Effect of non-pathogenic Pseudomonas strains on the severity of diseases caused by Botrytis cinerea and Alternaria alternata on tomato and Arabidopsis plants

Non-pathogenic Pseudomonadsare the main biocontrol agents that are used in plant disease management. In this study, effects of four strains of Pseudomonas fluorescens (Pf1, Pf2, Pf3, Pf4), and P. putida (P13) were studied for their ability to elicit induced systemic resistance against diseases caused by Botrytis cinerea and Alternaria alternata on tomato (Super Majar and Queen cvs) and Arabidopsis. The ability of biocontrol agents to colonize roots of tomato cultivars and Arabidopsis and induce resistance was shown to be highest for P13, and Pf3 strains and P13, and Pf3 were able to reduce the average lesion diameter of diseased leaves to 30% and 25%, compared to that of control, respectively. The ability of biocontrol agents for direct control the pathogens was also evaluated. The results revealed that P. putida (P13) was the best biocontrol agent as measured by the reduction in disease severity. P13 reduced the average lesion diameter of diseased tomato leaves by about 45%. Finally, Pf3 and P13 were identified as more powerful strains. Moreover, these strains could induce some level of resistance against various pathogens and they had the ability to enhance plant growth.