Abstract

Phytophthora infestans, the causal agent of late blight disease, poses a significant threat to tomato and potato crops worldwide. The present study investigated the potential of Bacillus velezensis-derived iturin A as a biocontrol agent against P. infestans, both in vitro and in greenhouse pot experiments. First, P. infestans was isolated and identified from infected leaf samples collected from fields. Concurrently, B. velezensis was isolated from the same soil and characterized through molecular techniques. Subsequently, the inhibitory activity of B. velezensis living cells and cell suspension against P. infestans was evaluated, showing significant inhibition rates of 85.4% and 95.6%, respectively. Extraction and identification of iturin A from B. velezensis revealed a concentration of 210 mg per gram of dried cyclic lipopeptides. Mass spectrometry and NMR analysis confirmed the presence and chemical characteristics of iturin A, validating its abundance in the B. velezensis strain. Antagonism tests of bioformulations containing varying concentrations of iturin A exhibited varying degrees of inhibition, with higher concentrations achieving complete suppression of P. infestans mycelium growth. Notably, bioformulations RPB4 containing iturin A (20 mg per ml) showed promising efficacy in greenhouse pot experiments, demonstrating the highest efficacy in reducing disease incidence and severity index, comparable to the chemical fungicide metalaxyl. Hence, the study deals with developing a sustainable alternative to chemical fungicides.

Key words: Antagonism tests Cyclic lipopeptide, Mass spectroscopy, Solanum lycopersicum