The Gossypium genus includes 45 diploid and 5 tetraploid cotton species of which only 2 diploids and 2 tetraploids are cultivated in different parts of the tropics and sub-tropics, leaving the remaining diploid and tetraploid species as potential genetic sources for novel trait introgression. The reniform nematode (Rotylenchulus reniformis Linford and Oliveira) poses significant problems to US cultivated Upland cottons (Gossypium hirsutum L., 2n=52), all of which lack high resistance. This work was in collaboration with the USDA-ARS team that focussed on introgressing reniform nematode-resistance from a diploid cotton species, Gossypium longicalyx Hutch. & Lee into G. hirsutum by creating a tri-species hybrid, HLA and backcross breeding (Bell et al., 2007; Robinson et al., 2007). The main objectives of this work were [1] to cytogenetically evaluate and help select superior types at each introgressed generation; [2] to identify molecular markers tightly linked to the reniform nematode-resistance gene and to map the resistance loci; [3] (A) to introgress germplasm on a genome-wide basis, (B) to evaluate introgressed germplasm for traits of economic importance other than reniform nematode resistance, and (C) to evaluate breeding methodologies in terms of this specialized breeding material. Reniform nematode resistant plants were of diverse cytogenetic constitution but individuals that modally formed 26II chromosomal configuration were identified at BC2F1, BC3F1, BC4F1, and BC5F1 generations. Three SSR markers, BNL3279_114, BNL1066_156, and BNL836_215 and one phenotypic marker, green-colored fuzz (Fzglon), were identified to be tightly-linked to the resistance locus. Extension of the association analysis and linkage estimation to 16 susceptible self progeny (BC1S1, BC3S1 and BC6S1) and 374 susceptible backcross hybrids (BC2F1-BC8F1) mapped the resistance locus to chromosome 11 of cotton with BNL3279_114 on one side and Fzglon on the other at 0.8 cM and 2.8 cM, respectively. Besides reniform nematode-resistance introgression, genome-wide introgression efforts were also conducted. Low micronaire and high fiber strength were the two most promising traits identified in the HLA-derived introgressed generations. Most of the introgressed generations had high variability for the fiber-quality traits than the commercial checks, thus providing more opportunities for selection and improvement.

Two sources of reniform nematode (Rotylenchulus reniformis) resistance in two Upland cotton (Gossypium hirsutum) developed from related cotton species, BARBREN-713 (Renl̳o̳n̳1̳ and Renl̳o̳n̳2̳ genes), and the LONREN germplasm lines (Renl̳o̳n̳ gene) are available to breeders. Stunting was observed in the LONREN source of resistance, but not for BARBREN. To investigate future use of LONREN germplasm, lines were developed with different combinations of genes from both the LONREN and BARBREN-713 germplasm lines. Marker assisted selection (MAS) was conducted identify these gene combinations within breeding population 1) Renb̳a̳r̳b̳1̳ +Renb̳a̳b̳r̳2̳ 2) Renb̳a̳r̳b̳1̳ + Renb̳a̳r̳2̳ + Renl̳o̳n̳ 3) Renb̳a̳r̳b̳2̳ + Renl̳o̳n̳ 4) Renb̳a̳r̳b̳2̳ 5) Renb̳a̳r̳b̳1̳ 6) Renb̳a̳r̳b̳1̳+Renl̳o̳n̳ 7) Renl̳o̳n̳ , and 8) a susceptible genotype. Two populations were identified and increased in 2015. Genotypes were inoculated with 0, 2300, or 5000 reniform nematodes. Seedlings were harvested at 90 days to collect plant measurements and RF of reniform nematodes from roots and soil. The Renbarb1 genotype was susceptible. No significant differences in genotypes were observed for root and shoot measurements, and there was no indication of stunting.