First report of zonate leaf spot of Cocculus trilobus caused by Cristulariella moricola in Korea

Cocculus trilobus DC., a vine in the Menispermaceae traditionally used as a medicinal herb in Asia, is widely distributed in most areas of Korea. In late August to November, 1999 to 2001, a zonate leaf spot was observed on Cocculus for the first time in the Chungnam, Kyonggi and Chungbuk districts. The high rainfall in 2000 appeared to favour disease more than the drier conditions in 1999 and 2001. Initial symptoms were small lesions with dark brown margins that later developed concentric rings (Fig. 1). Spots expanded and coalesced, causing defoliation (Fig. 1B, 1C).

Fungal structures were whitish under the light stereo-microscope, each consisting of a stout hyaline conidiophore bearing a highly branched cone-shaped or pyramidal multicellular conidium, together measuring up to 884 µm in length (Fig. 2). The conidial head ranged from 85 to 173 µm in width. Sclerotia were occasionally observed in older lesions. The morphological characteristics of conidia matched the previously reported descriptions of Cristulariella moricola (Hino) Redhead (=C. pyramidalis Waterman et Marshall) (Redhead, 1975; Niedbalski et al., 1979) (Fig. 2).

Because conidia are difficult to produce in culture, they were not used in pathogenicity tests. Instead, 10-mm diameter discs of mycelium on PDA/leaf extract agar were placed on surface-sterilised leaves. Inoculated plants were sprayed with distilled water, covered with polyethylene bags and incubated at 15-25^°C. Within one week, small leaf spots were observed from which C. moricola was reisolated. Control leaves inoculated with uncolonised agar discs remained healthy.

C. moricola has been reported on numerous woody and annual plants (Harada, 1998), often on different species growing in close proximity. Yokoyama et al. (1974) observed C. moricola on grape and on two nearby wild vines (Quamoclit angulata Bojer and Cocculus trilobus DC.). Recently, Lee & and Kim (2002) reported C. moricola causing a zonate leaf spot on a previously unreported host, a wild bean (Vigna vexillata var. tsusimensis) in Korea although the conidial heads were somewhat shorter and wider than those isolated from C. trilobus. In uplands surrounded by foothills where the disease on Cocculus has occurred, bean, red pepper and sesame are cultivated. There have been no reports of Cristulariella on plants adjacent to Cocculus trilobus. However, more studies on the host range and seasonal distribution of Cristulariella species may be needed.

This is the first report of the occurrence of Cristulariella moricola on Cocculus trilobus in Korea.