Inheritance of tolerance to alluminium toxicity in common beans(Phaseolus Vulgaris L.)
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Common bean (Phaseolus vulgaris) is an important nutritional component in the diet of more than 300 million people around the world. Its production is limited by drought and aluminium toxicity among other abiotic factors. Correction of acidity-related soil constraints such as aluminium toxicity using lime and phosphate fertilizers are beyond the capacity of resource-poor farmers in Zambia. This situation, therefore, calls for the need to make use of the genetic variation existing for adaptation to acid soils and aluminium tolerance among common bean genotypes to improve tolerance to aluminium toxicity so that locally grown common beans may be successfully grown in acidic soils. The objectives of this study were (1) to characterize common bean genotypes for aluminium tolerance (2) to investigate the type of gene action conditioning aluminium tolerance in common beans. The study was carried out at the University of Zambia and involved; (i) evaluation of 20 bean genotypes in nutrient solution (0 and 12 mgL-1 aluminium) to assess genotypic response, to aluminium stress (ii) creation of experiment population in North Carolina Design II, (iii) advancement of F1 to F2 generation and (iv) evaluation of F2 crosses for aluminium tolerance in the 12 mgL-1 aluminium nutrient solution. Data collected/derived were those associated with aluminium tolerance and included root length, shoot length, root biomass, shoot biomass, number of lateral roots and root/shoot ratio. Data were analysed using Genstat 14th version with means separated using Least Significant Difference (LSD 0.05). The ratio, σ2gcam + σ2gcaf) / (σ2gcam + σ2gcaf + σ2sca, was used to determine the type of gene action conditioning inheritance of aluminium tolerance and the relative importance of General and Specific Combining Ability variances. Narrow-sense heritability estimates for each set were calculated. The results showed highly significant P<0.001) differences among genotypes, aluminium concentration and interaction between genotypes and aluminium concentration for all studied traits except number of lateral roots where non-significant aluminium concentration was observed. The hypothesis that there is enough genetic variation among common bean genotypes for acid soils adaptation and aluminium toxicity tolerance was validated in this study. Five genotypes (SZ 3-3-B-B2, Lukupa, VTTT918/15-4-4, CIM-RMOO-321LN02 and LY4-4-B) were found to be tolerant, four (SZ9-7-B-B, Kabulangeti, BF13607-12 and SZ9-B-B-B2) moderately tolerant and eleven (NUA 45, BF13607-6, VTTT915/2-2, VTTT924/12-4, Kalungu, Chambeshi, Lyambai, NUA91, Solwezi parent, BF13572-11 and ARA 4) sensitive to aluminium toxicity. Moreover, SZ3-3-B-B2 identified as aluminium tolerant, with good general combining abilities for root length, shoot length and root biomass, was identified as suitable for use in breeding for aluminium tolerance in common beans. The results obtained in this study further showed that inheritance of aluminium tolerance based on root length, shoot length, shoot biomass and root/shoot ratio, was controlled by additive gene action. Root biomass, on the other hand, was found to be controlled by non-additive gene action. Narrow sense heritability estimates ranged from 10%-55% for root length, 26%-74% for shoot length, 6%-17% for root biomass, 25%-48% for shoot biomass and 10%-13% for root/shoot ratio. Based on these heritability estimates, selection for root length, shoot length and shoot biomass could result in rapid gain in selection because of their medium heritability estimates, while selection for root biomass and root/shoot ratio would result in slow gain in selection because of their low narrow sense heritability estimates.
- Agricultural Sciences