An In-Depth Examination into How Genotype, Planting Density, and Time of Sowing Affect Key Phytochemical Constituents in Nigella sativa Seed

Nigella sativa, also known as black cumin, is esteemed for its rich reservoir of health-benefitting phytoconstituents nestled within its seeds. The composition of its seeds can be influenced by factors such as genotype diversity and agricultural practices. Understanding these dynamics is important for maximizing the nutritional and medicinal attributes of the seeds. This study investigated how different genotypes, growing densities, and sowing times affect oil yield and phytoconstituents of Nigella seeds in Northern Australia. The aim was to find the optimal combination of these factors to maximize desirable compounds. Our findings revealed variability in oil yield and phytoconstituents among different genotypes, growing densities, and sowing times. No single genotype stood out as having elevated levels of all desired compounds. For instance, genotype AVTKS#5 had high total phenolic content (TPC) and antioxidant capacity, while AVTKS#8 and AVTKS#7 excelled in thymoquinone (TQ) and polyunsaturated fatty acids (PUFAs) and monounsaturated fatty acids (MUFAs), respectively. Planting density had a nuanced impact, with no significant effect on oil yield and CUPRAC values, but higher densities decreased TPC, FRAP, and TQ. Interestingly, seeds cultivated at 20 and 30 plants/m2 had higher ratios of MUFAs/SFAs, PUFAs/SFAs, and (MUFAs + PUFAs)/SFAs, indicating the importance of planting density in shaping fatty acid profiles. Sowing times also had a noticeable effect, with late sowing leading to a decrease in oil yield from 19% to 14%. May-sown seeds had higher TPC, FRAP, CUPRAC, and fatty acid ratios, while TQ levels peaked in June-sown seeds. Our study highlighted positive correlations among TPC, FRAP, CUPRAC, and TQ, emphasizing their collective contribution to the nutritional and medicinal potency of Nigella seeds. Fatty acids, on the other hand, showed no significant correlation with these parameters, indicating independent regulation. In summary, our comprehensive analysis provides insights into the factors (genotype and agronomic practice) that shape the phytochemical profile of Nigella seeds, and suggests better genotype, planting density, and time of sowing for the cultivation and quality production.