Actinobacteria for Biotic Stress Management

Actinobacteria are one of the active members of soil micro flora, and they play a key role in soil nutrients cycling and crop yield. Actinobacteria in rhizosphere of different plants produce various growth-promoting substances that stimulate growth of plants even under unfavorable environmental conditions such as drought, heavy metal-polluted soils, salinity, and nutrient deficiencies. Several Actinobacteria are involved in the solubilization of phosphate and zinc in soil which play significant role in number of metabolic pathways. They also produce plant hormones such as auxins and gibberellins which promote plant growth by increasing seed germination, root elongation, and dry weight of the root. Production of lytic enzymes such as amylase, protease, cellulase, chitinase, and glucanase plays an important role in plant disease control and in turn improves soil health. Various Actinobacteria are found to produce different types of siderophores which starve plant pathogens for iron and inhibit their growth. These multifaceted plant growth-promoting activities of Actinobacteria make them an agriculturally important organism. One of the most important members of this group known as Streptomyces species strain 5406 has also been practiced in China for biological control of pathogens of cotton plant. Actinobacterial role as PGP has been investigated in wheat, rice, and beans. Actinobacteria are also found to produce ACC (1-aminocyclopropane-1-carboxylate) deaminase which protects the plants under environmentally stressful conditions. This chapter summarizes the efforts of researchers to demonstrate the beneficial role of Actinobacteria on plant health and agricultural productivity.