Host Reactions Involved in the Recovery of Apricot Trees from Verticillium Wilt

Abstract

Verticillium-infected wood of apricot trees became darkened and host ray cells and fungal hyphae in discoloured wood were darkened, internally disorganized, and apparently inactivated. Verticillium was rarely isolated from discoloured wood and hyphae were not observed in normal wood. Extracts of discoloured wood inhibited spore germination, germ tube elongation, hyphal respiration, and hyphal growth of Verticillium. The degree of inhibition was related to the amount of discoloration and to the phenolic content of the extracts. Gums and tyloses formed in infected wood and prevented transport of conidia along the vascular tissue. Trees recovered from infection when uninfected lateral shoots were produced or when new wood was laid down around infected, discoloured wood containing inactivated Verticillium hyphae.