EVALUATION OF SOME GENOTYPES IN COTTON UNDER STRESS OF LONGEVITY OF THE PERIODS OF IRRIGATION.

water irrigation is one of the important factors for cotton cultivation, growth and production in various cotton growing countries, particularly in Egypt at the present time. To identify water stress tolerant for genotypes, it is vital to understand their genetic variation and its performance under water stress conditions. In the present work, some cotton genotypes belong to (Gossypium barbadense, L.) were used to apply two cycles of direct selection to improving productivity, as well as, acceptable fiber properties. The two cycles included two crosses i.e., the first cross (Giza 69 X Pima S 6) and the second cross (Giza 69 X Giza 88) which were evaluated under different water irrigation stress conditions. The control treatment conventional  irrigation (C) was the normal irrigation every 15 days interval. The first stress water irrigation treatment (S₁), was the irrigation every 30 days interval and the second stress water irrigation treatment (S₂), was the irrigation every 45 days interval. At maturity, data were recorded on yield and its components, and fiber properties were measured at Fiber Technology Department in Cotton Research Institute (C.R.I.), Agricultural Research Center (A.R.C.).
The results showed reduction in the means of all studied characters under (S₂) condition, i.e., yield components and fiber properties for all the genotypes and their generations. The genotypes exhibited an increase in the mean performances under the control treatment (C) condition for most studied traits in the generations and also treatment (S₁) condition, respectively, due to efficiency of two cycles of direct selection under condition of water irrigation stress. Yield components and fiber properties traits for F₃, F₄ and F₅ generations under control treatment had best and high values versus water stress conditions. The high and the best values were detected for well-watered control treatment conventional  irrigation (C) in all studied characters and in the  generations, while low and poor values were only detected for treatment (S₂) for all studied characters and in the generations.
 This study showed that some yield traits were regulated genetically and environmentally through tested cotton genotypes under water irrigation stress conditions. It was concluded that these yield traits would be used as indicator for screening cotton germplasm for different water irrigation stress conditions as well as for evolving high yielding water stress tolerant genotypes of cotton crop. These findings are useful in breeding programs for identifying and selecting genotypes involved on water stress tolerance in cotton. However, susceptibility index for  water irrigation stress were high in some families for most yield characters when compared with most fiber properties, because the fiber properties were largely controlled by genetic variation and influenced by environment conditions in the two populations (Giza 69 X Pima S 6) and (Giza 69 X Giza 88). These families are useful for the breeder may utilize such families in breeding programs aiming to improve yield and fiber characters under water irrigation stress conditions.
         Comparing mean performance of F₃ with those of F₄ and F₅ generations revealed increase in mean values for all characters with advanced generations from F₃ to F₄, indicating an accumulation of favorable alleles. F₄ generation showed high G.C.V.% and P.C.V.% values than those of the succeeding generation for all characters. The closer magnitude of G.C.V.% and P.C.V.% in F₅ generation  indicated that genetic had played greater role rather than environment for most characters. The G.C.V.% and P.C.V.% were high in both F₃ and F₄ generations as compared with F₅ generation due to high genetic variance and environmental variance in F₃ and F₄ generations, due to high genetic variance relative to environmental variance and low of genetic differences in F₅ from the rest of previous generations and to increase the homozygosity. The predicted advances were high for all studied characters in F₄ generation compare with F₅ generation, while the predicted advance in F₃ generation at under control treatment had higher values for all studied characters.