Health Status of Ready-to-Plant Grapevine Nursery Material in Canada Regarding Crown Gall and Description of the First Allorhizobium vitis Strain OP-G1 Isolated from British Columbia.

Crown gall disease of grapevines caused by Allorhizobium vitis causes significant damage to vineyards in cold-climate viticulture areas such as Canada and the northern United States. Introduction of the disease into vineyards occurs mainly through planting of infected but asymptomatic nursery material. Because A. vitis is not a regulated pest for import into Canada, no information on the health status of nursery material destined for import into Canada has previously been collected. This study evaluated the health status of ready-to-plant nursery material from domestic and international nurseries in regard to crown gall by determining the abundance of A. vitis in different plant sections via Droplet Digital PCR technology. In addition, different rootstocks from one nursery were compared. Results showed that A. vitis was present in planting material from all nurseries tested. The bacteria were nonuniformly distributed in dormant nursery material, and there was no difference in abundance between the rootstocks tested. In addition, the first A. vitis strain OP-G1 isolated from galls in British Columbia is described. Results showed that a minimum of 5,000 bacterial OP-G1 cells were needed for symptom expression, suggesting that the initiation of symptom development is not based on presence of bacteria in nursery material alone; a minimum threshold is needed, and environmental conditions need to be met.

Diversity of diatrypaceous fungi associated with grapevine canker diseases in California.

Eutypa lata is the most common diatrypaceous fungus in grapevine cankers. This study was undertaken to determine the presence and diversity of other members of the Diatrypaceae in grapevines in California. We isolated into pure culture 11 species of Diatrypaceae from the wood of diseased grapevines including Cryptosphaeria pullmanensis, Cryptovalsa ampelina, Diatrype oregonensis, D. stigma, D. whitmanensis, Diatrype sp., Diatrypella verrucaeformis and four putative species of Eutypella. Species were identified or grouped morphologically and by phylogenetic analyses of the complete sequence of the internal transcribed spacer (ITS) of the rDNA and beta-tubulin gene. Diatrypaceous fungi also occurred frequently on the native flora surrounding vineyards, thus serving as possible inoculum sources for these putative pathogens.

Effect of Temperature on Conidial Germination of Botryosphaeriaceae Species Infecting Grapevines.

Germination of conidia of eight botryosphaeriaceous fungi infecting grapevines was evaluated after 2, 4, 6, 12, and 24 h incubation under eight different temperatures (5, 10, 15, 20, 25, 30, 35, and 40°C). The effect of temperature on conidial germination was also evaluated in different stages (hyaline versus pigmented conidia) of the species Lasiodiplodia theobromae. Conidial germination of Botryosphaeriaceae species infecting grapevines was significantly affected by temperature. Overall, conidial germination increased significantly with longer incubation times, especially from 2 to 12 h. In most cases, germination of conidia was not significantly different between 12 and 24 h incubation. Conidia of botryosphaeriaceous species did not germinate (with the exception of Botryosphaeria dothidea and Neofusicoccum parvum) at 5°C, and only B. dothidea, Diplodia seriata, and L. theobromae showed high levels of conidial germination at 40°C. Optimum conidial germination temperatures (defined as the temperature in which germination reached at least 50% in the shortest incubation time) were 25°C for B. dothidea and Dothiorella iberica, 25 to 30°C for Spencermartinsia viticola, 30°C for Diplodia corticola, D. mutila, D. seriata, N. parvum, and hyaline L. theobromae, and 40°C for pigmented L. theobromae conidia. Successful conidial germination of species of Botryosphaeriaceae infecting grapevines was always observed between 10 and 35°C with the exception of Dothiorella iberica and pigmented L. theobromae conidia, neither of which germinated at 35 and 10°C, respectively. Results of this study show conidia of botryosphaeriaceous species infecting grapevines to be capable of germination under a broad range of temperatures including those considered to be extreme, which may explain the success of these species as grapevine pathogens throughout most of the grape-growing areas in both Northern and Southern Hemispheres.