= 1-5797/ ' for2d.f .=0

Second leaf

0N24

IN2-)-

7)

25-0-50)

Third leaf

0NI24

0N2-(-

Resistant4

6-5

Plants

;0 I

33 22

Segregating5752

inF2

2

14

Class

3 4

21 95

Susceptible43

45-5

with WL711 tested with race 39E134 to whichWL711 gave a fully susceptible reaction (Table 7).Plants of Sonalika gave consistently low reactionson both second and third leaves and WL711 wasuniformly susceptible. In contrast to the FI fromthe cross with Kharchia Local, the Fl from thiscross was resistant, varying between ON and 2 -I-.There was wide variation in the F2 but, again, noclear discontinuity on which to separate plantsinto resistant and susceptible classes. There weretoo many fully susceptible F3 families to indicatecontrol by a single gene but the data gave anacceptable fit to a 1.8.7 ratio expected for twocomplementary genes. Seed numbers for the F3families were more consistent in this test andabout 18 seedlings were tested for each family.

DISCUSSION

The data (Tables 3 and 4) show the similarity ofresponse to 17 races P. striiformis of the first ninecultivars of Table 3. These cultivars may there-fore be postulated to possess a resistance gene incommon. Singh & Johnson (1988) presented datato support the presence of the gene Yr2 in one ofthe nine cultivars, Kalyansona, and it may there-fore be postulated that they all possess Yr2.Additional support for the possible presence ofthis gene is the presence of Kalyansona, or itsderivatives, in the pedigrees of WL711, PBW54,PBW120, WG377, WH147 and WL1562. PV 18 inthe pedigree of WHI47 was identified as a sisterline of Kalyansona by Villareal & Rajaram(1984).

The remaining two cultivars, PWB 12 andWL2265, showed a similar reaction pattern cor-responding to the differential cultivar Lee forboth the British and the alien races, and couldtherefore be postulated to possess the gene Yr7.The pedigrees of these two cultivars both includea possible source of the gene Yr2. However, it isevident from the data in Tables 2, 3 and 4, andfrom the preceding discussion, that all the races inthese tests that possessed pathogenicity for Yr7also possessed pathogenicity for Yr2. It wastherefore not possible to detect Yr2 in the pres-ence of Yr7. In Table 2 the differential cultivarReichersberg 42 is also shown as possessing thegene Yr7. However, it is resistant to the races6E16, 6E0 and 66E0, to which Lee is susceptible.This is due to the possession of resistance inaddition to that controlled by Yr7 in Reichers-berg 42.

Singh & Johnson (1988) required two steps toestablish the presence of Yr2 in Kalyansona. Firstit was necessary to show that resistance of HeinesVll to the alien races 6E16, 6E0 and 66E0 of Pstriiformis was not due to Yr2 but to its possessionof another previously unrecognized gene orgenes. Secondly, the presence of Yr2 in Kalyan-sona was confirmed by crossing it with HeinesVII, a cultivar known to carry Yr2. Followinginoculation with race 108E9, a British race of P.striiformis that lacked pathogenicity for Yr2 butcarried pathogenicity for the other gene or genesin Heines VII, they found no fully susceptibleplant in an F2 progeny from the cross betweenKalyansona and Heines VII. This supported the

432 H. Singh et al.

hypothesis that Kalyansona possesses the geneYr2 and that the three alien races, 6EI6, 6E0 and66E0 therefore possess pathogenicity for thisgene.

Genctical evidence to support the hypothesisthat the gene Yr2 was present in WL7II andSonalika as well as in Kalyansona was obtainedby testing F2 populations from crosses betweenthem and with Heines VII using race 108E9, Thelack of any fully susceptible plants in these F2generations (Table 5) is taken as supportingevidence for the presence of Yr2. However, therewas considerable variation in the degree of resis-tance shown by individual F2 plants. Our hypoth-esis to explain this variation is that the expressionof Yr2 is strongly influenced by the geneticbackground. The limited usefulness of Heines VIIas a differential cultivar due to its variablereactions was reported by Fuchs (1960) andprobably reflects the variable expression of Yr2 aswell as any possible heterogeneity for the presenceof Yr2 itself. Repeated selection and ensured self-fertilization for several generations has produceda much more stable reaction in the slock ofHeines VII now used for differentiating races ofP. striiformis. Further evidence for the variableexpression of Yr2 comes from the behaviour ofthe differentia) cultivar Heines Kolben whichreacts as though it possesses Yr6 and also Yr2.However, in this genetic background Yr2 is onlyslightly expressed in seedlings (Johnson et at.,1986).

