New Insights into Esca of Grapevine: The Development of Foliar Symptoms and Their Association with Xylem Discoloration

A new study on the development of foliar symptoms of esca was carried out from 2004 to 2006 in five mature vineyards in Aquitaine, France. Symptoms were monitored for severity and changes over time. Initial foliar symptoms were characterized by the presence of drying zones or discolorations (reddening or yellowing), which are symptoms that have also been attributed to Black Dead Arm (BDA). Then, the less-severely affected leaves persisted throughout the summer and developed into typical “tiger-stripe” symptoms of esca. The most severely symptomatic leaves fell soon after symptoms appeared. Severely diseased vines showed typical apoplectic or acute forms of esca that did not differ from the severe BDA forms. The appearance of leafsymptomatic vines increased uniformly over time, reaching a maximum incidence by the end of July. A second survey in 41 European and Lebanese vineyards showed that longitudinal discolorations were visible under the bark of 95% of the vines showing foliar esca symptoms. These wood symptoms, also previously attributed to BDA, appeared as xylem orange-brown stripes. Thus, foliar symptoms of esca showed transitory phases which overlapped with some BDA descriptions. Most of these symptoms, in the west-palearctic regions that were investigated, were commonly associated with the presence of one or several xylem discolorations.

Occurrence of Grapevine Declines and First Report of Black Dead Arm Associated with Botryosphaeria obtusa in Lebanon

Grapevine, cultivated mostly in the Bekaa Plain, is one of the most important fruit crops in Lebanon. During July 2004, a survey was made in 11 vineyards of local table or wine grapes to evaluate the sanitary status of the grapevine industry as far as wood declines are concerned. The most common grapevine decline was esca. The two forms of the disease (mild and severe) were observed. The mild form was characterized by leaf symptoms consisting of interveinal necrotic spots with yellow or red chlorotic blotches on white and red cultivars. The severe form was characterized by dieback of one or more shoots, leaf drop, shrivelling, and drying of fruit clusters. In west Bekaa, on cv. Cabernet Sauvignon, some vines showed symptoms identical to those of Eutypa dieback such as stunted chlorotic shoots with small, distorted leaves; moreover, symptoms corresponding to black dead arm (BDA) such as wine red spots on the margins of leaves and dry spots were seen as reported earlier (1). Diseased vines of various cultivars were collected: 10 Cabernet Sauvignon (7 esca, 3 BDA, and 1 Eutypa dieback), 4 Beitamouni, 3 Carignan, 2 Teifihi, 1 Zeitouni, 1 Mourverdre, 1 Caladoc, and 1 Merlot. In wood, cross sections through the trunk were made that showed mainly central necrosis, white heart rot, brown red wood, and black spotting. Wedge-shaped lesions were the least common. Particularly for BDA, peeling off the bark revealed a brown streaking of the external wood. Isolations were made on malt agar (MA) with wood chips cut from the different necroses described above. Fungal identifications were based on morphological characteristics in comparison with French isolates after subculturing at 20 to 22°C: Fomitiporia sp. (F85-1), Phaeomoniella chlamydospora (F85-2), Eutypa lata (BX1-10, 8D, and 8F), and Botryosphaeria obtusa (F99-1). The fungus most frequently isolated from central necrosis with white heart rot was the basidiomycete Fomitiporia sp. (35% of vines). Cultures of Fomitiporia sp. on MA reached 4 to 5 cm in diameter after 2 weeks and were yellowish to brownish without conidia. P. chlamydospora (associated with esca, black goo, or Petri disease) was isolated from only 9% of vines investigated. Cultures of P. chlamydospora on MA were slow growing and reached 7 to 8 mm in diameter in the dark after 8 days. Colonies were white but became light green and later became dark green. Sporulation was abundant. E. lata (causing Eutypa dieback) was isolated from the vine of cv. Cabernet Sauvignon showing typical symptoms and from two vines showing symptoms of esca only. Two strains produced characteristic pycniospores, and all strains were identified using polymerase chain reaction (Primer Scar 10A-10B) (2). Among the saprophytic fungi isolated from the different kinds of necroses, either central, wedge-shaped, or under the bark, B. obtusa associated with BDA was found most commonly (65% of vines). Cultures of B. obtusa were gray brown with dense aerial mycelium. Pycnidia started to form after 4 to 5 days and conidia (20 to 26 × 9 to 16 μm) were dark brown when mature. These results are consistent with previous descriptions. To our knowledge, this is the first report of black dead arm in Lebanon. References: (1) P. Larignon et al. Phytopathol. Mediterr. 40:S336, 2001. (2) P. Lecomte et al. Appl. Environ. Microbiol. 66:4475, 2000.

Black Dead Arm and Basal Canker of Vitis vinifera cv. Red Globe Caused by Botryosphaeria obtusa in Chile

Several years ago, Vitis vinifera cv. Red Globe vines (over 6 years old), started to show disease symptoms approximately 10 weeks after bud break. Symptoms first appeared on the leaves at the base of the shoots and then spread to other leaves, continuing to appear throughout the growing season. Two forms of the disease (severe and mild) were observed, each case leading to premature leaf fall. The severe form was characterized by dieback of one or more shoots accompanied by leaf drop and shriveling and drying of fruit clusters. The mild form was characterized by wine-red spots on the leaf margins or the leaf blade, which coalesced to form large zones of necrosis between the veins and the margins of the leaf. Fruit clusters may wither. If the bark is scraped off, a brown streak, 1 to 2 cm wide, was often seen in the wood. The streaking began at the base of the affected shoot and extended upward to the ground level, eventually resulting in a basal canker. Botryosphaeria obtusa (Schwein.) Shoemaker (anamorph = Sphaeropsis malorum Berk.) was isolated from 86% of samples from vines that were 6 to 10 years old from 12 locations in IV, V, VI, and metropolitan regions of Chile. Isolations were made from brownstreaked wood. Isolates were identified on the basis of a previous description (1,2) and internal transcribed spacer (ITSI-5.8S-ITS2) rDNA sequences identical to those of B. obtusa (culture KJ9356, GenBank Accession No. AF027759). B. obtusa is established as one of the main fungi associated with black dead arm of grapevine (2,3). Pathogenicity tests were completed by inoculating approximately 20 μl of mycelial suspension via injection into the pith of 16 single-node, rooted cuttings of V. vinifera cv. Red Globe. Sixteen control cuttings were injected with an equal volume of sterile distilled water. Twenty weeks after inoculation, all B. obtusa-inoculated cuttings exhibited brown streaks in the wood extending 50 to 60 mm from the point of inoculation. The wood streaking observed in inoculated plants was identical to symptoms observed in naturally infected black dead arm vines in the vineyard. No symptoms were observed in the controls. B.obtusa was reisolated from the region of brown streaking in all the inoculated cuttings. B. obtusa was not isolated from the water-treated controls. To our knowledge, this is the first report of B. obtusa causing black dead arm and basal canker on Red Globe grapevine in Chile. The fungal isolates have been deposited in the plant pathology laboratory of the Sanidad Vegetal Department of Agronomy Faculty of the University of Chile under the name V. vinifera/B. obtusa from N 1 to 16. References: (1) G. Cristinzio. Inf. Fitopatol. 28:21, 1978. (2) P. Larignon and B. Dubos. Phytoma 538:26, 2001. (3) A. J. L. Phillips. J. Phytopathol. 146:327, 1998.