Combining Ability of Tannin Content and Protein Characteristics of Raw and Cooked Dry Beans

Tannin in dry bean (Phaseolus vulgaris L.) seeds has been associated with low protein availability and digestibility. Protein losses may occur during soaking and cooking and lessen the potential nutritional benefit from eating beans. The aim of the present study was to evaluate general combining ability (GCA) and specific combining ability (SCA) effects on tannin content and protein characteristics of dry and cooked beans. A fixed-effect model permitted the evaluation of parents for use in breeding programs to improve bean nutritional quality. Eight parents were crossed in diallel to produce the F₂ and F₃ generations on which combining ability mean squares and genetic effects were calculated. Tannin was determined by the vanillin-HCl method and protein of dry and cooked beans was measured using an infrared reflectance instrument. Protein loss during soaking and cooking was determined by subtracting the protein in cooked beans from that in dry beans. Significant differences were detected among parents and progeny for all traits, indicating the presence of genetic variability. Mean squares for both GCA and SCA were significant, indicating the presence of additive and dominance effects in the populations. Ratios of GCA:SCA mean square components were greater than unity for all traits, indicating that GCA predominated. Maternal effects influenced tannin content. The distribution of points representing the parental arrays along the regression line of the Wᵣ, Vᵣ graph revealed that genes with partial dominance controlled tannin content. Genes for protein content of raw and cooked beans showed partial dominance in some cases and complete dominance in other cases. Genes controlling the protein loss trait had the property of complete dominance. Seed protein contents of raw and cooked beans were correlated but raw bean protein and tannin were not. Study results suggested that it is not feasible to simultaneously breed for multiple traits, except for seed protein of raw and cooked beans. Screening for raw bean protein and tannin content should be done independently. Joint contribution from the USDA-ARS, and the Dep. of Crop and Soil Sciences and Dep. of Food Science and Human Nutrition, Michigan State Univ. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph.D, degree at Michigan State Univ. Approved for publication by the Michigan Agric. Exp. Stn. as Journal Article no. 12140. Research supported by USAID/BIFAD under a Title XII Bean/Cowpea CRSP Grant no. AID/DSAN-XII-G-0261.