Wednesday, November 15, 2006 - 10:00 AM
246-7
Reniform Nematode Resistance- Marker Development and Cytogenetics of the Gossypium longicalyx Introgression Products.
The reniform nematode (Rotylenchulus reniformis) is already a significant problem for US cotton producers, and the severity and acreage of damage have been increasing. Although no Upland cotton (Gossypium hirsutum) cultivar has high resistance to the reniform nematode, the wild African species, G. longicalyx is related to cotton and is immune to this pest. Intensive wide-cross breeding efforts at the USDA, College Station yielded two tri-species hybrids that involve G. longicalyx and G. hirsutum, but differ in the third parent -- either G. armourianum or G. herbaceum, respectively. The genomic compositions of these two hybrids, ADFD and ADAF, respectively, suggested that chromosomal abnormalities would abound in early backcross generations. Chromosome numbers and meiotic metaphase-I configurations that were assessed for most of the BC1F1, BC2F1, BC1S1, BC3F1, BC4F1 and BC5F1 plants revealed a progression toward 100% 52-chromosome individuals and increasing frequencies of resistant plants that form 26 bivalents at metaphase-I. Highly resistant plants with normal or nearly normal chromosomal constitution have been selected, yielding high levels of reniform nematode resistance into prospectively elite upland cotton. To identify closely linked molecular marker loci that could be used to screen for the resistance gene and employ marker-assisted selection (MAS), we have screened SSR markers across 12 highly resistant and 12 highly susceptible plants from a population of 144 classified BC2F1 plants. Linked SSR markers have been identified, revealing the chromosomal location and facilitating identification of more tightly linked markers.
Recorded presentation