Dry bean biofortification with iron and zinc

Authors: Cichy, Karen; CHIU, CHRISTINA - Michigan State University; ISAACS, KRISTA - Michigan State University; Glahn, Raymond

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 1/2/2021
Publication Date: 3/10/2022
Citation: Cichy, K.A., Chiu, C., Isaacs, K., Glahn, R.P. 2022. Dry bean biofortification with iron and zinc. In: Kumar, Shiv, Dikshit, Harsh Kumar, Mishra, Gyan Prakash, Singh, Akanksha, editors. Biofortification of Staple Crops. Singapore. Springer. p. 225-270. https://doi.org/10.1007/978-981-16-3280-8_10.
DOI: https://doi.org/10.1007/978-981-16-3280-8_10

Interpretive Summary: Biofortification, the process of increasing the nutritional value of foods through plant breeding, has been used to develop dry bean cultivars with increased amounts of iron and zinc. Iron deficiency affects 2 billion people globally including >50% women and preschool children in developing countries and causes 20% of death in women during childbirth. An estimated 17.3% of humans worldwide are at risk for insufficient zinc intake. Dry bean germplasm exhibit a wide range of seed iron and zinc concentrations and biofortification of beans for maximum levels of these micronutrients is possible through plant breeding. Biofortification efforts to develop high iron bean varieties have been underway since the early 2000s. Germplasm diversity screenings have revealed multiple high iron sources to use as parental lines in biofortification breeding programs. To date, at least 60 high iron bean varieties have been released in over 12 countries in eastern and southern Africa and Latin America. Bean breeders have combined the high iron trait with other traits important to farmers, including seed yield, disease resistance, and abiotic stress tolerance. One human efficacy study has been conducted that has demonstrated a positive effect of biofortification on human iron status. Iron from beans can have very low bioavailability due to seed coat polyphenols and phytic acid present in the bean. Evidence from in vitro and animal studies suggest beans without inhibitory polyphenols and with promotor polyphenols would have higher iron bioavailability and thus deliver more Fe. Going forward, a greater focus should be placed on breeding beans with high iron bioavailability in addition to high iron and zinc concentration.

Technical Abstract: Dry beans, a nutrient dense dietary staple in Africa, Latin America and the Caribbean, deliver nutrients such as protein, minerals, and folate, which are often in short supply in other staples. Beans are relatively rich in iron and zinc, two micronutrients for which dietary deficiencies impact billions of people globally. Wide genetic variability in beans seeds, from ~ 34 to 96 mg kg-1 for iron and 21 to 59 mg kg-1 for zinc, led to the recognition that biofortification of beans for maximum levels of these micronutrients is possible through plant breeding. Biofortification efforts to develop bean varieties with seed iron concentrations approaching 90 mg kg-1 have been underway since the early 2000s. Iron and zinc levels in seeds are positively correlated with each other, and although iron has been the major focus of biofortification efforts, zinc is often evaluated alongside iron. Germplasm diversity screenings have revealed multiple high iron sources in cultivated Andean and Middle American beans as well as wild P. vulgaris and genotypes from closely related species P. dumosus, P. acutifolius, and P. parvifolius. Both seed iron and zinc are moderately heritable traits and breeding with high iron donor parents based on phenotypic selection has been successfully utilized to achieve genetic gains. To date, at least 60 high iron bean varieties have been released in over 12 countries in eastern and southern Africa and Latin America. Bean breeders have combined the high iron trait with other traits important to farmers, including seed yield, disease resistance, and abiotic stress tolerance. The application of genomic approaches in breeding high iron beans has been limited. While numerous seed iron and zinc QTL studies have been undertaken and a meta-analysis identified 12 meta-QTL, 8 of which are for both increased iron and zinc, there has not been much traction in incorporation of these QTL in breeding. Since iron and zinc are quantitative traits controlled by many small effect QTL, breeders have not found marker assisted breeding on single or multiple QTL worthwhile. A genomic prediction approach, in contrast, utilizes thousands of random markers throughout the genome, may be a promising strategy to apply to breeding high iron and zinc beans and is currently being explored. The prospect of using a transgenic approach to develop high iron and zinc beans is limited at this time due to challenges with plant regeneration and public acceptance of GMO beans, that may change in the future and there are many potential candidate genes. The future of biofortification of beans with iron must also look beyond a pure focus on increasing concentration, as this approach relies on the assumption that higher Fe yields delivers more absorbable Fe. To date, one human efficacy study has been conducted that has demonstrated a positive although slight effect of biofortification on human iron status. Regardless of concentration, iron from beans can have very low bioavailability due to seed coat polyphenols and phytic acid present in the cotyledons. Evidence from in vitro and animal studies suggest beans without inhibitory polyphenols and with promotor polyphenols would have higher iron bioavailability and thus deliver more Fe. Therefore, redefining biofortification to focus on both iron bioavailability and iron concentration simultaneously in breeding programs has the potential to deliver substantially more nutritional benefits to consumers. The introduction of varieties labeled as high iron beans in Africa and Latin America has largely been met with interest and adoption by farmers and consumers, due to strong promotion and the development of varieties with superior yield and disease resistance. Going forward in addition to focusing on iron bioavailability, a greater focus should also be placed on zinc.