Influência da utilização de herbicidas sobre Rhizoctonia spp. e nas populações e atividade microbiana em solos do agreste de Pernambuco

Abstract

The Agreste Meridional region of the State of Pernambuco is an important producer of cowpea and common bean in Brazil. In recent years has been recorded a substantial increase in the use of herbicides and incidence of Rhizoctonia canker in these crops. The objectives of this study were to evaluate the influence of herbicides use on saprophytic and pathogenic activities of Rhizoctonia spp. in soils of Agreste Meridional region, and determine the impact of herbicides use on populations and microbial activity in soils. Soil samples were collected in areas destined to the cultivation of these legumes, 15 areas with and 15 areas without history of herbicides use. In the samples were estimated saprophytic and pathogenic activity of Rhizoctonia, population densities of microorganisms and microbial community respiration. The areas subjected to herbicide application presented levels of the activity saprophytic and pathogenic activities significantly (P≤0.05) higher than areas without herbicides. Only 26.7% of the area without herbicide application presented saprophytic activity greater than 80%, while in the areas with herbicides the saprophytic activity ranged from 96.9% to 100%. In most (66.7%) areas without herbicides the pathogenic activity was ≤10%, while in most areas with herbicides (53.5%) showed pathogenic activity exceeding 30%. Trichoderma populations were not detected in the areas with herbicides, while in areas without herbicide reached the mean density of 1.4 x104 CFU g-1 soil. The densities of total culturable fungi and actinomycetes were also lower in soils treated with herbicides, while the populations of total culturable bacteria, fluorescent Pseudomonas, endospore-forming bacteria, oligotrophic bacteria and copiotrophic bacteria were not adversely affected by the use of herbicides. There was no significant difference (P>0.05) between areas with and without the application of herbicides on the respiration of the microbial community.