Susceptibility of different grapevine (Vitis vinifera L.) cultivars to Diplodia seriata and Diplodia mutila

Research Note Phytochemistry Susceptibility of different grapevine (Vitis vinifera L.) cultivars to Diplodia seriata and Diplodia mutila Susceptibilidad de diferentes cultivares de vid vinífera (Vitis vinifera L.) a Diplodia seriata y Diplodia mutila M. Ramírez1  2  L.M. Pérez1  2  J.R. Montealegre1  2  1Universidad de Chile, Facultad de Ciencias Agronómicas, Departamento de Sanidad Vegetal, Laboratorio de Fitopatología y Control Biológico de Enfermedades. Casilla 1004, Santiago-Chile 2Asesorías e Inversiones Biostrategy Limitada. Hernando de Aguirre 1372, Providencia, Santiago, Chile Abstract Canes obtained from one-year-old stems of the grapevine cultivars Cabernet Franc, Malbec, Merlot, Sauvignon Blanc and Syrah (all non-grafted) were used as models to test their susceptibility to Diplodia seriata and Diplodia mutila. The results showed that the mean length of lesions caused by D. mutila was 3.2 times larger than that produced by D. seriata. In addition, the Cabernet Franc and Syrah cultivars were the most susceptible to D. mutila, while Merlot and Malbec were the least susceptible. No significant differences were observed between cultivars inoculated with D. seriata. The results are discussed in terms of the susceptibility of the different grapevine cultivars to both pathogens. Keywords: Botryosphaeriaceae; botryosphaeria die-back; grapevine; susceptibility Resumen La susceptibilidad de los cultivares de vid vinífera Cabernet Franc, Malbec, Merlot, Sauvignon Blanc and Syrah (todos patrón Franco) a Diplodia seriata y Diplodia mutila se analizó usando estacas como modelo. Las estacas se obtuvieron de sarmientos de un año de edad. Los resultados mostraron que la longitud promedio de las lesiones producidas por D. mutila era 3,2 veces mayor que la producida por D. seriata. Al comparar las lesiones producidas por D. mutila en los diferentes cultivares, se encontró que Cabernet Franc y Syrah fueron los más susceptibles, mientras que Merlot y Malbec fueron los menos susceptibles. Por otra parte, no se observaron diferencias significativas en el tamaño de las lesiones producidas por D. seriata en los diferentes cultivares. Los resultados se discuten con relación a la susceptibilidad de diferentes cultivares de vid vinífera al daño producido por ambos patógenos. Palabras clave: Botryosphaeriaceae; brazo muerto de la vid; susceptibilidad; vid Introduction Wine and table grapes (Vitis vinifera L.) are important crops covering diverse climate zones in Chile where they are cultivated on an estimated 182,000 ha, of which approximately 130,400 ha are managed for wine grape production (ODEPA, 2015). Botryosphaeria dieback is one of the predominant grapevine trunk diseases worldwide (Bertch et al., 2013). The frequency of symptoms associated with fungal attack on grapevine trunk wood diseases increased significantly worldwide during the last decade, including in Chile. Fungal species belonging to the Botryosphaeriaceae are responsible for the death of part of the plant, reducing the productivity and profitability of this crop (Gubler et al., 2010). Both D. seriata and D. mutila are associated with the Botryosphaeria die-back in Chile (Díaz et al., 2013; Morales et al., 2012). These fungi have been detected in table grape vineyards where no differences were observed among the Thompson Seedless, Red Globe and Flame Seedless cultivars, which were equally susceptible to infection by D. mutila, D. seriata and Spencermartinsia viticola (Morales et al., 2012). In addition, experiments carried out with axenic plants, trunks and shoots of the Carmenère cv. showed that there were no differences in pathogenicity between D. mutila and D. seriata (Díaz et al., 2013). However, the susceptibility of different wine grape cultivars to D. seriata and D. mutila has not been reported to date. Thus, the objective of this work was to compare the susceptibility of the grapevine cultivars Cabernet Franc, Malbec, Merlot, Sauvignon Blanc and Syrah (all nongrafted) to D. seriata and D. mutila, using detached grapevine canes as a model system. Materials and methods Fungal isolates Diplodia seriata (strain 1009) and D. mutila (strain 894), both pathogenic to grapevine plants and well characterized using morphological and molecular tests (Dr. Josep Armengol, Instituto Agroforestal Mediterraneo, Universidad Politécnica de Valencia, España, personal communication), were obtained from a microbiology laboratory fungal collection (Departamento de Sanidad Vegetal, Universidad de Chile). Both strains were cultured in potato-dextrose-agar (PDA, Difco) at 25 ºC in the dark for seven days (Úrbez- Torres and Gubler, 2009). Plant material One-year-old healthy canes from the wine grapevine cultivars Cabernet Franc, Malbec, Merlot, Sauvignon Blanc and Syrah (all non-grafted) were collected from local vineyards in the O’Higgins and Metropolitan Regions, Chile. The canes were cut from grapevine plants two weeks before pruning (June 2014 and 2016). Then, the canes were cut in 20 cm pieces and were maintained at 5 °C and 20% humidity for two months before use. Trials In vivo trials were performed using detached canes previously disinfected for three minutes with 70% ethanol and washed with sterile distilled water. A V-shaped wound was made with a scalpel in the internodes region. Mycelial plugs (6 mm diameter) obtained from pure cultures of D. seriata or D. mutila were used in inoculations, and PDA plugs were used for controls. The inoculated wounds were covered with Parafilm, and the detached canes were placed inside plastic boxes with a translucent cover. They were incubated in the dark at 25 ºC and 95% humidity. Visual observation of the canes was performed weekly to determine the disease’s development and to prevent its progress into the nodes. Each independent trial (2014 and 2016) consisted of 10 replicates per each of the five grapevine cultivars tested and was repeated twice. The length of necrotic lesions observed at the internode region after six weeks of incubation was measured on both sides of the inoculation point with calipers after careful removal of the bark (Savocchia et al., 2007; Úrbez-Torres and Gubler, 2009). After the length measurement, transversal sections of canes were obtained to visualize the lesion. The results were analyzed by ANOVA followed by Tukey’s test (p<0.05). Results Necrosis was observed in the internodes region of all the detached grapevine canes inoculated with D. seriata (strain 1009) or with D. mutila (strain 894). Additionally, a V-shaped lesion (a typical symptom of Botryosphaeria die-back) was observed in the transversal sections of the canes, an observation that was used only to confirm that necrosis was a consequence of the inoculation with D. seriata or with D. mutila. Oxidation of the tissue was observed in the control inoculated canes as a consequence of wounding. An exam (...truncated)