Genetic Variability and Association of Yield and Yield Related Traits in Bread Wheat (Triticun aestivum L.) Genotypes in Western Amhara Region Information on genetic variability and determination of the association of traits are important for successful plant breeding. Forty nine bread wheat genotypes were evaluated in western Amhara region with triple lattice design at two locations in 2018 main rainy season to evaluate the extent of genetic variability and association of yield and yield related traits in bread wheat genotypes. The result of analysis of variance showed significant difference among the tested genotypes for days to 50% heading, days to maturity, grain filling period, plant height, spiklets per spike, grain yield and thousand seed weight at both locations and including spike length, kernel per spike, hectoliter weight and harvest index at Adet. The highest GCV and PCV were observed in grain yield. High heritability in spike length and thousand seed weight accompanied with moderate genetic advance as percent of the mean were observed at Adet. Moderate heritability along with moderate genetic advance as percent of the mean was observed only for thousand seed weight at Debre Tabor which indicates the presence of additive gene action and direct selection on those traits can be possible at early generation for further improvement of bread wheat. Grain yield had significant positive correlation with most of the traits considered in the present study which indicates that direct selection based on those traits could be more effective to maximize grain yield of bread wheat. Above ground biomass yield and harvest index had the highest positive genotypic and phenotypic direct effect on grain yield for both locations. This implies the true relationship between those traits and grain yield so that due attention should be given on such traits during selection. According to D2 statistic forty nine bread wheat genotypes were grouped in to nine clusters. The first three principal components explained about 71.54% and 80.15% of the total variation at Adet and Debre Tabor respectively. The highest inter-cluster distance were observed between cluster II and VII, III and VII, and cluster V and VII at Adet and between cluster III and IX, III and VIII and between cluster II and IV for Debre Tabor. Hence, selection and hybridization between genotypes selected from those clusters based on traits which had significant positive correlation and direct effect on grain yield can be recommended for farther yield improvement of bread wheat in the tested locations. However it is one year result, it should be reputed for additional year to confirm this result. Keywords: bread wheat, cluster, correlation, genetic variability, path-coefficient, PCA 1 Chapter 1. INTRODUCTION 1.1 Background