Iron and zinc genetic biofortification of yellow common bean (phaseolus vulgaris l.) genotypes in Tanzania

Abstract

Iron and zinc deficiencies are the global leading micronutrient deficiencies particularly in developing countries such as Tanzania. Iron deficiency in humans causes anemia, whereas zinc deficiency leads to compromised immunity, decreased growth rate, and mental retardation. This study was conducted in the Northern, Eastern, and Southern Highlands of Tanzania from 2018 to 2020 to address the iron and zinc deficiencies in humans using genetic biofortification. The approach involved screening common bean genotypes for iron and zinc contents and the factors (such as phytic acid, and ferritin) that inhibit and or enhance their availability in the human gut. The genotypes with high seed iron and zinc contents were used in the genetic biofortification of the consumers’ preferred yellow bean varieties. Field experiments (involving 99 common bean genotypes) were conducted at TARI-Selian, SUA, and TARI-Uyole to screen common bean genotypes for seed minerals and yield. The genotypes were planted following alpha lattice design in three replications each contained five blocks with 20 plots. Data were recorded for days to 75% flowering, number of pods/plant, number of seeds/pod, 100 seed weight, and seed yield. Furthermore, the contents of seed iron, zinc, phosphorus, magnesium, manganese, ferritin, phytic acid, and phytic acid to mineral molar ratios were determined. Results showed that there were highly significant (P ≤ 0.001) effects between bean genotypes, environments, and genotype by environment interaction on seed yield, yield related traits, seed iron, and zinc contents. The highest and stable bean genotypes for seed iron and zinc contents and seed yield were identified. High phosphorus, magnesium, manganese, and low phytic acid and phytic acid to mineral molar ratio bean genotypes were also identified. Furthermore, the study developed F2 bean crosses with a 12.5 - 146.4 % increase in seed iron content and a 1.0 - 53.1 % increase in zinc content. Seventeen of the developed F2 crosses had a high seed iron content ≥ 70 mg/kg and seed zinc content ≥ 30 mg/kg, these include BF01, BF04. BF05, BF06, BF08, BF10, BF13, BF16, BF22, BF24, BF25, BF27, BF29, BF31, BF32, BF33, and BF35.