A study on bacterial softrot in witloof chicory

The production process of witloof chicory, which consists of the root production stage, the storage of the roots and the forcing of the chicory heads, was monitored for the presence of softrot bacteria. In the Netherlands, bacterial softrot in chicory is caused by Erwinia carotovora subsp . carotovora ( Ecc ) and Pseudomonas marginalis .Populations of these species colonised the chicory leaves during the root production stage causing softrot only in the forcing stage. The colonisation incidence, the number of populations of both pathogens present on the chicory leaves, increased during the root production. Ecc was inhibited by high radiation levels during the first months of the growing season of the plants. The colonisation incidence of the chicory leaves was influenced by the average temperature throughout the growing season but not by nitrogen fertilisation of the crop or rainfall. The colonisation incidence of the stored roots decreased from harvest time in September until December but increased thereafter. High colonisation incidences during storage coincided with high disease incidence during the subsequent forcing period of the roots.Bacterial softrot occurred during forcing of the roots in all three forcing seasons. Nitrogen fertilisation of the plants, root immersion with calciumchloride and the sampling year had significant effects on disease incidence. Aggregation of diseased chicory heads in forcing trays could be described by an aggregation parameter of the beta-binomial distribution. Studies on the enzyme activity of the softrot bacteria showed that nitrogen and calcium effects on disease severity could be explained by the influence of these treatments on the activity of two pectolytic enzymes of the bacteria. Reduction of bacterial softrot is possible by reduced nitrogen fertilisation during root production and by application of calciumchloride to harvested roots.