Fungal community associated with grapevine wood lesions in Lebanon

摘要

Aims: To detect and identify the cultivable microorganisms putatively associated with esca disease in representative Lebanese vineyards.Methods and results: Two field surveys were conducted in Lebanon in 2005 and 2007 to study the fungal community associated with grapevine wood lesions. A total of 68 vines showing typical esca symptoms were randomly sampled in 17 vineyards and cross sections were obtained of cordons and trunks. The shape and type of inner necrosis and discoloration were examined and isolations were made from the symptomatic wood. Isolation results showed that inner necrosis and isolated fungi were similar to those previously found elsewhere, namely in Central Europe or Mediterranean countries. Additionally, three methods for numerical evaluation of micro-organisms found were compared.Conclusion: Most fungal pathogens generally associated with grapevine trunk diseases were detected, of which the basidiomycete Fomitiporia mediterranea and species of the ascomycete family Botryosphaeriaceae were the most frequently encountered. Additionally, a large diversity of other wood colonizing micro-organisms was detected. The putative role of some of the obtained micro-organisms in the process of wood degradation related to esca disease is discussed.Significance and impact of the study: This isolation study is presently the most completed that was carried out with grapevine wood samples collected in Lebanon. Besides, it is the first to provide isolation results based on a classification of inner necrosis in five categories and to compare three criteria for numerical evaluation. This study also tends to further highlight that Botryosphaeriaceae species are common wood inhabiting fungi that should be associated with esca. IntroductionSince the end of the 20th century, the economical impact of trunk diseases has become a limiting factor for grapevine production in many countries around the world (Armengol et al., 2001). In adult vineyards, eutypa dieback, esca and Botryosphaeria dieback are considered to be the most destructive (Dubos, 2002; Mugnai et al., 1999; úrbez-Torres, 2011). These diseases are generally characterized by the development of typical inner necrosis into the grapevine wood and are assigned to infection by pathogenic fungi that deteriorate the perennial and vascular system.In Lebanon, with an area of cultivation of about 10600 ha, grapevine is one of the most important fruit crops, ranking third after stone and pome fruits, and is distributed in four districts: Bekaa valley (70%), North Lebanon (14%), Mount Lebanon (11%) and South Lebanon (5%) (Anonymous, 2010). The grape industry has markedly grown in the last 10 years. The table grape cultivars Beitamouni, Tfaifihi and Biadi are the most important native table grape varieties currently grown in Lebanon, however, new vineyards planted almost exclusively with imported international wine grape varieties (Cabernet sauvignon, Merlot, Syrah, Cinsault, Sémillon, Ugni blanc and Chardonnay) have been largely established mainly in the Bekaa valley. Up to the beginning of the 21st century, there was little information about the incidence of grapevine trunk diseases in Lebanon. But in recent years, the incidence of esca and grapevine decline has increased, resulting in reduced vigour and productivity and finally the death of branches or whole vines. A preliminary survey done in the West Bekaa valley in 2004 on 11 vineyards of local table or wine grapes (Choueiri et al., 2006) reported foliar symptoms of esca, eutypa dieback and black dead arm according to the description made by Larignon et al. (2001). However, it was later demonstrated that foliar symptoms attributed to black dead arm are in fact esca symptoms in their initial stage of development (Lecomte et al., 2012). In our survey, esca was the most common disease encountered, whereas eutypa dieback was rare.The expression of esca symptoms on the leaves is commonly associated with the development of different fungal pathogens in grapevine wood (Arnaud and Arnaud, 1931; Chiarappa, 1959; Dubos, 2002; Mugnai et al., 1999). Cross sections of the trunk of diseased vines generally reveal a variety of lesions and/or decay types (Larignon and Dubos, 1997; Larignon, 2004; Maher et al., 2012). The wood of older vines usually shows a white to yellow soft rot, from which basidiomycetes like Fomitiporia spp. (in Europe usually F. mediterranea; Fischer, 2002) may be isolated (Fischer and Kassemeyer, 2003). The wood lesions continue to extend as the vines age and dead tissue increases in volume and can cause, in severe cases, a sudden wilting of the canopy known as apoplexy (Mugnai et al., 1999).In the last two decades, the number of studies that have characterized grapevine wood-inhabiting fungi has increased. In the Mediterranean basin, previous studies had shown that vines affected with esca generally show the presence of the same range of phytopathogenic fungi, namely the mitosporic fungi Phaeomoniell