EFFECT OF TEMPERATURE ON GROWTH AND CERATO-ULMIN PRODUCTION OF OPHIOSTOMA-NOVO-ULMI AND O-ULMI

Ophiostoma novo-ulmi and 0. ulmi, previously named 'aggressive' and 'n on-aggressive' subgroups of the old species O. ulmi, are distinguished by a wide range of morphological, molecular, genetical and physiologi cal characters, observed both in vivo and in vitro. They show differen t virulence on elms of moderate resistance, that seems to be correlate d with the ability to synthesize phytotoxic compounds, of which the mo st important is cerato-ulmin (CU). To date, 0. novo-ulmi isolates have been considered the greatest producers of CU in contrast to 0. ulmi i solates, 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 cul ture caused by these temperature differences.