Bread wheat (Triticum aestivum L.) occupies the third position after rice and maize in terms of production and the second position after rice in terms of consumption in Nepal. In 2019–20, wheat was grown on 707,505 ha, with production and productivity of 2,185,288 mt and 2.92 mt/ha, respectively (MOALD, 2019). More than 1 million farmers collectively produce around two million tons of wheat each year, which is consumed as chapatis, rotis, momo dumplings, and noodles made from the grain. Wheat grain is known to be low in essential micronutrients, contributing to poor nutrition (CIMMYT, 2021). Despite the improvement in food availability, malnutrition is still a major challenge in developing countries like Nepal. Micronutrient malnutrition is severe in the Nepalese population. There is an 8.1% prevalence of undernourishment, 37.1% of stunting, 11.3% of wasting, and 30.1% of people are underweight (FAO, 2017). About 41% of women of reproductive age and 53% of children in Nepal were found to be anemic (Ministry of Health, 2017). More than three-quarters of apparently healthy women were found to be zinc deficient in Bhaktapur, Nepal (Chandyo et al., 2009).

In countries with a high incidence of micronutrient deficiencies, cereal-based foods represent the largest proportion of the daily diet (Bouis and Welch, 2010). About 2–3% of the GDP (US$ 250–375 million) is lost every year in Nepal on account of vitamin and mineral deficiencies (World Bank, 2012). Trace elements like zinc and iron have been shown to play key roles in supporting the human immune system and reducing the risk of infections (Calder, 2020). Moreover, intellectual ability is affected by a deficiency of iron and zinc (Mari et al., 1995; Falkingham et al., 2010). The diets of over two-thirds of the world's population reportedly lack one or more essential mineral elements: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I), and selenium (Se), and this can be remedied through biofortification (White and Broadley, 2009). To overcome micronutrient malnutrition, the development of biofortified crop varieties with the ability to harvest more essential nutrients from the soil is a low-cost, sustainable solution (Bouis and Welch, 2010; Bouis et al., 2011).

Cereals—mainly wheat, rice, and maize—are a major source of dietary energy, protein, and micronutrients for the resource poor people in Nepal. Wheat is a high-potential crop that can assist in reducing micronutrient-related malnutrition; this reduction can be enhanced through the integration of agronomic practices and the delivery of genetically improved micronutrient-rich wheat varieties that have been developed by breeding common cultivars with wild wheat that is rich in zinc and iron. In respect of wheat, wild wheat varieties Triticum dicoccoides, Aegilops tauschii, Triticum monococcum, and Triticum boeticum are among the most promising sources of high Fe and Zn, with high genetic variation for micronutrients, whereas improved wheat is low in micronutrients (Cakmak et al., 2000, 2004). Therefore, the biofortification breeding program at CIMMYT introgressed high Zn and Fe progenitors into elite wheat lines and successfully introduced novel QTLs for grain Zn and Fe in elite wheat lines with better yield potential, stress tolerance, and elevated grain Zn/Fe concentration (Velu et al., 2014).

Wheat breeding in Nepal has been mainly focused on grain yield, but the nutritional quality of wheat is a less-explored aspect. As the growing global momentum on the nutrition security, breeding for better nutrition has gained momentum in Nepal as well. Since 1960, Nepal has released 52 bread wheat and 2 durum wheat varieties. Beginning in 2015, the Nepal Agricultural Research Council (NARC) has introduced and initiated testing CIMMYT-developed biofortified wheat genotypes in different locations in the country. The fast-track testing, identification, release, multiplication, and dissemination of varieties have now been identified as one of the main options available for Nepalese breeders and agricultural scientists to combat hidden hunger. In this article, we evaluate different biofortified wheat lines developed by CIMMYT for zinc concentration, iron concentration, and several agronomic traits for 4 years at different national research centers, with the aim of selecting competitive national and region-specific best-performing biofortified wheat lines.

Multi-environment testing is a crucial part of wheat breeding programs to identify stable and high-yielding lines with better nutritional quality. Therefore, this study showed variable responses of a set of new biofortified wheat genotypes across contrasting environments in Nepal. This is the first proof-of-concept results from multi-environment testing of high Zn biofortified wheat lines in Nepal across diverse growing environments. This study was conducted in a fast-track mode where the high zinc wheat trials from CIMMYT, Mexico introduced into Nepal which were grown across multi-environment to identify stable and high yielding genotypes which combine high yield, high Zn and Fe, and disease resistance traits in the target environments of Nepal.

