Multipotential rhizobacteria simultaneously mitigate salinity stress and improve growth and physiological traits in black cumin (Nigella sativa L.)

Soil salinity impairs the growth, development, and the yields of the crops and contribute to increased agriculture productivity. Plant growth-promoting rhizobacteria (PGPR) help plant growth and mitigate soil salinity. The present study aimed to isolate multifarious rhizobacteria to simultaneously mitigate salinity stress and improve growth and physiological traits in black cumin. The study revealed the effects of Bacillus subtilis IGPEB 1, Bacillus altitudinis IGPEB 8, Bacillus endophyticus IGPEB 33, and Pseudomonas koreensis IGPEB 17 on the growth and physiological properties of Nigella sativa L. under salt stress. The results revealed that B. altitudinis IGPEB 8, B. endophyticus IGPEB 33, and B. altitudinis IGPEB 8 significantly increased the shoot length by 20.96% and 26.73% and total root length by 73.15%, respectively. B. endophyticus IGPEB 33 (T4) significantly enhanced total root length by 103.66%, projected area by 36.67%, and root surface area by 50.78%, respectively. Application of B. altitudinis IGPEB 8 (T3) and B. endophyticus IGPEB 33 (T4) enhanced total chlorophyll content by 73.36% and 85.51%, chlorophyll a by 74.46% and 80.00%, chlorophyll b by 66.66% and total chlorophyll by 45.71% and carotenoid contents by 55.55% and 79.62%, respectively, the antioxidant capacity, antioxidant enzymes' activities and relative water content of leaves by 8.25% and 9.07% compared to the control. The consortium of B. altitudinis IGPEB 8 and B. endophyticus IGPEB 33 positively influences physiological properties in Nigella sativa L. under salt stress.