1970 Volume 36 Issue 4 Pages 243-249
Observations were made on the processes of (1) wound periderm formation, (2) lignification (with phloroglucine-HCl), and (3) suberification (with Sudan III) of cut tuber surfaces of the highly resistant potato cv. Rishiri (R1) either inoculated with race 0 (incompatible) or race 1 (compatible) of Phytophthora infestans or non-inoculated. All experiments were conducted at 19-20°C. With cut tissue (control, noninoculated), renewed cell division first appeared on the surface two days after cutting, with subsequent cell division progressing toward inner tissue. Cell division occurring in a few cells located in succession from the cut surface toward the inner tissue resulted in the formation of a periderm. When the cut surface was inoculated with an incompatible race just after cutting, cell division was delayed, and the thickness of the periderm was reduced. In tissue inoculated with a dilute zoospore suspension, cell division first occurred in the cell directly adjacent to the browned cell, thereafter progressing toward the inner tissue. When inoculated with a concentrated zoospore suspension, cell division first occurred in the third cell away from the browned cell. Usually no cell division occurred in the second cell (the cells directly adjacent to the browned cell). The rapidity and extent of lignification and suberification also were reduced by infection with an incompatible race. Infection by a compatible race strongly inhibited the development of wound periderm structure.
Evidence was presented that the infection by the incompatible race itself can cause the formation of the periderm.
With aged tubers, the brown lesion progressed inward more deeply. The formation of the periderm was delayed and its extent also was reduced, as compared with fresh tubers. In extreme cases no periderm developed, even though the lesion has stopped developing.