Phytophthora ×stagnum nothosp. nov., a New Hybrid from Irrigation Reservoirs at Ornamental Plant Nurseries in Virginia

Abstract

A novel Phytophthora species was frequently recovered from irrigation reservoirs at several ornamental plant production facilities in eastern Virginia. Initial sequencing of the internal transcribed spacer (ITS) region of this species generated unreadable sequences due to continual polymorphic positions. Cloning and sequencing the ITS region as well as sequencing the mitochondrially encoded cytochrome c oxidase 1 and beta-tubulin genes revealed that it is a hybrid between P. taxon PgChlamydo as its paternal parent and an unknown species genetically close to P. mississippiae as its maternal parent. This hybrid has some diagnostic morphological features of P. taxon PgChlamydo and P. mississippiae. It produces catenulate hyphal swellings, characteristic of P. mississippiae, and chlamydospores, typical of P. taxon PgChlamydo. It also produces both ornamented and relatively smooth-walled oogonia. Ornamented oogonia are another important diagnostic character of P. mississippiae. The relatively smooth-walled oogonia may be indicative of oogonial character of P. taxon PgChlamydo. The new hybrid is described here as Phytophthora ×stagnum.

Diversity of Phytophthora species in Valdivian rainforests and association with severe dieback symptoms

“…One of these, P . × stagnum , which has P. chlamydospora as paternal parent and an unknown maternal parent close to P. mississippiae , was described from nursery irrigation reservoirs in Virginia and, prior to the present survey, has not been found elsewhere in the world (Yang, Richardson, & Hong, ). The other hybrids resulted from multiple reticulation events and had cox1 sequences identical to P. thermophila which, hence, was their maternal parent (Burgess, ; Nagel et al., ).…”

A unique species in Phytophthora clade 10, Phytophthora intercalaris sp. nov., recovered from stream and irrigation water in the eastern USA

“…This is a distinguishing characteristic that is not seen in other species of Phytophthora. Secondly, among the four heterothallic species that produce ornamented oogonia, P. intercalaris can be distinguished from Phytophthora cambivora by producing abundant hyphal swellings and chlamydospores in HSA and CA, from P. mississippiae by its lower optimum growth temperature in cV8A (25 vs 30 uC) and from Phytophthora | stagnum (Yang et al, 2014c) by not producing abundant hyphal swellings and chlamydospores in cV8A. Thirdly, P. intercalaris can also be easily identified by its distinct molecular profile, as illustrated through the sequences of the ITS region and cox1 and Btub genes.…”

Phytophthora Species in Rivers and Streams of the Southwestern United States

“…Numerous natural and artificial Phytophthora species hybrids have been characterized to date, typically with closely related parental genotypes (18)(19)(20)(21)(22)(23)(24)(25)(26). Species such as P. alni, a serious pathogen on Alnus trees in Europe, appear to be recently formed stable hybrid lineages with increased host specificity and virulence (25,26).…”

“…Within clade 6, the hybrid species P. ϫ stagnum nothosp. was frequently isolated from irrigation reservoirs and ornamental plant nurseries in Eastern Virginia (24). Multilocus sequence analysis revealed a hybrid isolate of P. lacustris ϫ P. riparia in the northwestern United States, and multiple hybrid populations were identified in Australia and South Africa among P. amnicola, P. thermophila, and Phytophthora taxon PgChlamydo (9,23).…”