The Probability of Detecting Clavibacter michiganensis subsp. sepedonicus by Indexing Seed Potato Lots with Serological Tests

Detection of the bacteria! ring pot pathogen {Clavibacter michiganensis subsp. sepedonicus) in seed potato lots by laboratory indexing complements visual inspection. The probability of detecting symptomless infections is a function of sample size and incidence of infection. We determined the incidence of asymptomatic stem and tuber infections in four potato cultivars at three levels of inoculum. At the high inoculum level, 51-93% of stems were infected at 80 days after planting, and 10-59% of the tubers were infected at harvest. The effect of the different percentages of infected stems and tubers on the probability of detection for simple random sampling was calculated for a constant sample size. The actual detection levels for two cultivars planted in field plots with predetermined incidence levels of ring rot infected plants were reasonably close to predicted probabilities