Abstract:
Assessment of genetic variability in crop species is one of the major activities of plant breeding which helps to design breeding methods and/or selection of genotypes for further evaluation to meet the diversified goals. Therefore, this field experiment was conducted to assess genetic variability for agronomic and grain quality traits and estimate the association among the traits, and to determine the direct and indirect effects of traits on grain yield of bread wheat genotypes. The field evaluation of 36 genotypes was conducted in 6 x 6 Triple Lattice Design at Haramaya University in 2019. Results of analysis of variance revealed highly significant and significant differences among genotypes for 9 quantitative traits. The variation observed among genotypes for grain yield ranged from 2319.99 to 7622.85Kg ha-1 . Four genotypes BW182119, BW182099, BW182118 and BW182126 showed superior yield performances over the other genotypes. Phenotypic (PCV) and genotypic (GCV) coefficient of variations ranged from 2.806 (days to physiological maturity) to 21.986 (biomass yield) and 2.227(days to physiological maturity) to 10.079% (thousand seed weight), respectively. Heritability (H2 ) in broad sense and genetic advance as percent of mean (GAM) ranged between 2.62 (harvest index) to 71.31 (thousand seed weight) and 0.30 (biomass yield) to 4087.94% (awn length), respectively. High heritability coupled with high genetic advance as percent of mean were found for days to physiological maturity, spike length and thousand seed weight. Characters like days to physiological maturity and number of seeds per spike had highly significant correlation with spike length at phenotypic level where as thousand seeds weight showed highly significant negative correlation with days to physiological maturity and number of seed per spike. Harvest index had significant negative association with spike length both at phenotypic and genotypic levels. Plant height had highly significant positive correlation with number of fertile tillers, above ground biomass, and adjusted grain yield both at genotypic and phenotypic levels whereas spike length showed highly significant positive correlation with plant height only at phenotypic level. This suggested that the two traits or number of fertile tiller and above ground biomass could be used as direct selection of genotypes for yield. The first four principal component axes (PCA) with Eigen values >1 accounted for 70.56% variation of genotypes. Euclidean distance ranged from 1.39 to 17.5 with the mean, standard deviation and coefficient of variation of 6.60, 2.81 and 42.93%, respectively. The genotypes were grouped into four distinct clusters of which Cluster I, II, III and IV consisted of 21(58%), 2(5.5%), 10(27.77%) and 3(8.33%) genotypes respectively. In terms of frequency distribution of qualitative traits out of 36 genotypes 18 genotypes were intermediate, 14 genotypes were dense and 4 genotypes were lax for spike density. Based on awn color, six genotypes had both yellow and brown awn color but all the remaining twenty four genotypes were categorized under white awn color with 66.7%. Very high diversity indices were recorded for kernel color and kernel covering (0.99) and also high for spike density (0.87) and awn color (0.63) but no diversity was observed for susceptibility to lodging. Generally, The present result is only an indication and we cannot reach a definite conclusion. Therefore, it is advisable to continue with this study over several years and locations.