Synthetic cultivar development in cumin: Enhancing yield and drought tolerance

Cumin (Cuminum cyminum L.) is a valuable spice crop with medicinal properties belonging to the Apiaceae family. While farmers often favor the cultivation of cumin, low seed yield, particularly under drought stress, poses challenges to its commercial production. Due to cumin small flowers, self-incompatibility, and cross-pollination attributes, the production of synthetic varieties through polycross breeding can be an effective method for improving seed performance and enhancing drought tolerance in cumin. This study, for the first time, investigates the breeding progress of cumin in three populations over two generations. The first generation resulting from polycross breeding (SYN2 population), along with parental genotypes, was evaluated for agro-morphological traits under normal and low-water irrigation conditions in two locations and compared with the SYN1 population. Additionally, genetic diversity among parental genotypes, SYN1, and SYN2 populations was examined using Start Codon Targeted Polymorphism (SCoT) markers. Low water stress negatively affected all studied traits, except for essential oil content. Improved seed yield, increased drought tolerance, and higher cuminaldehyde content were observed in the SYN2 population compared to parental genotypes. Estimation of genetic parameters indicated a higher heritability and heterosis for traits in the SYN1 population compared to SYN2. Furthermore, trait heritability in the SYN2 population was higher under normal irrigation condition than under water stress. The highest narrow-sense heritability in both SYN1 and SYN2 populations was associated with the thousand-seed weight. Positive and significant phenotypic and genotypic correlations between thousand-seed weight and seed yield were observed in the SYN1 population, while the SYN2 population exhibited the least negative impact of drought stress on this trait. Grouping populations through cluster analysis and principal coordinate analysis based on both molecular and agro-morphological data showed complete concordance, effectively distinguishing cumin populations from one another. The SCoT molecular marker confirmed the homogeneity of the improved populations, demonstrating high efficiency in assessing intra- and inter-population diversity. Molecular variance analysis revealed lower within-population diversity (29 %) compared to between-population diversity (71 %). Among populations, SYN1, equivalent to F2 generation, exhibited the highest level of molecular diversity based on diversity indices.