Modification of barley powdery mildew resistance gene Ml-a12 by induced mutation

Kernels from a barley line, 'Sultan-5', with powdery mildew resistance gene Ml-a12 were treated with mutagens. Among 10 381 M1 spikes progeny tested with Ml-a12 avirulent powdery mildew, 25 segregated mutants with infection types between 0–1 n and 3–4cn. The resistance of the mutants is race specific in the sense that it is expressed only with powdery mildew cultures that are Ml-a12 avirulent but not with an Ml-a12 virulent culture. Genetic analysis of 10 mutants revealed that 9 had mutant genes that were allelic to gene Ml-a12, and one had a recessive mutant gene inherited independently of Ml-a12 on which it acted as a suppressor. The high mutation frequency in gene Ml-a12 and the gradual inhibition of the expression of gene Ml-a12, by mutation or suppression, strongly supports the suggestion that the gene function is associated with incompatibility rather than with compatibility.Key words: barley, Hordeum vulgare, powdery mildew, Erysiphe graminis hordei, mutation, resistance, suppressor.