Phytophthora Diversity in Pennsylvania Nurseries and Greenhouses Inferred from Clinical Samples Collected over Four Decades

Abstract

The increasing movement of exotic pathogens calls for systematic surveillance so that newly introduced pathogens can be recognized and dealt with early. A resource crucial for recognizing such pathogens is knowledge about the spatial and temporal diversity of endemic pathogens. Here, we report an effort to build this resource for Pennsylvania (PA) by characterizing the identity and distribution of Phytophthora species isolated from diverse plant species in PA nurseries and greenhouses. We identified 1137 Phytophthora isolates cultured from clinical samples of >150 plant species submitted to the PA Department of Agriculture for diagnosis from 1975 to 2019 using sequences of one or more loci and morphological characteristics. The three most commonly received plants were Abies, Rhododendron, and Pseudotsuga. Thirty-six Phytophthora species identified represent all clades, except 3 and 10, and included a distinct subgroup of a known species and a prospective new species. Prominent pathogenic species such as P. cactorum, P. cinnamomi, P. nicotianae, P. drechsleri, P. pini, P. plurivora, and P. sp. kelmania have been found consistently since 1975. One isolate cultured from Juniperus horizontalis roots did not correspond to any known species, and several other isolates also show considerable genetic variation from any authentic species or isolate. Some species were isolated from never-before-documented plants, suggesting that their host range is larger than previously thought. This survey only provides a coarse picture of historical patterns of Phytophthora encounters in PA nurseries and greenhouses because the isolation of Phytophthora was not designed for a systematic survey. However, its extensive temporal and plant coverage offers a unique insight into the association of Phytophthora with diverse plants in nurseries and greenhouses.

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

“…Given their high sequence similarity (0.5% out of 3884 base pairs sequenced), it is probable that isolates were identified as P. europaea in studies preceding the formal description of P. abietivora and now would need to be reconsidered as P. abietivora. Molnar et al (2020) deciduous trees, which would fit with the P. europaea hosts already described. They also observed genetic variation between their strains and the P. abietivora type strain for the loci they sequenced (Bily et al 2022).…”

“…abietivora from A. fraseri and Tsuga canadensis as far as 1989. They also discuss the high similarity in the sequences with P. europaea , especially for the ITS (Molnar et al 2020). More recently, Bily et al (2022) isolated P. abietivora from multiple deciduous trees, which would fit with the P. europaea hosts already described.…”

“…Given their high sequence similarity (0.5% out of 3884 base pairs sequenced), it is probable that isolates were identified as P. europaea in studies preceding the formal description of P. abietivora and now would need to be reconsidered as P. abietivora. Molnar et al (2020) reported the identification of P. abietivora isolates from the collection of the Pennsylvania department of agriculture. They could track the first isolation of P.abietivora from A. fraseri and Tsuga canadensis as far as 1989.…”

Diversity of Phytophthora Species Detected in Disturbed and Undisturbed British Soils Using High-Throughput Sequencing Targeting ITS rRNA and COI mtDNA Regions

“…In recent years, several outbreaks caused by Phytophthora (P. ramorum, P. kernoviae, P. lateralis, P. pseudosyringae, and P. austrocedri) have emerged in Britain and also worldwide to cause significant mortality on a range of woody hosts [1][2][3][4][5][6][7]. As we witness the devastating impact of Phytophthora on the natural ecosystem, an increasing number of studies have looked at species composition in diverse environments such as nurseries [8][9][10][11], agricultural and urban environments [12][13][14], and semi-and natural environments [15][16][17][18][19][20]. As a result, many new species have been recovered with a lot of these not formally described yet.…”

Global invasion history of the emerging plant pathogen Phytophthora multivora

“…Phytophthora plurivora is a widespread pathogen in temperate forests of the northern hemisphere, where it is frequently associated with root and stem diseases [ 19 , 20 ]. The species is also reported on ornamental plants in European and North American nurseries [ 21 , 22 ], and it was shown P. plurivora had been introduced to North America from Europe [ 23 ]. Moderate genetic diversity and lack of genetic population structure in the European population suggested an introduced origin, but due to incomplete sample collection, the centre of origin of the species could not be determined.…”