Studies Of Enoinia Soft Rot Disease On Potato
Murphy, Peter J.
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E. caroiooora subsp. caroiouora (Ecc), the soft rot bacteria of potato, survives for a long period in lenticels and suberized wounds during storage. The disease is more severe when the environmental conditions favour its development, therefore, managing soft rot disease is a difficult task. Washed and brushed potato tubers, which were artificially inoculated using different inoculation methods, were used in this study to detect the population of Ecc in tuber. The number of Ecc were assessed by a plate assay on selective agar medium (CVP). This study also highlights the relationship between artificial tuber inoculation and the population of Ecc in the tubers. The effect of chlorine solution and drying treatment were also examined as a means to reduce soft rot development on potatoes. Although low numbers of Ecc were found in the tubers, the lenticel sampling method could detect the bacteria more effectively than the peel method. However, both methods were time consuming and labour intensive. It is suggested that serological methods of detection should be investigated in further studies. The result of experiments quantifying the colonization of soft rot bacteria revealed a poor correlation between the inoculation level of Ecc and the population of Ecc in the tubers. This study showed a slightly higher number of Ecc were re-isolated from tubers inoculated with 106 cfu/ml, both by the dipping and by the infiltration methods. This level of inoculation was used as the preferred inoculation level of Ecc for further experiments. This study revealed that chlorine could not eliminate Ecc from the lenticels, both on washed and brushed potato tubers. Similarly, when chlorine was used in combination with drying Ecc was not eliminated from the tubers. Nonetheless, either chlorine or drying treatment could reduce the potential of soft rot development of brushed potato tubers. The effect was most dramatic with the drying treatment. Overall the results suggest that disease development did not correlate with the number of bacteria in lenticels. It seemed difficult to eliminate all bacteria from lenticels. Even if the number of Ecc present were low, but the conditions for their growth were ideal (i.e. a moist environment), disease would rapidly develop.