Genetic Nature of Responsiveness of Cotton Populations to Environmental Stresses

This study was a genetical approach to investigate the genetic nature of cotton plants to response with heavy metals stresses, in order to reuse treated water in irrigating this crop. The work was extended to study the adaptability and stability of cotton genotypes to such stress conditions. Also, these cotton genotypes were subjected for clustering analysis based on their tolerance indices to heavy metals to help in choosing genotypes that are more tolerant to such metals. To achieve these goals, a set of cotton genotypes, G. barbadense L, were screened for their response to cadmium (Cd), lead (Pb) and nickel (Ni) and six genotypes were chosen and used as parents representing low and high tolerant genotypes. Giza 83 (P1), Giza 90 (P2), and Giza 91 (P3) were high tolerant parents and Giza 70 (P4), Pima S6 (P5) and Giza 87 (P6) were low tolerant parents.A set of crosses were made using the high tolerant parents as females and the low tolerant parents were served as male parents to obtain nine F1 crosses. Selfed seeds of the parental genotypes and seeds of their nine F crosses were grown in a complete randomized block design experiment. Thirty days old plants were treated with heavy metals solutions at concentration of 70 ppm Cd, 20 ppm Pb and 40 ppm Ni ions as sprayers. One week later, four plant samples were taken from each replicate for laboratory analysis. The fifty days old plants were retreated again with the same heavy metals and the same concentrations, in order to study their effects on fertility and yield. Samples of mature floral buds were taken for microscopic examination, representing four plants from each replicate. At maturity, cotton yield was ginned from ten individual plants for each replicate in each treatment. All these estimates were used in calculating two response parameters: induced reduction%, as an index of sensitivity to heavy metals and tolerance% as tolerance index.