DRY-ROT DISEASE OF THE POTATO

Inoculation of wounded tubers at intervals throughout the storage season showed that, after harvesting, resistance to infection by F. avenaceum was maintained for a longer period than resistance to F. caeruleum , although eventually the tubers became equally susceptible to both fungi. Tubers were less readily infected through clean-cut than through scarified wounds. Resistance to infection was greater when an interval elapsed between wounding and inoculation than when the wound was inoculated immediately; this was related to an increase in the intrinsic ability of the cells near the wound to resist infection rather than to suberization of the wounded surface or wound periderm formation.
Histological studies showed that F. caeruleum grew through the intercellular spaces and that the adjacent host cells remained alive, often for considerable periods, whereas F. avenaceum killed and penetrated the cells with which it came into contact. Restriction of incipient or established lesions caused by F. caeruleum and of incipent lesions caused by F. avenaceum was associated with suberin deposition on the host cell walls and in the intercellular spaces; in established lesions caused by F. avenaceum , restriction was attributed to an increase in the intrinsic resistance of the adjacent host cells, similar to that found near a wounded surface.