Studies on Endophytic Actinobacteria as Plant Growth Promoters and Biocontrol Agents

The exploration of microbial resources is necessary for plant growth promotion, biological control, and reducing the agrochemicals and fertilizers for sustainable agriculture. Bacteria and fungi are distributed in the biosphere including the rhizosphere and help the host plants by alleviating biotic and abiotic stress through different mechanisms and can be used as bioinoculants for biocontrol and plant growth promotion. Actinobacteria are among the most abundant groups of soil microorganisms. They have been studied for their function in the biological control of plant pathogens, interactions with plants, and plant growth promotion. Streptomyces is the largest genus of actinobacteria. Streptomyces acts as both plant growth promoter and also as plant disease suppressor by various mechanisms like an increase in the supply of nutrients such as phosphorus, iron, production of IAA, and siderophore production. Endophytic actinobacteria help in plant growth-promoting through multiple ways by producing plant hormones; controlling fungal disease through antibiosis and competition. This review briefly summarizes the effects of actinobacteria on biocontrol, plant growth promotion, and association with plants as endophytes.