Browsing by Author "Sharma, Santosh"

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    Increasing the Genetic Diversity of U.S. Northern Corn Belt Hybrids with Tropical and Temperate Exotic Germplasm
    (North Dakota State University, 2011) Sharma, Santosh
    The NDSU EarlyGEM or the Early Germplasm Enhancement of Maize (Zea maize L.) is a long term incorporation program designed to increase the genetic diversity of short season hybrids. Starting in 1999, exotic GEM breeding crosses derived from temperate accessions: BR52051, CH05015; tropical accessions: SCR01, CUBA17, FS8B; and tropical hybrid DKB844 along with late checks: B73, Mo17, and Iowa Stiff Stalk Synthetic (BSSS), were adapted to short-seasons and incorporated via a modified backcross (BC) procedure. This study was designed to assess the genetic diversity in exotic derived BC1:S1 lines and their competitive potential as sources of new and unique hybrids. Useful genetic diversity was evaluated with testers belonging to opposite heterotic groups, LH176 representing a non stiff stalk and TR3026 x TR2040 a stiff stalk testers and were tested in five North Dakota environments over two years (2009 and 2010). All the traits showed highly significant (P<0.01) differences across genotypes except root and stalk lodging. Among 236 experimental testcrosses, 64 were statistically not different (LSD, 0.05) to industry hybrids for grain yield. BC derived lines from BR52051, CHO5015, DKB844 showed diverse alleles for low grain moisture (below 87 relative maturity days) at harvest and high grain yield. SCR01, BR52051, CHO5015 and CUBA117 derived lines produced hybrids with high grain oil (4. 9% vs. 4.1%) and grain protein (10.4% vs. 9.1%) contents compared to top checks. The results showed that the exotic incorporations are the sources of unique new alleles for early maturing maize not present in existing US germplasms (e.g. B73, Mo17, and BSSS). Even though each exotic cross was unique to integrate diverse alleles, utilizing multiple unique exotic crosses for incorporation showed large variation for specific traits. Phenotypic correlations of traits showed grain moisture played the most important role for short season hybrid development. Exotic incorporation through NDSU EarlyGEM has shown a new way of breeding early maturing maize keeping the breeding program open and genetic diversity high.
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    Quantitative Genetics of Drought Resistance in Early Maturing Maize (Zea Mays L)
    (North Dakota State University, 2015) Sharma, Santosh
    Drought stress is paramount in limiting worldwide maize (Zea mays L.) production and productivity. In addition, drought has limited expansion of maize production to marginal conditions in areas including western North Dakota (ND) and eastern Montana (MT) where short-season drought tolerance is essential. The development of new cultivars in these dryer areas has been slow in part due to unavailability of reliable field phenotyping methods for breeding purposes and existing insufficient information on the genetic control of agronomic and grain quality attributes under drought stress. Our objectives were (1) to investigate root and stalk quantitative traits as novel field phenotyping methods for drought resistance, (2) to examine the variability and genetic control of agronomic and grain compositional attributes across soil moisture regimes, and (3) to discuss implications of findings for developing new maize cultivars under drought stress environments. Ninety-four partial diallel crosses including 47 diverse maize inbred parents and checks were tested in 12 water stress (WS), well-watered (WW) and random drought (RDT) environments in 2013 and 2014. A new high throughput non-destructive maize phenotyping method for drought tolerance is proposed, including the quantitative traits visible brace root number count and its spread width. Additive gene action was predominant in most of the agronomic and grain quality attributes, while non-additive gene action was important for grain yield, root lodging, stalk diameter, and grain oil content. Root and stalk lodging were negatively associated (P < 0.01) with brace root count and spread width. The estimates of narrow sense heritability were higher for brace root spread width (0.23) and number of brace root count (0.24) as compared to grain yield (0.06) and root lodging (0.1) in WS environments. High relative narrow sense heritability (> 0.40) was estimated for grain compositional attributes except for grain protein and amino acids. Stress environments were largely associated for grain oil and total and extractable starch contents (> 0.60). A reciprocal recurrent selection program can be vital to develop cultivars with high grain yield and quality in drought stress.