Survey of the Phytophthora species diversity revealsP. abietivoraas a potential Phytophthora root rot pathogen in Québec Christmas tree plantations

Christmas trees are an economically and culturally important ornamental plant in North America. Many microorganisms are pathogens of firs cultivated as Christmas trees. Among those, Phytophthora causes millions of dollars in damage to plantations annually. In Canada, it is still not known which species are responsible for Phytophthora root rot (PRR) of cultivated Abies species. Between 2019 and 2021, soil and root samples were collected from 40 Christmas tree plantations in Québec province. We used soil baiting and direct root isolation to assess the diversity of culturable Phytophthora spp. The obtained isolates were identified with a multi-locus sequencing approach, and we used the sequencing data to place them along the Phytophthora phylogeny. A total of 44 isolates from six different Phytophthora species were identified, one fitting the provisional species P. sp.□kelmania□. A seventh taxa, represented by a group of 10 isolates, could not be assigned to any known Phytophthora species. Among the known species, Phytophthora abietivora was the most prevalent isolated species associated with PRR. Pathogenicity trials confirmed the pathogenicity potential of P. abietivora on both Fraser and balsam fir seedlings. Our studies provide a first snapshot of the Phytophthora diversity in Québec’s Christmas tree productions and describe multiple potential first associations between Phytophthora species and Abies balsamea and A. fraseri .