The Brazilian pepper-tree (Schinus terebinthifolius Raddi) native to Brazil, recently has become an aggressive perennial weed in southern Florida. During a survey in December 1995, a foliar disease was observed on several pepper-tree plants in Palm Beach County. Disease symptoms consisted of dark, reddish-purple necrotic lesions, either with or without dry necrotic centers, that were distributed randomly over the leaf surface. Infected leaf samples from two separate sites were plated on potato dextrose agar (PDA; Difco) and water agar and incubated at 25°C in the dark. A fungus resembling a Rhizoctonia sp. was consistently recovered. To prove Koch's postulates, the fungus was grown on PDA for 10 to 14 days, and the cultures blended in a Waring blender. Metamucil (Procter & Gamble) was added to the mixture at the rate of 0.5% wt/vol, and the suspension was used to spray and inoculate 2- and 3-month-old Brazilian pepper-tree seedlings. Seedlings were sprayed until the inoculum dripped off the foliage and after inoculation were maintained at 100% relative humidity. After 48 h in the dew chamber the inoculated seedlings were moved to a greenhouse bench and examined for infection 5 and 10 days later. Inoculation was completed three times with the leaf lesions occurring 94 to 100%. A Rhizoctonia sp. was recovered from the lesions that appeared on the challenged plants. A determination of the anastomosis group was performed by plating it against the tester isolates of R. solani, AG1-1A, AG2-2IV, AG-3, AG-4, and AG-5. In two separate tests anastomosis (imperfect fusion) (1) was observed between the recovered Rhizoctonia sp. and tester strain AG2-2IV of R. solani. The fungus was identified as R. solani, and this is the first report of R. solani causing a leaf lesion of Brazilian pepper-tree in Florida. The potential of this R. solani as a biological control agent of Brazilian pepper-tree remains to be tested.
Reference: (1) B. Sneh et al. Identification of Rhizoctonia Species. American Phytopathological Society, 1991.
