Genetic Properties of Drought Resistance Indices

Inheritance of several yield-based drought resistance indices was studied by a halfdiallel method using seven winter wheat varieties. The parental lines were such chosen as to represent a broad range of drought stress resistance. The experiment was conducted in a split-plot design at the research farm, Faculty of Agriculture, Zanjan University, Iran, in ۱۹۹۸. Irrigated vs. rainfed regimes were considered as the main plots. The F۱ hybrids and parental varieties constituted the subplots. From the grain yield data, some drought resistance indices such as geometric mean productivity (GMP), mean productivity (MP), standard superiority measure (SP), stress susceptibility index (SSI), stress tolerance index (STI), superiority measure (P), and tolerance (TOL) were calculated. Genetic components of variance and heritabilities were estimated using Gardner and Eberhart’s Method ۳, Model II. Significant differences among parents and F۱s were observed for all indices except for SSI and TOL. Significant general combining abilities (GCA) were obtained for GMP, MP, P, SP, STI, and TOL but not for SSI. Therefore, except for SSI, other indices could be regarded as heritable. The specific combining ability (SCA) effects were also highly significant for GMP, MP, P, SP, and STI. However, additive variances were more important than dominance ones. Narrow-sense heritability estimates were very low for SSI, low for TOL, but moderate for GMP, MP, P. SP, and STI. Thus selection based on the latter indices could be more promising than on SSI and TOL. It seems that SP and STI might be better yield-based drought resistance indices to be employed in plant breeding programs, because of their moderate narrow-sense heritabilities and the inherent ability of selecting high yielding genotypes in either stressed or non-stressed conditions.