COMBINING ABILITY ANALYSIS OF RESPONSE TO COLD STRESS IN MAIZE

Diallel crosses of eight inbred lines of maize (Zea mays L.) were evaluated for their response to cold stress. Data were recorded on yellowing, purpling and drying of leaves in field experiments conducted in four environments (E) (two sowing dates at two locations) and electrical conductivity in the laboratory; and these were subjected to combining ability analysis. The mean squares due to crosses and crosses X E interactions were significant for all the traits evaluated, indicating the presence of genotypic variation and genotype X E (GE) interaction. Both general combining ability (GCA) and specific combining ability (SCA) contributed significantly to the variations due to genotypes and GE interaction. The magnitude of fixed variance components indicated that GCA and SCA were of similar importance in the expression of drying of leaves, GCA was of greater importance than SCA in yellowing and purpling of leaves, and SCA in electrical conductivity. The GCA X E and SCA X E interactions accounted for similar variation in yellowing of leaves but for greater variation in purpling and drying of leaves than GCA. The interaction components were larger than those of SCA for all three traits. Two inbred lines (CM202, H104) had low GCA effects and three hybrids (CM202 x H104, CM202 x J54, H104 x J54) had low mean performance for yellowing and drying of leaves. Except in one case, the SCA effects of these hybrids for these traits were not significant. Electrical conductivity was significantly correlated with yellowing of leaves only, but the magnitude was too low (r2=0.21 to be useful while selecting for less yellowing.