First record of leaf scald caused by Rhynchosporium secalis in a natural population of Hordeum vulgare subsp. spontaneum in Turkey

During surveys carried out in Spring 2002, severe leaf blotch symptoms were found on wild barley, Hordeum vulgare subsp. spontaneum, in the Sanliurfa province of South Eastern Anatolia, Turkey. Lesions occurred over most of the surface of the flag, second and third leaves and the ligules but not on the barley ears. Small leaf segments with lesions were surface sterilised, rinsed in sterile distilled water and blotted dry with sterile filter paper, before being incubated at 18°C in the dark for seven days on 2.5% wheat germ agar (WGA). Rhynchosporium secalis was routinely isolated from lesions. The identity of the fungus was confirmed by spore morphology and mycelial growth. Two week-old cultures, derived from single germinating conidia, were used to prepare a spore suspension adjusted to 2x10⁵ spores per ml, containing one drop of wetting agent (Tween 20) per 100 ml. This was sprayed onto the third leaf stage of 40 day-old H. vulgare subsp. spontaneum plants until droplets formed. Plants were grown in plastic pots and kept at 18-20°C in a greenhouse. Similar control treatments were performed, using only sterile water. All plants were enclosed in a plastic bag for 48 h after spraying. Lesions similar to those observed in the field occurred within 15 days on the plants sprayed with R. secalis, but not on the healthy control plants.

R. secalis is an important disease of cultivated barley, H. vulgare (Abbot et al., 1992) and was first noted in Turkey in 1937 (Iren, 1964). It also occurs on Hordeum murinum, H. distichon and H. jubatum (Caldwell, 1937). There is an unpublished report of leaf scald caused by R. secalis on 'wild barley' (sic) in Israel (AHD Brown, Pers. Comm.) and it is likely that such occurrences are more widespread than recorded in the literature. However, this is the first confirmed record of R. secalis on natural populations of H. vulgare subsp. spontaneum.