Complexities underlying the breeding and deployment of Dutch elm disease resistant elms.

Dutch elm disease (DED) is a vascular wilt disease caused by the pathogens and with multiple ecological phases including pathogenic (xylem), saprotrophic (bark) and vector (beetle flight and beetle feeding wound) phases. Due to the two DED pandemics during the twentieth century the use of elms in landscape and forest restoration has declined significantly. However new initiatives for elm breeding and restoration are now underway in Europe and North America.

Phylogeography and population structure of the global, wide host-range hybrid pathogen Phytophthora × cambivora.

Invasive, exotic plant pathogens pose a major threat to native and agricultural ecosystems. Phytophthora × cambivora is an invasive, destructive pathogen of forest and fruit trees causing severe damage worldwide to chestnuts (Castanea), apricots, peaches, plums, almonds and cherries (Prunus), apples (Malus), oaks (Quercus), and beech (Fagus). It was one of the first damaging invasive Phytophthora species to be introduced to Europe and North America, although its origin is unknown.

The Destructive Tree Pathogen Originates from the Laurosilva Forests of East Asia.

As global plant trade expands, tree disease epidemics caused by pathogen introductions are increasing. Since ca 2000, the introduced oomycete has caused devastating epidemics in Europe and North America, spreading as four ancient clonal lineages, each of a single mating type, suggesting different geographical origins. We surveyed laurosilva forests for around Fansipan mountain on the Vietnam-China border and on Shikoku and Kyushu islands, southwest Japan.

A versatile method for assessing pathogenicity of to ash foliage.

We describe a method for inoculating rachises of (European or common ash) with which is faster than previous methods and allows associated foliar symptoms to be assessed on replicate leaves. A total of ten ash seedlings were inoculated with five isolates of and lesion development assessed over four weeks. A five-point disease progress scale of symptom development was developed from no lesion (0), lesion on rachis (1), "pre-top dead," with curling of distal leaflets and bending of the rachis (2), top dead, with wilting and death of distal leaflets (3) to leaf abscission (4).

Mitotic Recombination and Rapid Genome Evolution in the Invasive Forest Pathogen .

Invasive alien species often have reduced genetic diversity and must adapt to new environments. Given the success of many invasions, this is sometimes called the genetic paradox of invasion. is invasive, limited to asexual reproduction within four lineages, and presumed clonal.

Development and Validation of Polymorphic Microsatellite Loci for the NA2 Lineage of Phytophthora ramorum from Whole Genome Sequence Data.

Phytophthora ramorum is the causal agent of sudden oak death and sudden larch death, and is also responsible for causing ramorum blight on woody ornamental plants. Many microsatellite markers are available to characterize the genetic diversity and population structure of P. ramorum.

Contrasting microsatellite diversity in the evolutionary lineages of Phytophthora lateralis.

Following recent discovery of Phytophthora lateralis on native Chamaecyparis obtusa in Taiwan, four phenotypically distinct lineages were discriminated: the Taiwan J (TWJ) and Taiwan K (TWK) in Taiwan, the Pacific Northwest (PNW) in North America and Europe and the UK in west Scotland. Across the four lineages, we analysed 88 isolates from multiple sites for microsatellite diversity. Twenty-one multilocus genotypes (MLGs) were resolved with high levels of diversity of the TWK and PNW lineages.

Four phenotypically and phylogenetically distinct lineages in Phytophthora lateralis.

Until recently Phytophthora lateralis was known only as the cause of dieback and mortality of Chamaecyparis lawsoniana in its native range in the Pacific Northwest (PNW). Since the 1990s however disease outbreaks have occurred increasingly on ornamental C. lawsoniana in Europe; and in 2007 the pathogen was discovered in soil around old growth Chamaecyparis obtusa in Taiwan, where it may be endemic.

Discovery of a fourth evolutionary lineage of Phytophthora ramorum: EU2.

Phytophthora ramorum is a recently introduced, aggressive Phytophthora species that has caused extensive mortality of oak and tanoak trees in the western USA and Japanese larch trees in the UK. P. ramorum is also present on Rhododendron, Camellia, and Viburnum in the nursery industry, which is thought to have been the pathway for its spread into new geographic regions including forests and natural ecosystems.

Phytophthora himalsilva sp. nov. an unusually phenotypically variable species from a remote forest in Nepal.

The Himalaya have received little investigation for Phytophthora species. In a remote forest in Western Nepal ten isolates of an unknown Phytophthora were recovered from the rhizosphere of Quercus, Castanopsis, Carpinus and Cupressus spp. The Phytophthora, formally named here as a P.

Molecular characterisation of two novel double-stranded RNA elements from Phlebiopsis gigantea.

