Effects of temperature and water stress on the virulence of Botryosphaeriaceae spp. causing dieback of grapevines and their predicted distribution using CLIMEX in Australia

Pathogenicity and virulence of the Botryosphaeriaceous fungi Botryosphaeria dothidea, Diplodia seriata, Lasiodiplodia theobromae and Neofusicoccum parvum were confirmed by inoculation of trunks and cordons on mature grapevines (Vitis vinifera 'Chardonnay'), inoculation of two-year-old potted grapevines in a glasshouse comparing water stressed versus non-water stressed vines, and by inoculation of one-year-old detached canes incubated at 25, 30 and 35°C. All four species were pathogenic with N. parvum the most virulent species followed by L. theobromae, B. dothidea and D. seriata in all pathogenicity assays. Incubation at 30°C resulted in increased virulence in most isolates. However, variation in virulence was observed for different isolates of the same species at 35°C. Significant intra- and inter-species variation in virulence was also observed between water stressed and non-water stressed vines. Optimal temperatures for colony growth and growth rate were also studied in an attempt to understand the variability observed in the pathogenicity tests. L. theobromae was the most rapidly growing species at the optimal growth temperature of 31.3°C followed by B. dothidea at 31.6, N. parvum at 30.2 and D. seriata at 27.6°C. At 25°C L. theobromae was also the fastest growing species with a growth rate of 1.07 mm h-1 followed by D. seriata at 0.87 mm h-1, N. parvum at 0.86 mm h-1 and B. dothidea at 0.83 mm h-1. Using these data the climatic prediction software, CLIMEX, was used to study the possible distribution of the four species in Australia.