First Report of Pilidium concavum on Bergenia crassifolia in France.

Abstract

Bergenia crassifolia (L.) Fritsch (elephant's ears or Siberian tea) (Saxifragaceae) is a perennial rhizomatous plant with pink flowers appearing at the end of winter. Since 1990, large, brown, and necrotic spots have been observed on numerous B. crassifolia plants at the University of Sciences in Nice, France. Spots appeared each year in the spring on newly emerged leaves and enlarged up to 1 to 3 cm in diameter during the summer, sometimes affecting more than half of the leaf surface. Leaves with spots were collected from May to November and placed in a humid atmosphere. Black, sessile, discoid conidiomata developed on the spots and exuded a pink, then brown, spore mass. When a mass was transferred onto a 1% malt agar medium, mycelium grew and then numerous, relatively spherical conidiomata (0.5 to 2.5 mm in diameter) developed and exuded a pink slimy mass, which contained many conidia. The mycelium grown at 24°C in the dark was scarce and pale, pink-beige. Under the light, the fungal culture was much darker with a fluffy mycelium and numerous conidiomata. The base of the conidiomata was dark; conidiophores were hyaline and showed little segmentation. Unicellular, cylindrical, fusiform conidia were hyaline, 5.4 to 8 μm long, and 1.4 to 1.9 μm wide. The morphology and size of conidia were comparable with previous descriptions of Pilidium concavum (Desm.) Höhn. (2,3). The ITS1-5.8S-ITS2 region of two isolates was amplified by PCR with primers PN3 and PN10 according to Mendes-Pereira et al. (1) and sequenced. The 421-nt sequence (GenBank Accession No. FM211810) was 100% identical to that of the P. concavum specimen voucher BPI 1107275 (GenBank Accession No. AY487094). P. concavum was reported to be on stored or rotting leaves or fruits of many dicotyledonous plants (2). To validate Koch's postulates, pieces of mycelium cultures with conidiomata (28 days old) were placed onto the upper surface of leaves of healthy B. crassifolia plants (10 to 12 pieces per plant). The leaf epidermis was previously wounded with a needle and a drop of melted paraffin was poured onto each piece of mycelium to prevent desiccation. Agar plugs without the fungus were placed similarly on wounded leaves of two control plants. Four inoculated and two control plants were incubated in growth chambers at either 24 or 18°C (16 h of light per day, 15,000 lx, 80% humidity). At 24°C, brown spots developed from 90% of the inoculation sites, whereas spots were observed for only 18% of the sites at 18°C. Such spots did not develop on control plants. After 2 months, healthy leaves as well as those with necrotic spots were put in humid chambers. Conidiomata formed after 4 weeks and exuded the same pink mass, which contained numerous conidia and from which the fungus was reisolated. Similar symptoms were also observed in several other locations in France and in botanical gardens in Akureyri (Iceland) and Métis (Canada), from which P. concavum was reisolated. To our knowledge, this is the first report of P. concavum on B. crassifolia.