白菜軟腐細菌(Erwinia aroideae)的越冬及传佈

It has been experienced that in Peking immediately after the soil is defrozen in the spring, no trace of soft-rot bacteria can be isolated from the field soil, although this organism can be readily isolated from the undecomposed residues of the Chinese cabbage in the field, if there is any. The soft rot of the Chinese cabbage in cellar develops throughout the storage period. It is therefore convinced that the-primary source of infection of the soft rot of the Chinese cabbage is either from the undecomposed residues from the field or from the debris in the cabbage cellar. The seed Chinese cabbage from the cellar after overwintering is planted out at the end of march and meanwhile carries the soft rot organisms to the field. Furthermore, a number of insects serves as spreaders. Isolations of a number of insects found either in cabbage cellar or in spring cabbage fields reveal that 76% of Sarcophaga sp., 66.8% of Fannia sp., 4% of Apis mellifera, 40% of Athalia rosae and 30% of Plutella maculipennis are found to carry soft-rot organisms both externally and internally. The results of an field experiment point out that the early diseased cabbage plants in the field serve as centers of infection of the soft-rot disease. The bacteria are disseminated in the field by the irrigation water. However, only those cabbage plants which are wounded at the basal part are liable to the attack. It is therefore suggested that in addition to the control of insect pests in connection with the adequate cultural practice, the thoroughness of eliminating the centers of infection by prompt removal of the diseased plants from the field every time before irrigation must be observed. In the present paper a rapid method for determining the pathogenic soft-rot bacteria from the soil is described.