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.
Highlights
The genus Phytophthora includes many agriculturally and ecologically important plant pathogens
In the Maximum likelihood (ML) phylogenetic tree based on cox 1 sequences of P. 6stagnum and other selected species, P. 6stagnum isolates clustered in a distinct taxon which is closely related to P. mississippiae (Figure 1), indicating the maternal parent of P. 6stagnum is genetically close to P. mississippiae
Sequence analyses of the cox 1, internal transcribed spacer (ITS), and beta-tubulin genes have demonstrated that Phytophthora 6stagnum is a hybrid species with a species genetically close to P. mississippiae as its maternal and P. taxon PgChlamydo as its paternal parent
Summary
The genus Phytophthora includes many agriculturally and ecologically important plant pathogens It currently contains approximately 120 species [1]. These species were traditionally divided into six groups by morphological features [2]. They have been classified into 10 clades according to phylogenetic analyses of nuclear and mitochondrial sequences [3,4,5,6,7,8]. Members of this genus are capable of surviving in a variety of terrestrial and aquatic habitats [9]. Most clade 1 species such as P. infestans [9] and P. hedraiandra [10] appear as terrestrial pathogens which attack above-ground plant tissues, while many species in subclade 6b and clade 9 are often associated with aquatic environments such as irrigation reservoirs [11,12,13,14,15,16,17], rivers and riparian ecosystems [18,19]
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