Breeding Common Beans (Phaseolus Vulgaris L.) for Higher Grain Yield, Iron and Zinc Concentration in Kenya

Abstract

Around the world today, legumes are among the most consumed crops and the species especially Phaseolus vulgaris. Bean yields vary due to varietal differences and also the environmental conditions. Its nutrient content varies greatly among the genotypes. For example, the concentrations of iron and zinc minerals are not the same in the different varieties grown around the world today. Most of the varieties grown by farmers in the different communities in Kenya have lower or no zinc or iron minerals. Therefore, bio fortification of this crop is necessary to help in fighting mineral deficiency among people who depend on dry beans as a staple food. The broad objective of this research was to improve the mineral (iron and zinc) content of some elite dry bean varieties while maintaining a higher yield. The specific objectives of the study were: (i) To determine the effects of environments on the yield of selected dry bean varieties and lines that have higher concentrations of iron and zinc (ii) To determine the combining ability of selected parents for yield and minerals (iron and zinc) concentration. For the study of the effects of environment yield, thirty-six genotypes of dry beans were set up in an experiment in two environments, Kenya Agricultural and Livestock ِResearch Organization (KALRO) in Embu and Mwea, Kirinyaga County. Alpha lattice design was used and was replicated three times. The first experiment was planted in May of 2018 and the second one was planted in November of 2018. Meanwhile, for the second objective, eight parents including four high-yielding varieties and four bean lines with higher iron and zinc minerals were selected for crossing. They were mated in half diallel design and the parents were included. After crossing, twenty-eight F1 progenies were produced and planted to generate F2 progenies. The F2 progenies were evaluated together with the parents in two environments of KALRO Mwea and KALRO Embu using alpha lattice design between March and July of 2019. Agronomic data plant health data, and yield data were collected and analyzed. Significant variation of the traits among the genotypes, and between locations in terms of both agronomic and yield traits was reobserved. Genotype KATRAM matured in 74 days while NUA692 matured in 86 days for NUA692, pods number per plant which ranged from 8 pods NUA686 to 10.4 pods in NUA680, and grain yield which ranged from 352 Kg/ha for NUA595 to 697Kg/ha for NUA680, days to flowering varied from 38 days for NUA636 to 48 days for NUA666 in Mwea site. In Embu, days to flowering ranged from 38 days (NUA636) to 47 days (NUA666), days to maturity varied from 67.4 to 77.5 for KATRAM and NUA692 respectively. Pod number per plant ranged between 8.1 and 12 pods. Among the genotypes,

yields varied from 318Kg/ha for NUA666 to 642Kg/ha for EMBEAN14. The correlation between the pod number and seed yield in Kg/ha was positive. Five genotypes (EMBEAN14, NUA680, CHELALANG, WAIRIMU, and TASHA) showed stability in performance across the two sites and the two seasons. Evaluation of the twenty-eight progenies generated after crossing showed that the environmental effects were significant for percentage emergence; while genotypes had a highly significant effect also on all the agronomic traits. The Genotype by Environment (GxE) interaction showed significant effects also on all agronomic traits plus both root rot and bean fly incidence. There was a significant general combining ability (GCA) (P<0.05) effect for yield on genotypes WAIRIMU, CIANKUI, NUA604, and NUA640. There was a significant GCA effect for both Iron and Zinc concentration with genotypes NUA680 and NUA640 ranking as the first and second in GCA for iron concentrations while genotypeNUA604 and NUA 680 ranked first and second in GCA for zinc concentration. For SCA, the genotypes WAIRIMU x KATB9, NUA730 x CIANKUI, NUA730 x NUA640, CIANKUI x NUA640, WAIRIMU x NUA680, WAIRIMU x NUA604, showed higher specific combining ability for seed yield, weight of 100 seed and number of seeds per pod. Across the two sites, among the 28 crosses studied, concentrations of Fe and Zn in the seeds were found to be high with Fe (>70 ppm) and Zn (>30 ppm). The variation among the material's general combining ability (GCA) and specific combining ability (SCA) that showed that there was both additive gene effects and non-additive gene effects. This is because high GCA indicates additive gene action while SCA indicates non additive gene action.