The root-knot nematode, Meloidogyne incognita (Kofoid and White)Chitwood, is a pest of cotton, Gossypium hirsutum L., on lighter infested soils. Aub634 is the only cotton reported to have a high level of resistance to the root-knot nematode. This research examines the possibility that hybrids between moderately resistant primitive cottons might yield selections that are as resistant as Aub634.

All possible single crosses were made between Aub634, T19, T5, T75, T78, T487, and M8 without regard to reciprocal effects. Three inch plastic pots in greenhouse beds were filled with methyl bromide-fumigated soil and inoculated with 10,000 M. incognita (race 3) eggs. The experiment was planted one week after inoculation in a randomized complete block design with six replications. A replication consisted of five plants of each hybrid. After six weeks the M. incognita eggs were washed off the roots with 1.05% NaOC1 for four minutes and counted.

The hybrid source of variance for eggs/plant wa highly significant. Subsequent combining ability analysis showed that general combining ability (GCA) was highly significant and specific combining ability (SCA) was significant. T75 had a GCA effect for resistance (-15,900) which was as high as that for Aub634 (-15,600). Significant SCA effects were observed when MB was crossed with Aub634 (-14,600) and with T78 (11,100). Though not significant, crosses between T5, T78, and T487 accessions had SCA for resistance. Comparison of GCA and SCA variance estimates revealed that T78 was the only parent to not uniformly transmit its effect.

In summary, T75 had a GCA for resistance as high as that for Aub634 and hybrids between T5, T78, and T487 had SCA for resistance. These hybrids will be screens for transgressive segregation in the F₂ generation.