Evaluation of drought tolerance in some black cumin (Nigella sativa L.) landraces

Increasing consumer demand for medicinal plants needs to develop agro-management and planning correctly. Black cumin is one of the important and valuable medicinal plants and, due to its frequent application in the pharmaceutical industry, is cultivated in different parts of Iran but, limiting environmental factors have a negative impact on its growth and production. Drought is one of the main inhibitors for crop production in Iran and many arid and semi-arid regions. Production and potential yield of black cumin also can affect by drought stress. There are not many reports available about drought tolerance of black cumin. Therefore, this research focused on response of 10 black cumin genotypes to water-stress condition.
In order to study the effects of drought stress on morpho-physiological traits including oil and grain yield of black cumin an investigation was carried out in Abadeh (city of Fars province) in 2014. The experimental design was split plot based on complete randomized block design with three replications. Water-stress and well-water conditions as main factor and 10 black cumin genotypes were used as sub-factor. Application of drought stress was seedling to ripening stages. Plant height, number of lateral branches, number of follicles per plant, number of seeds per follicle, number of seeds per plant, 1000 grain weight, grain yield, oil content, oil yield, proline content, total soluble sugars and potassium content of black cumin genotypes were measured in both stress and non-stress conditions. Descriptive statistic parameters for all the above measured traits and stress tolerance index (STI) for oil and grain yield were calculated. Data subjected to analysis of variance and means comparison using SAS and Excel soft wares.
Analysis of variance showed that the effect of drought stress for all the measured traits, genotype effect for the most of traits except for the number of follicles per plant, grain yield, oil content percentage, proline and total soluble sugars contents, and interaction between drought and genotype for all traits except for grain yield, oil yield, and proline content were significant. Arak genotype had the highest values for plant height, seed number per follicle, number of seeds per plant and potassium content in water-stress condition. Classification of genotypes using three-dimensional plots of stress tolerance index, stress and non-stress oil and grain yields showed that Arak and Indian were tolerant genotypes for grain and oil yields respectively. Stress intensity results indicated that proline content and number of lateral branches (SI=0.59) more affected by drought stress.
Morpho-physiological traits of black cumin affected by drought stress. There is enough genetic diversity for drought tolerance among black cumin genotypes. So, based on these results improvement of drought tolerance of black cumin is possible. These results can be used in breeding programs to improving drought tolerance of black cumin.