EVALUATION OF THE GENETIC VARIATION FOR SOME GENOTYPES IN COTTON (GOSSYPIUM BARBADENSE L.) TO WATER STRESS

Abstract

Sixteen cotton genotypes representing a wide range of cotton characteristics, were used in two concurrent trials (laboratory and field) at Sakha Agric. Res. Station under well-watered and water-limited regimes during 2016 and 2017 seasons. The objectives were to determine genotypic variability among cotton varieties in their response to deficit water stress and to detect the most suitable genotypes, traits and selection procedure for water stress condition. The genotypes were evaluated for water deficit stress in laboratory by the simulation of water potentials with polyethylene glycol-6000 (0.0 and -0.4 MPa), at 25oC using aerated hydroponic culture box. After 18 days the following seedling traits were measured, root length (cm) (RL), root fresh weight (g) (RFW), root dry weight (g) (RDW), shoot length (cm) (SHL), shoot fresh weight (g) (SHFW) and shoot dry weight (g) (SHDW). Field trail conducted to measure vegetative traits, yield and yield components and fiber traits. Analysis of variance for the growing seasons 2016 and 2017 revealed significant differences with respect to water regimes, genotypes and water regimes x genotypes for most of the studied traits, confirming the presence of genotypic variability among the studied cotton genotypes. Mean values exhibited decreasing in traits from normal to water deficit conditions in all traits except for maturity (M). The relative reduction (RD%) varied from 1.25% for pressley index(PI) to 51.6% for lint yield/plant (LY/P). Fiber traits were the lowest affected traits by water stress. G. 88, G. 93 and Suvin were less affected by water stress for seedling traits. For vegetative traits, G.77, G.94, G.89xG.86, Ashmouni, Menoufi and Suvin showed higher values under water deficit. Regarding to yield and yield components traits G.89xG.86, Menoufi, Suvin and G.86 showed the highest water deficit tolerance with acceptable production under limited water regime. On the other hand, most of extra-long staple cotton varieties G.87, G.88 and G.93 were most susceptible to water deficit stress in production term. Drought susceptibility index (DSI) showed significant negative correlation with yield under water deficit regime suggesting DSI as a useful predictor of drought tolerance in cotton and confirming the need of performing genotype evaluation under water stress in case of breeding for water deficit tolerance. Generally, the extra-long genotypes were more susceptible to water deficit stress than long staple genotypes for fiber traits. Correlation coefficients between all the studied traits under well watered and limited water regimes over two years revealed that, yield was positively correlated with yield components traits and plant height (PH); and negatively correlated with most fiber traits. The path coefficient analysis revealed positive and negative direct effect of traits on seed cotton yield (SCY/P). The highest direct effect on SCY/P was exhibited by bolls/plant (B/P) (1.36) followed by boll weight (BW) (0.91) and lint percentage (L%) (0.53). The highest indirect effect of most of yield and vegetative traits were through B/P and BW. These results confirming that, selection to improve productivity under water deficit stress could be more effective throughout direct selection for B/P and BW. Factor analysis revealed that first three components accounted for about 88.51% % of the total variation among the studied traits. Results exhibited the importance of LI, SI, L%, BW, LY/P, SCY/P and PH traits in factor 1 and B/P, SCY/P and LY/P in factor 2 confirming the importance of these traits in the total variance to improve productivity under deficit water stress.