Phyllosphere bacterial strains Rhizobium b1 and Bacillus subtilis b2 control tomato leaf diseases caused by Pseudomonas syringae pv. tomato and Alternaria solani

Abstract

Aims: Show that tomato leaf phyllosphere bacteria are candidates for biocontrol of tomato leaf diseases. Methods and Results: Seven bacterial isolates from surface-sterilized Moneymaker tomato plants were tested for growth inhibition of 14 tomato pathogens on potato dextrose agar. Biocontrol assays were conducted with tomato leaf pathogens, Pseudomonas syringae pv. tomato (Pto) and Alternaria solani (A. solani). Two potential isolates showing the greatest inhibition were identified by 16S rDNA sequencing as Rhizobium sp. (isolate b1) and Bacillus subtilis (isolate b2), both produce protease and isolate b2 cellulase. Both reduced tomato leaf infections by Pto and A. solani in detached leaf bioassays. Both bacteria b1 and b2 reduced pathogen development in a tomato growth trial. Bacteria b2 also induced the tomato plant salicylic acid (SA) immune response pathway. Disease suppression in biocontrol assays with b1 and b2 varied between five commercial tomato varieties. Conclusions: Tomato phyllosphere bacteria when used as phyllosphere inoculants, inhibited tomato diseases caused by Pto and A. solani.