Identification of resistance to Thielaviopsis basicola in diploid cotton

A screening program to find sources of resistance to Thielaviopsis basicola in cotton identified a diploid cotton (Gossypium arboreum, PI 1415) with a pparent high resistance to this pathogen. Seedlings were obtained from self -pollinated seed taken from the resistant plant (PI 1415) and grown in grow th chamber tests with the cultivars (tetraploid G. hirsutum) Paymaster HS-2 6 and Paymaster Tejas as controls. Seedlings were grown for 20 days in natu rally infested field soil and evaluated for root growth and root necrosis. In all tests, PI 1415 had less (P = 0.001) root necrosis than the cultivars HS-26 and Tejas. A triadimenol seed treatment also resulted in less (P = 0 .001) root necrosis for all three cotton genotypes, and the response was ad ditive with level of disease resistance. Incorporation of the resistance fa ctor from PI 1415 into tetraploid upland cotton may greatly reduce damage b y black root rot, especially in combination with fungicide seed treatments.