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Combining Ability Analyses and Relationships Among Yield, Yield Components, and Architectural Traits in Dry Bean¹

Among dry bean, Phaseolus vulgarls L., cultivars developed for monoculture cropping systems in the tropics, small-seeded cultivars often yield more than those with medium and large seeds. However, in many countries consumers prefer larger seeds. To develop high-yielding, large-seeded cultivars, knowledge is needed regarding the inheritance of, and relationships among yield, yield components and architectural traits. Therefore, lines with small seed (<26 g/100 seed), medium (26 to 40 g/100 seed), and/or.large (=40 g/100 seed) from each of three growth habits (I, II and III), which are commonly grown in monoculture, were crossed in a diallel fashion to obtain a complete set of 72 crosses. The F₁ and F₂ generations were evaluated in separate consecutive seasons at two locations, Palmira (mollisols) and Popayan (inceptisols), in Colombia. All traits studied showed F₁ heterosis over the midparent. Yield heterosis of the F₁ over the high parent averaged 36% in Palmira and 23% in Popayan; and heterosis values tended to increase in crosses between parents of increasingly divergent growth habits. General combining ability (GCA), determined by Grifling's Method 4, Model 1 analysis, was more important than specific combining ability for yield and yield components in both the F₁ and F₂ analyses. In both the F_I and F₁ diallel analyses, the same parents, A375 and A457, were identified as having the largest positive GCA effects for both yield and seed weight. Determinate (Type I) parents tended to have positive GCA effects for branches/plant, and negative GCA effects for the remaining architectural traits in either one or both locations, whereas the opposite was true for the indeterminate (Types II and Ill) parents. Yield was positively correlated with pods/m2, seeds/pod and all architectural traits except branches/ plant. In contrast, seed weight was negatively correlated with yield, nodes/branch, nodes/plant, and nodes on the main stem; and positively correlated with main stem internode length and main stem length. The genetic correlations among traits suggest that selection for increased main stem internode length and main stem length should result in simultaneous improvement in both yield and seed weight; however, the resulting plant type may prove too viny and prostrate for monocu|ture cropping systems.

Key Words: Phaseolus vulgaris L. • Heterosis, Reciprocal effects • General combining ability effects • Additive variance • Phenotypic correlations • Genotypic correlations • Growth habit • Seed size

² Post-doctoral fellow (presently, scientist, N.P.I., University Research Park, Salt Lake City, UT 84108) and bean breeder, respectively.

Received for publication April 24, 1984.