Since all the three races are virulent on variety Lee (Yr7) the segregation for this locus cannot be detected. However, a segregation of one locus in the cross CPAN 1360 x Lee against race 38A; of two loci in the cross Tobari 66 x Lee against race 20A, in cross Sonalika x Lee against race 31; and in crosses CPAN 1444 x Lee and HD 2009 x Lee against race 38A, and three loci in the crosses; in CPAN x Lee (for races 20A and 31) and Tobari 66 x Lee (against race 20A) suggested the presence of resistance genes other than Yr7 in the corresponding parents.

In their crosses with Compair (Yr8), the varieties CPAN 1360, CPAN 1444, DH 2009 and Tenori 71 showed two to three gene segregation indicating that genes other than Yr8 occur in these varieties giving resistance to race 38A.

The Nudif TP 250 genes (Yr1+Yr6) are indicated to be present in varieties CPAN 1444, Sonalika, HD 2009, Tanori 71 and Tobari 66 on the similar assumptions made above.

A Iimitation in the present set of materials may be attributed to the lack of information on the genetic nature of variety Agra Local, the susceptible variety used in the experiment. It was susceptible to the races used in the present study but this cannot be taken as an evidence that the variety is universal susceptible. Moreover, Lee (Yr7) was also susceptible to the three races. Studies of SAWHNEY & LUTHRA (1970) have already hinted at the resemblance of reaction pattern of Agra Local with that of an International differential variety for yellow rust (Michigan Amber). The latter variety is suggested to carry Ya2 + Yr7 (Anonymous, 1979). So long as a parasite culture carrying a matching virulent gene is not used, the capacity of the resistance gene in Agra Local, if present, to confer resistance will remain undiscovered and the particular allele will segregate as recessive alleles for susceptibility. This point gains favour from PERSON & MAYO's (1974) explanation on the genetic limitations on models for specific interactions.

Table 1. Seeedling reaction of varieties with undetermined genes for resistance, tester Yr-lines and F₁ hybrids between varieties and testers and Agra Local against races 20A, 31 and 38A of Puccinia striiformis

Table 2. Segregation betaviour of crosses between varieties with undetermined res-genes and tester lines when tested at seedling stage in F₂ against three races of P. striiformis

References

Anonymous 1979. European yellow rust-nursery. List of varieties 1979 (Unpublished).

JAIN, R. & GANDHI, S.M. 1978. Genetics of stem rust resistance in variety Timgalen. Indian J. Genet. 38: 252-257.

KOCHHAR, S., GILL, K.S. & NANDA, G.S. 1982. Genetic analysis of some component lines of Kalyansona multilines of bread wheat to three races of yellow rust. Indian J. Genet. (In press).

LUPTON, F.G.H. & MACER, R.C.F. 1962. Inheritance of resistance to yellow rust in seven varieties of wheat. Trans. Brit. Mycol. Soc, 45: 21-45.

SAWHNEY, R.N. & LUTHRA, J.K. 1970. New resistance genes of wheat to Indian races of stripe rust (Puccina struformis). SABRAO News Letter, 2: 155-156.

PERSON, C. & MAYO, G.M.E. 1974. Genetic limitations on models of specific interaction between a host and its parasite. Can. J. Bot. 52: 1339-1347.

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