To achieve introgression, two male-sterile and virtually female sterile, triple-species hybrid plants carrying resistance from G. longicalyx were increased in number via vegetative propagation and approximately 10,000 flowers on the resulting plants were pollinated with pollen from G. hirsutum to obtain 670 viable seed, producing a highly morphologically variable, first backcross generation of plants. Approximately half of this first generation of 670 plants were nematode resistant but most were functionally sterile or had low female fertility. However, after numerous attempts to cross with pollen from agronomic G. hirsutum, highly fertile progeny from 28 of the original, nematode resistant first backcross plants were obtained and advanced four to eight backcrosses into upland cotton.

Various agronomic upland cotton genotypes were used as recurrent parents, and numerous advanced backcross plants in various progeny families were ultimately obtained that were indistinguishable from recurrent parents under greenhouse and field conditions. Cytogenetics studies indicated chromosomes were normal after the third backcross. Altogether, more than 3,000 progeny were phenotyped for nematode resistance. At the first, third, sixth, and seventh backcross, segregating self populations were generated and evaluated for nematode resistance directly, or by bioassaying progeny from test crosses.

Concurrent with this effort, SSR markers were strategically screened to identify markers linked to the resistance and suitable for marker assisted selection. More than 500 phenotyped plants were employed to identify six markers closely linked to the resistance gene.

We present in this poster and its attached handouts, a diagrammatic representation of all phenotyped progeny in all lineages, along with the resistance phenotype assignment and the marker information obtained for the most useful marker identified for every plant examined. Taken together, this information shows that: 1) The trait is consistently inherited like a single dominant gene; 2) The full level of resistance is recovered repeatedly at each backcross in all agronomic backgrounds; 3) The trait appears unlinked to undesirable traits; and 4) Co-dominant markers closely linked to the resistance gene have been identified.