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

Abstract

AbstractChristmas trees are an economically and culturally important ornamental plant in North America. Many microorganisms are pathogens of firs cultivated as Christmas trees. Among those,Phytophthoracauses 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 cultivatedAbiesspecies. 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 culturablePhytophthoraspp. The obtained isolates were identified with a multi-locus sequencing approach, and we used the sequencing data to place them along thePhytophthoraphylogeny. A total of 44 isolates from six differentPhytophthoraspecies were identified, one fitting the provisional speciesP.sp.□kelmania□. A seventh taxa, represented by a group of 10 isolates, could not be assigned to any knownPhytophthoraspecies. Among the known species,Phytophthora abietivorawas the most prevalent isolated species associated with PRR. Pathogenicity trials confirmed the pathogenicity potential ofP. abietivoraon 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 betweenPhytophthoraspecies andAbies balsameaandA. fraseri.