Biological control of Fusarium wilt and growth promotion in pigeon pea (Cajanus cajan) by antagonistic rhizobacteria, displaying multiple modes of pathogen inhibition

Abstract

Fusarium udum is one of the most important pathogens impacting the production of pigeon pea (Cajanus cajan) legume. Legume growers depend heavily on pesticides; however, toxicity danger to farmers, consumers, non-target organisms as well as environmental health cause huge concern. Besides, the rise of fungicide resistance is problematic. The objectives of this study were to decipher the multiple mechanisms of biological control in previously identified two promising rhizobacteria (Pseudomonas sp. NS 1 and Bacillus sp. NS 22) in vitro and evaluate their disease suppression and plant growth promotion ability in pigeon pea in vivo. These rhizobacteria inhibited F. udum mycelia growth and biomass in vitro and reduced wilt disease severity in plants grown in Fusarium-infested soil in controlled environmental conditions. Fungicidal action of these rhizobacteria was due to the production of numerous biocidal compounds including different antifungal metabolites, chitinolytic (endochitinase, exochitinase, chitobiase) and other cell wall degrading lytic enzymes (proteinase, cellulose, amylase, pectinase, lipase), siderophores, and antifungal volatile compounds such as ammonia and cyanide. In planta assay, these rhizobacteria made the plant more resistant to fungal attacks through the induction of systemic defense in host tissue by improving the status of different defense enzymes (phenylalanine ammonia lyase, polyphenol oxidase, and peroxidase) and phenolics. Furthermore, these two bacteria significantly reduced disease severity, root mortality, and at the same time, promoted shoot and root elongation in pigeon pea seedlings as compared to the absolute, pathogen, and chemical control. In nutshell, Pseudomonas sp. NS 1 and Bacillus sp. NS 22 displayed the potential as biofungicides and biofertilizers to prevent F. udum induced disease incidence and promote plant growth in an integrative disease and nutrient management approach of sustainable agriculture practices.