The estimation of lesion diameter of citrus canker is one of the most common parameters used in the evaluation of the interaction of strains x genotypes, host resistance, and epidemiology. However, there is no information indicating the sample size for adequate disease measurement, considering the diameter of lesions. In the present work, our objective was to determine the number of samples needed to estimate the diameter of citrus canker lesions. The following factors of variation were considered: three host genotypes, two methods of inoculation, and two evaluators. The diameter evaluations were made considering, or not, the yellow halo, when present. Estimates of lesion diameter with average errors smaller than 3% are impracticable because of the excessive sample size (at least forty lesions/plant). Smaller errors occurred when only the necrosis was considered during the evaluations. Precise estimates of lesion diameter, with errors smaller than 10%, are achieved with sample size between five and fifteen lesions/plant, independently of the citrus genotype and age of lesions.
Xanthomonas citri subsp. citri; phytopathometry; citrus
