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To improve the nutritional quality of maize, introgression of the opaque-2 (o2) trait to normal maize lines is essential. The QPM donors used in present study were; CML 161, DMR QPM 58, CML 176 and CML 141 whereas, normal maize inbreds were CM 212, V338, V361, V336, V341, V351, CM141 and V335. All the selected lines were subjected to parental polymorphism survey between non QPM and QPM lines using CIMMYT based three SSR primers viz., phi057, umc1066 and phi112. Two markers viz., phi 057 and umc1066 exhibited co-dominant reaction while phi 112 was dominant in nature. Finally two combinations CM141 × CML 176 and V335 × CML 161 were considered for conversion programme. Foreground selection was exercised using opaque-2 specific marker umc1066 in BC1 and BC2 generations while background as well as foreground selection was exercised in BC2F1 generation to recover the genome of recurrent parent up to extent of 82.5 to 98.5 percent with the help of 98 SSR markers distributed across the genome. The tryptophan concentration in endosperm protein was significantly enhanced in all the three classes of kernel modification viz., less than 25%, 25-50% and more than 50% opaqueness. So, the converted maize lines had almost twice the amount of Lysine and Tryptophan than normal maize inbreds.

Combining ability and heterosis for different morphological and quality traits were studied under three environments using 10 inbred lines, 45 single cross hybrids and three commercial hybrids as checks at SHIATS, Allahabad, India during monsoon, 2014. Ten simple sequence markers (SSR) were used to quantify genetic distance, which was further used to analyse relationship with combining ability and heterosis in single cross hybrids. Pearson’s correlation and linear regression were analysed to identify the important factors determining heterosis and per se performance of hybrids. Variances due to general combining ability (GCA) and specific combining ability (SCA) were found to be significant for all but their interaction with environments were significant only for morphological traits. SSR marker bnlg 1523 was found as a potential marker for discriminating maize inbred lines at molecular level as it has high PIC (0.71) and gene diversity (0.74). Significant positive association were recorded for per se performance with mid parent heterosis (MPH) and best parent heterosis (BPH) along with high coefficient of determination for days to 50% tasseling, days to 50% silking, days to 50% maturity, seed fill duration, number of grain rows/cob, number of grains/row, 100 seed weight, grain yield/plant, starch, protein and oil content. Moreover, F1’s grain yield showed significant positive relationship with varying degree to MPH, BPH and SCA of hybrids in all environments. Correlation of SSR based genetic distance with heterosis and combining ability was significant positive for oil content but non-significant positive or negative for other traits indicating the significant role of SSR based genetic distance for determining heterosis and combining ability of oil content. Besides, SCA was found as a key determinant for heterosis and mean performance of all morphological and quality traits.

The mechanism of resistance in maize to the stored product insects such as the maize weevil (MW), Sitophilus zeamais Motsch and the larger grain borer (LGB), Prostephanus truncatus Horn has been investigated in relation to secondary chemistry and other biochemical and physical characteristics of maize genotypes. Performance parameters of weevils (number of eggs laid, number of progeny, Dobie index, grain consumption) were negatively and significantly correlated (r = -0.8, P = 0.05) to the most abundant phenolic of grain, E-ferulic acid. With P. truncatus, the weight loss of grain also showed a negative correlation with E-ferulic acid while percent damage of kernels by insects was negatively correlated to p-coumaric acid. These phenolic acids were found in highest concentration in the pericarp and cell walls of the endosperm by fluorescence microscopy. Phenolic acid content was also found to correlate strongly with hardness of the grain, which may be related to the mechanical contributions of phenolic dimers to cereal cell wall strength. In the aleurone layer phenolic acid amines have been detected that have toxic effects on insects.

