PSEUDOMONAS SAVASTANOI ENDOPHYTIC BACTERIA IN OLIVE TREE KNOTS AND ANTAGONISTIC POTENTIAL OF STRAINS OF PSEUDOMONAS FLUORESCENS AND BACILLUS SUBTILIS
S. Krid, A. Rhouma, I. Mogou, J.M. Quesada, X. Nesme, A. Gargouri
Forty nine endophytic bacterial isolates were obtained from knots on olive stems induced by Pseudomonas savastanoi pv. savastanoi (Pss) and from symptomless leaves of olive trees naturally infected with Pss from six orchards from different locations in Tunisia. Populations of all endophytic bacteria were higher in knots (1-14 106 CFU/g) than in leaves (5-21 104 CFU/g). A 16S rDNA sequence analysis revealed the presence of many saprophytic bacteria associated with Pss, such as Pantoea agglomerans, Enterobacter sp., Pseudomonas sp., P. fluorescens, Stenotrophomonas maltophilia and Burkolderia cepacia. In the leaves, however Pss was often associated with Bacillus subtilis and an Acinetobacter species. Screening of antagonistic activity of 18 isolates associated with Pss in knots or leaves showed that only one strain of P. fluorescens and one strain of B. subtilis were highly antagonistic against Pss. The active compound produced by B. subtilis is a protein whereas that produced by P. fluorescens is not.