On germination the chlamydospores produce germ tubes that infect host roots, penetrating to the xylem tissues (Belarbi-Halli and Mangenot, 1986). The hyphae grow upwards into the stem and microconidia are also carried upwards in the xylem vessels. As the infection spreads, lateral hyphae colonize the adjacent tissues, which develop a reddish-brown discoloration. When the terminal bud is killed the tree dies and the fungus colonizes the dying host tissues, forming further chlamydospores (Louvet, 1977).