Pea-Saving Partners: Bacillus and Pseudomonas combat downy mildew in pea crops

Abstract

Downy mildew (DM) is a destructive disease that significantly reduces the yield and quality of important pulses (legumes) and horticultural crops, particularly during humid and cool seasons. This disease is caused by obligate and host-specific oomycete pathogens. Controlling the pathogen is challenging due to its long-term survival as spores and its rapid mutation. Use of chemical pesticides has been the most effective method to control DM pathogens, but their environmental hazards are a global concern. Current research is focused on exploring the potential of microbial biological control agents (MBCA), particularly rhizobacteria strains of the genera Bacillus and Pseudomonas, which have shown suppression of plant pathogens. However, to date, no MBCA has been reported to be effective against DM pathogens in pulses. We investigated the effectiveness of Bacillus and Pseudomonas strains as potential biopesticides against the pea downy mildew pathogen Peronospora viciae f. sp. pisi (Pvp). In our study, in vitro bioassays showed 100% inhibition of Pvp spore germination compared to the control. In planta antagonism assays further demonstrated significant suppression (>80%) of Pvp sporulation in pea plants sprayed with strains of Bacillus velezensis or P. fluorescens or their filtrates. The drench application also showed significant effects where either a Pseudomonas or cold-adapted Bacillus strain was used. We observed a synergistic effect for the dual foliar application of the microbes compared to individual application (27.6 to 46.7% suppression). Furthermore, the results from the molecular biomass analysis were consistent with the results of the sporulation assays. This demonstrates the strong interactive and promotive benefits of using Bacillus and Pseudomonas as biocontrol agents Based on these results, we conclude that these MBCAs could be effective in combatting Pvp infections in the field.