First Report of Colletotrichum destructivum on Curly Dock.

Abstract

Curly dock (Rumex crispus L.) is a perennial deciduous plant in the family Polygonaceae. It is widely distributed in grasslands and orchards and is an important weed that is traditionally used as a medicinal herb. During the summers of 2000 and 2001, a severe anthracnose disease was observed on leaves of mature curly dock in the foothills near the western coastal area of Muchangpo, Ungchon, the district of Chungnam in Korea. Initial symptoms usually appeared in June as a small number of slightly soaked spots on leaves. Typical symptoms, generally observed in late July and August following a long, rainy, hot period, consisted of a number of brown leaf spots that expanded and often twisted, resulting in discoloration of whole parts to blackish brown or slightly reddish brown and defoliation. A fungus, which was isolated from the leaf lesion, was identified as Colletotrichum destructivum O'Gara based on previous descriptions (1,3). The fungus was characterized by conidia, which were long, relatively narrow, and straight to slightly curved with abruptly tapered and obtuse ends, complex appressoria, and cultures with apricotto salmon-colored sectors that lacked sclerotia. Conidial size ranged from 4.0 to 6.4 μm (average 4.8) × 10 to 23 μm (average 16.5). Setae were slender and straight but frequently flexuous, subulate, brown, and variable in length. C. destructivum has a teleomorph, Glomerella glycines (Hori) Lehman & Wolf, but the species is not well known, and the connection has not been studied in detail. The isolate has been deposited in the IMI Culture Collection as isolate IMI387103. The dimensions of conidia from the isolate matched those of C. destructivum N150 (GenBank Accession No. AF325064) isolated from Nicotiana tabacum (3). C. destructivum is distinguishable from C. gloeosporioides, whose spores are short and cylindrical with obtuse apices tapering slightly to a truncate base. Pathogenicity of the isolate was determined on 5-week-old leaves of curly dock. Leaves were inoculated with a conidial suspension of the fungus (approximately 1 × 106 conidia per ml), placed in a moist chamber for 3 days, and subsequently transferred to a growth chamber maintained at 25°C. Within 7 days after inoculation, symptoms appeared that were similar to those originally observed on leaflets. Uninoculated control (sprayed only with distilled water) leaves exposed to the same environmental conditions remained healthy. C. destructivum was consistently reisolated from infected leaves. C. destructivum has been reported as a pathogen on approximately 15 genera, including Medicago sativa, Trifolium spp., Cuscuta spp., and N. tabacum (1,3), and two fungal species, C. erumpens and C. rumicis-crispi, have been reported to cause anthracnose on R. crispus. To our knowledge, R. crispus represents a previously unreported host for C. destructivum causing anthracnose, although C. gloeosporioides has been reported as a pathogen of R. crispus in Korea (2).