EFFECT OF BEAN SEED TREATMENT WITH FLUORE SCENT PSEUDOMONAS SPP ON RHIZOCTONIA-SOLANI CONTROL

The effect of bean seed treatment with fluorescent Pseudomonas sop. is olates was evaluated for Rhizoctonia solani control. In preliminary sc reening 64 isolates were tested. Bean seeds, cv. IPA-6, were immersed in the bacterial suspensions (10(8) cells/ml) prepared in 0,1 M MgSO4 solution and then sown in trays containing natural soil previously inf ested with the pathogen (RS-1 isolate) at a concentration of 50 mg of substrate (colonized rice)/kg of soil. The evaluation of disease inten sity was carried out after 8 days, using a grade scale from 0 to 4, wh ere 0 = without symptoms and 4 = maximum of symptoms. The isolates FR- 38, TR-48 e CR-26, showed best disease control and were identified as Pseudomonas putida. These isolates were evaluated under greenhouse con ditions in relation to different R. solani isolates (RS-1, RS-2, RS-3, RS-4, and RS-5), different inoculum concentrations (5, 10, 20, 50 and 100 mg/kg of soil), and under field conditions in relation to two ino culum concentrations (3 and 6 g/m(2) of soil) of the pathogen. The res ults showed great variation in performance of P. putida isolates on R. solani control in all situations. The isolate FR-38 was the best bioc ontrol agent in relation to RS-2 pathogen isolate, while CR-26 showed the best performance in relation to RS-4. FR-38 showed better efficien cy than other isolates and than Quintozene treatment at the smallest p athogen inoculum concentration (5 mg/kg of soil), while TR-48 was the best at 20 mg of inoculum/kg of soil. Under field conditions, consider ing the average of the two inoculum concentrations, FR-38 presented be tter efficiency than other bacterial isolates and than Quintozene. The mechanism of action of P. putida against R. solani could not be under stood.