Biological control of bacterial wilt disease-causing pathogens: A sustainable approach for increasing crop production

Abstract

India is the second largest global producer of vegetables and accounts for about 15?% of the world's vegetables production. The production of vegetables is affected by infection of crops with several diseases throughout their life cycle. Among the diseases, bacterial wilt caused by Ralstonia solanacearum in crops such as tomato (Lycopersicon esculentum), potato (Solanum tuberosum), chili (Capsicum annum), tobacco (Nicotiana tabacum), eggplant (Solanum melongena), and pepper (Capsicum annum) is a major disease contributing to production loss of 10.80–92.62% per unit area in India. The incidence of this disease is much severe during summer due to high temperature (28–36°C) and high moisture (50–100%), which favor the activity of the pathogen (R. solanacearum). Currently, adopted disease management practices like chemical application, use of resistance varieties, and manual removal of infected plants are of limited success to control the disease. The use of naturally occurring microorganisms in the rhizosphere of crop plants as a biocontrol agent offers an alternate source, and is gaining greater importance nowadays. Many effective plant growth-promoting rhizobacteria (PGPR) such as Pseudomonas spp., Bacillus spp., Burkholderia spp., Serratia spp., and Streptomyces spp. are abundant in rhizospheric soil. Moreover, rhizospheric soils are regarded as a source of natural, effective, and valuable antagonists for the purpose of biological control. The use of PGPR to suppress pathogen (R. solanacearum)-causing bacterial wilt in crops has lately become successful, and thus is gaining greater importance. The PGPR control disease by producing siderophore, hydrogen cyanide (HCN), secondary metabolites/antibiotics such as pyoluteorin, phenazines, pyrrolnitrin, 2,4-diacetylphloroglucinol (2,4-DAPG), 1,2-benzene dicarboxylic 46 acid, bis(2-ethylexyl) ester, 2,6-di-T-butyl-4-methelyne-2,5-cyclohexadiene-1, and antifungal enzymes such as cellulase, chitinase, and protease. Production of antibiotics is one of the primary mechanisms involved in disease suppression. Among many antibiotics, 2,4-DAPG, a polyketide produced by bacteria showing broad-spectrum antiviral, antifungal, antibacterial, antitumor activities, and phototoxic properties, has received considerable attention. Thus, the 2,4DAPG-producing genotypes can be exploited to suppress bacterial wilt disease in crop plants.