The evidence for the presence of resistance inaddition to Yr2 in Sonalika was also investigatedgenetically. Wellings et at. (1988) showed thatcertain races of P. striiformis found in Australiacould differentiate resistance in the Australiancultivar Avocet. This resistance was given theprovisional designation YrA. Similarity of reac-tions of Sonalika to those of Avocet indicated thepresence of YrA in Sonalika, Wellings e/a/, (1988)stated that preliminary genetic data indicatedthat the resistance designated as YrA was inher-ited as if controlled by a pair of dominantcomplementary genes. The data for the Fl of thecross between Sonalika and Kharchia Localinoculated with race 39E134 indicated that theresistance was recessive. However, resistance wasdominant in the Fl from the cross betweenSonalika and WL711 tested with the same race(Tables 6 and 7), The segregation of F3 familiesfrom both crosses included too many familiesclassified as uniformly susceptible for the resis-tance to be controlled by a single gene. The datafrom the cross with WL711 (Table 7) fitted the 1

(resistant): 8 (segregating): 7 (susceptible) familiesexpected if control were due to two independentcomplementary genes. The F3 data from the crosswith Kharchia Local (Table 6) deviated signifi-cantly from this ratio but fitted it more closelythan they fitted a 1:2:1 ratio. It is possible thatthe slight excess of families classified as resistantwas partly due to the difficulties of classificationand partly because of the limited number ofseedlings assessed in some families. It seemsprobable that the resistance detected in Sonalikawith race 39E134 corresponds to that designatedas YrA by Wellings et at. (1988), The datatherefore support their observation that the resis-tance can be inherited as if controlled by twoindependent complementary genes. Because ofthe varying reactions of the Fl plants it is notpossible to suggest the degree of dominance of thegenes involved in resistance to race 39E134.Confirmation that the resistance was controlledby complementary genes would require sepa-ration of the two genes into separate lines andreconstitution of the resistant phenotype by inter-crossing them.

The resistance of Sonalika to race 6E16 wassurprising because our data indicated that thisrace possessed pathogenicity for Yr2 and R. W.Stubbs (personal communication) indicated thatthis isolate of P. striiformis also possessed patho-genicity for the YrA resistance. This wouldindicate that Sonalika possessed resistance inaddition to »2plu5 Xr/i, The data supported thishypothesis in showing that resistance to race6E16 was due to a gene or genes different fromthose giving resistance to race 39E134. Thesimplest hypothesis from the F3 data (Table 6)would be that this resistance was due to a singleincompletely dominant gene. However, the lownumber of uniformly resistant families found inthe F3 indicates the need for further data toconfirm this suggestion.

Although resistance in Sonalika to races 6E16and 39E134 appears to be under the control ofdifferent genes, the significant contingency /^ testsfor the distribution of F2 plants and F3 familiesshown in Table 6 indicates that the inheritance ofresistance to the two races is not independent.This could be due to linkage of the genes or tointeraction in their expression, but further workwould be required lo clarify this.

The presence of Yr2 in widely used Indianwheat cultivars makes it probable that mostisolates of P. striiformis collected in the parts ofIndia where these are grown would carry patho-genicity for Yr2. Sharma et ai (1972) reported the

Resistance to yellow rust in Indian wheat cultivars 433

spread of races with pathogenicity for Kalyan-sona in India in 1970 and 1971, The data of Singh& Johnson (1988) showed that such races neednot possess pathogenicity for Heines VII, thedifferential cultivar commonly used internation-ally to detect pathogenicity for Yr2.

