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 apparent high resistance to this pathogen. Seedlings were obtained from self-pollinated seed taken from the resistant plant (PI 1415) and grown in growth chamber tests with the cultivars (tetraploid G. hirsutum) Paymaster HS-26 and Paymaster Tejas as controls. Seedlings were grown for 20 days in naturally 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 additive with level of disease resistance. Incorporation of the resistance factor from PI 1415 into tetraploid upland cotton may greatly reduce damage by black root rot, especially in combination with fungicide seed treatments.