Factors affecting ring rot development in root-inoculated potato plants originating from stem cuttings

Some of the factors that affected ring rot development in potato plants grown from stem cuttings and root-inoculated withCoryncbacterium sepedonicum were investigated. Isolates ofC. sepedonicum cultured and stored for a, year on agar media were as virulent as those that had been cultured for almost 5 months. Isolates cultured for periods over 2 years gradually lost their virulence; however, decline in virulence was not as rapid as had been previously reported. One isolate became more virulent by inoculating and recovering it from a susceptible potato plant. Ring rot symptoms developed more rapidly in the cultivar Red Pontiac than in the cultivar Netted Gem; however, disease severity eventually reached the same level in both cultivars. The more mature the plants were when inoculated, the greater was the rate of ring rot development. Duration of exposure of wounded roots to inoculum of the pathogen did not affect disease development. No ring rot bacteria were recovered from plants originating from apical cuttings of ring-rot-infected potato plants that exhibited partial wilting. By this technique, plants infected withC. sepedonicum were freed from this pathogen quickly and effectively.