SUMMARY

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 pres-ent different structural features and act on plant cells by very different mechanisms. Their sensitivity to tempera-ture differed, with optimum growth rates for P. chlamy-dospora 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. Al-kaline pH, which reduced mycelial growth, increased the formation of conidia in P. chlamydospora, whereas the same effect was observed for acidic pH in P. ale-ophilum. Unlike P. chlamydospora, P. aleophilum pene-trated the lignified walls in host xylem cells degrading the hemicellulose, cellulose and lignin components. However, the deleterious effect of these two fungi can-not explain all the observed wood-degrading processes occurring during esca disease. These agents may facili-tate the access of opportunistic saprophytes whose mode of action should now be investigated