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International audience; Esca is a devastating disease of grapevines involving xylem-inhabiting fungi. Among these, Phaeomoniella chlamydospora and Phaeoacremonium aleophilum are considered as the causal agents. We show that they present different structural features and act on plant cells by very different mechanisms. Their sensitivity to temperature differed, with optimum growth rates for P. chlamydospora at 25°C, and for P. aleophilum at 30°C. Low temperatures (5°C) applied over a long period (40 days) did not affect the viability of either fungus, whereas high temperatures (35°C for P. chlamydospora and 40°C for P. aleophilum) rapidly suppressed their growth. Alkaline pH, which reduced mycelial growth, increased the formation of conidia in P. chlamydospora, whereas the same effect was observed for acidic pH in P. aleophilum. Unlike P. chlamydospora, P. aleophilum penetrated the lignified walls in host xylem cells degrading the hemicellulose, cellulose and lignin components. However, the deleterious effect of these two fungi cannot explain all the observed wood-degrading processes occurring during esca disease. These agents may facilitate the access of opportunistic saprophytes whose mode of action should now be investigated.

Salicylic and acetylsalicylic acids applied on excised leaves of Cassia fasciculata modify the dark-induced (scotonastic) and light-induced (photonastic) leaflet movements. They inhibit the scotonastic movements in a dose-dependent manner from 1 x 10(-4) to 1 x 10(-3) molar and they promote the photonastic movements at an optimum concentration of 5 x 10(-4) molar. These results suggest that these phenolic compounds do not act specifically on the K(+) uptake, which was shown to be inhibited by their action on other materials.