DISTRIBUTION, FREQUENCY AND DIVERSITY OF BACILLUS-THURINGIENSIS IN OLIVE TREE ENVIRONMENTS IN SPAIN

Bacillus thuringiensis was isolated from samples collected from olive tree related habitats (olive groves, olive storage facilities and oil mills) of different olive producing regions in Spain. This bacterium w as found in a high percentage (92%) of samples. From 72 samples analys ed, 2244 sporulating colonies were selected and observed under phase c ontrast microscopy, From these, 414 colonies (18%) were classified as B. thuringiensis based on the production of parasporal crystals. A gre at variability of spore, crystal size and morphology was observed. The results indicate that olive groves are as rich as soil olive mills an d olive storage facilities regarding the B. thuringiensis population. Analysis by SDS-PAGE of the proteins in the parasporal crystal showed a considerable heterogeneity between B. thuringiensis strains. This wa s especially relevant in samples obtained from oil mills and storage c entres, indicating the high polymorphism in this species. Strains isol ated from the same sample showing the same SDS-PAGE profile were not c onsidered different, and lust one of them was selected for further tes ts. A total of 188 out of the 414 B. thuringiensis isolates were shown to be different strains and rested for their toxicity against adult a nimals of the olive fly Bactrocera oleae. Approximately 40% of the str ains caused similar or higher mortality than the dipteran active strai n B. thuringiensis israelensis (45% mortality). Most strains (71%) pro ducing a toxicity high er than 65% came from olive mills and olive sto rage facilities. Three of these strains exhibited a mortality higher t han 70% in our test conditions.