Experiments were conducted during the crop season 2005-06 to evaluate cotton germplasm under irrigated and drought regimes. The germplasm was evaluated for different physiological and morphological traits. The accessions showing higher cotton yield were used as a criterion for selection of drought tolerant and susceptible parents. Three susceptible and three tolerant parents were planted during cotton growing season and crossed on flowering stage. The hybrids were evaluated at seedling and mature plant stage during the crop season 2006-07 under irrigated and drought regimes. All traits under study were subjected to analyses of variance. Traits showing significant genotypic variation were analyzed following simple additive dominance model to estimate heritability and inheritance pattern. The objective of study is to explore genes having potential for high yield and fiber quality under drought environments in genetic material available by crossing the genotypes in diallel fashion that may be used in future breeding program. Gene action and combining ability were studied by analyzing diallel cross data between six cotton varieties viz., FH-113, PB-899, MNH-789, (drought tolerant), and CIM-506, FH-901, CRIS-466, (drought susceptible). A considerable reduction in almost all parameters was shown under stress conditions. Diallel analysis showed that characters like monopodial branches, sympodial branches and staple strength showed additive genetic effects and traits like plant height, number of bolls, boll weight, yield., staple length, staple fineness, GOT, seed index, lint index, relative water content, leaf temperature and relative cell injury showed additive and dominant genetic effects under normal conditions and water stress conditions, traits like staple strength and relative cell injury showed additive genetic effects and traits like plant height, monopodial branches, sympodial branches, number of bolls, boll weight, yield, staple length, staple fineness, GOT, seed index, lint index, relative water content, leaf temperature showed additive and dominant (non-additive) genetic effects. PB-899 proved the best general combiner for traits like plant height and staple length, FH-113 proved the best general combiner for traits like monopodial branches, sympodial branches, number of bolls, yield , seed index, relative water content, leaf temperature and relative cell injury, MNH-789 proved the best general combiner for traits like boll weight, GOT and CIM-506 proved the best general combiner for staple fineness, staple strength and lint index under normal and water stress conditions. Heritability estimates for yield and yield related traits and most of traits were high under normal and water stress conditions and had maximum ability to transfer genes to the next generation. So, selection of desirable parents and gene combinations for high yield on the basis of these traits under both conditions will be effective for future breeding programs. Breeders may utilize good general combiners in breeding programs for improvements of cotton traits. It is recommended that breeders should breed for superior combining ability aimed at improving overall GCA for yield and fiber quality. xviAbstract Experiments were conducted during the crop season 2005-06 to evaluate cotton germplasm under irrigated and drought regimes. The germplasm was evaluated for different physiological and morphological traits. The accessions showing higher cotton yield were used as a criterion for selection of drought tolerant and susceptible parents. Three susceptible and three tolerant parents were planted during cotton growing season and crossed on flowering stage. The hybrids were evaluated at seedling and mature plant stage during the crop season 2006-07 under irrigated and drought regimes. All traits under study were subjected to analyses of variance. Traits showing significant genotypic variation were analyzed following simple additive dominance model to estimate heritability and inheritance pattern. The objective of study is to explore genes having potential for high yield and fiber quality under drought environments in genetic material available by crossing the genotypes in diallel fashion that may be used in future breeding program. Gene action and combining ability were studied by analyzing diallel cross data between six cotton varieties viz., FH-113, PB-899, MNH-789, (drought tolerant), and CIM-506, FH-901, CRIS-466, (drought susceptible). A considerable reduction in almost all parameters was shown under stress conditions. Diallel analysis showed that characters like monopodial branches, sympodial branches and staple strength showed additive genetic effects and traits like plant height, number of bolls, boll weight, yield., staple length, staple fineness, GOT, seed index, lint index, relative water content, leaf temperature and relative cell injury showed additive and dominant genetic effects under normal conditions and water stress conditions, traits like staple strength and relative cell injury showed additive genetic effects and traits like plant height, monopodial branches, sympodial branches, number of bolls, boll weight, yield, staple length, staple fineness, GOT, seed index, lint index, relative water content, leaf temperature showed additive and dominant (non-additive) genetic effects. PB-899 proved the best general combiner for traits like plant height and staple length, FH-113 proved the best general combiner for traits like monopodial branches, sympodial branches, number of bolls, yield , seed index, relative water content, leaf temperature and relative cell injury, MNH-789 proved the best general combiner for traits like boll weight, GOT and CIM-506 proved the best general combiner for staple fineness, staple strength and lint index under normal and water stress conditions. Heritability estimates for yield and yield related traits and most of traits were high under normal and water stress conditions and had maximum ability to transfer genes to the next generation. So, selection of desirable parents and gene combinations for high yield on the basis of these traits under both conditions will be effective for future breeding programs. Breeders may utilize good general combiners in breeding programs for improvements of cotton traits. It is recommended that breeders should breed for superior combining ability aimed at improving overall GCA for yield and fiber quality.