Maize is a valuable source of food and feed worldwide. Maize endosperm protein is, however nutritionally poor due to the reduced levels of two essential amino acids, lysine and tryptophan. In this study, recessive opaque2 (o2) allele that confers enhanced endosperm lysine and tryptophan, was introgressed using marker-assisted backcross breeding into three normal inbred lines (HKI323, HKI1105 and HKI1128). These are the parental lines of three popular medium-maturing single cross hybrids (HM4, HM8 and HM9) in India. Gene-based simple sequence repeat (SSR) markers (umc1066 and phi057) were successfully deployed for introgression of o2 allele. Background selection using genome-based SSRs helped in recovering > 96% of recurrent parent genome. The newly developed quality protein maize (QPM) inbreds showed modified kernels (25-50% opaqueness) coupled with high degree of phenotypic resemblance to the respective recipient lines, including grain yield. In addition, endosperm protein quality showed increased lysine and tryptophan in the inbreds to the range of 52-95% and 47-118%, respectively. The reconstituted QPM hybrids recorded significant enhancement of endosperm lysine (48-74%) and tryptophan (55-100%) in the endosperm. The QPM hybrids exhibited high phenotypic similarity with the original hybrids for morphological and yield contributing traits along with responses to some major diseases like turcicum leaf blight and maydis leaf blight. The grain yield of QPM hybrids was at par with their original versions under multilocation testing. These elite, high-yielding QPM hybrids with improved protein quality have been released and notified for commercial cultivation, and hold significant promise for improving nutritional security.

Traditional yellow maize though contains high kernel carotenoids, the concentration of provitamin A (proA) is quite low (<2 μg/g), compared to recommended level (15 μg/g). It also possesses poor endosperm protein quality due to low concentration of lysine and tryptophan. Natural variant of crtRB1 (β-carotene hydroxylase) and lcyE (lycopene-ε-cyclase) cause significant enhancement of proA concentration, while recessive allele, opaque2 (o2) enhances the level of these amino acids. Development of biofortified maize enriched in proA, lysine and tryptophan thus holds significance in alleviation of micronutrient malnutrition. In the present study, marker-assisted stacking of crtRB1, lcyE and o2 was undertaken in the genetic background of four maize hybrids (HQPM1, HQPM4, HQPM5, and HQPM7) popularly grown in India. HP704-22 and HP704-23 were used as donors, while four elite QPM parents viz., HKI161, HKI163, HKI193-1, and HKI193-2 were used as recipients. CrtRB1 showed severe segregation distortion, while lcyE segregated as per the expectation. Recovery of recurrent parent genome (RPG) among selected backcross progenies ranged from 89 to 93%. Introgressed progenies possessed high concentration of proA (7.38–13.59 μg/g), compared to 1.65–2.04 μg/g in the recurrent parents. The reconstituted hybrids showed an average of 4.5-fold increase in proA with a range of 9.25–12.88 μg/g, compared to original hybrids (2.14–2.48 μg/g). Similar plant-, ear-, and grain- characteristics of improved versions of both inbreds and hybrids were observed when evaluated with their respective original versions. Mean lysine (0.334%) and tryptophan (0.080%) of the improved hybrids were at par with the original versions (lysine: 0.340%, tryptophan: 0.083%). Improved hybrids also possessed similar grain yield potential (6,301–8,545 kg/ha) with their original versions (6,135–8,479 kg/ha) evaluated at two locations. This is the first study of staking crtRB1-, lcyE-, and o2-, favorable alleles in single genetic background. The improved inbreds can be effectively used as potential donor for independent and/or simultaneous introgression of crtRB1, lcyE, and o2 in the future breeding programme. These biofortified maize hybrids, rich in proA, lysine and tryptophan will hold great promise for nutritional security.

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Sweet corn has recently experienced sharp rise in demand worldwide. Recessive sugary1 (su1) and shrunken2 (sh2) that enhances kernel sweetness have been abundantly used in sweet corn breeding. Analyses of genetic diversity among sweet corn inbreds assume great significance for their effective utilization in hybrid breeding. A set of 48 diverse sweet corn genotypes encompassing su1su1, sh2sh2 and su1su1/sh2sh2 types were analyzed using 56 microsatellite markers. A total of 213 alleles with mean of 3.8 alleles per locus were generated. Two unique-and 12 rare-alleles were identified. The average PIC and genetic dissimilarity was 0.50 and 0.73, respectively. Cluster analysis grouped the inbreds into three major clusters, with each of the su1su1-, sh2sh2-and su1su1/sh2sh2-types were broadly clustered together. Principal coordinate analyses also depicted the diverse origin of the genotypes. The study identified inbreds for synthesis of pools and pedigree populations to develop novel inbreds. The study led to the identification of prospective heterotic combinations in various genetic backgrounds (sh2sh2 9 sh2sh2, su1su1 9 su1-su1, su1su1/sh2sh2 9 su1su1/sh2sh2, sh2sh2 9 su1su1/ sh2sh2 and su1su1 9 su1su1/sh2sh2).

