Arbuscular mycorrhizal fungi, phosphate-solubilizing bacteria, and zinc foliar application improve physiological responses in black cumin (Nigella sativa) under drought stress

Abstract

Abstract This research aimed to improve the physiological response of Nigella sativa to drought stress using arbuscular mycorrhizal fungi, phosphate-solubilizing bacteria, and zinc foliar application. The results demonstrated that the reduction in irrigation water significantly impacted photosynthetic pigments, relative water content, electrolyte leakage, proline content, leaf-soluble sugars, soluble proteins, biological yield, and grain yield. In addition, in 2018 and 2019 years elevated drought stress decreased total chlorophyll (63 and 71%), carotenoids (59 and 59%), relative water content (22 and 25%), soluble proteins content (34 and 35%), biological performance (48 and 55%), and grain yield (66 and 67%). Furthermore, it increased electrolyte leakage (112 and 104%), proline (128 and 120%), and soluble sugars content (44 and 38%). The combined use of arbuscular mycorrhizal fungus (AMF) and Phosphate barvar-2 bio-fertilizer (PB2) (containing two types of phosphate-solubilizing bacteria: Pseudomonas putida P13 and Pantoea agglomerans P5) alleviated for the decrease in the measured traits. Consequently, applying bio-fertilizer increased biological performance (59 and 60%) and grain yield (58 and 58%) and decreased electrolyte leakage (34 and 31%) compared to no bio-fertilizer application. Moreover, the combination of AMF and PB2 increased the grain nitrogen (66 and 40%) and grain phosphorus (27and 36%). Zinc foliar application increased grain elements content, photosynthesis pigment, proline, soluble sugars content, soluble protein content, relative water content and biological performance. Furthermore, it decreased electrolyte leakage. Bio-fertilizers and zinc foliar application mitigated the detrimental effects of drought stress on the quality, grain yield, and biological performance of black cumin by improving the physiological mechanisms.