Identification and genetic analysis of durable resistance to the rust diseases of wheat

摘要

Durable resistance to a plant disease is defined as resistance that remains effective when a cultivar is widely grown for a long period (years) in an environment favourable to that disease. This definition has received implicit criticism by being described as retrospective. It is not a valid criticism because it is a fact of life that there is no quicker way of first identifying such resistance, and those who claim that there is, by testing in special areas of intense disease, are mistaken. Across the many diseases of numerous crop plants, there is no single genetic system associated with durable resistance - its control varies from single genes combinations of a few genes, to systems that are legitimately described as polygenic. Numerous resistancegenes have been identified that control resistance to each of the three rust diseases of wheat. However, most of these have not provided durable resistance and epidemics of the diseases have occurred. Over a long period of time, certain cultivars have been identified as displaying durable resistance to one or more of these three rust diseases. Genetic analysis of these has identified some single genes, contrary to the expectation that their resistance would be poiygenic. For stem rust, Sr 1 has been associated with durable resistance, and also Sr 31 carried on the now widespread 1B-IR wheat/rye translocated chromosome. For leaf rust and stripe (yellow) rust cultivars possessing the gene combination Lr34/Yrl8 are associated with durable resistance, butdo not account for all durable resistance to these two diseases. Also, neither gene provides adequate resistance in highly rust-conducive environments. Intensive cytogenetic and molecular analysis of some European wheats showed effects of several chromosomes, some positively and some negatively, on resistance. Prospects for using this information to improve the potential for breeding new cultivars with durable resistance to the rust diseases will be considered.