Role of microbial seed priming and microbial phytohormone in modulating growth promotion and defense responses in plants

Abstract

Plant growth and development are greatly affected by various biotic and abiotic stresses. Various strategies are utilized to minimize stresses in plants. Seed priming with beneficial microorganisms is one of the most beneficial methods to improve plant growth and development and induce systemic tolerance in plants towards biotic as well as abiotic stresses. Seed priming is a method of conditioning the seeds by plant growth-promoting microbes which provide better abilities to the plant to withstand various environmental challenges beginning from seed germination. Seed priming with beneficial microorganism is also known as biopriming that enhances seed germination, protects germinating seed from different phytopathogens, and provides suitable conditions for establishment of the plant. Bio-priming has several mechanisms to stimulate morphogenesis and plant immunity, viz., production of phytohormones, induced expression of plant growth-promoting genes, increased nutrient status into the plant, mycoparasitism, antibiosis, induced phenolic production, activation of antioxidant production, and systemic defense activation. Some important microorganisms that synthesize phytohormones include Azotobacter spp., Pantoea agglomerans, Rhodospirillum rubrum, Rhizobium spp., Bacillus subtilis, Pseudomonas fluorescens, Paenibacillus polymyxa, Trichoderma spp., Pseudomonas putida, Rhizobium phaseoli, Bacillus cereus, and Acinetobacter calcoaceticus. The main objective of this chapter is to enlighten the importance of seed priming with microorganisms and the role of different phytohormones produced by them in modulating growth, development, and defense activation in the host plant.