Endophytic Microbes in Crops: Diversity and Beneficial Impact for Sustainable Agriculture
Endophytic microbes are ubiquitous in most plant species. Endophytic microbes enter plants mainly through wounds, naturally occurring as a result of plant growth or through root hairs and at epidermal conjunctions. Besides gaining entrance to plants through natural openings or wounds, endophytic microbes appear to actively penetrate plant tissues using hydrolytic enzymes like cellulase and pectinase. Diverse community structure of endophytes can be analyzed using culture dependent and culture independent method. Endophytic bacteria belong to different phyla such as Acidobacteria, Actinobacteria, Ascomycota, Bacteroidetes, Basidiomycota, Deinococcus Thermus, and Firmicutes. Endophytic archaea (Euryarchaeota) were reported using only culture independent method. Endophytic microbes were most predominant and studied and belonged to three major phyla Actinobacteria, Proteobacteria, and Firmicutes. Among reported genera Achromobacter, Bacillus, Burkholderia, Enterobacter, Herbaspirillum, Pantoea, Pseudomonas, Rhizobium, and Streptomyces were dominant in most host plants. Along with common endophytic microbial genera, there were many niche specific microbial genera that have been reported from different host plants. Application of associative microbes for sustainable agriculture holds immense potential. Endophytic microbes are known to enhance growth and yield of plants by fixing atmospheric nitrogen and solubilization of phosphorus, potassium, and zinc; production of phytohormones (cytokinins, auxins, and gibberellins) ammonia, hydrogen cyanide, and siderophores; and possession of antagonistic activity as well as reducing the level of stress ethylene in host plants. Endophytes seem to contribute to plant fitness and development, displaying beneficial traits that can be exploited in agricultural biotechnology. The interactions between endophytes and plants can promote plant health and play a significant role in low input sustainable agriculture for both food and nonfood crops. This chapter summarizes part of the work being done on endophytic microbes, including their isolation, identification, diversity, distribution, and applications for sustainable agriculture.