Leaf Blotch of Poplar Caused by a New Species of Septotinia

Abstract

SUMMARY A leaf blotch on young plantation trees of hybrid poplar clones in the eastern United States is caused by a hitherto unknown species of Septotinia, described as S. populiperda. Large areas of the leaf blades may become affected and extensive premature defoliation may result. Sporodochia with white masses of conidia are found on both surfaces of the leaf spots, usually developing in concentric circles on the upper surface. Spermadochia with verticillately branched spermatiophores bearing masses of spermatia form on fallen leaves, and small black sclerotia may be found along the veins. Apothecia have not been observed in nature but were produced in pure culture on sterilized sand, following the spermatization of receptive bodies with compatible spermatia. The leaves of trees of five hybrid poplar clones and of two species of poplar were inoculated in the greenhouse with a suspension of ascospores. Typical leaf blotches with sporodochia and conidia were produced on two clones of the hybrid Populus charkowiensis × P. trichocarpa.