Centre for Advanced study in Botany, University of Madras, Guindy Campus, Chennai-600025.
Plant growth-promoting rhizobacteria (PGPR) are root-colonizing bacteria that benefit plants by increasing plant growth and/or can induce a systemic resistance in plants. The finding that some strains of PGPR can elicit systemic disease protection against viruses has renewed interest in PGPR for practical application in agriculture and horticulture. We report here results of Bacillus subtilis against Peanut bud necrosis virus in Cowpea (Vigna unguiculata). The strains we used are B. subtilis Nm1 and 168. Both the strains reduced the disease incidence, but B. subtilis Nm1 performed better of the two in reducing the disease incidence. Strain Nm1 was effective in inducing disease resistance as it produced enormous amount of siderophores than strain 168. Results demonstrated that the application of two bacilli strains as 10% foliar spray was found to be effective and resulted in significant growth promotion that was correlated with induced resistance in cowpea, whereas the virus incidence was 100% in controls (virus inoculated, but not treated with bacilli). The phenolic and salicylic acid content was enhanced in appreciable level in PGPR treated plants than in controls. Studies on mechanisms indicate that elicitation of resistance by B. subtilis is associated with cytochemical alterations. Investigations into the signal transduction pathways of elicited plants suggest that B. subtilis activate similar pathways. Treated plants demonstrate increased shoot and root growth, enhanced stem diameter, and rapid development of roots. Disease protection is observed, but the most reproducible effect is growth promotion which results in yield increases. PGPR application is effective under lab conditions and offers a natural mechanism for biological control of plant disease.
