STEM-RUST RESISTANCE IN CANTHATCH HEXAPLOID WHEAT INDUCED BY A NONSUPPRESSOR MUTATION ON CHROMOSOME 7DL

A recessive null mutation induced in the common wheat cultivar 'Canthatch' by ethyl methanesulphonate permits the expression of resistance to several cultures of stem rust to which this cultivar is susceptible. This susceptibility is due to a dominant suppressor on chromosome 7DL that inhibits resistance conferred by a gene or genes located elsewhere on the genomic complement. Genetical and cytogenetical evidence indicated that the mutation is simply transmitted and was induced either at the suppressor locus or at a locus closely linked with it, more than 50 crossover units from the centromere. Tentative results suggest that in addition to 'Canthatch', other backcross derivatives of the cultivar 'Thatcher', such as 'Katepwa' and 'Columbus', possess both the suppressor and the inactivated resistance gene(s). Consequently, incorporation of the mutant allele into these cultivars should permit the expression of inhibited resistance.