GENETIC STUDIES ON SOME TRAITS RELATED TO DROUGHT TOLERANCE IN RICE

Abstract

This investigation aimed to evaluate some genotypes of rice (Oryza sativa L.) under different irrigation conditions in order to study their genetic behavior to assess their drought tolerance. The genetic materials used in this investigation were six parental varieties and their six populations (P1, P2, F1, F2, BC1 and BC2) for three crosses were obtained from crossing among them. These populations were evaluated during 2010 and 2011 seasons at the Rice Research and Training Center, Sakha, Kafr El-Sheikh, Egypt. The parental varieties were Giza 177, IRAT1444, Sakha 105, IRAT 170, IR 64 and Azucena. The irrigation applied were two levels of flash irrigation, the first level was irrigation every 8 days and the second was irrigation every 12 days as well as control (irrigation every 4 days). The obtained results revealed that genotypic mean squares were highly significant for all studied traits, indicating the presence of real differences among genotypes. Furthermore, the variation due to irrigation levels and genotype x levels interaction were also highly significant for all traits except for flag leaf area. The results indicated the presence of significant differences among crosses for all studied traits under the three levels of irrigation. However, the results also revealed the presence of a highly significant difference among populations within crosses as well as among populations within each cross for all studied traits under the three irrigation levels, indicating that these genotypes gave different performances under different irrigation conditions. The second cross (Sakha 105 x IRAT 170) was the best combination, which recorded the highest values for most of the studied traits except for leaf rolling score and drought susceptibility index (DSI). The second and third crosses exhibited highly significant (MP) heterotic values for most of the studied traits except for fertility percentage. Positive inbreeding depression values were associated with high significant positive heterosis, indicating the role of dominance genes in the genetic expression of these traits. This fact is emphasized by high values of heritability in broad sense with low values of heritability in narrow sense for most of the studied traits. Positive and highly significant genotypic and phenotypic correlations were found between yield and flag leaf area and all studied root traits under drought conditions. Therefore, the hybrid rice breeding programs should be taken these traits in consideration for improving yield and its components under drought stress.