A Barcode-Based Phylogenetic Characterization of Phytophthora cactorum Identifies Two Cosmopolitan Lineages with Distinct Host Affinities and the First Report of Phytophthora pseudotsugae in California

Abstract

A collection of 30 Phytophthora cactorum and 12 P. pseudotsugae (subclade 1a) strains isolated from several recent surveys across California was phylogenetically compared to a worldwide collection of 112 conspecific strains using sequences from three barcoding loci. The surveys baited P. cactorum from soil and water across a wide variety of forested ecosystems with a geographic range of more than 1000 km. Two cosmopolitan lineages were identified within the widespread P. cactorum, one being mainly associated with strawberry production and the other more closely associated with apple orchards, oaks and ornamental trees. Two other well-sampled P. cactorum lineages, including one that dominated Californian restoration outplantings, were only found in the western United States, while a third was only found in Japan. Coastal California forest isolates of both Phytophthora species exhibited considerable diversity, suggesting both may be indigenous to the state. Many isolates with sequence accessions deposited as P. cactorum were determined to be P. hedraiandra and P. ×serendipita, with one hybrid lineage appearing relatively common across Europe and Asia. This study contains the first report of P. pseudotsugae from the state of California and one of the only reports of that species since its original description.

Evaluation of the Ability of Seven Active Ingredients of Fungicides to Suppress Phytophthora cactorum at Diverse Life Stages, and Variability in Resistance Found among Isolates

“…The host specificity was revealed in this species of plant pathogen, where isolates originating from strawberry plants are significantly more virulent to this host than to others, or are even totally unable to infect other host species. Conversely, isolates from woody plants are unable to attack strawberry plants [ 4 , 18 , 76 , 77 ]. Finer structuring into genetic lineages was revealed, which is associated with the genetic background of this species [ 39 ]; this division also roughly respects the host-specific grouping.…”

“…However, as documented by the estimated value of the resistance factor [ 43 ] for fluopicolide, in relation to fungicides, even isolates of the group W do not behave like wild population strains [ 43 , 44 , 45 ]. Since P. cactorum is assumed not to be indigenous to Europe [ 18 ], the resistance of the entire European population could be influenced by the features of genotypes which were introduced in Europe.…”

“…The first disease incidence of leather rot caused by P. cactorum was reported in the United States in 1924 [ 13 ]; other cases were gradually reported in Europe and also in Asia, while the first description of crown rot was reported in 1952 in Germany [ 14 ], in 1988 in Sweden [ 15 ], in 1990 in Finland [ 16 ] and in 1992 in Norway [ 17 ]. Although the widespread distribution of this pathogen in Europe was reported by the aforementioned researchers, P. cactorum is considered an alien species to the European continent, which is evidenced by its low genetic variability, close phylogenetic relatedness to other non-native species, and high virulence to host plant species which are indigenous to Europe [ 1 , 18 ].…”

Bunyaviruses Affect Growth, Sporulation, and Elicitin Production in Phytophthora cactorum

“…Phytophthora cactorum is a genetically variable species with two cosmopolitan lineages associated with strawberry and woody species (apple, oak, ornamental trees), respectively [5]. Finnish isolates from birch have been inferred to represent the most earlydiverging lineage within the species and separate phylogenetically from the two cosmopolitan lineages [5].…”

“…Phytophthora cactorum is a genetically variable species with two cosmopolitan lineages associated with strawberry and woody species (apple, oak, ornamental trees), respectively [5]. Finnish isolates from birch have been inferred to represent the most earlydiverging lineage within the species and separate phylogenetically from the two cosmopolitan lineages [5]. Isolates from woody species, including Finnish isolates from birch, have caused little or no crown rot symptoms when inoculated in strawberry, but strawberry isolates have caused necrotic lesions on B. pendula [6][7][8].…”