Disease Note.

Licorice Rot of Carrot Caused by Mycocentrospora acerina in Western Washington. D. A. Inglis, WSU Mount Vernon REU, 1468 Memorial Hwy., Mount Vernon, WA 98273. O. C. Maloy, Department of Plant Pathology, Washington State University, Pullman 99164. Plant Dis. 78:1122. Accepted for publication 20 July 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1122A.

Dark, water-soaked areas (3-5 cm long) associated with cracking occurred on the taproots of nearly 1,089 metric tons of slicing carrots (Daucus carota L. cv. Gold Pride) grown in muck soils in western Washington in 1992, making them unsuitable for processing. Dark, torulose hyphae observed in affected tissues yielded Mycocentrospnra acerina (R. Hartig) Deighton. On potato-dextrose agar, the fungus had pink aerial mycelium, dark submerged hyphae consisting of chlamydospore-like cells, and long tapering conidia, each with a swordlike appendage. Seedlings grown in vermiculite mixed with dried, macerated cultures (1:20 w/v) developed severe lesions from which M. acerina was reisolated. The fungus occurs on many hosts throughout Europe and causes crown rots of celery, parsnip, and parsley. Licorice rot was reported on carrots grown in New York in the mid-1940s. It also was reported from the Pacific Northwest on Osmorhiza in 1937, and on Viola in 1946. M. acerina is persistent in soil and especially damaging to crops grown in muck soils in cool maritime climates, or to crops already damaged. Carrot rust fly (Psila rosae (Fabricius)) injury possibly contributed to licorice rot severity in Washington in 1992.