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Uri Lavi, Emanuel Lahav, Chemda Degani, Shmuel Gazit, and Jossi Hillel

Genetic variance components for avocado (Persea americana Mill.) traits were estimated to improve avocado breeding efficiency. The additive and nonadditive genetic variance components were calculated from the variances between and within crosses. In all nine traits examined, i.e.-anise scent, fruit density, flowering intensity, fruit weight, harvest duration, inflorescence length, seed size, softening time, and tree size-a significant nonadditive genetic variance was detected. Additive genetic variance in all traits was lower and nonsignificant. The existence of major nonadditive variance was indicated also by narrow-sense and broad-sense heritability values estimated for each trait. Therefore, parental selection should not be based solely on cultivar performance. Crosses between parents of medium and perhaps even low performance should also be included in the breeding program.

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Frank M. Elia, George L. Hosfield, James D. Kelly, and Mark A. Uebersax

A knowledge of the relative proportion of additive and nonadditive genetic variances for complex traits in a population forms a basis for studying trait inheritance and can be used as a tool in plant breeding. A North Carolina Design II mating scheme was used to determine the inheritance of cooking time, protein and tannin content, and water absorption among 16 genotypes of dry bean (Phaseolus vulgaris L.) representative of the Andean Center of Domestication. Heritability and the degree of dominance for the traits were also calculated to provide guidelines for adopting breeding strategies for cultivar development. Thirty-two progeny resulted from the matings and these were assigned to two sets of 16 progeny each. Variances due to general combining ability (GCA) and specific combining ability (SCA) were significant for the traits. The GCA was larger in all cases. Narrow-sense heritability for protein, tannin, water absorption, and cooking time averaged 0.88, 0.91, 0.77, and 0.90, respectively. Degree of dominance estimates indicted that the traits were governed by genes with partial dominance except, in one case, tannin had a degree of dominance value of zero, indicating no dominance. The phenotypic correlation (-0.82) between water absorption and cooking time justifies using the water absorption trait as an indirect selection method for cooking time. With regard to parent selection in crosses, significant differences between GCA females and GCA males suggested cytoplasmic influences on trait expression. Hence, the way a parent is used in a cross (i.e., as female or male) will offset trait segregation. Using fast-cooking bean cultivars in conjunction with fuel-efficient cooking methods may be the best strategy to conserve fuelwood and help reduce the rate of deforestation in East and Central Africa.

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Xuan Wu, Shuyin Liang, and David H. Byrne

readily improved, as it has the highest additive and nonadditive genetic variance. Furthermore, given its low genotype × environment (G × E) variance, selection would be effective during the first growth phase of the rose plant. The other two traits will