Abstract:
Black cumin (Nigella sativa L.) is an annual spice used for flavoring of food, cosmetics and other industrial products, besides oleoresins and essential oils are valuable sources for health care used for medicinal purposes in Ethiopia. However, variety development was started recently and mainly dependent on introduction of breeding materials. As first step for the improvement of the crop, this study was conducted to assess the genetic variability and to estimate the association of trait, and determine the direct and indirect effects of yield related traits on seed yield of black cumin genotypes. A total of 25 black cumin genotypes were tested in 5x5 simple lattice design atDebre-Zeit Agriculture Research Center in 2018/2019. The results from analysis of variance revealed the presence of significant difference among the genotypes for all quantitative traits except day to flower duration. The variation of the genotypes for seed yield was between 1863.33 and 2873.33 kg ha-1with a mean of 2287 kg ha-1. The seeds of genotypes had average oleoresin of 31.76% and 1.34% of essential oil in the range between 20.75 and 38.75% and 0.596 and 2.780%, respectively. The genotypic (GCV) and phenotypic coefficients of variation (PCV) for 10 traits estimated in the range between 3.91 and 48.36% and 6.90 and 48.94%, respectively, Broad sense heritability (H2) and genetic advance as percentage of mean (GAM) ranged from 32.16 to 99.74 and 4.58 to 98.61%, respectively. High to moderate estimates of GCV, PCV,H2and GAM observed for number of capsules, essential oil and oleoresin contents of seeds, number of secondary branches and number of capsules. Seed yield showed positive and significant correlation with thousand seed weight, plant height, number of primary and secondary branches per plant, number of capsules per plant and number of seeds per capule at genotypic and phenotypic levels. Seed yield had also si gnificant phenotypic correlation with oleoresin content of seeds. Plant height, number of primary branches, number of capsules per plant and number of seeds per capsule also had high and moderate positive direct effects on seed yield at genotypic and phenotypic levels suggested the direct selection of genotypes for these traits will be effective to identify genotypes for high seed yield. The first four principal component axes (PCAs) accounted 70.62 % of the total variability in which PCA1 contributed 28.43%, and PCA2, PCA3, and PCA4 exhibited 18.91%, 13.30%, and 9.98% contribution to the total variability, respectively. Euclidean distance computed from 12 traits as estimate of genetic distances for all possible pairs genotypes ranged from 1.94 to 8.27. The 25 black cumin genotypes were grouped into 10 distinct clusters from Euclidean distance matrix and dendrograms constructed based on the Unweighted Pair-group methods with Arithmetic Means (UPGMA). Cluster II and IV consisted of 9 (36%) and 5 (20%) of the total genotypes, respectively. The three clusters (III, VI, and X) each consisted of two and the five clusters (I, V, VII, VIII, and IX) constructed only by one genotype. The research results showed the presence of variations among genotypes and suggested that further evaluation of black cumin germplasm in Ethiopia to seed yield, essential oil and oleoresin contents of seeds