GENETIC STUDIES OF DROUGHT TOLERANCE IN COTTON (Gossypium hirsutum L.)

Abstract

Fifty lines of Gossypium hirsutum L. were screened at seedling stage in glasshouse for drought tolerance. From the germplasm two drought tolerant and two susceptible lines showing genetic divergence will be identified and crossed to obtain hybrid seed . The hybrid seed was planted to develop F 1 generations. Some of the plants from F 1 generation were selfed for F 2 and some back crossed to both the parents (P 1 and P 2 ) to develop seed for back crosses (B 1 and B 2) . All the six generations, P 1, P 2 , F 1 , F 2 , B 1 and B 2 were studied in field under normal and water stressed conditions using completete block design with three replications. During the crop season, water stress will be developed by supplying 50% less irrigations than the normal. Data was recorded on different plant traits related to drought tolerance, yield and fiber quality. The inheritance pattern of various traits was studied using generation means analysis technique. Estimates of narrow sense heritability and nature of correlation among various traits was examined. There were significant differences among six generations (P 1 , P 2 , F 1 , F 2 , B 1 , B 2 ) of two crosses for all the studied plant traits of crosses NIAB-78 × CIM-446 and CIM-482 × FH 1000 under both normal all drought conditions. Generation means analysis indicated additive, dominance and epistatic genetic effects played role in the inheritance of all the traits under both normal and drought condition. Two parameter model [md] provided best fit of observed to the expected generation means for number of bolls per plant under normal conditions in cross NIAB-78 × CIM-446 and for number of monopodial branches of the same cross under drought conditions. In case of cross CIM-482 × FH- 1000 two parameter model [md] was found fit for Fiber fineness under normal conditions. The dominace or dominace × dominance effects were observed for some traits in both the crosses under both normal and drought conditions. Some plant traits showed [i], [j] and [l] type of interactions together which indicated complex inheritance of these traits. In the generation variance analysis only additive effects were involved in the inheritance of most studied plant traits but generation means analysis showed that additive, dominance and epistatic effects were involved in the inheritance of these traits. The narrow sense heritability estimates of infinity generation (F∞) were consistently higher than F 2 generation. High narrow sense heritability estimates 0.67, 0.66 and 0.65 were observed for number of sympodial branches, number of bolls per plant and seed cotton yield, respectively for cross-1 (NIAB-78 × CIM-446) under normal conditions and narrow sense heritability estimates 0.79, 0.69 and 0.58 were observed for boll weight, seed cotton yield and relative leaf water content respectively under drought conditions for cross-1. Seed cotton yield had positive significant correlation with boll weight, fibre length, fibre strength, lint percentage and relative water content except fibre fineness, exised leaf water loss, leaf temperature and leaf area in cross-1 (NIAB-78 × CIM-446) under normal and drought conditions and in cross-2 (CIM-482 × FH-1000) under normal conditions. The information derived from these studies will provide guideline to cotton breeders in breeding of drought tolerant cotton cultivars.