In the case of susceptible seedlings of the JHL cultivar, obser-
vations of cross-sections of root samples inoculated with Foa,
showed that all cortex tissues were colonized after one week
(Fig. 1B and C). Close examination of infected root ultrastructure
showed that the colonization was accompanied by a marked wall
modification including primary wall alteration and middle lamella
dissolution (Fig. 2B) as compared to the preserved cell-wall archi-
tecture in untreated roots (Fig. 2A). The host cells underwent
a complete degradation; but the pathogen hyphae did not exhibit
any apparent disorganization (Fig. 2C). The observed disruption of
root cells coincided with the occurrence of macroscopically visible
symptoms (e.g. an important softening of root tissues) leading to
plant death.