Epidemiology of botryosphaeriaceous species associated with grapevines in New Zealand

Botryosphaericeous species affect most grapevines tissues leading to dieback and wood decay. During sampling of vineyards across New Zealand, botryosphaeriaceous species were found in brown necrotic lesions on grapevine trunks (42%), green shoots (20%), canes (17%), plant debris on the ground (7%), weak buds (8%), leaves (3%) and shrivelled flowers (3%). The isolates, identified by morphological and molecular methods as Neofusicoccum australe, N. luteum, N. parvum, Diplodia mutila and D. seriata, were also found in dieback on twigs and branches of non-grapevine woody hosts living around the vineyards. All isolates were pathogenic on wounded grapevine green shoots, except D. seriata. On wounded trunks of potted vines of scion varieties Cabernet Sauvignon, Chardonnay, Pinot noir, Riesling, and Sauvignon blanc, with mycelial or conidial inoculum, the disease developed to a similar extent (P>0.05) with all species except D. seriata, and N. luteum was the most pathogenic. A microscopy investigation of conidium infection showed that 24 h after inoculation, conidia of N. luteum had not germinated and was shed from attached non-wounded leaves and shoots but had germinated and developed mycelium quickly on detached or wounded green leaves and shoots. Longitudinal stem sections showed mycelium within xylem vessels. Buds, green shoots, canes and trunks were susceptible to infection. In trunks of young vines, N. luteum progressed more quickly upward than downward, while bud and shoot infection could progress downward to infect adjacent tissues. As little as two conidia per wound on detached green shoots led to infection. A 12 month investigation of spore dispersal, in a Canterbury vineyard detected conidia of Neofusicoccum spp. (59.8%) and Diplodia spp. (40.2%) in rainwater traps throughout the year. The conidia were identified by molecular methods as N. australe, N. luteum and N. parvum, (the Neofusicoccum spp.) which were most abundant and D. africana, D. olivarum, D. cupressi or D. mutila (the Diplodia spp). No botryosphaeriaceous species conidia were collected on Vaseline®-coated slides set up to trap air-borne spores. When effects of environmental factors on conidial development and viability were investigated, they demonstrated that the conidia were well-adapted to the vineyard environment. The temperature ranges for conidial germination, growth and development varied between N. luteum, N. australe, N. parvum and D. mutila (P