Effect of temperature on cerato-ulmin production by Ophiostoma ulmi and O. novo-ulmi.

Ophiostoma novo-ulmi and O. ulmi, previously named «aggressive» and «non-aggressive» subgroups of the old species O. ulmi, are distinguished by a wide range of morphological, molecular, genetical and physiological characters, observed both in vivo and in vitro. They show different virulence on elms of moderate resistance, that seems to be correlated with the ability to synthesize phytotoxic compounds, of which the most important is cerato-ulmin (CU). To date, O. novo-ulmi isolates have been considered the greatest producers of CU in contrast to O. ulmi isolates, that synthesize very little or no toxin. We demonstrate that the synthesis of CU is temperature-dependent and that the two species seem to have different temperature optima for its production. However, while the difference in CU production is linked to temperature, it is not a consequence of differences in fungus growth in liquid shake culture caused by these temperature differences