Nutrient and Pest-Managing Microbial Inoculants for Sustainable Production of Rice

Rice production is mostly dependent upon chemical fertilizers and pesticides across the globe; however, extensive use of these in rice crop has shown adverse effects on environment and human health. Besides, continuous application of these chemicals in rice cultivation has also deteriorated the soil physical conditions and quality. Achieving higher sustainable yield through microbial technology could be one of the better options under rice cultivation system. Rice-specific biofertilizers and biopesticides are one of the possible substitutes of dangerous chemical products as these are host-specific, eco-friendly, and cost-effective. These are actually organic formulations containing living microorganisms like bacteria, fungi, and algae that are capable of exhibiting various plant growth promoting (PGP) traits. Numerous biofertilizers such as nitrogen (N) fixing microorganisms (Azolla, Cyanobacteria, Azotobacter, Azospirillum, etc.), phosphate, potassium, zinc solubilizing microorganisms (Pseudomonas, Bacillus, Aspergillus, Arbuscular mycorrhiza, etc.), and sulfur oxidizing microorganisms are being used in rice cultivation. Heterotrophic N-fixing microbes fix nitrogen from 15.6 to 22 kg N ha−1 year−1 in rice field. Moreover, cyanobacteria and Azolla could supplement the N need of rice crop by replacing 30–50% of the requisite chemical N, whereas phosphate and potassium solubilizing bacteria may reduce chemical P and K fertilizer applications by 15–30% without any significant reduction in rice yield. Besides biofertilizers, microbial pesticides (bacteria, fungi, and viruses) could perform as antagonists and entomopathogens against various rice pests. About 23 bacterial antagonists from the genera Bacillus, Pseudomonas, Serratia, and Erwinia have been found, which prevent rice diseases like sheath blight, stem and sheath rot, brown spot, and blast. Similarly, the most popular entomopathogens used mainly to manage rice insects (leaf folder, brown leaf hopper, yellow stem borer, etc.) are Metarhizium anisopliae, Beauveria bassiana, and Bacillus thuringiensis. Overall, researchers are interested in PGP microbes as biofertilizers and biocontrol bioinoculants and therefore, various such microbes are now commercialized for several crops including rice. This chapter describes the biofertilizers and microbial pesticide formulations exclusively used in rice to enhance its production and productivity by exhibiting their desirable mechanisms and PGP functions.