ABSTRACT This study aimed to determine the minimum number of plants per plot to assess the field resistance in common bean to white mold. Thirteen cultivars were inoculated with six isolates of Sclerotinia sclerotiorum and evaluated in a randomized block design with three replications and plots consisting of 1-m rows with 15 plants. Plants were inoculated by the straw test as proposed by Petzoldt and Dickson (1996), to evaluate partial resistance in a greenhouse. Eight days after inoculation the disease severity was evaluated on a 1-9 diagrammatic scale, where 1 = asymptomatic plants to 9 = plant death. To determine the minimum number of plants per plot, the following methods were used: maximum curvature, segmented linear model, quadratic segmented model and the relative CV model. There were significant differences among cultivars and isolates and no significant cultivar - isolate interaction. It was observed that eight plants per plot is an adequate number to assess the reaction of common bean to white mold.
breeding; Sclerotinia sclerotiorum; experimental design; resistance to the pathogen