The importance of the cultivar Kalyansona inIndia and the occurrence of its susceptibility toyellow rust led to genetical investigations of itsresistance to this disease and to suggestions that itmight possess Yrl (see Mclntosh, 1988) or a genein common with a gene in the European springwheat cultivar Opal designated as Yr4b (Kochharet al., 1982), The susceptibility of Kalyansona inour tests to races lacking pathogenicity for thesegenes, present, respectively, in the differentialcultivars Chinese 166 and Hybrid 46 (Tables 2, 3and 4), showed that our stocks of Kalyansona didnot contain either of these genes. Similarly, ourdata for Sonalika indicates that it does notpossess the gene Yr8 as suggested in one report(see Johnson et al., 1987), There could be numer-ous causes for these apparently erroneous diag-noses of genes in Kalyansona and Sonalika,among which could be the great complexity inspecific pathogenicity in races of P. striiformisand the genetical complexity of the differentialcultivars currently used to classify the variation.

ACKNOWLEDGEMENTS

We thank the Overseas Development Adminis-tration for financing part of the project and theAssociation of Commonwealth Universities forsupporting visits of H.S. and D.S. Technicalassistance of A, J, Taylor and G. M. B. Smith isgratefully acknowledged,

REFERENCES

Fuchs E, (1960) Physiologische Rassen bei Gelbrost(Puccinia glumarum [Schm.) Erikss, et Henn.) auf

Weizen, Nachrichtenblatt des Deutschen Pftanzen-schutzdienstes 12, 49-63,

Johnson R.. Stubbs R.W.. Fuchs E. & ChamberlainN.H. (1972) Nomenclature for physiologic races ofPuccinia striiformis infecting wheat. Transactions ofthe British Mycological Society 58, 475-480.

Johnson R.. Stubbs R.W.. Kirmani M.A.S.. RisviS.S.A. & StatlerG.D. (1987) Discussion of a methodresulting in erroneous postulation of the gene Yr8 forresistance to Puccinia striiformis in Pakistani wheatcultivars. Cereal Rusts Bulletin 15, 13-19.

Johnson R.. Taylor A.J. & Smith G.B.M. (1986)Resistance to British races of Puccinia striiformis inthe differential wheat cultivars Heines Kolben andHeines Peko. Cereal Rusts Bulletin 14, 20-23.

Kochhar S.. Gill K.S. <& Nanda G.S. (1982) Geneticanalysis of resistance of some component lines ofmultilines of Kalyansona wheat to three races ofyellow rust. Indian Journal of Genetics 42, 271 279.

Lupton F.G.H. & Macer R.C.F. (1962) Inheritance ofresistance to yellow rust (Puccinia glumarum Erikss.& Henn.) in seven varieties ofwheat. Transactions ofthe British Mycological Society 45, 21-45.

Mclntosh R.A. (1988) Catalogue of gene symbols forwheat. Proceedings of the 7th International WheatGenetics Symposium (Ed. by T. E. Miller & R. M. D.Koebner). /PSR, Cambridge 1988. pp, 1225-1323,

Sharma S.K.. Joshi L.M. & Nagarajan S. (1972) Newvirulence of yellow rust on Kalyansona variety ofwheat. Proceedings of the European and Mediterra-nean Cereal Rusts Conference. Prague 1972 Vol I,263-265.

Singh H. & Johnson R. (1988) Genetics of resistance toyellow rust in Heines VH, Soissonais and Kalyan-sona. Proceedings of the 7th International WheatGenetics Symposium (Ed. by T. Miller and R. M. D.Koebner). IPSR, Cambridge 1988. pp. 885 890.

Villareal R. & Rajaram S. (1984) Semidwarf breadwheat. Names; Parentage; Pedigrees; Origin,CIMMYT, 1984. pp 37.

Wellings C.R.. Mclntosh R.A. & Hussain M. (1988) Anew source of resistance to Puccinia stritformis f. sp.tritici in spring wheats (Triticum aestivum). PlantBreeding 100, 88-96.