| Effectiveness of newly described leaf rust resistance
genes against Indian cultures of standard races and biotypes of leaf rust
in wheat. R.N. SAWHNEY and L.B. GOEL Division of Genetics, Indian Agricultural Research Institute New Delhi-110012, India Success in developing rust resistant cultivars depends upon a knowledge of effectiveness of the resistance genes against the local strains of pathogen in a geographic region. SAWHNEY et al. (1977) published a comprehensive account of seedling infections and field reactions of a series of isogenic lines/cultivars, each with a known leaf rust resistance gene, to Indian races of leaf rust pathogen. Lines carrying Lr9 and Lr19 were reported to be fully effective to all the 14 races/biotypes of leaf rust when tested in seedling individually and at adult plant stage in field conditions. Other isogenic lines/stocks except that with Lr22 were reported to confer seedling resistance to one or more races of leaf rust. The designated series for leaf rust resistance genes has since been expanded. The information on all the presently known genes resistance to leaf rust for adult plant responses at several locations throughout the country was reported recently (SAWHNEY et al. 1982a). This communication reports on interactions of genotypes with the additional designation genes for resistance to leaf rust when tested in seedling individually with races/biotypes 12, 12A, 20, 77, 77A, 104, 104A, 107, 162, 162A, that are most prevalent and virulent in the country. The tests were conducted at temperature not exceeding 20C. Seedling resistance is supplemented by adult plant response when tested in field conditions. Table 1 lists the infection types produced on the genotypes each with known gene designated for resistance to leaf rust. It may be seen that a leaf rust resistance gene, Lr24, derived from Agropyron elongatum, and obtained in three stocks, Agent, Sear's 3Ag/3D, and white seeded recoymbinant (TR380-27 x 4/3 Ag 3-14) was observed fully effective to all the 10 races. Both Sear's 3Ag/3D and TR 380-27 x 4/3 Ag 3-14 were also reported to have complete resistance in seedling to all the currently maintained stem rust races in the country (SAWHNEY & GOEL 1981) and to both leaf and stem rust in adult plant stage (SAWHNEY et al. 1982 a and b). The stem rust resistance of these stocks is attributed to a known stem rust resistance gene Sr24. Both of these genes inherited together as a part of the alien chormosome sector (MCINTOSH 1976). Use of white seeded stock (TR380-27 x 4/3 Ag 3-14) for breeding resistant varieties is of added advantage when white seeded varieties are consumers' preference. Lr25: This gene was also observed to be completely effective when tested in 'Transac', a wheat line produced with a translocation of wheat chromosome 4A from non-homoeologous 2R chromosome of Rosen Rye. The genotype was observed to produce low co-efficient of infection in field conditions (SAWHNEY et al. 1982a). Cultivar 'Kavkaz' with Lr26 from rye was found to produce IT (O;) against each of the races tested. Furthermore, 'Kavkaz' was observed completely free of leaf rust infection in adult plant for the two seasons all over the country. Two of the other stocks with Lr26 (WRT ID/1R and 'Benno'), however, were observed to produce infection of low intensity which suggests that 'Kavkaz' has possibly additional gene(s) for resistance to leaf rust. This additional resistance is most probably due to complementary or additive gene interaction with Lr3, another leaf rust resistance gene known to be present in 'Kavkaz' |
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