Key message: Intensive public sector breeding efforts and public-private partnerships have led to the increase in genetic gains, and deployment of elite climate-resilient maize cultivars for the stress-prone environments in the tropics. Maize (Zea mays L.) plays a critical role in ensuring food and nutritional security, and livelihoods of millions of resource-constrained smallholders. However, maize yields in the tropical rainfed environments are now increasingly vulnerable to various climate-induced stresses, especially drought, heat, waterlogging, salinity, cold, diseases, and insect pests, which often come in combinations to severely impact maize crops. The International Maize and Wheat Improvement Center (CIMMYT), in partnership with several public and private sector institutions, has been intensively engaged over the last four decades in breeding elite tropical maize germplasm with tolerance to key abiotic and biotic stresses, using an extensive managed stress screening network and on-farm testing system. This has led to the successful development and deployment of an array of elite stress-tolerant maize cultivars across sub-Saharan Africa, Asia, and Latin America. Further increasing genetic gains in the tropical maize breeding programs demands judicious integration of doubled haploidy, high-throughput and precise phenotyping, genomics-assisted breeding, breeding data management, and more effective decision support tools. Multi-institutional efforts, especially public–private alliances, are key to ensure that the improved maize varieties effectively reach the climate-vulnerable farming communities in the tropics, including accelerated replacement of old/obsolete varieties.

Lysine and tryptophan are two essential amino acids and these are deficit in maize grain thus posing the problem of nutritional deficiencies in the consumers. A wide range of deficiency symptoms like cognitive disorder, kwashiorkor disease, reduced appetite, impaired skeleton development, delayed growth and aberrant behaviour are associated with lysine and tryptophan deficiency. These amino acids are also important to cure the Pellagra disease. Researchers identified several mutants in maize especially opaque‐2 which are responsible for higher lysine and tryptophan contents. Few years later, it was observed that opaque‐2 mutant has several pleiotropic effects on maize grain and plant. Efforts of researchers are spanning over the period of four decades to develop quality protein maize (QPM). QPM is described as nutritionally superior maize with high lysine and tryptophan contents and desired kernel characteristics as compared to its normal maize counterparts. Biological value of QPM was almost equivalent to egg protein. Breeding of maize for quality protein is based on three genetic systems like opaque‐2 genetic system, endosperm modifier genetic system and associated gene systems. Keeping in view the importance of QPM, current review article is compiled to discuss the genetic basis, genetic systems and breeding strategies. Timeline for various events is also drafted like discovery of various mutants, several conventional and modern approaches for development and deployment of QPM varieties across the world. Despite its nutritional benefits, the rate of adoption of QPM is generally at low pace in the developing world and this review article discuss the challenges and potential opportunities for QPM adoption.

Prevailing vitamin A deficiency is a malnutrition repercussing retarded growth, weak immune system and night-blindness in human beings. Pro-vitamin A enriched maize hybrids could be a strategy for combating vitamin A deficiency, mostly prevailing in children and women of Nepal. With the objective to investigate superior pro-vitamin A enriched ‘bio-fortified’ maize cultivars, twice replicated experiments were laid out in α-lattice design over two consecutive growing seasons of 2019 and 2019/20 at the National Maize Research Program (NMRP), Rampur, Chitwan, Nepal. The results revealed that the difference among tested hybrids was glaring for all agro-morphological, yield, and yield components traits. Among the evaluated traits, days to 50% anthesis and silking, plant and ear height, numbers of kernel rows per cob, grains per row, and grain yield varied significantly among the tested maize hybrids. Effect of planting season was significant for grain yield where winter maize produced 32% higher grain yield than spring maize. HPO16-2, HPO49-3, HPO49-5, and HPO49-2 were the 38-61% high yielding ‘bio-fortified’ maize genotypes than normal hybrid check. Therefore, these hybrids might be the potential higher-yielding future pro-vitamin A enriched maize hybrids to resolve food insecurity, malnutrition, trade deficit on maize grains and specially to combat vitamin A deficiency in Nepal.

Zinc deficiency affects one third of the population worldwide, and vitamin A deficiency is a prevalent public health issue in Sub-Saharan Africa and South-Asia, including Nepal. Crop biofortification is the sustainable solution to these health—related problems, thus we conducted two different field trials in an alpha lattice design to identify zinc and provitamin A biofortified maize genotypes consistent and competitive in performance over the contrasting seasons (Season 1: 18 February to 6 July 2020 and Season 2: 31 August to 1 February, 2020/21). In our study, the performance of introduced maize genotypes (zinc—15 and provitamin A biofortified—24) were compared with that of the local check, focusing on the overall agro-morphology, yield attributes, yield, and kernel zinc and total carotenoid content. Zinc and total carotenoid in the tested genotypes were found in the range between 14.2 and 24.8 mg kg⁻¹ and between 1.8 and 3.6 mg 100 g⁻¹. Genotypes A1831-8 from zinc and EEPVAH-46 from provitamin A biofortified maize trial recorded kernel zinc and total carotenoid as high as 52.3, and 79.5%, respectively, compared to the local check (DMH849). The provitamin A genotypes EEPVAH-46 and EEPVAH-51 (total carotenoid: 3.6 and 3.3 mg 100 g⁻¹), and zinc biofortified genotypes A1847-10 and A1803-42 (20.4 and 22.4 mg kg⁻¹ zinc) were identified as superior genotypes based on their yield consistency over the environments and higher provitamin A and zinc content compared to the check. In addition, farmers can explore August sowing to harvest green cobs during December-January to boost up the emerging green cob business.