Abstract:
Assessment of genetic diversity and 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 including breeding for drought stress conditions. Field experiment was conducted to assess the genetic diversity among bread wheat genotypes, to determine the association among traits, and estimate the direct and indirect effects of traits on grain yield. A total of 33 bread wheat genotypes and 3 released varieties were evaluated in 6 x 6 Simple Lattice Design at Goro and Ginnir research station of Sinana Agricultural Research center, in 2019 cropping season. The analysis of variance computed for each location and over two locations revealed highly significant differences among genotypes for all studied traits except for stand count and hectolitre weight. Location and interaction of genotype x location also had a significant effect on the performance of genotypes for most of the traits. The variation of the genotypes for grain yield was ranging from 2.8 to 4.4 t ha-1 . Estimated phenotypic coefficient of variations (PCV) and genotypic coefficient of variations (GCV) coefficient of variations were ranged from 0.00 to 26.98% and 6.96 to 24.98%, respectively. Heritability in a broad sense and genetic advance as percent of the mean (GAM) were ranged from 43.91 to 85.76 and 3.3 to 47.6%, respectively. The estimates of GCV and PCV, H2, and GAM were high for biomass yield, spike length and primary root length over two locations. Grain yield had shown positive and highly significant correlation with spike length, number of spikelets per spike, number of kernels per spike, thousand seed weight, harvest index, and primary root length at both genotypic and phenotypic levels, however, grain yield had shown negative and highly significant correlation with days to heading and maturity at both genotypic and phenotypic levels at both locations. Spike length, number of spikelets per spike, and harvest index had shown a high and positive direct effect on grain yield at both genotypic and phenotypic levels which suggested that the direct selection of genotypes for these traits will be effective to identify genotypes for high grain yield. The first three Principal Component analysis (PCA1 to PCA3) with Eigenvalues >1 accounted for the total variation of 82.25%. The genetic distances among the 36 bread wheat genotypes estimated using Euclidean distance showed a value ranging from 1.60 to 13.71, with the values of mean, standard deviation, and coefficient of variation of 5.24, 1.85, and 35.34%, respectively. The genotypes were grouped into four distinct clusters of which Clusters II, III, I, and IV consisted of 41.66%, 27.8%, 22.2%, and 8.3% genotypes, respectively. The wheat genotypes understudy showed variations for morphological and agronomical drought-related traits such as plant waxiness, early ground cover, leaf morphology, and stay greenness. Out of 36 tested genotypes for the qualitative traits with ‘good’ and ‘very good’ scales accounted 41.7% for waxiness, 33.4% for early ground cover, and 33.3% for stay greenness traits. The largest proportion of bread wheat genotypes showed leaf curling morphology which is one of the morphological traits for drought stress wheat characterization. Generally, the result of this research showed the presence of high diversity among bread wheat genotypes for yield and drought tolerance morphological markers that could be potentially be exploited in the future wheat breeding programs for drought-stress areas