Sclerotinia rot of carrot, caused by Sclerotinia sclerotiorum, is an economically important disease that causes yield loss ill stored carrots. To examine the relationship between infection of leaves in the held and disease development in roots, the histopathology of sclerotinia rot within carrot crowns was investigated. Petioles of mature greenhouse-grown carrots were inoculated with mycelium of S. sclerotiorum. Disease progression was monitored in carrots in the greenhouse and in carrots that were harvested and placed in cold storage at 4 degrees C. Disease progressed more rapidly through carrot crowns in storage than in carrots in the greenhouse. and this differential reaction was associated with changes in tissue response to infection. A thick layer of cells that stained red with safranin O and a zone of leaf abscission were observed at the base of infected petioles of carrots that remained in the greenhouse, and these responses were associated with restricted disease progress. Cellular staining occured rarely and leaf abscission was not detected in carrots that were harvested and placed in cold storage. These results demonstrate a possible preharvest resistance response to S. sclerotiorum in carrot, which was absent in carrots that were harvested and placed in cold-storage conditions. This study contributes, to an improvement in understanding of the differential development of this disease in carrots before and after harvest.
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