Participatory Breeding, Association Mapping and Inheritance of Iron and Zinc Accumulation in Common Bean (Phaseolus vulgaris L.)

Abstract

In the Democratic Republic of Congo (DRC), particularly in North-Kivu province, the prevalence of iron deficiency affects over 36% of pre-school children and at the national level, 71% and 53% of pre-school and pregnant women. Iron biofortified common beans with high yield potential is a promising strategy to address mineral deficiencies in this region where cereal/bean-based diets are the most important. The objectives of this study were to : i) determine farmers’ varietal preferences, production constraints and perceptions of biofortified (iron and zinc) common bean in DRC ; ii) evaluate the cooking time and quality of cooked beans of the new high-performing second-generation biofortified common beans ; iii) assess the genetic variability and yield stability of iron and zinc biofortified common bean genotypes ; iv) determine the mode of inheritance of seed iron and zinc concentration and reduction of polyphenols in common bean ; and v) identify quantitative trait loci (QTLs) associated with high seed iron and zinc contents in common bean accessions and local varieties cultivated in DRC. In the first study, results from 180 and 140 farmers surveyed in Lubero and Beni territories in North-Kivu province indicated that farmers plant a mixture of traditional and improved varieties. Average bean yield in the two territories is less than 800 kg ha-1. Farmers do not use fertilizers or pesticides. High yield is the primary attribute farmers expect from improved seeds followed by earliness in Lubero territory where the crop takes four to six months to mature. In Beni territory, a part from the yield, priority trait is resistance to abiotic stresses. Major constraints to common bean productivity in these territories include lack of high yielding varieties resistant/tolerant to pests and diseases, low soil fertility and adapted to climatic changes and variability, wandering of animals that decimate common bean crops and small land sizes. Respondents were not aware that there are common bean varieties with high mineral concentration. However, a half of the respondents knew that iron is involved in blood structure in reference to the tablets women use during pregnancy. They indicated that no biofortified common beans are grown by farmers but they wished to test performance of the new iron and zinc dense beans. In the second study, from 285 second-generation biofortified common bean lines, farmers selected 124 performing genotypes which had from 14.2 to 26.8 pods per plant compared to local varieties whose pods varied from 8.7 to 13.0 per plant. These genotypes had yellow and lighter seed coats. Hydration coefficient varied from 1.4 to 3.4 among biofortified types and from 1.7 to 2.0 among local lines. Cooking time varied from 73 to 170 minutes among biofortified genotypes with an average of 118 minutes and from 120 to 144 minutes among local lines with an average of 134 minutes. However, the percentage of beans remaining whole after cooking was high (93.0 to 99.8%) for local lines than for biofortified lines (21.3 to 100%). From the study on genetic variability and yield stability involving 160 iron and zinc dense lines, yield and iron and zinc levels were high for biofortified genotypes than for the local varieties. Three biofortified genotypes, G4-24A, BF08-01-47B and RWV 2359 had significantly higher grain yields (4699.7, 2818.3 and 2690.9 kg ha-1) compared to the checks. Three biofortified genotypes RK 11, BF08-07-22 and BF08-26-162 combined iron and zinc concentration significantly higher than those for the high iron and zinc checks. Broad-sense heritability and genetic gain under selection were high for pod length (95.3 and 63.57%). Heritability was moderate for 100-seed mass (57.2%) and seed iron (68.3%) and genetic gain was low for all other traits. Yield stability assessment showed no ideal genotype across locations. However, biofortified genotypes BF08-14-96B, BF08-7-19B and BF08-14-51C, were the most stable and had more than 1,800 kg ha-1 of grain yield. Genotype G4-24A, which was the best yielding genotype, was the most unstable. In the fourth experiment on inheritance of iron, zinc and polyphenols in common bean, broad sense heritability was important for all the study characters (>0.70) indicating the importance of genetic effects controlling the inheritance of characters. No significant GCA effects were observed among the testers and lines for iron, zinc and total polyphenols. However, among hybrids, significant negative SCA effects were observed for hybrid RW582x041/1 for total polyphenols. On the other hand, significant positive SCA effects were observed for hybrid RW547x720/12 for iron. The fifth experiment aimed to identify QTLs associated with seed iron and zinc using high density DArTSeq SNP markers on 183 dense iron and zinc common bean introductions and five local genotypes. Typically, the study population can be structured into four subpopulations. Two QTLs associated with seed iron were found on chromosomes 1 and 3 and two other QTLs associated with zinc were found on chromosomes 6 and 9. Thirteen genes were proposed as candidate genes controlling iron and zinc in common bean. One gene was located on chromosome 1, seven on chromosome 3, three on chromosome 6 and two on chromosome 9. These genes belong to four families : NHE, ABC, ZIP and MATE genes. It is possible to alleviate mineral deficiencies and increase farmers’ returns using candidate common bean genotypes with high yield potential and high iron and zinc amounts in Lubero and Beni territories in North-Kivu province.