Breeding for "low-gossypol seed and high-gossypol plants" in upland cotton. Analysis of tri-species hybrids and backcross progenies using AFLPs and mapped RFLPs

This work aims at breeding upland cotton [Gossypium hirsutum L., 2(AD)(1) g enome] with a reduced level of gossypol in the seeds for optimal food and f eed uses, and a high gossypol level in the remaining organs for resistance to pests. Two tri-species Gossypium hybrids, (G. thurberi-G. sturtianum-G. hirsutum and G. hirsutum-G. raimondii-G. sturtianum) including G. sturtianu m (2C(1)) as a donor, G. thurberi (2D(1)) and G. raimondii (2D(5)) as a bri dge species, were created. Recurrent selection initiated with these tri-spe cies hybrids produced backcross (BC) progenies expressing the "low-gossypol seed and high-gossypol plant" trait at different levels. We used AFLP mark ers to assess the genetic similarity among the germplasm and RFLP probes to tag the introgression of specific chomosome segments from the parental spe cies. Five pairs of AFLP primers generated 477 fragments, among which 417 ( 87.4%) were poly morphic. The genetic similarity between the upland cotton and the wild species ranged from 29.5 to 43.2%, while similarity reached 80 % between upland cotton and BC3 plants. Introgression of species-specific A FLPs was evident from all the parental species and confirmed the hybrid ori gin of the analyzed progenies. Southern-blot analysis based on 49 RFLP prob es allowed us to trace the introgression of parental DNA segments in the tr i-species hybrids and in three generations of backcross. Introgression was evident from 11, 8 and 7 linkage groups of G. sturtianum, G. raimondii and G. thurberi respectively. The types of introgression revealed by RFLP probe s are discussed, and breeding schemes to enhance recombination are proposed . The ability to trace DNA segments of known chromosomal locations from the donor G. sturtianum through segregating generations is a starting point to map the "low-gossypol seed and high-gossypol plant" traits.