INDUCED SUPPRESSIVENESS TO Rhizoctonia solani KÜHN BY THE ADDITION OF DIFFERENT VEGETABLE AMENDMENTS TO THE SOIL

Abstract

Organic matter of several origins is used in the agriculture to stimulate microbial activity and to limit the activity of plant pathogens. Its decomposition induces the activity of some microorganisms that are useful to other species establishing synergistic and antagonistic relationships that maintain the biological balance. The present work aimed to evaluate the effect of different vegetable amendments incorporated in the soil on the incidence of root-rot, caused by Rhizoctonia solani. In greenhouse, plastic trays containing 4 kg of cultivated soil were inoculated with 104 propagules of Rhizoctonia solani g-1 of soil and in each tray it was incorporated the equivalent of 10 t/ha plant of debris mater of the following species: Panicum miliaceum, Sorghum maximum, Dolichos lab-lab, Canavaria ensiformis, Braquiaria brizanta, Panicum maximum and Crotalaria juncea. The incorporation of the vegetable amendments were realized simultaneous by and the soil was maintained near field capacity for 60, 30 and 0 days, before the bean cultivar Pérola was sown. Symptom intensity was evaluated 15 days after the emergence, using a descriptive scale, varying from 0 to 8. After the completion of the experimental microbial population was estimated in the soil samples collected
from each plastic tray serial dilution test using selective culture media. Bacteria and fungi colonies were counted after a seven days incubation period and those of actinomycetes after ten days. Results showed that only vegetable materials incubated for 60 days were able to reduce disease index. No significant differences were observed among the studied plant species. The relationship among number of propagules of fungi, actinomycetes, and bacteria with the disease index revealed that the amendments with a larger induced microbial population in the soil were those that presented smaller disease index.

KEY-WORDS: Rhizoctonia root rot; biological control; soil microbial population.