Phytotoxins produced by Pestalotiopsis guepinii, the causal agent of hazelnut twig blight

Turkey is the biggest producer of hazelnut (Corylus avellana L.) in the world, with a total cultivation area of more than 600,000 hectares, a total annual yield over 800,000 tonnes, and an average yield of around 1.2 tonnes ha in 2008 (FAO, 2008). Several bio-constraints negatively affect hazelnut production, such as pests, diseases and weeds (Anonymous, 1995). Among them Pestalotiopsis guepinii (Desm.) Stey causes hazelnut twig blight. P. guepinii was first reported on hazelnut in Turkey (Yürüt et al. 1994), and then on walnut (Juglans spp.) and gum mastic tree (Pistacia lentiscus var. Chia) (Karaca and Erper, 2001; Göre et al., 2010). It causes symptoms consisting of blight and drying. Small necrotic spots appear on hazelnut leaves and shoots at an early stage; the spots expand if environmental conditions are favorable. Eventually, the leaves wilt and dry, and shoots turn brown, especially those on young branches. Some plant pathogenic fungi can produce phytotoxins which play an important role in the development of the disease and in the appearance of symptoms, such as chlorosis, necrosis, epinasty, and wilting (Yoder, 1980; Ballio and Graniti, 1991; Upadhyay and Mukerji, 1997; Evidente and Mot