Management of melon bacterial blotch by plant beneficial bacteria

Plant beneficial bacteria (PBB) have shown potential for disease control and are particularly important in the management of bacterial diseases, which are poorly controlled by conventional methods. In melon, bacterial fruit blotch caused by Acidovorax citrulli is a seedborne disease that is particularly destructive under certain conditions. PBB strains were screened for their ability to protect seeds and leaves from bacterial fruit blotch, and their antibiosis activity and plant colonization were studied. When Bacillus sp. RAB9 was applied to infected seeds, it reduced the area under the disease progress curve (AUDPC) by 47% and increased the incubation period (the time between inoculation and the first visible symptoms) by 35%. Three of the selected strains (JM339, MEN2 and PEP91) displayed antibiosis against A. citrulli. The RAB9^Rif-Nal mutant colonized seeds epiphytically and roots and stems endophytically. Paenibacillus lentimorbus MEN2 sprayed on melon seedlings protected leaves, and when challenged with A. citrulli, it reduced the AUDPC (by 88%), disease index (by 81%) and incidence (by 77%). Given that the production of both melon seedlings and commercially grown greenhouse melons is increasing, biocontrol strategies may well be integrated into bacterial blotch management programs.