Experimental planning for assessing common bean lines regarding the severity of angular leaf spot

The severity of angular leaf spot can be assessed by artificially inoculating common bean plants at the V2 stage. Accurate and precise selection of lines resistant to this disease by breeding programs depends on adequate experimental planning. The objective of this study was to determine the number of replications and the minimum number of plants per plot for precise and accurate assessment of lines regarding the severity of angular leaf spot in beans inoculated at the V2 stage. Seventy carioca common bean cultivars were inoculated to assess their reaction to races 63–23 and 63–63 of Pseudocercospora griseola. Angular leaf spot severity data was obtained from nine plants per plot and three replications; plot sizes differing from 1 to 9 plants were sampled in analyses with two and three replications per experiment. For each number of plants per plot, 1000 samples were taken. The accuracy and coefficient of variation were obtained for each of the 1000 samples for each number of plants per plot in analyses with two and three replications. Pearson correlation was calculated between the mean severity of the cultivars in each sample for each number of plants per plot, and the mean severity of the cultivars using nine plants in the plot. Experimental precision increased with the number of plants assessed. The use of two replications and six plants per plot were sufficient to accurately and precisely assess the severity of angular leaf spot in bean lines artificially inoculated at the V2 stage.