Effect of moisture regimes on combining ability variations of seedling traits in sunflower (Helianthus annuus L.)

Abstract

Seedlings traits provide a reliable and rapid technique for evaluating large numbers of genotypes for abiotic stresses. Experiments on sunflower were carried out under two moisture regimes in controlled conditions to study their modifying effect on phenotypic expression and combining ability of seedling traits such as root length (RL), shoot length (SL), root weight (RW), shoot weight (SW), root-to-shoot ratio (R:S), lateral root number (NLR), lateral root density (LRD), wilting rate index and recovery percent (R%), and their genotypic correlation with achene yield. Variation among breeding lines for relative decrease in the seedling traits under the moisture stress regime indicated their differences in moisture sensitivity. Genetic variation for all seedling traits was low over environments, but high within environments. Moisture regimes modified phenotype, ranking among parents, and combining ability of seedling traits. Relative contribution of specific combining ability to total variation decreased under the moisture stress regime for all root-based traits, with a corresponding increase in general combining ability due to either female, male or both. The moisture stress regime was favourable for the expression of additive genetic variability. All seedling traits except SL showed significant correlation with achene yield, which also signified their importance for improving achene yield under drought regimes. From the breeding point of view, R% and RW were more useful traits for evaluating genotypes for drought tolerance. Key words: Sunflower, seedling traits, genetic variability, drought tolerance