Three drought-tolerant and four drought-susceptible breeding lines from the Univ. of Minnesota's New Guinea impatiens breeding program were crossed in all combinations (reciprocals and selfs) using a complete diallel crossing scheme. Progeny of each cross were grown using standard cultural practices and data was taken on the morphological traits shown to be related to drought tolerance in previous studies. Data was taken on leaf thickness, leaf width, leaf length, leaf area, and leaf dry weight. From these data the leaf length:width ratio and leaf dry weight/unit area (g·cm–2) were calculated. Mean squares for general and specific combining ability were estimated using Griffing's Model 1, Method 4. Differences between crosses were highly significant (P < 0.001) for all traits examined. Means squares for specific (SCA) and general (GCA) combining ability were significant indicating that both additive and non-additive gene effects are important in the inheritance patterns of these characters. For all traits, GCA was greater than SCA indicating that the additive component had the greatest influence on gain from selection for these traits. These findings agree with other estimates of GCA and SCA for these characters in other crops species. The importance of non-additive effects (SCA) on inheritance of these traits explains why we were able to make rapid improvement in drought tolerance in New Guinea impatiens and the role of additive effects (GCA) on drought tolerance indicates that we can continue to make substantial progress improving drought tolerance in New Guinea impatiens. The impact of these findings on strategies to improve drought tolerance in New Guinea impatiens will be discussed in this presentation.
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