Editorial: Development of Healthy and Nutritious Cereals: Recent Insights on Molecular Advances in Breeding

Abstract

Editorial on the Research Topic Development of Healthy and Nutritious Cereals: Recent Insights on Molecular Advances in Breeding Worldwide more than 2 billion people are affected by micronutrient deficiencies and most of them are residing in the developing countries of Asia, Africa and Latin America (Kennedy et al., 2002). Malnutrition is linked with heavy dependence on monotonous cereal staples without much dietary diversification or nutrient supplementation. Even though significant efforts have been made over the last six decades to improve production and productivity in most food crops, it lacked associated nutritional improvement (Bouis and Welch, 2010). So, the modern varieties do not have enough variability for several nutrients, making poor rural populations vulnerable to micronutrient deficiencies. More than two dozen mineral elements, vitamins, antioxidants, and health beneficial compounds must be supplied in optimal quantities daily for normal growth and development of humans. Biofortification of cereals with elevated levels of essential micronutrients, vitamins, and reduced levels of toxic elements help to address malnutrition and is a cost-effective approach in reaching target groups, especially rural populations (Bouis and Saltman, 2017). The sustainable development goals and the Lancet Commission Report have emphasized the need for promoting nutritious diets to eradicate malnutrition (Willet et al., 2019; https://sustainabledevelopment.un.org). Among these, deficiencies of iron (Fe), zinc (Zn), and vitamin A are major global health problems. As successful examples, one high Fe rice and several high Zn rice varieties have been successfully released for commercial cultivation (Palanog et al., 2019). Presently we have a better understanding of the genetic, physiological, and molecular basis, as well as the influence of environmental factors on nutrients accumulation in cereal grains (Swamy et al., 2016; Garcia-Oliveira et al., 2018; Ludwig and Slamet-Loedin, 2019). However, there is a need to integrate our understanding to achieve the goals of biofortification and review the current progress and the prospects for nutritious crops. In this Research Topic, we selected manuscripts on various aspects of nutritional improvement in cereals. Fourteen articles published in our special editorial topic, five of them provided updated review of cereals nutritional enhancement, and nine of them were original research articles on understanding the molecular basis of different grain nutrients and grain quality traits in cereals. Focusing on improving grain protein quality, Chandran et al. successfully pyramided Lysine, Tryptophan, and Provitamin A into Maize varieties based on opaque-2 and β-carotene through marker assisted selection (MAS). The improved lines possessed high lysine, tryptophan, and β-carotene content, but they had only slight yield reduction. Even though these lines can be used as genetic resources for maize improvement, they are not yet commercially viable, since successful biofortified crops should have similar or even higher yield along with the other desirable traits. Also aiming at improving protein content in rice, Jang et al. identified multiple genomic regions responsible for amino acid content (AAC) and protein content (PC). They identified two novel loci qAAC6.1 and qAAC7.1 and several transgressive segregants for both traits. These loci can be used for quantitative trait loci (QTL) pyramiding programs to develop rice lines with high protein content. It is quite interesting to note pleotropic effect of heading-date genes on protein content of rice. Xie et al. reported that in three nearly isogenic lines (NIL), the rice florigen genes RFT1 have a strong negative effect on the amino acids content governed by the Zhenshan97 allele with the genomic region consisting of 14 QTLs located in proximity to Hd3a. Bhuvaneswari et al. characterized 93 aromatic Chakhao rice germplasm from Manipur province of India. Wider variations were observed for the agro-morphological, grain quality and nutraceutical traits. The total anthocyanin content ranged from 29.8 to 275.8 mg.100g⁻¹ DW, while total phenolics ranged from 66.5 to 700.3 mg GAE.100g⁻¹ DW. The germplasm with higher levels of anthocyanin compounds such as cyanidin-3-O-glucoside (C3G) and peonidin-3-O-glucoside (P3G) are useful for improving the antioxidant properties in rice. Focusing on micronutrient biofortification, Ashokkumar et al. comprehensively reviewed recent advances in breeding for improved folate, provitamin A, and carotenoids content in rice, wheat, maize, and pearl millet. They discussed in detail the genetic variation, trait discovery, genes/QTL identification for nutritional traits and their introgressions into elite genetic backgrounds. Prasanna et al. carried out a detailed global analysis of molecular breeding for nutritional improvement in maize, a species where systematic efforts have been made to develop and deploy cultivars biofortified with quality protein maize (QPM), provitamin A, and kernel zinc. The limited germplasm characterization, lack of genetic variability, and diagnostic markers for some of the mineral elements is a constraint for breeding. Broadening the genetic base through exploitation of landraces and wild species, use of genomics technologies, market-driven breeding strategies, strengthening of seed systems, and collaborative interdisciplinary efforts were emphasized. Genetic Engineering (GE) and Genome Editing (GEd) technologies are the way forward for improving the traits with no variability and to achieve the target levels of multiple nutrients in cereals. Babu et al. characterized 40 rice genotypes for agronomic, yield and micronutrient traits. They identified stable high Zn donor lines and genome wide association analysis resulted in identification three loci on...