Bacillus spp.: A Promising Biocontrol Agent of Root, Foliar, and Postharvest Diseases of Plants

Biological control of plant disease is gaining momentum as it offers an alternative and supplement to synthetic chemicals. Microorganisms from diverse groups have successfully been used as biocontrol agents (BCA) due to their capacity of suppressing harmful microbes with a wide array of mechanisms such as competition, antibiosis, and resistance induction in the host plant. Bacillus spp. is among the highly potent bacterial BCAs used for controlling principally rhizosphere and to a lesser extent foliar diseases of plants. The capacity of Bacilli to produce spores which are extremely resistant to high temperatures, unfavorable pH, and lack of nutrients or water are determining factors for using these organisms in a formulation. These spores are produced by the bacteria when environmental conditions are unfavorable to help these microorganisms to survive in the phytosphere and ward off the growth of harmful microbes. Bacillus subtilis strain QST 713 that has been used in the commercially available plant disease control product “Serenade” showed excellent disease suppression in diverse environmental conditions and crop varieties. This product along with many other similar products is now considered as an essential component of any integrated disease management effort due to their compatibility with many chemicals used for disease control. Many other strains of Bacillus subtilis and species of Bacillus have also been used for seed treatment, induction of systemic resistance, and suppression of both root and foliar disease-causing organisms. Major agrochemical companies have shown interests and diligently work in incorporating Bacillus-based products in their portfolio. Significant efforts have been made to unravel the genetic makeup of these beneficial Bacilli that encode a wide range of antimicrobial products. An appreciable number of polypeptides, polyketides, and related products have been identified and characterized by which they achieve competitive edge in the plant rhizosphere or form biofilm on root surface. Continued interest and research on this BCA in twenty-first century will make Bacillus-based formulations most widely used plant disease management tool.