First report of orchid (Orchis laxiflora) as a host of Sclerotinia minor, discovered in Turkey

In Erzurum, Turkey, during June and July of 2002, Orchis laxiflora Lam. Plants were affected by a previously undescribed disease. Initial symptoms consisted of a soft, watery rot at the crown and stem. Diseased tissue turned black, extending along the stem, before plants wilted and collapsed (Fig. 1).

The pathogen was isolated from symptomatic stem sections, surface disinfected for 1 min in 0.5 % NaOCl, plated on potato dextrose agar (PDA) and incubated at 25°C. The organism isolated produced white mycelia and small (0.5 to 2.5 mm) black sclerotia characteristic of Sclerotinia minor Jagger (Pratt, 1993) (Fig. 2). This pathogen was consistently isolated from these plants. Symptoms were reproduced in the greenhouse by inoculating stems of 4-month-old plants with mycelial plugs (6 mm diameter) from 5 day old PDA cultures. Inoculated plants were enclosed in transparent plastic bags for 3 days. Control plants were treated similarly, except that the agar disks did not contain the fungus. All plants were incubated in a greenhouse at 21 to 23°C with a 12h photoperiod. After 2 weeks, inoculated O. laxiflora plants wilted and collapsed. S. minor was reisolated from necrotic crown and stem tissues. No disease symptoms were observed on uninoculated plants. The experiment was repeated and results were similar to the first inoculations. S. minor causes diseases on an extremely broad array of host plants worldwide. A recent listing of hosts by Melzer et al. (1997) included 21 families, 66 genera, and 94 species. This is the first report of O. laxiflora as a host of S. minor.