Web blight caused by the fungus Thanatephorus cucumeris (Rhizoctonia solani anastomosis group 1 IA ) is one of the most important diseases of cowpea (Vigna unguiculata) in the north of Brazil. There is no information about the effect of epidemiological parameters on development of the disease under controlled conditions. The aims of this work were to identify the type and inoculum concentration of R. solani, the susceptible phenological states and the leaf wetness periods for disease development in greenhouse conditions. In the first study we tested the use of mycelia fragments (mf) and sclerotia as source of inoculum; in the second experiment, the effect of different inoculum concentrations (0, 10³, 10(4),10(5) and 10(6) mf.mL-1); in the third experiment, the effect of leaf wetness period was tested by maintaining cowpea plants at 0, 6, 12, 24 and 48 hours of leaf wetness after the inoculation, and in the last experiment the effect of phenological states was tested by inoculating cowpea plants at the stages of cotyledonal leaf, trifoliate leaves, flowering and pod filling. The highest severity values of disease were observed with the plants inoculated in the flowering phenological state with 10(6) mf.mL-1 and six hours of leaf wetness. These parameters can be utilized to establish an inoculation methodology for R. solani on cowpea plants under controlled conditions.
Rhizoctonia solani; Thanatephorus cucumeris; Vigna unguiculata; epidemiology; Blackeye bean
