Fusarium wilt, caused by Fusarium oxysporum f.sp. tracheiphilum, is an important disease of cowpea (Vigna unguiculata) in Northeastern Brazil. An experiment was carried out in field microplots to evaluate the influence of Fusarium wilt intensity on cowpea yield losses. The soil in microplots was infested with a mixture of two pathogen isolates. A crescent gradient was obtained by adding 1.2 x 10² to 5.3 x 10(4) cfu/g of pathogen-colonized substrate. Five days after the infestation, two cultivars were planted: 'BR-17 Gurguéia' and 'IPA-206', classified as highly and moderately susceptible to F. oxysporum f.sp. tracheiphilum, respectively. At harvest, the yield of the cultivars per microplot was determined through the number of pods per plant, total weight of seeds per plant, and the weight of one hundred of seeds. After harvest, the severity of Fusarium wilt was evaluated in all plants using a descriptive scale and calculating the disease intensity index. Significant differences (P=0,05) were not observed in either disease intensity or yield losses between the two cultivars. Losses in seed yield ranged from 9.11 to 80.30% and from 8.30 to 86.51% in the cultivars BR-17 Gurguéia and IPA-206, respectively. The model of simple linear regression, without data transformation, fitted the data in relation to Fusarium wilt intensity and yield losses of both cultivars.
