DETECTION OF CLAVIBACTER-MICHIGANENSIS SUBSP SEPEDONICUS IN POTATO STEMS AND TUBERS GROWN FROM SEED PIECES WITH VARIOUS LEVELS OF INOCULUM

An indirect sandwich enzyme-linked immunosorbent assay (ELISA) was used to monitor potato stems of three cultivars for the presence of the ring rot pathogen, Clavibacter michiganensis subsp. sepedonicus, during the growing season and in progeny tubers after harvest. The highest ELISA values were obtained with the highest concentration of bacteria used to inoculate seed pieces in all cultivars tested. Low ELISA values were obtained for stems and progeny tubers selected from plants grown from seed inoculated at lower bacterial concentrations. Estimates of bacterial densities in stems and progeny tubers by immunofluorescence indicated that low ELISA values were most probably caused by low bacterial numbers. It is suggested that the sensitivity of ELISA for detecting the ring rot pathogen in potato stems and progeny tubers is a function of the concentration of bacteria in individual seed pieces.