Enzymatic Maceration of Witloof Chicory by the Soft Rot Bacteria Erwinia carotovora Subsp. carotovora: The Effect of Nitrogen and Calcium Treatments of the Plant on Pectic Enzyme Production and Disease Development

Disease incidence of bacterial soft rot caused by Erwinia carotovora subsp. carotovora and activities of bacterial pectolytic enzymes were studied in witloof chicory. Disease incidence after forcing of the chicory heads was enhanced by the nitrogen treatment and reduced by the calcium treatment of the chicory plants prior to forcing. Significant differences in susceptibility to bacterial soft rot were found for the tested chicory cultivars. Disease severity after 96h ranged from 6% in Clause R2 to 100% in Bea and Tabor. Chicory cultivars Rumba and Salsa showed a final average severity of 65–70%. Activity of the pectolytic enzymes, polygalacturonase and pectate lyase increased in artificially inoculated chicory heads of cultivar Rumba and was not affected by calcium and nitrogen treatments of the plants. Polygalacturonase showed highest activity 48h after inoculation while pectate lyase activity increased throughout 72h of incubation. Maceration of the chicory tissue and bacterial growth increased continuously until 96h after inoculation, when more than 60% of the chicory heads was macerated by pectolytic enzymes of the bacteria. Enzyme activity of Erwinia carotovora subsp. carotovora grown on chicory cell wall extracts was influenced by nitrogen and calcium treatments of the chicory plants. The activity of polygalacturonase reached its highest level at 48h after incubation and pectate lyase activity peaked at 24h followed by a continuous decrease until 72h after inoculation.