High-Resolution Recombination Dissection Around Alien Chromosome Segments Containing Genes for Resistance to Reniform Nematodes

Reniform (Rotylenchulus reniformis) nematodes are plant pathogens with a wide host range and wide global distribution.  They cost the US over $100M per year in lost cotton yield, quality and other expenses. The resistance trait was introgressed by hybridizing the African diploid with a synthetic hexaploid (2([AD]₁D_2-1)) “bridge” to create a tetraploid [AD]₁D_2-1F₁ tri-species hybrid originally. We have released two LONREN lines: LONREN-1 and LONREN-2. Collaborative field-testing of LONREN lines revealed variable levels of debilitated seedling growth and yield. Various laboratory tests suggest that that Ren^lon lines may be hypersensitive to the nematode, and differentially susceptible to certain soil pathogens.  Several lines of evidence indicate that neighboring genes affect resistance to other pathogens, as well as field and fiber performance. Genetic dissection and characterization of this region is needed, so we have mounted a map-based approach to recover recombinants that retain the alien resistance gene and minimize the flanking alien segments. Flanking linked SSR markers:  BNL3279, BNL1231, BNL1066, CIR316, CIR069.  We will report on efforts to identify more markers near the Ren^lon gene, and the differential selection among nearby recombinant events found to date.  In follow-through research, we will saturate the region with crossovers and markers for high-resolution mapping and genetic dissection of the Ren^lon gene, eliminating nearly all other alien genes.  The most closely flanking recombinants will be biologically tested for resistance and/or agronomic performance.  Selected derivatives will be valuable breeding parents for cultivar development.