Effect water activity on in vitro mycelial growth of Neofusicoccum spp. infecting blueberry

B.A. Latorre, G.A. Diaz, and M.P. Reed. 2012. Effect of water activity on mycelial growth of Neofusicoccum spp. infecting blueberry. Cien. Inv. Agr. 39(1): 221-228. Stern canker in blueberries Vaccinium corymbosum L.) is a disease which is widely distributed around the world and of growing importance in Chile, associated with Neofusicoccum species. The purpose of the present work was to study the effects of water activity (a(w)) and temperature on mycelial growth in vitro of N. arbuti, N. australe and N. parvum, obtained from blueberries with symptoms of stem canker. According to the results obtained, 25 degrees C was the optimum temperature for mycelial growth of)V. arbuti, N. australe and N. parvum. These species presented minimal growth at 35 degrees C and none at 0 and 5 degrees C. The effect of a(w) on mycelial growth was significant (P <= 0.001) and varied with the species of Neofusicoccum and the temperature. At 25 degrees C, the optimum temperature, the three species of Neofusicoccum presented minimum growth with a(w) of 0.900 and 0.920, while optimum mycelial growth was found with a(w) equal to 0.990. Independent of the Neofusicoccum species, the effect of temperature (T) and a(w) on mycelial growth was best explained by y = -721.62 + 0.24T + 788.92(w), (R-adj(2) = 0.77, P <= 0.001), suggesting that T and a(w) jointly explained 77% of the total variation on mycelial growth of Neofusicoccum spp. The results obtained provide important information for a better understanding of the biology of these plant pathogenic fungi, and suggest that temperature and a could be important parameters for understanding factors that affect the inoculum production, colonization and infection by Neofusicoccum spp. in blueberry plantations.