The genetics of maize grain resistance to the maize weevil, Sitophilus zeamais Motsch., infestation was analyzed by means of additive linear models which considered genetic contributions of maize caryopsis through embryo, endosperm and pericarp. Specific traits associated with these grain tissues were: phenolic acids (pericarp, embryo), proteinase inhibitors (endosperm, embryo) and hardness of grain (pericarp, endosperm, embryo). The susceptibility of the grains to weevil infestation was measured by feeding, consumption and reproductive activities of insect populations. Inbred lines of quality protein maize (QPM), contrasting in resistance to maize weevil infestation, were used for the genetic analysis of resistance. Concentrations of phenolic acids in grain have a highly negative and significant correlation with indices of susceptibility of maize to the maize weevil. However, the correlation between susceptibility of grain and contents of proteinase inhibitors in the endosperm is low, although negative and significant. Resistance of pericarp-testa to compression forces was the only rheological trait of grain inversely correlated with susceptibility of maize to colonization by maize weevils, but neither the correlation coefficient nor the significance was high. The negative relationship of biochemical and biophysical traits of maize grain with feeding and reproductive activities of insects on the grain, suggests detrimental effects of these grain characteristics on the colonization success of insect populations. The estimated genetic parameters for additivity of endosperm and dominance of pericarp associated with the expression of phenolic acid concentration in the grain were highly significant and inversely correlated to estimated susceptibility parameters of genetic action. Estimated parameters of genetic action for proteinase inhibitor concentration in endosperm were nonsignificant,

The improvement of protein quality in maize so far has been based on recessive opaque2 (o2) mutant that along with endosperm-modifiers led to development of quality protein maize (QPM). Recent discovery of nutritional benefits of recessive opaque16 (o16) mutant was of immense significance for further improvement of protein quality. In the present study, o16 was introgressed into o2-based parental inbreds (HKI161, HKI193-1, HKI193-2 and HKI163) of four commercial QPM hybrids (HQPM-1, HQPM-4, HQPM-5 and HQPM-7) released in India, using marker-assisted backcross breeding. Background selection led to high recovery of recurrent parent genome (RPG) to maximum of 95%, and introgressed progenies showed considerable phenotypic resemblance for plant-, ear-and grain-characteristics to their respective recurrent parents. Selection of markers for o2 and o16 led to development of pyramided lines (o2o2/o16o16) that possessed as high as 76% and 91% more lysine and tryp-tophan over the recurrent parents, respectively. Reconstituted hybrids showed an average enhancement of 49% and 60% in lysine and tryptophan over the original hybrids, with highest enhancement amounting 64% and 86%, respectively. This is first report of enhancement of both lysine and tryptophan by o16 in maize genotypes adaptable to sub-tropics. Moderate variation in lysine and tryptophan was also observed in pyramided lines. Multi-location evaluation of reconstituted hybrids revealed similar grain yield and attributing traits to their original versions. This study signified the role of o16 as supplementary to o2 for nutritional quality enhancement in maize, and improved elite inbreds and hybrids developed here hold great significance in maize biofortification programme.

Biofortification of a natural snack like popcorn is important for improved nutrition and health of children and adults. This study was aimed at introgressing opaque-2 gene, a high lysine/tryptophan gene into the genetic background of popcorn. Field experiments were carried out at the Teaching and Research Farm (TRF) of the Federal University of Technology, Akure (FUTA) during the 2016 dry and wet season while biochemical and molecular analyses were carried out in the Biochemistry Laboratory, FUTA and Bioscience Laboratory, International Institute of Tropical Agriculture (IITA) respectively. Nine parental genotypes were used which comprised three popcorn maize varieties and six Quality Protein Maize (QPM) varieties. F1s were developed by crossing the parent genotypes using North Carolina mating design I. The F1s developed were evaluated for gene action and heritability. The ten F1 were also advanced to F2 by self pollination. Segregated kernels from each genotype were screened on the light box. Kernel modification 2 (25% opaque) and 3 (50% opaque) were selected. Selected kernels were analyzed biochemically for protein and tryptophan contents. The allelic state of opaque-2 gene in the selected F2s was determined using SSR marker phi 112. Additive gene effect and narrow- sense heritability were found to be most important for traits such as days to 50% flowering, days to 100% flowering, ear height and 100 grain weight. Protein and tryptophan contents and quality index for unpopped and popped F2 of crosses of QPM and popcorn were significantly higher than popcorn checks. Protein and tryptophan contents and quality index of F2s of crosses of QPM and popcorn reduced significantly when subjected to heat treatment. Unpopped protein content, unpopped tryptophan content and popped tryptophan content were highly correlated with one another. Phi 112 SSR marker showed dominant pattern of polymorphism, amplifying DNA fragments between 154bp and 160bp for the ten F2.