Soil Microbes-Medicinal Plants Interactions: Ecological Diversity and Future Prospect

Plants live in association with microbes in both above- and belowground part, as some are beneficial and some are harmful to the plant. Microbes which are found within the plant tissue, namely, endophytes, can have beneficial, neutral, or detrimental effects on plant health and development. Several works have been done on plant-microbe interactions and microbial diversity of rhizospheric region of medicinal plants. Therefore, plant secondary metabolite and root exudates which include various sugars and organic acids influence biogeochemical reactions and thus plant metabolism. Signaling molecules like strigolactones induce the colonization of the mycorrhiza fungi with plant root and stimulate the germination of the parasitic plant such as Striga. Similarly, the flavonoids secreted by leguminous roots increase the growth of symbiotic and nonsymbiotic nitrogen-fixing bacteria and also attract pathogenic oomycetes as well. Root-associated microflora and endophytes (fungi or bacteria) help plant growth by secreting the plant hormone (auxin/cytokinin) and nutrients like phosphorus, nitrogen, and iron. Microbial association with root may induce plant resistance against the several biotic and abiotic stresses, such as toxic metals, pathogens, drought, high temperature, saline soils, adverse soil pH, and transplant shock. Study the plant-microbe interaction in the era of next-generation sequencing opens a new way to understand their association as well as help in improvement of sustainable agriculture. Finding answers of these questions “Who is there?” and “What are they doing?” extended by “How do they live under given conditions?”, “How do they respond to environmental changes and perturbations?”, “How do they interact with each other?”, and “How do they affect plant growth and development?” may be used in the future to support plant growth and improve crop yield. Exploration of endophytic or rhizospheric microbes in the future for enhancement of secondary metabolites in medicinal plants might be a new vista opened for the sustainable agriculture practices. In this chapter, we will focus our attention to the role of medicinal plant-microbe interaction to root and shoot in positive and negative aspect.