Genetic diversity of Ethiopian black cumin (Nigella sativa L.) based on morpho-agronomic characteristics

This study was conducted to investigate the variability of Ethiopian black cumin genotypes by using morpho-agronomic traits. Sixty-four genotypes were tested at Debre Zeit and Kulumsa Agricultural Research center in 2021 using an 8 × 8 simple lattice design with two replications. Analysis of variance revealed significant (p ≤ 0.001 or p ≤ 0.01) differences among the genotypes for all traits studied, except the number of primary branches per plant. The effect of location was significant (p ≤ 0.001 or p ≤ 0.05) for all traits except the number of primary branches per plant. It is expected to improve all phenological traits as well as seed yield and yield-related qualitative traits by 4–41% over improved varieties by the selection of the top 5% landraces. Thus, through selection, it would also be possible to shorten the flowering and maturity periods of the genotypes. High broad sense heritability values coupled with high to moderate genetic advance as a percentage of mean values were shown by the number of capsules per plant and plant height which indicates possibilities for improvement of these traits through selection. Plant height, number of primary branches per plant, number of seeds per capsule and thousand seeds weight had a positive and significant phenotypic and genotypic association with seed yield per hectare. Plant height and seed yield per plant had a positive direct effect on seed yield per hectare phenotypically and genotypically. This would be a direct selection criterion for further improvement of the genotypes. The principal component analysis of 12 quantitative traits exhibited 81.5% of the total variance captured by the first four principal components (PCs). Days to 50% flowering, days to full blooming, days to maturity, number of seeds per plant, and seed yield per plant were the main contributor traits for the variation in the first and second PCs. The genotypes were grouped into three different clusters (C-I = 35.93%, C-II = 9.38%, and C-III = 54.69%) based on 12 quantitative traits with significant inter-cluster distances. This clearly showed that there was sufficient diversity among the genotypes which can be exploited for the future black cumin improvement program.