Potential Biocontrol Effect of the Phylloplane Bacterium Bacillus mojavensis ABC-7 on the Olive Knot Disease

Abstract

Olive knot disease, caused by Pseudomonas savastanoi pv. savastanoi, is one of the most important biotic stress for olive cultivation in most olive cultivation areas, particularly in Mediterranean countries. It conducts to intense damage in olive groves, causing heavy production losses. Bacillus mojavensis A-BC-7, a natural colonizer of symptomless olive phylloplane, was determined as potential biocontrol agent against olive knot disease strain ITM317- Rif, a mutant strain resistant to Rifampicin (100 ppm). Bioassays on one-year-olive plants were carried out to survey the antagonism of A-BC-7 controlling knot development and pathogen populations when co-inoculated with the pathogen on stems with different ratios. Results showed that A-BC-7 was able to decrease knot weights and pathogen population size, producing less necrotic tumors. In particular, when we applied the mixture suspensions of ITM317-Rif+A-BC-7 with the ratio 1:9 that resulted of 43.11% of overgrowth inhibition at 30 days after inoculation, which increased to reach about 59% at 60 days after inoculation and then 75% at 90 days after inoculation. That may pose epidemiological consequences.