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First Report of St. John's-Wort Anthracnose Caused by Colletotrichum gloeosporioides in Switzerland

In Switzerland, the increase in St. John's-wort (Hypericum perforatum L.) production was accompanied by the appearance of anthracnose caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. The disease was first observed in 1995. In 1999, most of the 20 ha of St. John's-wort planted in Switzerland were grown organically, at an average gross income per hectare per year of 30,000 U.S. dollars. Anthracnose can destroy this perennial crop in the first year of cultivation, especially when it is grown in more humid areas and heavy soils. The restriction of fungicide use in organic farming can lead to a complete loss of the crop in such cases. Typical symptoms observed in the field were brown, sunken stem-girdling lesions and the reddish color of infected plants. In a later stage, aerial plant parts dried completely causing death. Acervuli that formed on stem lesions were sparsely setose. No saete occurred when the pathogen was grown on potato dextrose agar and ascospores of the teleomorph Glomerella cingulata (Stoneman) Spauld. & Schrenk were observed. Strain AN16 was sent to CABI Bioscience Identification Services (Egham, U.K.) who confirmed our identification. A conidial suspension (10⁷ spores per ml) of AN16 was prepared and used to inoculate two St. John's-wort accessions, Hp 7 and Hp 9. Inoculation occurred under highly conducive conditions in the greenhouse. Symptoms developed on all infected plants 1 week after inoculation. One week later, the more susceptible Hp 9 was killed, whereas the more resistant Hp 7 showed only occasional stem lesions. Koch's rules were completed by reisolating the pathogen from infected plants.