Genetic mapping, marker assisted selection and allelic relationships for the Pu(6) gene conferring rust resistance in sunflower

Rust resistance in the sunflower line P386 is controlled by Pu(6), a gene which was reported to segregate independently from other rust resistant genes, such as R(4). The objectives of this work were to map Pu(6), to provide and validate molecular tools for its identification, and to determine the linkage relationship of Pu(6) and R(4). Genetic mapping of Pu(6) with six markers covered 24.8 cM of genetic distance on the lower end of linkage Group 13 of the sunflower consensus map. The marker most closely linked to Pu(6) was ORS316 at 2.5 cM in the distal position. ORS316 presented five alleles when was assayed with a representative set of resistant and susceptible lines. Allelism test between Pu(6) and R(4) indicated that both genes are linked at a genetic distance of 6.25 cM. This is the first confirmation based on an allelism test that at least two members of the R(adv)/R(4)/R(11)/ R(13a)/R(13b)/Pu(6) cluster of genes are at different loci. A fine elucidation of the architecture of this complex locus will allow designing and constructing completely new genomic regions combining genes from different resistant sources and the elimination of the linkage drag around each resistant gene.