The effect of plant growth promoting rhizobacteria on agro-morphological traits of black cumin (Nigella sativa L.) under water deficit stress

Introduction Black cumin (Nigella sativa L.) as an annual medicinal plant which belongs to the Rununculaceae family is suitable for semi-arid regions. The researchers reported many medicinal properties for this plant such as bloating reduce, pain reduce, anorexia reduce and anti-cancer. Water is one of the most important environmental factors in plant growth that its reduction limiting crop yield. Drought stress can be effective on vegetative growth, flowering, pollination and fertilization, fruit formation and yield and reduces each of these factors. In recent years, the use of plant growth promoting rhizobacteria through different mechanisms against Salt and Drought Stresses can increase plant tolerance to environmental stresses. The aim of this study was to investigate the effect of plant growth promoting rhizobacteria on yield and yield components of Black cumin under water deficit stress Materials and methods To evaluate the effect of plant growth promoting rhizobacteria on agro-morphological traits of Black cumin under water deficit stress, an experiment was done during 2014-2015 growing season at the research field of the faculty of agricultural, Shahrekord University as split-plot factorial in a Randomized Complete Block Design with three replications. The main factor including water deficit in three levels (100, 75 and 50 present of water requirement) and the sub factor was PGPRs at seven levels (control, Bacillus sp. Strain A, Bacillus amyloliquefaciens, Bacillus sp. Strain B, Azotobacter chroococcum, Pseudomonas putida and Azopirillum lipoferum). The amount of irrigation water was calculated using plant water requirement. Before the final harvest, to measure traits, five plants were randomly taken from each plot and yield and yield components was recorded. SAS and Excel softwares implemented for statistical analysis and the means were compared using LSD test. Results and discussion The results showed that by increasing water deficit stress the amount of the number of branch, Plant height, seed number per capsule, the number of capsule per plant, 1000 seed weight, biological yield, grain yield and harvest index was decreased. So 50% of water requirement treatment cause to decrease 18.4, 28.4 and 12.3 percent in biological yield, grain yield and harvest index compared to 100% % of water requirement. the use of bacteria significantly improved all these traits compared to non-inoculated. Among the bacterial treatments the maximum and minimum seed number per capsule, 1000 seed weight, biological yield and grain yield obtained in Bacillus amyloliquefaciens treatment and non-inoculated, respectively. Also, the results indicated that the interaction effect between water deficit stress and bacteria inoculation, except the number of branch and Plant height, were significant on all of traits. B. amilolykofosins application under 100% water requirement treatment had the highest seed number per capsule, 1000 seed weight, biological yield and grain yield (increased by 38.7%, 17.13%, 24.8% and 35.2%, respectively) as compared to non-inoculated. So, plant growth promoting rhizobacteria by different mechanisms such as phosphate solubilization, dinitrogen fixation, ACC deaminase and antifungal activity, IAA and siderophore biosynthesis are responsible for the plant growth promotion and increased yield under different environmental stresses. Conclusions The results of this study showed that increasing water deficit stress causing significant reduction of all traits. However, the use of bacteria reduced the effects of stress and increased these traits compared to non-inoculated at all water deficit stress levels. Also among bacterial treatments, Bacillus amyloliquefaciens, Bacillus strain A and strain B had the most effect on stress improvement.