The reniform nematode (Rotylenchulus reniformis Linford & Oliveira) is an important problem in U.S. cotton, and all cultivars support high R. reniformis populations. The objectives of this research were to find better sources of resistance to R. reniformis than are known within G. hirsutum L. and G. barbadense L. and to determine if any of these sources are also resistant to the root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood. A two-tiered study evaluated 1866 primitive accessions of G. hirsutum and 907 of G. barbadense. To quickly eliminate highly susceptible genotypes, tier one compared one plant per accession with six plants of susceptible ‘Deltapine 16’ and six of moderately resistant G. barbadense ‘TX-1348’ in the greenhouse for resistance to the reniform nematode. Tier two used fully replicated experiments in growth chambers to test promising accessions from tier one experiments against R. reniformis and M. incognita separately. Plants were inoculated 2 wk after planting in 500-cm3 pots and nematodes extracted from soil 7 wk later. Most accessions were highly susceptible, and only 5% of G. hirsutum and 12% of G. barbadense accessions had fewer R. reniformis than TX-1348. In growth chambers, 34 of 78 accessions (44%) suppressed R. reniformis (P ≤ 0.05) compared with Deltapine 16. G. hirsutum accessions TX-2469, TX-1586, TX-748, TX-25, TX-1828, and TX-1860; and G. barbadense accessions GB-127, GB-1083, GB-1141, GB-1143, TX-110, GB-1147, GB-207, GB-833, GB-210, GB-212, GB-126, GB-581, GB-1113, GB-1081, TX-502, GB-485, GB-536, and GB-262 had > 10% and < 34% of the R. reniformis on Deltapine 16 and were classified moderately resistant. TX-1828, TX-25, and TX-1860 were root-knot nematode resistant. G. barbadense accessions GB-49, GB-13, GB-264, GB-171, and GB-713 had < 11% of the R. reniformis of Deltapine 16 (P ≤ 0.01) and were classified resistant. G. barbadense GB-713 had 3% of the R. reniformis of Deltapine 16 in three experiments.
