Abstract:
The study of genetic variability is the critical step in crop improvement programs either to use
the natural variation that already exists or produce genetic variation. This study was
conducted to assess the genetic variability of 20 bread wheat genotypes and determine
associations among yield, yield related traits and protein content. The experiment was laid
out in randomized complete block design with three replications during 2017 at Raare
research site of Haramaya University. The results from analysis of variance revealed the
presence of significant difference (P<0.01) among 20 bread wheat genotypes for 14
quantitative traits but not for days to grain filling, number of productive tillers and number of
kernels per spike. Moreover, the genotypes had mean grain yield in the range between 5564.2
kg/ha for (ETBW7790) and 7945.7 kg/ha for (variety Jalanne) with overall mean of 6582.73
kg/ha; and in the range of 9.20 for (Qulqulluu) to 12.87for (ETBW7790) for grain protein
content. The estimates of phenotypic (PCV) and genotypic (GCV) coefficient variations
ranged from 1.96 to 20.05% and 1.37 to 13.91%, respectively, in which the lowest and the
highest estimates were computed for hectoliter weight and peduncle length, respectively. A
high and moderate values of PCV and GCV were computed for peduncle length, whereas
moderate PCV and GCV values were for spike length, thousand kernel weight and harvest
index. The estimated values of broad sense heritability (H
2
B) and genetic advance as percent
of mean (GAM) ranged from 48.14 to 92.74 and 1.98 to 20.69%, respectively. High H
2
B and
GAM values obtained for spike length while high H
2
B coupled with moderate GAM values for
number of spikelet per spike, thousands kernel weight, biomass yield, harvest index, grain
protein content and wet gluten content suggesting improvement of the traits through selection
could be fairly easy. Grain yield had positive and significant association with harvest index
but negative and significant correlations with spike length both at genotypic and phenotypic
levels. Harvest index and spike length also exerted positive and negative direct effects on
grain yield, respectively, both at genotypic and phenotypic levels. Both spike length and
harvest index had positive indirect effects on grain yield through thousands kernel weight and
hectoliter weight at genotypic level. This suggested harvest index but not spike length could
be considered for indirect selection of genotypes for high yield. The first five principal
components explained cumulatively 82.76 % of the total variation observed among bread
wheat genotypes. The Euclidean distance for all possible pairs of 20 bread wheat genotypes
ranged from 1.54 to 8.60 and genotypes were grouped into eight distinct clusters. Cluster III
consisted of five genotypes (25%), Cluster I, IV and VII consisted of each three genotypes,
Cluster II and VIII constructed each by two genotypes and Cluster V and VI consisted of only
G10 and Jalanne variety, respectively. The selection to be made from genotypes grouped
under Cluster I, VI and VIII, consisted genotypes that had high yield and protein content. In
conclusion, it was observed the presence of considerable variations and genetic divergence
among bread wheat genotypes that could be a good opportunity for breeders to develop
variety (ies) either by further evaluation of high performing genotypes or through Heterosis
breeding by crossing of genotypes with varied desirable traits of different clusters.