Phytophthora in Horticultural Nursery Green Waste—A Risk to Plant Health

Abstract

Phytophthora is a genus of destructive plant pathogens. Certain species are damaging to native ecosystems, forestry, and the horticultural sector, and there is evidence of their dissemination in plant imports. Horticultural nurseries are central nodes of the plant trade and previous studies have found a high diversity of Phytophthora associated with plant nursery stock. It was subsequently hypothesized that green waste disposal sites in nurseries could harbour diverse Phytophthora communities and act as a pathogen reservoir and conduit, facilitating further Phytophthora infection of nursery stock and its spread into the wider environment. This project identified Phytophthora species associated with green waste at three Scottish nurseries by sampling material from waste piles, water run-off from piles, and roots from discarded plants. Species were identified using a baiting method and sequencing of environmental DNA. Plant nursery green waste was shown to harbour diverse and varied Phytophthora species assemblages, with differences among nurseries reflecting biosecurity management practices. Eighteen Phytophthora species were detected in the samples, including the highly destructive pathogens P. ramorum and P. austrocedri. Results suggest that the improved management of waste, for example through effective on-site composting, is essential to reduce the risk of Phytophthora pathogens spreading from nurseries into the wider environment.

Phytophthora spp. diversity in commercial nursery stocks shown through examination of plant health practices for growers and traders of ornamental plants

“…For these reasons and during the last decade, large scale investigations have aimed to characterize Phytophthora diversity in plant nurseries, and have been implemented at national level, with the scope to identify the greatest phytosanitary risks in individual nurseries and in the production links between nurseries. Examples are the outcomes obtained in Oregon, United States of America, by Parke et al (2014), and by Schiffer-Forsyth et al (2023) in the United Kingdom as part of the PHYTO-THREATS project (Green et al, 2020(Green et al, , 2021. Through results of extensive diagnostic services based on molecular techniques, both of these studies provided foundations for implementing systems approaches in nursery production, by providing information on Phytophthora spp.…”