MAPPING OF THE LEAF RUST RESISTANCE GENE LR3 ON CHROMOSOME 6B OF SINVALOCHO MA WHEAT

The Lr3 gene for resistance to race 66 of Puccinia recondita present i n hexaploid wheat cv. Sinvalocho MA was mapped on chromosome 6B, using intervarietal polymorphic RFLP loci and the Amp-BI isozyme gene as a centromere marker. The RFLP markers were located mainly in two subregi ons of chromosome 6BL. Six RFLP loci clustered in the centromeric regi on and one other, Xmwg798, cosegregated with the Lr3 gene. C-banding a nalysis of the leaf rust resistant standard 'Sinvalocho MA' line and t hree naturally occurring susceptible lines of 'Sinvalocho MA' revealed a terminal deletion on 6BL that covered 20% of its length in one susc eptible line. Because Xmwg798 was missing in this line, both Xinwg798 and Lr3 were allocated to the deleted segment. Distorted segregations were observed for the proximal markers, suggesting a selection against gametes carrying the centromeric region of 'Sinvalocho MA'.