Screening of a novel biological control agent targeting the phytopathogen Xylella fastidiosa

In autumn 2013, a disease outbreak affecting olive trees occurred in Gallipoli, a restricted area in the southern of Italy. It was the occurrence of the Olive Quick Decline Syndrome (OQDS) caused by a devastating xylem bacterium, the so called Xylella fastidiosa subsp. pauca De Donno strain. In spite of the pertinent research effort and the several published experiments devoted to control the disease, so far there are no control measure available to eliminate the bacteria from a diseased host plant. Therefore, the aim of this study was the screening of antagonistic activity of epiphytic bacteria isolated from the phyllosphere of 8 different host plant species of Xf (Olea europaea, Polygala myrtifolia, Rosmarinus officinalis, Nerium oleander, Laurus nobilis, Myrtus communis, Prunus dulcis and Prunus avium) . In vitro dual culture tests showed that 12 out of 89 isolates inhibited Xf growth with an appearance of clear zones between 4.0 and 24.0 mm. Biochemical tests and 16S rRNA gene sequencing revealed different bacterial species belonging to Pantoea agglomerans (1), Microbacterium oxydans (1), Microbacterium spp. (2), Microbacterium oleivorans (1), Microbacterium phyllosphaerae (1), Stenotrophomonas rhizophila (1), Curtobacterium flaccumfaciens (1), Sphingomonas molluscorum (1), Delftia acidovorans (2) and Pseudomonas graminis (1). Based on results obtained in this study, among the 12 isolates able to reduce the growth of X. fastidiosa, P. agglomerans being the most efficient. Taking into consideration that P. agglomerans and D. acidovorans have potential ability to cause human infections, this aspect will be carefully monitored and, as clarified, the antagonistic efficacy of all isolates will be tested in vivo and under natural field conditions.IT; PPT; mouroumarwa88@gmail.co