Physiological and biochemical responses of black cumin to vermicompost and plant biostimulants: Arbuscular mycorrhizal and plant growth-promoting rhizobacteria

The aim of this research was to find a natural method for increasing black cumin (Nigella sativa Linn) growth by using microbial soil amendments and, at the same time, decrease reliance on mineral fertilizers. We investigated the influence of mineral fertilizer (NPK), vermicompost (VC), Pseudomonas fluorescens (PF), Azotobacter chroo-coccum (AC), Azospirillum brasilense (AB), and arbuscular mycorrhizal fungi (AMF) on plant weight, chlorophyll (Chl) content, relative water content (RWC), total soluble sugar (TSS), proline, glycine betaine (GB), and leaf micronutrients of black cumin during 2020 and 2021. VC and AMF treatments nearly doubled the fresh and dry weights of plants compared to control plants. The highest Chl a (1.62 mg g(-1)) was observed in PF-treated plants, while Chl b in VC (0.62 mg g(-1)) and AMF (0.60 mg g(-1)) showed higher amounts compared with control plants. The RWC ranged from 69% in control to 83.3% in plants treated with VC in the second year. The TSS in all treated plants was higher than in control plants, and the highest for NPK (129.6 mg g(-1) compared to 77 mg g(-1)). NPK yielded the highest proline (158.6 mu mol g(-1)) and AMF resulted in the maximum GB (5 mu mol g(-1)) in the first-year plants. The highest Zn content was reported in AC and AMF-treated plants, and Fe in VC and AMF also showed higher amounts compared with control plants. Cu and Mn with all fertilizers, particularly upon AB and AMF application, were higher than in control plants. Heat map (HA) analysis showed Chl b, GB, and TSS as sensitive traits upon fertilization. AMF colonization and VC, due to their high potential for increasing RWC, Chl content, and micronutrient uptake, they can be recommended as the most effective fertilization treatments for yielding optimum growth in black cumin. AMF colonization is an appealing and more effective alternative to synthetic fertilizers for cumin cultivation. AMF and VC application can be suggested as sustainable agricultural fertilizers containing useful microorganisms to improve the growth performance and mineral composition of black cumin. The amount of dillapiole in EO derived from inoculated black cumin plants with P. fluorescens and G. mosseae was increased.