Utilização de Rhizoctonia sp. binucleada no biocontrole de damping-off causado por Rhizoctonia solani Kühn AG-4 HG-I

With the intent of looking for and testing new biocontrol agents for the control of soil-bome pathogens, this research was carried out using five binucleated Rhizoctonia spp. (BNR) isolates to control Rhizoctonia solani AG-4 HG-I isolate. BNR isolates SJ 06 (AG E), SJ 10, SJ 11 and SJ 12 (AG A), and SJ 08 were characterized by hyphae anastomosis and ITS1-5.8S rDNA-ITS2. The methods used for the biocontrol tests were the water agar, soil agar, and soil. The crops used were soybean, bean, peanut, lettuce, tomato, bell pepper, cucumber, broccoli, melon and pumpkin cultivars. The tests were performed with the purpose of evaluating the protective effect of the BNR isolates on all cultivars, based on the classification of disease severity. Hence, it was possible to estimate the percentage of protection provided by the biocontrol agent against the pathogen. In both the water-agar method and the soil agar method, the majority of the isolates were not efficient in biocontrol due to the fact that these methods allow only two days of antagonist growth before they came in contact with the pathogen. Meanwhile, with the soil method, where the BNR isolates were allowed to develop for one week with the seedlings before confrontation with the pathogen, SJ 11 and SJ 12 presented the most effective protection. Isolate SJ 11 protected 100% of bell pepper, 62.5% of broccoli, 92.3% of pumpkin and 61.9% of soybean. Meanwhile, isolate SJ 12 presented the following protection percentages: 95,2%, 63,0%, 60,7%, 100,0%, 71,4% and 77,8%, in soybean, tomato, lettuce, pumpkin, peanut and bell pepper, respectively.