Two diagrammatic scales were developed to assess the severity of bacterial blight of cowpea, caused by Xanthomonas axonopodis pv. vignicola in cowpea cultivars with oval and lanceolate leaflets, considering the limits for minimum and maximum severity of the disease, as well as intermediate levels. The levels were determined in accordance with the "Weber-Fechner's Stimulus Responses Law", representing: 0.05; 0.25; 1.00; 3.40; 9.70; and 17.70% for diagrammatic scale with oval leaflets and 0.10; 0.35; 1.10; 3, 50; 9.30; and 19.10% for lanceolate leaflets. The scales were validated by means of their accuracy and precision. To calculate these factors, linear regression analysis of actual disease severity and the estimated ones with and without the use of the scales. Twelve non-experienced evaluators estimated 50 leaflets with different levels of severity bacterial blight. For this, the accuracy and precision of the evaluators was assessed. With the use of diagrammatic scales, there were satisfactory levels of accuracy and precision. Thus, the diagrammatic scales proposed were considered appropriate to assess the severity of bacterial blight of cowpea and can be used in epidemiological studies, to evaluate the reactions of genotypes to the disease.
epidemiology; quantification; phytopatometry; Vigna unguiculata; Xanthomonas axonopodis pv. vignicola
