ASSESSMENT AND EXPLOITATION OF GENETIC VARIATION FOR RESISTANCE TO PUCCINIA RECONDITA FOR STABILIZING WHEAT PRODUCTION

Abstract

Adult plant responses to infection with pathotype 77-5 and a mixture of important pathotypes of Puccinia recondita were determined in the series of near-isogenic lines/stocks each carrying a known leaf rust resistance gene and certain lines each with a newly described stem or stripe rust resistance genes. Near isogenic lines/stocks with single leaf rust resistance genes LrIB, Lr23, Lr36, Lr3B, Lr4I, Lr42, Lr44, Lr45, besides Lr9, Lrl4b, Lrl4ab, Lr19, Lr2I, Lr22a, Lr24, Lr25, Lr2B, Lr29, Lr30, Lr32, Lr34, Lr35 and Lr37 that were reported to be effective in earlier studies, exhibited partial to complete resistance. Most of these genes, either effective throughout life or only in adult plants, were derived from alien sources and have not so far been exploited in Indian wheat br~eding programmes. Leaf rust resistance in a near-isogenic line with stem rust resistance gene (Sr39) indicated additional leaf rust resistance that is likely to be linked' :with this stem rust resistance gene. Leaf rust resistance in two of the near-isogenic lines with stripe rust resistance gene Yr24 backcrossed to cv. Meering was partly due to Meering. Higher resistance to leaf rust in these lines than in Meering could be attributed to additional gene(s) that may be linked with the stripe rust resistAnce gene. Pathotype 77-5 is a very virulent strain and attacks most of the genes for resistance to leaf rust originating from T. aestivum. Identification of leaf rust resistances, particularly against pathotype 77-5 provided useful and diverse sources for str:!.tegic use in future breeding programmes. Seedling tests of the newly described resistance genes to a number of leaf rust pathotypes identified Lr4I, Lr42, Lr44 and Lr45 as additional genes that confer over-all resistance to leaf rust. A number of genetically enhanced germplasm lines with different resistance genes were developed. Two of the wheats Vaishali and Vidisha with alien resistances of Thinopyrum ponticum (Lr24/Sr24) have recently been released and notified. Commercial exploitation of these resistances was the first attempt in the Indian subcontinent.