ARS | Publication request: Differential production of sclerotia by isolates of Sclerotinia sclerotiorum from Alaska.

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 10, 2006
Publication Date: July 20, 2006
Citation: Leiner, R.H., Winton, L.M. 2006. Differential production of sclerotia by isolates of Sclerotinia sclerotiorum from Alaska. Canadian Journal of Plant Pathology 28(3):435-440.

Interpretive Summary: White mold is a plant disease caused by a fungus, Sclerotinia sclerotiorum, that overwinters easily in Alaska. Sclerotinia sclerotiorum was collected from lettuce plants with symptoms of white mold. Two isolates were used in experiments to measure the amounts of fungal propagules produced on vegetables. The data show that hundreds of new propagules, called sclerotia, can form on a single head of lettuce or cabbage, when given time to decompose completely. The sclerotia produced on cabbage and carrot were bigger than sclerotia forming on crops with a lower concentration of carbohydrates, lettuce and celery. These results are important to vegetable producers in Alaska because the data suggest that one part of cultural control for white mold is to minimize the time that crop debris is left in the field before tillage. Like weed seeds, the fewer number of sclerotia going into field soil may mitigate disease pressure in future years.

Technical Abstract: Sclerotinia sclerotiorum (Lib.) De Bary was isolated from lettuce (Lactuca sativa L.) grown in Alaska. Sections of cabbage (Brassica oleracea L. var. capitata L.) were inoculated with isolates designated A and B. Sclerotia of S. sclerotiorum were counted and weighed after the host tissue decomposed. Isolate A produced an average of 42 sclerotia weighing 1.9 g on 100 g cabbage cv. Balbro, which was twice as many and triple the biomass produced by isolate B. Lettuce, carrot (Daucus carota L. ssp. sativus (Hoffm.) Arcang.), and celery (Apium graveolens L.) were also inoculated to measure production of sclerotia. On three cultivars of lettuce, isolate A had greater size and similar number of sclerotia compared to isolate B. On carrot and celery, differences between isolates of S. sclerotiorum were less pronounced, but the difference between hosts was significant. The average size of sclerotia was 73 mg on carrot and 18 mg on celery for isolate A, and 60 mg on carrot and 16 mg on celery for isolate B. Isolates A and B were distinct in the rRNA gene intergenic spacer sequences. Each isolate had identical sequences to those reported for isolates from USA and Canada, and isolate B was identical to a set from New Zealand. Both isolates belong to a relatively recently evolved group exhibiting significant associations between genotype and both geography and host species. In agricultural fields, one infection of white mold on lettuce or cabbage can produce hundreds of new sclerotia that may affect disease levels in future years. Cultural control for white mold can include minimizing the amount of sclerotia on crop residue by disking soon after harvest.