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ThesisItem Open Access Genetic diversity and effects of selective intermating on genetic variability in bread wheat (Triticum aestivum L. em. Thell)(CCSHAU, 2018) Preeti; Panwar, I.S.The present investigation “Genetic diversity and effects of selective intermating on genetic variability in bread wheat (Triticum aestivum L. em. Thell)” was conducted to evaluate 75 bread wheat genotypes to assess magnitude of genetic diversity among wheat germplasm lines for grain yield, its components and quality traits. The character association for yield and quality traits was also studied. Analysis of variance revealed considerable amount of variability among genotypes for most of the characters under study. Sedimentation value followed by grain yield per plot, and harvest index exhibited high GCV. The differences between GCV and PCV values were minimum for most of characters which show least environmental influence. Heritability estimates were high for all the characters except plant height (cm), number of effective tillers per meter, number of grains per ear, biological yield per plot(g), harvest index (%). Sedimentation value (ml) followed by grain yield per plot (g) exhibited high genetic advance as per cent of mean alongwith high heritability estimates. The grain yield per plot showed significant and positive correlation with number of effective tillers per meter, number of grains per ear, 1000-grain weight, biological yield per plot and harvest index and significant negative correlation with canopy temperature (post-anthesis 7 and post-anthesis 21 days) in normal as well as heat stress environment. Harvest index, biological yield per plot (g), effective tillers per meter in both normal and heat stress environment had positive direct effect on grain yield. So, direct selection for these traits will be effective to increase the grain yield. On the basis of Euclidean cluster analysis, 75 genotypes were grouped into 9 clusters in both the environments, which indicated the presence of considerable amount of genetic diversity among the genotypes studied. Cluster II and cluster IX showed maximum genetic divergence in both the environments and also having higher mean values for important yield traits and thus involving genotypes of cluster II and cluster IX in hydbridization programme is advocated in order to achieve high yielding segregants. Second experiment aimed at comparing the variability under different systems of selective intermating. On comparison of the selective intermated populations and F2 populations of two crosses Cross I (WH542/WH1080) and Cross II (WH1105/RAJ3765//WH283) the higher mean values were obtained in all selected intermated populations SIM-I, SIM-II and SIM-III in order and wider range values for genetic variability in SIM-III compared to F2 populations of two crosses for most of the characters studied which might be due to additional variability released by selective intermating accumulating favourable genes. The efficiency of intermating over F2 was witnessed in this investigation in terms of days to heading, number of tillers per plant, number of grains per ear,1000 grain weight (g), biological yield per plant (g) and grain yield per plant (g) and other yield related traits. The wider range accompanied by a higher values of mean, phenotypic coefficient of variation, heritability and genetic advance as percentage of mean for biological yield per plant(g) and grain yield per plant(g) in selective intermated populations provides opportunity for further selection in intermated populations for further yield improvement in bread wheat.