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Effect of Environments and Genetic Backgrounds on Evaluation of Cotton Isolines¹

This study was conducted to measure the influence of genetic backgrounds in cotton (Gossypium hirsutum L.) and of environments on the effects that two traits, Okra leaf L⁰₂ and frego bract (fg), exert on lint yield and its components. The genetic backgrounds used were DES 24-8ne, a normal leaf and bract strain; ORH 55, an Okra leaf and frego bract strain; and two F₃ plant selections derived from the cross of DES 24-8ne X ORH 55. For each of the four genetic backgrounds, four near-isogenic lines were produced among all homozygous combinations of normal vs. Okra leaf and normal vs. frego bract. The 16 genotypes were evaluated for lint yield in 1979 and 1980 under two insect-control regimes (for a total of four environments). One regime was produced by applying early-season insecticides; the other was produced by applying no early-season insecticides and by growing plants of mustard [Brassica juncea (L.) Czern. & Coss.] near the plots to enhancearly-season insect infestations. Lint yield varied greatly among years, averaging 742 and 479 kg/ha for 1979 and 1980, respectively. Cotton grown with and without early-season insect control yielded 667 and 554 kg/ha, respectively. The effect of Okra leaf on lint yield and its components was influenced greatly by environments but relatively little by genetic backgrounds. Average yield of Okra and normal leaf types was 597 and 625 kg/ha, respectively. Bract types were more sensitive than leaf types to environments and genetic backgrounds. Normal-bract isolines, however, yielded more lint in all environments than did their frego-bract counterparts. The average yield for normal and frego-bract types grown under the insect control regime was 751 and 582 kg/ha; and under the no control regime was 674 and 435 kg/ha, respectively. Varying environments were more important in the evaluation of these traits than varying genetic backgrounds.

Key Words: Gossypium hirsutum L. • Host-plant resistance • Frego bract • Okra leaf • Genotype x environment interaction

² Research geneticist, USDA-ARS, Cotton Physiology and Genetics Research Unit, Stoneville, MS 38776.

Received for publication June 23, 1981.