Annuals and herbaceous perennials tolerant or resistant to phytophthora species in the landscape

Abstract

Plants of one or two cultivars of 16 annuals and 14 herbaceous perennials were evaluated based on desirability and anecdotal evidence of resistance to Phytophthora root or crown rot. Six plant cultivars served as susceptible controls. Three landscape beds were established in North Carolina and each was infested with three species of Phytophthora: P. nicotianae, P. drechsleri, and P. tropicalis. Plants were regularly rated for disease incidence and symptomatic plants were assayed to determine the presence of Phytophthora species. Ten cultivars of annuals and seven cultivars of herbaceous perennials did not exhibit symptoms of Phytophthora root or crown rot or other disease throughout the season (June 4 to October 15, 2018). Phytophthora spp. were recovered from seven and six cultivars of the evaluated annuals and herbaceous perennials, respectively. Phytophthora nicotianae, P. drechsleri, or P. cryptogea were recovered from a susceptible host in each landscape bed. P. tropicalis was recovered from one plant cultivar evaluated. Phytophthora cryptogea was recovered from three plant cultivars, although this species was not intentionally introduced in the landscape beds. We identified 22 plant cultivars within 13 herbaceous plant species that grew vigorously in landscape beds infested with species of Phytophthora.