BIOLOGICAL-CONTROL OF SEPTORIA LEAF-SPOT OF POPLAR BY PHAEOTHECA-DIMORPHOSPORA

Phaeotheca dimorphospora, a Deuteromycotina fungus found to be antagon istic in vitro against Septoria musiva and other tree pathogens, was t ested for its-ability to suppress Septoria leaf spot on poplar. In an in vitro leaf disk assay, P. dimorphospora significantly reduced the s ize of the necrotic area caused by S. musiva on Populus tremuloides, P . grandidentata, and P. X berolinensis. In the greenhouse, both pre- a nd posttreatment of cuttings of P. X berolinensis with P. dimorphospor a resulted in a significant reduction in the severity and in the rate of development of Septoria leaf spot. P. dimorphospora was reisolated from poplar leaves 1 mo after inoculation. Application of P. dimorphos pora culture filtrate and its medium extract on the foliage of poplar also reduced disease severity.