Читать книгу Dry Beans and Pulses Production, Processing, and Nutrition - Группа авторов - Страница 48

Dry beans are recognized as a nutrient‐dense food rich in protein, dietary fiber, folate, and minerals. Iron (Fe) and zinc (Zn) are two essential minerals for humans. While only small quantities are required in the diet, 7–27 mg Fe and 2–12 mg Zn daily, there are widespread deficiencies throughout the world. Two billion people globally suffer from iron deficiency (Wessells and Brown, 2012). An estimated 17.3% of humans worldwide are at risk for insufficient zinc intake (Maxfield and Crane 2020). Iron and zinc deficiencies are most common in people consuming diets rich in cereals and legumes with limited animal protein (Cordain 1999). Biofortification of staple crops, including dry beans, is one approach that has been taken to address these widespread micronutrient deficiencies. Biofortification efforts are largely facilitated by the international organization, Harvest Plus.

Fig. 2.7. Canned beans with differences in processing quality: (a) Navy beans with many splits and poor processing quality; (b) Navy bean with acceptable processing quality; (c) Black bean that appears brown following processing; and (d) Black bean that maintains black color following processing. (For color detail, please see color plate section.)

Source: Original images by author, K. A. Cichy.

Iron biofortification has been a major bean breeding initiative since 2003, primarily implemented through the International Center for Tropical Agriculture in collaboration with various national programs. HarvestPlus set iron biofortification targets at increases of at least 22 mg/kg above locally consumed varieties (Andersson et al. 2017). To date, at least 60 high iron bean varieties have been released in over 12 countries in eastern and southern Africa and Latin America (Saltzman et al. 2017; Beebe 2020). Breeding progress has been made largely through phenotypic selection for increased levels of raw seed iron concentrations. The large variability for iron and zinc levels in dry bean germplasm has facilitated breeding progress. Screening of the CIAT core collection of 1072 bean lines of Mesoamerican, Andean, and mixed‐origin beans has revealed genetic variability for seed Fe and Zn concentrations ranging from 34 to 96 mg/kg and 21 to 60 mg/kg, respectively (Islam et al. 2002). Iron concentrations as high as 152 mg/kg have been reported for some bean genotypes from race Chile (Paredes et al. 2009).

While there have been at least seven QTL studies published on the inheritance of iron and zinc, applying these to marker assisted selection has not proved to be worthwhile (Freyre et al. 1998; Blair et al. 2009, 2010, 2011; Cichy et al. 2009, 2014; Blair and Izquierdo 2012). Any one QTL typically only provides the potential for a few ppm increase in iron or zinc, and these small levels would easily be confounded with environmental variation. Levels of Fe and Zn in the seed are influenced by the environment, especially soil fertility levels (Cichy et al. 2009; White and Broadley, 2009; Katuuramu et al. 2021). Genomic selection may hold promise to improve breeding gains. Future work is also likely to be more directed to iron bioavailability, as opposed to iron concentration, to achieve the maximum nutritional benefits to the consumer (Katuuramu et al. 2021).