Vitamin A deficiency is one of the major health problems worldwide. Traditional yellow maize possesses very low provitamin A (proA) concentration in endosperm. The influence of rare alleles of β‐carotene hydroxylase (crtRB1) and lycopene epsilon cyclase (lcyE) genes capable of enhancing proA concentration was studied in four BC2F2 populations generated using subtropical inbreds and CIMMYT‐HarvestPlus lines. The occurrence of severe segregation distortion for crtRB1 gene was observed, while lcyE gene was segregated as per Mendelian ratio. Genotype with favourable allele of crtRB1 (CC) had a significant effect on β‐carotene (BC) (7.9‐fold), β‐cryptoxanthin (BCX) (twofold) and proA (5.5‐fold) accumulation, compared to unfavourable genotype (C+C+). Genotype with favourable allele of lcyE (LL) showed 2.1‐fold, 1.6‐fold and twofold significant enhancement in BC, BCX and proA, respectively, over unfavourable genotype (L+L+) in pooled analysis. Of the nine genotypes, double homozygote (CC/LL) had the highest mean BC (12.60 μg/g), BCX (4.44 μg/g) and proA (14.82 μg/g), and combined effect was significantly better than individual gene effects or any other combinations. The information generated here would be useful in designing strategy for proA enrichment in subtropical maize.

Waxy corn possesses 95-100% amylopectin, compared to 70-75% in normal maize, owing to mutation in gene encoding a granule-bound starch synthase I. Amylopectin is used as an ingredient in textile, adhesive and paper industries. Further, waxy green cob is popular as breakfast item in South Asia and an important constituent of diet in north-eastern states of India as well. We developed a series of waxy inbreds from diverse exotic sources and through introgression breeding. To characterize and unravel the genetic relationships, 24 diverse waxy inbreds were analysed using 77 SSRs distributed throughout the genome. The study generated a total of 203 polymorphic alleles, with a mean of 2.69 alleles per locus. A total of nine unique and 20 rare alleles were detected. The polymorphism information content ranged from 0.08 to 0.68 with an average value of 0.40. Molecular profiling suggested sufficient attainment of homozygosity among the inbreds. Jaccard's dissimilarity coefficient between pairs of genotypes varied from 0.26 to 0.83 which revealed the diverse nature of the inbred lines. Cluster analyses grouped 24 genotypes into three major clusters. Principle coordinate analysis based on SSR also depicted the diverse origin of the genotypes as per the pedigree more reliably than agro-morphological traits. These inbreds were also promising for various cob and grain characteristics including grain yield. The study identified a set of potential cross-combinations that can be planned to develop highly heterotic waxy hybrid combinations. This is the first report of development and characterization of waxy inbreds in India.

Maize grains are the important source of food and energy, but possess very low proA (< 2.5 µg/g) compared to target level of 15 µg/g set by HarvestPlus to alleviate VAD. Favorable allele having variation in 5' untranslated region (UTR) of () gene enhances concentration of proA in maize. To identify the sequence variation in 5' UTR of , a set of diverse 13 inbreds of indigenous and exotic origin was characterized for allelic constitution of. Inbreds possessed wide variation in proA (1.62-23.12 µg/g) with a mean of 9.64 µg/g. The proA in CIMMYT-HarvestPlus genotypes having favorable allele of was very high (22.28 µg/g), whereas the Indian inbreds with the same allele possessed very low proA (2.48 µg/g). Eight genotypes viz., HKI161, HKI163, HKI161-PV, HKI163-PV, HKI193-1-PV, HKI193-2-PV, HP704-22 and HP704-23 revealed the presence of favorable allele, while VQL1, DMRIL47, MGU-PV-123/C6, HKI193-1 and HKI193-2 showed the presence of unfavorable allele of gene. Sequence comparison of favorable allele of Indian (HKI161 and HKI163) and exotic genotypes (HP704-22 and HP704-23) revealed seven having three transitions ( and : G to A,: C to T) and four transversions (: C to G, : T to G,: G to C and : G to T). Four (: position 446, : position 458,: position 459 and : position 483) discriminated the low- and high- proA lines having favorable allele of. These hold significance in enrichment of proA in maize for marker development and their use in marker-assisted selection.

Prolificacy assumes significance for development of high‐yielding baby corn hybrids. “Sikkim Primitive” is a native landrace of North‐Eastern Himalaya, and is the highest prolific maize germplasm. So far, the genetics of prolificacy in “Sikkim Primitive” has not been deciphered. Here, a prolific inbred (MGU‐SP‐101) developed from “Sikkim Primitive” was crossed with four non‐prolific inbreds viz., LM13, BML7, HKI161 and HKI1128. Six generations (P1, P2, F1, F2, BC1P1 and BC1P2) of the crosses were evaluated at two locations during rainy season 2018. MGU‐SP‐101 possessed 2.50–3.78 ears per plant compared to 1.06–1.86 among non‐prolific inbreds. The variation for ears was the highest in F2s (1–8), followed by BC1P1 (1–7) and BC1P2 (1–5). The quantitative inheritance pattern of prolificacy with prevalence of non‐allelic interactions of duplicate epistasis type has been observed. Dominance × dominance effect was predominant over additive × additive and additive × dominance effects. Total number of major gene blocks ranged from 0.41 to 2.86, thereby suggesting the involvement of at least one major gene/QTL governing the prolificacy. This is the first report of genetic dissection of prolificacy in “Sikkim Primitive”.