Grapevines are planted on 180,000 ha in Chile. In 2010 and 2011, necrotic lesions and hard texture were observed on woody tissue on 10-year-old vines of cvs. Cabernet Sauvignon, Carménère, Moscatel de Alejandría, and Pedro Jimenez in Ovalle (lat. 30°58′ S) and Cauquenes (lat. 35°58′ S). Symptoms were on 10 to 25% of the arm cross sections, resembling symptoms caused by Botryosphaeriaceae (4). Prevalence of 5% was estimated visually in Ovalle (n = 920 grapevines) and Cauquenes (n = 350 grapevines). Small pieces (3 mm) of necrotic tissues from the margins of lesions in cordons (n = 32) were surface sterilized (96% ethanol, 15 s), and plated on acidified PDA plus 0.5 ml/liter of 92% lactic acid, 0.005% tetracycline, 0.01% streptomycin, and 0.1% Igepal CO-630 (Sigma-Aldrich, St. Louis, MO) (APDA). The plates were incubated at 20°C for 14 days. Isolates (n = 12) were obtained from the yellow to dark green slimy colonies with white irregular margins, staining brown the underside of APDA plates. Black acervuli and ellipsoid to fusiform conidia were obtained. Conidia were triple septated, with hyaline upper and bottom cells and brown middle cells (n = 30) of 17.7 ± 1.2 × 5.8 ± 0.8 μm. A basal conidial appendage (6.2 ± 1.0 μm) was always obtained, but conidia having appendages at both ends also were observed. Morphologically, these isolates were identified as Seimatosporium botan Sat. Hatak. & Y. Harada (2). The identification of isolates sei-302 and sei-316 was confirmed by amplifying and sequencing the region ITS1-5.8S-ITS2 of rDNA using ITS4 and ITS5 primers (GenBank Accession Nos. JN088482 and JN088483). BLAST analyses showed 100% similarity with S. botan (Accession No. HM067840) (2). Pathogenicity tests were conducted with isolates sei-302 and sei-316 on detached green shoots (GS) and on rooted 2-year-old vines ‘Carménère.’ Rooted vines were inoculated at the base of canes and trunks. Inoculations were performed by placing a mycelial agar plug taken from APDA on a wound aseptically made with a cork borer. Wounds were sealed with Parafilm to avoid a rapid dehydration. The inoculated GS were incubated for 2 weeks in a moisture chamber (relative humidity >80%) at 20°C. Inoculated 2-year-old vines were placed in a lath-house for 7 and 15 months for canes and trunk inoculation, respectively. An equal number of GS and vines were inoculated with sterile agar plugs and left as controls. Necrotic lesions with mean of 23.7 ± 2.5 mm on GS, 50.5 ± 3.4 mm on canes, and 41.9 ± 2.3 mm on trunks developed. No significant difference (P < 0.05) was obtained in lesion length between S. botan isolates. After 7 months, 40% of inoculated canes had died. No symptoms were observed in GS controls and rooted control vines treated with sterile agar plugs. S. botan was reisolated from 93 to 100% of the inoculated samples. Previously, S. botan was reported as pathogenic in Paeonia suffruticosa (1), and Seimatosporium sp. was isolated from V. vinifera in California, but their pathogenicity was not demonstrated (3). To our knowledge, this is the first report of pathogenic isolates of S. botan associated with trunk disease of grapevines. These results contribute to the knowledge of the trunk disease of grapevines worldwide.
References: (1) Y. Duan et al. Plant Dis. 95:226, 2011. (2) S. Hatakeyama et al. Mycoscience 45:106, 2004. (3) Z. Morales et al. Phytopathol. Mediterr. 49:109, 2010. (4) J. R. Úrbez-Torres. Phytopathol. Mediterr. 50:S5, 2011.