Phomopsis Blight: A New Disease of Pieris japonica Caused by Phomopsis amygdali in the United States.

ABSTRACT

Pieris japonica, also known as Japanese andromeda, is an economically valuable broadleaf evergreen used in landscapes across the United States. From spring 2010 to 2012, P. japonica 'Mountain Fire' plants growing in Maryland nurseries were observed with a high incidence of stem canker, shoot dieback, and blight symptoms. Necrosis was evident on shoot tips and often advanced into lateral shoots, as well as to the crowns, leading to plant death. Phomopsis amygdali, known as a destructive pathogen of peach and almond, was consistently isolated from symptomatic plants. P. amygdali also caused similar symptoms on Mountain Fire test plants following inoculations. P. amygdali was consistently recovered and its identity was confirmed with both morphological and molecular tools, thus fulfilling Koch's postulates. In addition, nursery sampling in 2012 revealed that P. amygdali could also be isolated from asymptomatic plants. In all instances, infected plants were shipped from a West Coast nursery, indicating that this pathogen was inadvertently introduced to new locations. P. amygdali may be emerging as an important pathogen in nurseries because this is the first known association of this pathogen with an ornamental plant species.