The multi-environment data showed moderate heritability of grain yield, grain iron concentration, and grain zinc concentration in the 8th HPYT and these traits have the ability to transmit to the next generation. Grain yield had low heritability in both years, while grain iron concentration had moderate heritability in the 6th HPYT and low heritability in the 7th HPYT. The difference in the result might be due to various factors including different genetic materials used and different environmental conditions. Heritability for grain zinc concentration was moderate in all 3 years. Badakhshan et al. (2013) reported high heritability of grain zinc concentration. Despite the moderate heritability for grain Zn, the genotype × environment interaction specifically environmental factors such as available soil Zn, pH, CaCO₃, and soil organic matters plays a major role in terms of grain Zn accumulation.

Among the locations, the grain iron concentration in Doti was found to be higher than in the other locations. This might be because of the higher soil iron concentration in Doti than in the other locations. However, the grain iron and zinc concentrations were very low in Surkhet compared with the other locations, perhaps because of the low iron and zinc concentrations in the soil in Surkhet.

The highly positive correlation of the number of tillers per square meter with grain yield shows that grain yield could be increased by increasing the number of tillers. Indirect selection for higher-grain-yielding genotypes could be done based on the number of tillers per square meter trait. Similar results were reported by Sharma (1995); Okuyama et al. (2004), and Waqar-Ul-Haq et al. (2010), while Kashif and Khaliq (2004) reported a highly negative correlation between grain yield and fertile tillers.

The positive correlation between the grain iron and grain zinc concentrations shows that these two traits can be improved simultaneously in a breeding program. This finding is in line with the studies by Morgounov et al. (2007); Velu et al. (2012); Liu et al. (2014); Chatrath et al. (2018), and Ghimire et al. (2019).

The negative correlation of grain iron with grain yield shows that increasing grain yield will decrease the grain iron concentration. Liu et al. (2014) and Chatrath et al. (2018) also reported a negative correlation of grain yield with grain iron. This might be due to the dilution effect (Oury et al., 2006; Liu et al., 2014). The positive correlation between grain yield and grain zinc shows that an increase in grain yield increases grain zinc concentration; Chatrath et al. (2018) also reported a similar relationship, although Liu et al. (2014) had reported a negative correlation of grain yield with grain zinc concentration.

The grain iron and zinc concentrations were positively correlated with plant height. This shows that taller genotypes yield more grain iron and zinc than dwarf ones. This might be explained by taller genotypes possibly having a lower dilution effect. According to Velu et al. (2017), the increase in grain zinc and iron in taller genotypes might be because of their larger kernel size and lower yield levels. However, Morgounov et al. (2007) reported a significant negative correlation of grain iron and zinc concentrations with plant height. The nutritionally-biofortified CIMMYT derived wheat genotypes evaluated in this study contain high yield and increased grain Zn over the local checks. This study led to the identification and release of five biofortified wheat varieties in Nepal. The new varieties including Zinc Gahun 1, Zinc Gahun 2, Bheri-Ganga, Himganga, and Khumal-Shakti were direct selections from the CIMMYT derived HarvestPlus Yield Trials which were evaluated across environments in Nepal. These varieties are replacing old disease susceptible varieties in Nepal and the fast-track seed multiplication and dissemination is underway to reach more farmers in the coming years.

Large variations were found among the genotypes for grain yield, grain iron, and zinc among high zinc elite lines evaluated across environments in Nepal during the 4 years of testing, showing the remarkable potential for improving grain yields and grain iron and zinc concentrations. Spatial variability affected grain yields as well as grain iron and grain zinc concentrations. However, the multi-environment testing identified stable and promising genotypes suitable for diverse environments of Nepal ranging from hilly mountains to terai regions. The cluster analysis identified promising genotypes with high yields along with high grain zinc and iron concentrations which can be used in further breeding programs. Grain iron and zinc concentrations can be improved simultaneously during wheat breeding for better nutritional quality. Indirect selection for higher yield can be done based on a higher number of tillers per m².

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/Supplementary Material.

DT thapa-field research, data analysis, and conceptualization of manuscript write up. MSu field research, data analysis, and manuscript write up. RY, BJ, BA, KS, PM, KP, SGu, SGh, NG, and NA field research and data generation at different research stations of Nepal agricultural research council. MSa data analysis and manuscript write up. VM grain zinc and iron analysis. AJ, RS, and VG providing germplasm for research and review and final manuscript edit. All authors contributed to the article and approved the submitted version.

This research was supported by a grant from HarvestPlus Challenge Program, the Bill and Melinda Gates Foundation [INV-003012] and co-funded by the Foreign, Commonwealth and Development Office (FCDO) of the UK Government to CIMMYT.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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