CONFIRMATION OF NONSUPPRESSOR MUTATION OF STEM RUST RESISTANCE IN CANTHATCH COMMON WHEAT

A mutation induced in the common wheat cultivar Canthatch (Triticum aestivum L.) results in resistance to several races of stem rust (Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. and E. Hem.) to which Canthatch is susceptible. Previous evidence indicated the mutation behaved as a nonsuppressing allele on chromosome arm 7DL, which permitted the expression of resistance normally inhibited by a suppressor also located on 7DL. However, to eliminate the possibility that the improved resistance resulted from a mutation to a resistance gene, additional experiments were undertaken. Chromosome 7D of the susceptible cultivar Chinese Spring was substituted by the corresponding chromosome of the resistant mutant, Canthatch-NS, and of Canthatch. Also, pentaploids were produced from crosses of susceptible tetraploids 'Pelissier' durum wheat and Tetraprelude with the resistant Canthatch mutant. The 7D substitutions of Canthatch-NS and Canthatch, as well as the pentaploids, were fully susceptible. Consequently, the mutation induced in Canthatch-NS was not of a resistance gene, thus confirming the previous conclusion that it behaves as a nonsuppressing allele.