Plant growth promoting rhizobacteria mitigate drought and salinity stresses, and improve the physiological and agronomic performances in crops: A systematic review

Drought and salinity are environmental factors that negatively impact crop productivity in arid and semi-arid climates. Plant growth promoting rhizobia (PGPR) can help mitigate the harmful effects of drought and salinity on plant growth and productivity. This systematic review aims to summarize studies on PGPR and their mechanisms for reducing the impacts of drought and salinity, as well as to explore the effects of PGPR on different crops to improve agronomic indicators focusing on recent findings. Search was performed on PubMed, Web of Sciences and Google Scholar for papers published from 2013 to 2022. A total of 174 papers were analyzed in this review. The results showed that the PGPRs were found to increase the activity of antioxidant enzymes and stimulate plant growth under adverse conditions. The PGPRs also reduced electrolyte leakage and malondialdehyde contents, while increasing exopolysaccharide, chlorophyll, and relative water contents, for mitigating both drought and salinity stresses. PGPR strains are effective in increasing root and shoot length, root and shoot dry weight, leaf area, and leaf content. Most of the studies regarding the applications of PGPRs to enhance abiotic stress tolerance in crops were conducted under laboratory and/or greenhouse conditions, with Asia having the highest number of publications on cereals. This review shows the potential for PGPR to manage soil salinity and drought across diverse crops and ecologies. Studies on the roles of PGPRs for crop production at the field level to achieve large-scale adoption with agronomic and economic improvements are recommended.