THE RELATION OF BARK MOISTURE TO THE DEVELOPMENT OF CANKER DISEASES CAUSED BY NATIVE, FACULTATIVE PARASITES: IV. PATHOGENICITY STUDIES OF CRYPTODIAPORTHE SALICELLA (FR.) PETRAK, AND FUSARIUM LATERITIUM NEES., ON POPULUS TRICHOCARPA TORREY AND GRAY, P. 'ROBUSTA', P. TREMULOIDES MICHX., AND SALIX SP.

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Abstract
In the field, Cryptodiaporthe salicella has been found only on Salix sp., and Fusarium lateritium on nursery-grown Populus trichocarpa Torrey and Gray. However, the pathogens for these diseases attacked P. trichocarpa, P. 'robusta', P. tremuloides Michx., and Salix sp. when inoculations were made on cuttings which were allowed to dry gradually in a dormant condition. The development of the diseases in the field and in the laboratory was related to the moisture content of the host bark. Canker growth occurred only when the relative turgidity of the bark was below 80%. The possibility of employing similar methods of investigation for the discovery and evaluation of canker diseases of importance in disease-testing programs is discussed.