STUDIES IN THE BACTERIAL DIE‐BACK AND CANKER DISEASE OF POPLAR

Abstract

The bacterial die‐back and canker of poplar is characterized by dark necrotic areas in the leaves, die‐back accompanied by cracks in the bark of 1–4‐year‐old branches, and by cankers on the trunk and branches of different ages. The cankers may be ‘closed’ or ‘open’ and when moist exude slime containing bacteria. The disease is caused by Pseudomonas syringae f. sp. populea , a new forma specialis closely resembling Ps. syringae in bacteriological characters but differing from it in parasitism. The association of the slime with the bacteria is essential for the production of typical lesions. Inoculations with the pathogen alone, or in association with other organisms produce atypical symptoms. The bacteria attack the cortical parenchyma and occasionally invade the xylem vessels.