Can fungal epiphytes reduce disease symptoms caused by Phytophthora ramorum?

Abstract

Leaf infection of ornamental species by Phytophthora ramorum has a significant impact on the spread of this disease. Fungicides have had limited success at controlling this disease. With increasing concerns that repeated fungicide applications will exacerbate the potential for fungicide resistance and mask symptoms, alternative control measures are desired. The potential of biological control has not been thoroughly examined. Fungi, isolated from soil, were screened in dual culture with P. ramorum for antagonistic activity. Three isolates, identified as Penicillium daleae, Metarhizium anisopliae, and Penicillium herquei, were selected for further testing on the aerial plant parts of rhododendrons. Different factors, including culture age, application timing, dose response, and additives in the formulation were studied to determine their effects on the antagonists to reduce leaf necrosis. Although responses were variable for the different antagonists, this study showed that fungi applied to the leaf surface could reduce necrosis caused by P. ramorum. The method developed can be used for screening potential antagonists in planta.