Linkage Mapping of Resistance to Reniform Nematode in Cotton following Introgression from Gossypium longicalyx (Hutch. & Lee).

Reniform nematodes (Rotylenchulus reniformis Linford & Oliveira) decrease U.S. production of Upland cotton (Gossypium hirsutum L., 2n = 52, 2[AD](1)) by more than US$100 million yr(-1). We report here on the mapping of a gene for extreme resistance that was introgressed from the African species G. longicalyx (Hutch. & Lee, 2n = 2x = 26\\; 2F(1)). The responsible allele, designated Ren(Ion), was localized to chromosome 11 by first screening A-subgenome simple sequence repeat (SSR) marker loci for parental polymorphism and then for association with resistance. The three most strongly coupled SSRs and a G. longicalyx gene conferring green seed fuzz, designated Fzg(Ion), were screened against 984 resistant and susceptible individuals of multiple backcross generations. We used marker data and pedigrees to identify nonrecombinant heterozygous parents and thereby avoid bias from repeated sampling of a recombination event. We constructed linkage maps after progeny testing a small population (147) and after implementing three alternative approaches better suited to larger populations-marker-assisted genotyping analysis, applying a cut-off value as population-wide genotyping criterion, and genotype-selective sampling. The maps concordantly indicated the order to be Fzg(Ion)-Ren(Ion)-BNL3279_114-BNL1066_156-BNL836_215, with most Ren-proximal bilaterally flanking markers within 6 cM of each other. The results will clearly facilitate use of Ren(Ion) in breeding, additional mapping, genomics, and prospective cloning.