Drought stress is a serious abiotic factor that adversely affects cotton yield and fiber properties. The objectives of this study were to screen several genotypes of cotton belong to Gossypium barbadense L. for drought tolerance, study drought indices, correlations, and path-coefficient analysis. Fourteen long-staple kinds of cottons cultivated, and obsolete cultivars were screened for drought tolerance at normal irrigation and drought-stressed experiments for two years. Mean squares indicated significant (p ≤ 0.01) differences among genotypes in the separate and combined analysis. The effect of years showed significant (p≤ 0.05 to p≤ 0.01) differences in most cases. The interaction of genotypes by years was significant for all traits except few cases. The reduction % caused by drought stress in SCY/P ranged from 31.44 to 39.39 with an average of 33.93. Among ten tolerant indices STI, MP, GMP, HM and DI could be considered the best tolerant indices to detect both of tolerant and susceptible genotypes. The correlation of SCY/P under normal irrigation was high with LY/P, Lint %, NB/P, LI and BW, moderate with NS/B and upper half mean length, and low with DFF, Pressley index and negative with Micronaire reading. However, the picture was different under drought stress, in which drought affected lint rather than seeds. The direct and indirect effects of SCY/P components varied greatly under both environments, and LY/P, NB/P and NS/B should be considered as selection indices under normal irrigation, NB/P and NS/B under stress when selection practiced for SCY/P.
Egyptian Journal of Agronomy http://agro.journals.ekb.eg/ 1324 T RADITIONAL breeding is an important way to develop drought-tolerant varieties. There is a dire need to develop cotton cultivars that can produce acceptable yields in water limited. This work aimed to compare single trait selection and independent culling levels for six traits in improving the seed cotton yield (SCY/p) under water deficit and normal irrigation. The genetic material was the F 2 -population of the cross Giza 90 ˟ Giza 95 (long staple). In the F 2 , the phenotypic (PCV%) and genotypic (GCV%) coefficients of variability were mostly higher under normal irrigation than under drought stress. The correlations among traits indicated that SCY/p depended mainly upon number of bolls, boll weight and seed index, and moderately on lint index, and the early plants had high yields. The GCV and PCV were greatly depleted by selection and were higher in most cases under drought stress than under normal irrigation. Independent culling levels preserved genetic variability more than single trait selection. Narrow sense heritability was mostly high under normal irrigation. The selections of both methods were evaluated in the F 4 under both environments. Selection for SCY/p under normal irrigation increased SCY/p by 16.9% under normal irrigation and 8.90% under stress, while selection under stress increased SCY/p by 12.05 and 10.69% of the mid-parent under the respective environments. Single trait selection proved that selection under optimum environment performed well under optimum, and selection under drought stress was better under stress. Otherwise, ICL method of selection did well under drought stress.
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