Malnutrition has emerged as one of the major health problems worldwide. Traditional yellow maize has low provitamin-A (proA) content and its genetic base in proA biofortification breeding program of subtropics is extremely narrow. To diversify the proA rich germplasm, 10 elite low proA inbreds were crossed with a proA rich donor (HP702-22) having mutant crtRB1 gene. The F2 populations derived from these crosses were genotyped using InDel marker specific to crtRB1. Severe marker segregation distortion was observed. Seventeen crtRB1 inbreds developed through marker-assisted pedigree breeding and seven inbreds generated using marker-assisted backcross breeding were characterized using 77 SSRs. Wide variation in gene diversity (0.08 to 0.79) and dissimilarity coefficient (0.28 to 0.84) was observed. The inbreds were grouped into three major clusters depicting the existing genetic diversity. The crtRB1-based inbreds possessed high β-carotene (BC: 8.72μg/g), β-cryptoxanthin (BCX: 4.58μg/g) and proA (11.01μg/g), while it was 2.35μg/g, 1.24μg/g and 2.97μg/g in checks, respectively. Based on their genetic relationships, 15 newly developed crtRB1-based inbreds were crossed with five testers (having crtRB1 gene) using line × tester mating design. 75 experimental hybrids with crtRB1 gene were evaluated over three locations. These experimental hybrids possessed higher BC (8.02μg/g), BCX (4.69μg/g), proA (10.37μg/g) compared to traditional hybrids used as check (BC: 2.36 μg/g, BCX: 1.53μg/g, proA: 3.13μg/g). Environment and genotypes × environment interaction had minor effects on proA content. Both additive and dominance gene action were significant for proA. The mean proportion of proA to total carotenoids (TC) was 44% among crtRB1-based hybrids, while 11% in traditional hybrids. BC was found to be positively correlated with BCX (r = 0.68) and proA (r = 0.98). However, no correlation was observed between proA and grain yield. Several hybrids with >10.0 t/ha grain yield with proA content >10.0 μg/g were identified. This is the first comprehensive study on development of diverse proA rich maize hybrids through marker-assisted pedigree breeding approach. The findings provides sustainable and cost-effective solution to alleviate vitamin-A deficiency.

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Silk is a high-value, low-volume product, produced by an important insect commonly known as the silkworm. Sericulture serves as a source of livelihood for farmers besides being an important source of economy for many countries including India. Sustainable production of premium silk depends on continuous production of quality foliage as feed for silkworms obtained from host plants. The production of silk is significantly hampered when host plants are subjected to biotic and abiotic stresses. The foliage harvest could be enhanced when these constraints are efficiently managed by the development of stress-resistant host cultivars. Improved stress-resistant cultivars have been developed using conventional breeding strategies and used in commercial cultivation. However, the highly heterozygous genetic nature of the hosts makes it difficult to understand the inheritance and expression of these quantitative traits. Adoption of appropriate conventional breeding strategies along with genomics tools such as genome-wide association studies, transcriptomics, proteomics, metabolomics and advanced OMICS approaches could prove handy in the development of improved and stress-resistant cultivars. Deeper understanding of the mechanism of tolerance to various stress is required in breeding for improved cultivars. The number of stress-tolerant cultivars is scanty and therefore, holistic management of these stresses through an inter-disciplinary approach could be the most suitable strategy. Adoption of appropriate cultural practices and control measures is necessary for sustainable production under stress regimes. This comprehensive review holds great importance in improving silkworm host cultivation and to researchers in the field of sericulture.