A Seven-Parent Diallel Cross in Onions to Evaluate General and Specific Combining Ability and their Interaction with Years and Locations1

Abstract

Abstract A diallel analysis was used to estimate combining ability of several traits in onion (Allium cepa L.) and evaluate the importance of interactions of general combining ability (GCA) and specific combining ability (SCA) with locations and years. All possible crosses among 7 inbred lines of diverse origin and known horticultural performance were tested for 2 years at the same 3 locations for yield, maturity, bulb traits, and storage quality. Highly significant differences among crosses were detected for all traits. The partitioning of among-cross variation showed that all GCA main effects were highly significant, and SCA main effects were significant for all traits but ring thickness. Cross × environment interactions were primarily due to the interactions of GCA effects with environments. The GCA × year interaction was significant for bulb firmness and centers/bulb, and the GCA × location interaction was significant for yield. While first-order interactions involved only GCA effects, all traits showed significant second-order interactions of both GCA and SCA with years and locations. Variance components of GCA were predominant for all characters, and ratios of GCA to SCA ranged from 2:1 for centers/bulb to 13:1 for % of storage loss. Variance components of GCA × environmental interactions at all levels and for all traits were always smaller than those for GCA main-effect components. For the traits maturity and % of storage loss, the SCA × year × location component was larger than the SCA component. Correlations of GCA effects between environments suggested that significant interactions of GCA were sometimes due to a 1) change in rank of effects from environment to environment and 2) a change in rank and change in variance.