First report of Pestalotiopsis guepinii causing twig blight on hazelnut and walnut in Turkey

Hazelnut (Corylus avellana L.) is the most important crop in the Blacksea Region of Turkey. Disease symptoms consisting of blight and drying of the hazelnut twigs have been observed for several years. Leaves wilt and dry and shoots turn brown, especially on young branches (Fig.1). A fungus with white mycelia producing numerous acervuli with black droplets of spore masses was observed on and isolated from diseased tissue. Conidia were 21.2 - 26.1 x 6.8 - 8.1 µm, with dark median cells, four transverse septa, 2 or more (especially 3) apical appendages 16.5 - 26.1 µm long and a basal appendage 4.2 - 7.8 µm long (Fig. 2). Based on these morphological characteristics, the fungus was identified as Pestalotiopsis guepinii (Desm.) Stey. (Sutton, 1980). The same symptoms were observed on a diseased walnut (Juglans regia L.) twig recently (Fig. 3). Isolations from diseased walnut tissue yielded the same fungus.

Two year old hazelnut and five year old walnut trees in a nursery were used in the pathogenicity test. A conidial suspension of the fungus (1x 10⁶ conidia per ml) was sprayed on young hazelnut and walnut twigs. Twigs on control trees were sprayed with the same amount of sterilised distilled water and all twigs were covered with polyethylene bags during the entire incubation period to maintain high moisture. Disease symptoms were observed on inoculated twigs after 12-15 days. Control twigs remained symptomless. Inoculated twigs were blighted and became brown. The fungus was reisolated both from diseased hazelnut and walnut twigs, confirming Koch's postulates.

The pathogen was previously isolated from hazelnut in Turkey, but its pathogenicity was not mentioned (Yürüt et al.,1994). This is the first report of Pestalotiopsis guepinii causing blight on hazelnut and walnut twigs in Turkey. Additional research is needed to determine the distribution and economic importance of the disease on both crops.