Strong resistance to reniform nematode (Rotylenchulus reniformis) was previously introgressed from the F-genome diploid species Gossypium longicalyx (2n = 2x = 26) into Upland cotton (G. hirsutum L., 2n = 4x = 52, 2[AD]1), and attributed to the gene Renlon. Two resistant elite lines were released, but their seedlings are differentially stunted in nematode-infested fields. Here, we report on the development of linked SNPs and their use to disrupt “linkage drag” around Renlon. Using advanced backcross-inbred lines with previously identified proximal (PCO) or distal crossover (DCO) events near Renlon, we chose 18 Renlon–linked SNP markers for mapping across two large (880) BC1F1 seed populations. Few recombi... More
Strong resistance to reniform nematode (Rotylenchulus reniformis) was previously introgressed from the F-genome diploid species Gossypium longicalyx (2n = 2x = 26) into Upland cotton (G. hirsutum L., 2n = 4x = 52, 2[AD]1), and attributed to the gene Renlon. Two resistant elite lines were released, but their seedlings are differentially stunted in nematode-infested fields. Here, we report on the development of linked SNPs and their use to disrupt “linkage drag” around Renlon. Using advanced backcross-inbred lines with previously identified proximal (PCO) or distal crossover (DCO) events near Renlon, we chose 18 Renlon–linked SNP markers for mapping across two large (880) BC1F1 seed populations. Few recombinants occurred (7 of 1760). Using two of the closest Renlon–linked SNPs to select from a BC1F1 seed population (17,600), we identified 5 homeologous recombinants, but none separated the stunting and resistant phenotypes. We then compared homologous recombination rates using equally sized DCO × PCO INTERCROSS and BACKCROSS populations (n = 88). Many more recombinants occurred among progeny of the INTERCROSS (22) than the BACKCROSS (1). This finding suggests that the best SNP-based strategy for interspecific breeding with the F genome and other homeologous genomes may be to use large-scale MAS to select nearby flanking homeologous recombinants in early generations, map them to identify the two closest PCO and DCO types, then intermate them and use MAS to identify homologous recombinants.
