indirect plant growth promotion in grain legumes: Role of Actinobacteria

Abstract

Grain legumes (beans, pulses, and oilseeds) are protein-rich crops and to a larger extent diversify farming systems. These crops are often confronted by a number of biotic and abiotic stresses in the natural environment resulting in a significant reduction in their productivity. Management options employed to counter such stresses include cultural and agronomical practices apart from the use of chemicals. Among others, biological control using beneficial microbes is environmentally safe and sustainable solution to minimize the deleterious effects of biotic and abiotic stresses in grain legumes. Microbes are known to exhibit a number of mechanisms conferring resistance to plants. Many such useful organisms, termed plant growth-promoting microbes (PGPM), have been studied extensively for their role in agriculture. Among the microbes studied, plant growth-promoting Actinobacteria (PGPA) have been gaining popularity. These microbes are a group of important free-living, spore-forming organisms exploited for their role in producing many agriculturally important substances. These microbes have shown the ability to both suppress pathogen inoculums employing one or more mechanisms of antagonism (hyperparasitism and the production of lytic enzymes, antibiotics, and siderophores) and also resist abiotic stresses (drought, salinity, heavy metals, heat, etc.) by lowering the levels of ethylene by producing 1-aminocyclopropane-1-carboxylate (ACC) deaminase. It is not only important to identify such microbes but also to extrapolate these findings and achieve similar results under field conditions. This chapter focuses on the common mechanisms reported for Actinobacteria majorly streptomycetes and to a lesser extent by non-streptomycetes in protecting the crop plants particularly grain legumes. We believe it also helps to encourage further investigations especially with the lesser explored non-streptomycetes.