Petal spotting of hydrangea flowers caused by Corynespora cassiicola: old pathogen — new disease

Abstract

Diseased hydrangeas (Hydrangea macrophylla) were found growing in gardens of highland localities of the states of Rio de Janeiro and Minas Gerais (Brazil). Distinct multiple purple spots in flowers that gave an unsightly chicken-poxed (varicella-like) appearance to the inflorescences were found along with leaf necrosis. The severity of the disease seriously impairs the ornamental value of this highly popular garden plant. The fungus Corynespora cassiicola was found associated with leaf and flower lesions. Brush inoculation of leaves with conidia obtained from a flower isolate resulted in the formation of leaf spots identical to the ones observed in the field. Although this fungus is known to be a pathogen of hydrangea foliage this is the first time the fungus is recognised to cause a flower disease on this host. The flower disease, here called petal spotting of hydrangea, and the fungus involved are described and illustrated.