Harnessing genetic diversity in wheat to enhance grain nutrition and yield for biofortification breeding.

Abstract

Background: Iron (Fe) and zinc (Zn) deficiencies affect more than two billion people globally. Moreover, phytic acid (PA), an essential phosphorus storage molecule, acts at the same time as an inhibitor of Fe and Zn, forming insoluble complexes; thus, there is a need for balanced compositions of these three substances. Biofortification breeding in staple food crops to combat malnutrition is a straightforward approach. However, evaluating the genetic diversity of the gene pool and the trade-offs between grain nutrients and morphophysiological and yield traits is important. Grain colour is influenced by nutrient composition, including that of minerals such as iron. Therefore, diverse germplasms of 813 genotypes, including Triticum aestivum, Triticum durum, and Triticosecale, were screened for grain colour. A core collection of 26 genotypes was evaluated for the micronutrient concentration over two growing seasons. Further, five contrasting genotypes were chosen to estimate the bioavailability of Fe and Zn.

Results: High diversity of grain Fe (31-54 mg kg^-1) and Zn (15-38 mg kg^-1) was found among the genotypes. High heritability estimates (> 80%) and genetic advance as a percentage of the mean (GAM; > 20) for quality traits indicated strong genetic control supported by a strong positive correlation between grain colour and micronutrients. For morphophysiological and yield traits, moderate heritability and GAM indicated that genotypic and environmental factors contributed to the inheritance of these traits. Overall, the Fe and Zn concentrations and their bio-availabilities were highest for bread wheat (34-52 mg kg^-1 Fe, 25-37 mg kg^-1 Zn, 5 PA:Fe and 7 PA:Zn molar ratios), followed by Triticosecale (44-46 mg kg^-1, 27-30 mg kg^-1 Zn, 6 PA:Fe and 9 PA:Zn molar ratios) and durum wheat (36-48 mg kg^-1 Fe, 24-31 mg kg^-1 Zn, 8 PA:Fe and 13 PA:Zn molar ratios).

Conclusions: The desirable genotypes (E-1 coded as TA87, for example) with characteristics of amber/yellow grain colour, high grain yield (5020 kg ha^-1), Fe (51 mg kg^-1), Zn (37 mg kg^-1) and low PA:Fe and Zn ratios (5.3 and 7.4, respectively) should be selected for future breeding programs. The study paves the way to simplify the biofortification breeding efforts by identifying (i) grain colour as a potential morphological marker for Fe, (ii) enhanced bioavailability in bread wheat compared to durum and triticale, (iii) mineral concentration and yield can be improved simultaneously to combat malnutrition without yield penalty. However, the association of grain nutrients and colour should be evaluated in diverse environments to assess stability and heritability of the marker trait as well as nutrients. This information will aid in the selection of suitable breeding approaches for biofortification and yield enhancement for improved food security.