Metodologia de inoculação, variabilidade e controle de Rhizoctonia solani na cultura da cenoura

Abstract

Rhizoctonia solani is a complex pathogen, formed by a group of related but genetically isolated species, grouping on the basis of hyphal anastomosis. They can cause damping-off of carrot seedlings resulting in a stand reduction of the initial seedling development, and, as a soil inhabitant it is able to survive as a saprophyte or as survival structures (sclerotia), being difficult to detect before causing damage. Despite the importance of this pathogen in carrot fields, few is the information about the disease epidemiology and control. Hence, the objectives of this work, were to characterize isolates of R. solani, adjust an inoculation methodology and evaluate the efficacy of fungicides in the control of seedling damping-off. Three isolates of R. solani were obtained from an infected field, where one belonged to AG4 and two isolates were not compatible by anastomosis with any other anastomosis group. The best form to inoculate was done at 10% of the soil in the top 0-2 cm layer, using a density of 72 mg of inoculum per kilo of soil. The most efficient fungicides were pencicuron in the treatment of row and seed, reducing the number of damped-off seedlings and azoxistrobin enhanced seedling emergence. The field-isolate and the tester belonging to AG4, were the more aggressive in the carrot crop at temperature of 20ºC. It is necessary more specific studies for each active ingredient tested, aiming more specific doses to seed and row treatment in carrot fields, as well as, to test pathogenicity of strains of R. solani in other temperatures that can cause infection of the studied crop by this pathogen.