Phytophthora aquimorbida sp. nov. and Phytophthora taxon 'aquatilis' recovered from irrigation reservoirs and a stream in Virginia, USA

Abstract

Two distinct subgroups (L2 and A(-2)) were recovered from irrigation reservoirs and a stream in Virginia, USA. After molecular, morphological and physiological examinations, the L2 subgroup was named Phytophthora aquimorbida and the A(-2) designated as Phytophthora taxon 'aquatilis'. Both taxa are homothallic. P. aquimorbida is characterized by its noncaducous and nonpapillate sporangia, catenulate and radiating hyphal swellings and thick-walled plerotic oospores formed in globose oogonia mostly in the absence of an antheridium. P. taxon 'aquatilis' produces plerotic oospores in globose oogonia mostly with a paragynous antheridium. It has semi-papillate, caducous sporangia with variable pedicels, but it does not have hyphal swelling. Analyses of ITS, CO1, β-tubulin and NADH1 sequences revealed that P. aquimorbida is closely related to P. hydropathica, P. irrigata and P. parsiana, and P. taxon 'aquatilis' is related to P. multivesiculata. The optimum temperature for culture growth is 30 and 20 C for P. aquimorbida and P. taxon 'aquatilis' respectively. Both taxa were pathogenic to rhododendron plants and caused root discoloration, pale leaves, wilting, tip necrosis and dieback. Their plant biosecurity risk also is discussed.

Distribution and diversity of Phytophthora across Australia

“…Most species are known pathogens; however, within Clades 6 and 9 there are many predominantly aquatic species that are only opportunistically pathogenic (Brasier et al 2003;Jung et al 2011;Hansen et al 2012;Hong et al 2012). Many pathogens of agricultural crops cluster in Clades 1, 2, 7 and 8.…”

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

“…Approximately 80 novel species of Phytophthora have been described since 2000, with 16 of these novel species (plus many provisional species) first recovered from aquatic ecosystems. Specifically, these include P. amnicola (Crous et al, 2012), P. borealis (Hansen et al, 2012), Phytophthora chlamydospora (5Phytophthora taxon Pgchlamydo) (Brasier et al, 2003;Hansen et al, 2015), P. fluvialis (Crous et al, 2011), P. lacustris (Nechwatal et al, 2013), P. moyootj (Crous et al, 2014) and Phytophthora taxon aquatilis (Hong et al, 2012) from stream water, Phytophthora aquimorbida (Hong et al, 2012), P. hydrogena (Yang et al, 2014b), Phytophthora hydropathica (Hong et al, 2010), P. macilentosa (Yang et al, 2014a), P. mississippiae , P. stricta (Yang et al, 2014a) and P. virginiana ) from irrigation water and Phytophthora pluvialis (Reeser et al, 2013) from canopy drip. These species, along with Phytophthora gonapodyides, exemplify endemic and dominant species in aquatic environments worldwide, while their less-frequent presence in terrestrial environments indicates the potential variation in composition of species of Phytophthora between aquatic and terrestrial habitats.…”

Comparative Analysis of Water Quality between the Runoff Entrance and Middle of Recycling Irrigation Reservoirs

“…A variety of plant pathogens including bacteria, fungi and oomycetes are present in the RIRs [23], among which Phytophthora species are the most economically important to nursery production. Phytophthora species, such as P. gonapodyides and P. pini have been reported to survive best at temperature 20-25 °C [9,24] and a few high-temperature tolerant species, such as P. aquimorbida, P. hydrogena, P. hydropathica, P. insolita, P. irrigata, and P. virginiana have an optimal growth temperature of 35 °C [4][5][6][7][8]. Temperature differences between these two sampling points of within 1 °C would not alter the temperature biome for pathogen activities.…”

“…Phosphorous becomes less available to the plants when pH is above 7.2 [3]. Water temperature (T) [4][5][6][7][8][9], pH [10], dissolved oxygen (DO) [11], EC [12] and oxidation-reduction potential (ORP) [13] also affect the survival and growth of plant pathogens in the same reservoirs.…”