SPONTANEOUS GENETIC-VARIATION FOR LEAF RUST REACTION IN SINVALOCHO MAWHEAT

Spontaneous off-type plants for leaf rust reaction to Argentine races 66 and 77 of Puccinia recondita tritici were found at rates of 3.4 per 1000 and 0.44 per 1000, respectively, in the progeny of self-pollinat ed (bagged) spikes of Sinvalocho MA wheat. Leaf rust reaction changes were associated to aneuploidy in most cases. The variation to race 66 was associated to monosomy of chromosome 6B or probably deletions on c hromosome arm 6BL. Some off-type plants however showed, in subsequent generations, changes for reaction to race 77 or simultaneous changes t o races 66 and 77 as well as changes in leucine aminopeptidase isozyme expression, which cannot be explained on grounds of allelic dosage. T he origin of these genetic and chromosomal changes is not clear in som e cases, however, a common origin could be suggested by the presence o f transposonlike elements.