Iviwe Notununu;Lucy N. Moleleki;Ashira Roopnarain;Rasheed Adelek

Microbiology and Environmental Biotechnology Research Group, Agricultural Research Council—Natural Resources and Engineering, Private Bag X79, Pretoria 0001 (South Africa);Department of Biochemistry, Genetics and Microbiology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Lynnwood Rd, Hatfield, Pretoria 0002 (South Africa);Unit for Environment Science and Management, North-West University (Potchefstroom Campus), Potchefstroom 2520 (South Africa;Microbiology and Environmental Biotechnology Research Group, Agricultural Research Council—Natural Resources and Engineering, Private Bag X79, Pretoria 0001 (South Africa)

drought and heat stress;pgpr;tolerance;abiotic stresses;maize plants;induc

Drought and heat are major environmental stresses that continually influence plant growth and development. Under field conditions, these stresses occur more frequently in combination than alone, which magnifies corresponding detrimental effects on the growth and productivity of agriculturally important crops. Plant responses to such abiotic stresses are quite complex and manifested in a range of developmental, molecular, and physiological modifications that lead either to stress sensitivity or tolerance/resistance. Maize (Zea mays L.) is known for its sensitivity to abiotic stresses, which often results in substantial loss in crop productivity. Bioaugmentation with plant growth-promoting rhizobacteria (PGPR) has the potential to mitigate the adverse effects of drought and heat stresses on plants. Hence, this is considered a promising and eco-friendly strategy to ensure sustainable and long-term maize production under adverse climatic conditions. These microorganisms possess various plant growth-promoting (PGP) characteristics that can induce drought and heat tolerance in maize plants by directly or indirectly influencing molecular, metabolic, and physiological stress responses of plants. This review aims to assess the current knowledge regarding the ability of PGPR to induce drought and heat stress tolerance in maize plants. Furthermore, the drought and heat stress-induced expression of drought and heat stress response genes for this crop is discussed with the mechanisms through which PGPR alter maize stress response gene expression.