First record of downy mildew caused by Pseudoperonospora cubensis on bottle gourd in Korea

Bottle gourd (Lagenaria siceraria), grown widely for food, medicinal and other purposes, is cultivated in Korea. In September 2005, plants showing typical symptoms of downy mildew were found in a commercial field at Hoengsong, Korea. Infection resulted in yellowish or pale green lesions on upper leaf surfaces, with a dark grey fungal growth developing on lower surfaces. The lesions are angular and delimited by leaf veins (Fig. 1). A specimen was deposited in the U.S. National Fungus Collection (BPI 871275). The sporangiophores (230-500 x 5-7.5 µm) are hyaline, tree-like, straight to substraight, monopodially branched 4-6 orders, emergent from stomata, and not or slightly swollen at the bases (Fig. 2). Sporangia are operculate, ellipsoidal, olivaceous brown and measured 20-35.8 x 15-23.8 µm (l/w = 1.43-1.55) (Fig. 3-4). Morphological observation showed that this fungus is unequivocally in the genus Pseudoperonospora, and highly concordant with the previously described characteristics of P. cubensis (Waterhouse & Brothers, 1981).

The amplification and sequencing of the ITS rDNA was performed using procedures outlined by Cooke et al. (2000), and the sequence of the region was deposited in GenBank (accession number DQ409815). Comparison of the sequences available in the GenBank database revealed that the present ITS sequence is identical to P. cubensis found on Cucurbita moschata (AY608619), and shows only one base pair substitution with an ITS sequence from Cucumis sativus (AY608616) within the family Cucurbitaceae.

Based on morphological and molecular approaches, the pathogen was identified as Pseudoperonospora cubensis. This fungus is one of the most important pathogens for common cucurbit crops worldwide. There are no previous reports of P. cubensis on Lagenaria siceraria in Korea, although it has been found in other parts of Asia and USA (Farr et al., No Date; Lebeda & Widrlechner, 2003). This is the first report of a downy mildew on bottle gourd in Korea.