NUCELLAR CALLUS OF FEMMINELLO LEMON, SELECTED FOR TOLERANCE TO PHOMA-TRACHEIPHILA TOXIN, SHOWS ENHANCED RELEASE OF CHITINASE AND GLUCANASE INTO THE CULTURE-MEDIUM

Phoma tracheiphila is the causative agent of the disease mal secco. Ci trus cultivars differ substantially in respect to their sensitivity to the pathogen P. tracheiphila and its toxin. Some cultivars (e.g., 'Fe mminello' lemon) are inherently sensitive while others (e.g., 'Tarocco ' orange) are tolerant. Cell lines derived from nucellar tissue of 'Fe mminello', 'Tarocco' and a cell line selected for tolerance to the fun gal toxin ('Femminello-S') were used to study host-pathogen interactio n. Our results showed that calli or conditioned media of 'Tarocco' and 'Femminello-S' inhibited the size of co-cultivated fungal colonies wh en compared to 'Femminello'. In addition, conditioned medium of 'Taroc co' as well as 'Femminello-S', but not 'Femminello', promoted bursting of hyphal tips. A ten-fold increase in chitinase and glucanase enzyma tic activity, as evaluated by radiometric assay and laminarin hydrolys is respectively, was detected in 'Femminello-S' extracellular extracts as compared to 'Femminello'. An increase in chitinase was also shown by immunoblot analysis. Our findings suggest a positive correlation be tween the presence of chitinase and glucanase in the conditioned media of the cultured cells and the tolerance of those cells to P. tracheip hila toxin.