Thesis Abstract

<p> One hundred and eighty-nine (189) wheat genotypes were evaluated in multi-environments (Tel-hadya (Syria), Dongola (Sudan) and Wadmedani (Sudan)) for heat tolerance from 2011 to 2012. Genomic mapping of the quantitative trait loci underlying heat tolerance in the crop was also performed. The field experiment was laid out in an alpha lattice design. The data obtained were subjected to restricted maximum likelihood (REML) for generation of best linear unbiased estimates (BLUEs). The heat tolerance study in the two seasons (early and late) in Tel-hadya, Syria showed that days to heading, days to maturity and grain filling duration, plant height and grain yield were significantly (p &lt;0.05) reduced in late season when compared with their performance in the early season. The grain loss due to heat stress in the late season compared to the early season was in the range of 58 to 88%.The effect of heat stress on days to heading, days to maturity and grain filling duration, plant height and grain yield of the crop varied across the sites (Late season in Tel-hadya, Dongola and Wadmedani). The decreased effect of heat stress was most pronounced in late season in Tel-hadya than in the two sites in Sudan. The Additive Main effects and Multiplicative Interaction (AMMI) estimates showed 20 top yielding genotypes in all the sites with a grain yield range of 2.593 t/ha in Gen135 tor 2.893t/ha in Gen117. In terms of their AMMI stability values ranking, Gen 60, Gen 68, Gen101, Gen155 and Gen118 were ranked first, second, third, fourth and fifth, respectively. The broad sense heritability estimates for grain yield ranged from 0.297 (Dongola) to 0.449 (Late season in Tel-hadya). Other traits like grain filling duration, plant height and one thousand kernel weight showed moderate to low broad sense heritability across the sites. The path coefficient analyses across the three sites showed that days to heading, canopy temperature and grain filling duration had reduced direct effect on the grain yield, while biomass and harvest index showed positive direct effect on the grain yield. Days to maturity showed negative direct influence on the grain yield in the late season in Tel-hadya, but positive direct effect was observed in the two environments in Sudan. The broad sense heritability of days to heading ranged from 0.804 (Wadmedani) to 0.908 (Late season in Tel-hadya), while days to maturity ranged from 0.68 (Dongola) to 0.793 (Late season in Tel-hadya). The structure analysis revealed that the wheat germplasm studied had seven sub-populations. The linkage disequilibrium (LD) analysis obtained showed that the LD decay was approximately at 25cM. The genome wide association mapping of the quantitative trait loci associated with heat tolerance showed that few markers were consistently detected in the three environments, while many were environment- specific. <br></p>

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