GENETIC RESEARCH AS THE VALID BASE OF STRATEGIES FOR BREEDING RUST RESISTANT WHEATS

It is known that few wheat cultivars maintain their resistance to rust diseases for a long period of time, particularly when crop population s become genetically more uniform. A number of genetically diverse, so far unexploited, sources of rust resistance in the natural as well as mutagenized population of wheat cultivars were identified. Several of these genes were placed in agronomically superior well-adapted backgr ounds so that they could be used as pre-breeding stocks for introducin g genetic diversity for resistance in a crop population. Some of these stocks when employed as parents in several cross combinations in a br eeding programme have generated a number of promising cultivars with d iversity for resistance. Many presently grown wheats in India, near-is ogenic lines each with Lr14b, Lr14ab, Lr30 and certain international c ultivars were identified as possessing diverse sources of adult plant resistance (APR) to leaf rust. Prolonged leaf rust resistance in some of the Indian cultivars was attributed to the likely presence of Lr34 either alone or in combination with other APR components. Tests of all elism carried out in certain cultivars that continue to show adequate levels of field resistance confirm the presence of Lr34, which explain s the role that this gene has played in imparting durability for resis tance to leaf rust. Also, Lr34 in combination with other APR component s increases the levels of resistance, which suggests that combination of certain APR components should be another important strategy for bre eding cultivars conferring durable and adequate levels of resistance. A new adult plant leaf rust resistance source that seems to be associa ted with durability in 'Arjun' has been postulated. Likewise, cultivar s possessing Sr2 in combination with certain other specific genes have maintained resistance to stem rust. Further, non-specific resistances that were transferred across widely different genotypes into two of t he popular Indian wheats provided easily usable materials to the natio nal breeding programmes for imparting durable resistance to stripe rus t.