Effect of water activity and temperature on growth of Alternaria alternata on a synthetic tomato medium.

Alternaria alternata is a toxigenic fungus, predominantly responsible for Blackmould of ripe tomato fruits, a disease frequently causing substantial losses of tomatoes, especially those used for canning. The objective of this study was to determine the effect of water activity (a(w), 0.904, 0.922, 0.954, 0.982) and temperature (6, 15, 21 and 35 degrees C) on germination and radial growth rate on a synthetic tomato medium of a cocktail inoculum of five strains of A. alternata isolated from tomato fruits affected by Blackmould. The shortest germination time (1.5 days) was observed at 0.982 a(w), both at 21 degrees C and 35 degrees C. The germination time increased with a reduction on a(w). The fastest growth rate was registered at 0.982 a(w) and 21 degrees C (8.31 mm/day). Growth rates were higher when a(w) increased. No growth or germination was observed at the lowest a(w) level evaluated (0.904) after 100 days of incubation at 6 degrees C and 15 degrees C. A temperature of 6 degrees C caused a significant reduction in growth rates, even at the optimum a(w) level. The knowledge on the ecophysiology of the fungus in this substrate is necessary to elaborate future strategies to prevent its development and evaluate the consumer health risk.