Plant Growth-Promoting Microbes for Sustainable Agriculture

Abstract

Microbes are an integral part of living soil not only in transforming nutrients in the soil but also with multiple functions in influencing soil health. There are specific microbes which help the plant to grow well in their presence by various mechanisms. The direct mechanism may include fixation of atmospheric nitrogen, synthesis of various phytohormones and enzymes, and solubilization of minerals in the soil, while the indirect mechanism includes inhibiting phytopathogens. Hence, such plant growth-promoting rhizobacteria (PGPR) need to be harnessed and exploited for sustainable agriculture. Some of the representative PGPR group includes Azotobacter, Azospirillum, Acinetobacter, Agrobacterium, Arthrobacter, Bacillus, Burkholderia, Pseudomonas, Serratia, Streptomyces, Rhizobium, Bradyrhizobium, Mesorhizobium, Frankia, and Thiobacillus. Demonstrations of these PGPR and their beneficial traits under glasshouse and field conditions are documented for a range of crops including cereals, legumes, fruits, vegetables, herbs, and ornamentals. Several industries are commercializing the potential PGPR strains as biofertilizers and as biocontrol agents. However, successful commercialization of PGPR in many developing countries is a distant dream largely due to the lack of well-developed technology, quality carrier material, quality control legislation, training programs, and on-farm demonstrations. The development of quality PGPR inoculum and its application will definitely lead to an ideal sustainable agricultural system. Further, PGPR is known for not only reducing the emission of greenhouse gases (GHGs) and carbon footprint but also increasing nutrient-use efficiency.