No abstract

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.

Vitamin A deficiency in humans is a widespread health problem. Quality protein maize (QPM) is a popular food rich in lysine and tryptophan, but poor in provitamin A (proA). Here, we report the improvement of an elite QPM inbred, HKI1128Q for proA using marker-assisted introgression of crtRB1-favourable allele. HKI1128 was one of the parental lines of three popular hybrids in India and was converted to QPM in our earlier programme. Severe segregation distortion for crtRB1 was observed in BC 1 F 1 , BC 2 F 1 and BC 2 F 2 . Background selection by 100 SSRs revealed mean recovery of 91.07% recurrent parent genome varying from 88.78% to 93.88%. Across years, introgressed progenies possessed higher mean β-carotene (BC: 9.22 µg/g), β-cryptoxanthin (BCX: 3.05 µg/g) and provitamin A (proA: 10.75 µg/ g) compared to HKI1128Q (BC: 2.26 µg/g, BCX: 2.26 µg/g and proA: 3.38 µg/g).High concentration of essential amino acids, viz. lysine (mean: 0.303%) and tryptophan (0.080%) in endosperm, was also retained. Multi-year evaluation showed that introgressed progenies possessed similar grain yield (1,759-1,879 kg/ha) with HKI1128Q (1,778 kg/ha). Introgressed progenies with higher lysine, tryptophan and proA hold immense potential as donors and parents in developing biofortified hybrids. K E Y W O R D Sbiofortification, lysine, provitamin A, quality protein maize, tryptophan, β-carotene hydroxylase

The enhancement of lysine and tryptophan in maize is so far basedon opaque2(o2) mutant, that along with the endosperm-modifiersled to development of Quality Protein Maize[QPM]. Though many mutants improving the endospermic protein quality were discovered, they could not be successfully deployed. Recently discovered opaque16 (o16)mutant enhances the lysine and tryptophan content in maize endosperm. In the present study, the influence of o16 on the endosperm modification was analyzed in four F2 populations, two each segregating for o16 allele alone and in combination with o2. The recessive o16o16 seed endosperm was found to be vitreousphenotypically similar to wild-O16O16. The mutant did not influence the degree of kernel opaqueness in o2o2 genetic background as opaqueness in o2o2/O16O16 and o2o2/o16o16 was similar. Grain hardness of o16o16 was comparable with the normal and QPM maize. The pattern of microscopic organization of proteinaceous matrix and starch granules, and zein profiling of the storage protein in o16o16 were found to be similar with normal maize endosperm, but distinct from the o2o2-soft genotype. The pattern in o2o2/o16o16 was unique and different from o2o2 and o16o16 as well. Here we demonstrated the effects of o16 on physico-biochemical characteristics of endosperm and report of o16 possessing negligible influence on kernel modification and hardness, which holds a great significance in maize quality breeding programme.

In the present study, two F 2 populations derived by crossing wild type-(CML533 and CML537) and o16-donor line (QCL3024) were raised and genotyped. The recessive o16o16 possessed nearly twofold more lysine (0.247%) and tryptophan (0.072%) in mutants, than wild type (0.125% lysine and 0.035% tryptophan) across populations. However, o16o16 showed wide variation for both lysine (0.111-0.376%) and tryptophan (0.027-0.117%) across populations, suggesting the role of modifier loci. The study did not show any significant correlation (r=0.14) between lysine and tryptophan, however some segregants with highlysine (>0.300%) and-tryptophan (>0.090%) were identified. Some of the segregants with o16o16 possessed comparable lysine and tryptophan with o2o2 genotypes. These o16o16 segregants may serve as novel genetic resource in the QPM breeding programme, and some of them can be used for enhancement of both lysine and tryptophan in place of o2 mutant. This is the first ever report of influence of o16 on accumulation of tryptophan in maize.