Abstract: The inoculation of potted transplants with different water contents in the greenhouse showned that water deficiency was a predisposition of the development of the poplar canker. A close correlation was found to exist among phenolics, phenylalanine ammonia-lyase(PAL) and host resistance. In the healthy transplants with high relative turgidity values, phenylalanine ammonia-lyase activity increased, meanwhile, the contents of some phenolic acids measured by high pressure liquid chromatography were high. The results of plate test and inoculation experiments of potted transplants injected with catechol solution demonstrated that catechol was a major inhibitor in living bark.

Key words: Poplar canker, Predisposition, Phenylalanine ammonialyase, Catechol