The incomplete sequences of two large, 10-12 kbp, double-stranded RNAs (dsRNAs) found in the TW-2 isolate of the saprophytic fungus, Phlebiopsis gigantea (Pg) are reported. Both PgV-TW2 dsRNA1 and dsRNA2 potentially encode fusion proteins which are apparently expressed by a translational frameshifting mechanism. The C-terminal region of both predicted proteins was 21% identical and contained the eight motifs conserved in RNA-dependent RNA polymerases of dsRNA mycoviruses and had highest similarity with members of the family Totiviridae, but possibly do not form virions.

Sequence of RNA-dependent RNA polymerase genes provides evidence for three more distinct mitoviruses in Ophiostoma novo-ulmi isolate Ld.

Three of the twelve double-stranded (ds) RNAs, dsRNAs 1a, 1b and 3b, which are located in the mitochondria of a diseased isolate, Ld, of the Dutch elm disease fungus, Ophiostoma novo-ulmi have been cDNA cloned and sequenced. Examination of the sequences of the RdRp genes predicted from the nucleotide sequences of the three dsRNAs suggest that they constitute the genome of three new mitoviruses.

Molecular characterization of a partitivirus from Ophiostoma himal-ulmi.

The complete nucleotide sequences of two double-stranded (ds) RNA molecules, S1 (1,744 bp) and S2 (1,567 bp), isolated from an isolate HP62 of the Himalayan Dutch elm disease fungus, Ophiostoma himal-ulmi, were determined. RNA S1 had the potential to encode a protein, P1, of 539 amino acids (62.7 kDa), which contained sequence motifs characteristic of RNA-dependent RNA polymerases (RdRps).

Phytophthora captiosa sp. nov. and P. fallax sp. nov. causing crown dieback of Eucalyptus in New Zealand.

A locally severe crown disease of exotic plantation Eucalyptus trees has been recorded periodically in New Zealand since 1986. Symptoms include leaf spots, petiole infection and twig and small branch lesions. Outbreaks of disease are episodic and individual trees may show marked variation in crown symptoms ranging from unaffected to total defoliation.

Determination of the 5'- and 3'-terminal sequences completes the sequences of the two double-stranded RNAs of Penicillium stoloniferum virus S.

The two genomic segments of Penicillium Stoloniferum virus S (PsV-S), a member of the Partitiviridae, were recently sequenced and published. We independantly sequenced PsV-S and showed that the original sequence was missing nucleotides at both the 5' and 3' termini of both segments. We determined the correct sequence in three independent experiments and found the segments to be 1753 bp (encoding the RNA-dependant RNA polymerase) and 1581 bp (encoding the Capsid Protein).

Selective acquisition of novel mating type and vegetative incompatibility genes via interspecies gene transfer in the globally invading eukaryote Ophiostoma novo-ulmi.

The Dutch elm disease fungus Ophiostoma novo-ulmi, which has destroyed billions of elm trees worldwide, originally invaded Europe as a series of clonal populations with a single mating type (MAT-2) and a single vegetative incompatibility (vic) type. The populations then rapidly became diverse with the appearance of the MAT-1 type and many vegetative incompatibility types. Here, we have investigated the mechanism using isolates from sites in Portugal at which the rapid evolution of O.

Cloning and sequence analysis of the MAT-B (MAT-2) genes from the three Dutch elm disease pathogens, Ophiostoma ulmi, O. novo-ulmi, and O. himal-ulmi.

There were two successive pandemics of Dutch Elm Disease (DED) in Europe, parts of Asia and North America in the last century, caused by two ascomycete fungal species, Ophiostoma ulmi and O. novo-ulmi. A third DED species, O.

Phytophthora kernoviae sp. nov., an invasive pathogen causing bleeding stem lesions on forest trees and foliar necrosis of ornamentals in the UK.

A new Phytophthora pathogen of trees and shrubs, previously informally designated Phytophthora taxon C, is formally named here as P. kernoviae. P.

A double-stranded RNA from a Phytophthora species is related to the plant endornaviruses and contains a putative UDP glycosyltransferase gene.

A new dsRNA was isolated from a Phytophthora isolate from Douglas fir. Sequence analysis showed the dsRNA to consist of 13 883 bp and to contain a single open reading frame with the potential to encode a polyprotein of 4548 aa. This polyprotein contained amino acid sequence motifs characteristic of virus RNA-dependent RNA polymerases (RdRps) in its C-terminal region and motifs characteristic of RNA helicases in its N-terminal region.

Phytophthora alni sp. nov. and its variants: designation of emerging heteroploid hybrid pathogens spreading on Alnus trees.

In 1993 a destructive new Phytophthora pathogen of riparian Alnus trees was discovered in the UK and subsequently shown to be present in other parts of Europe. The new Phytophthora comprised a group of emergent heteroploid hybrids, probably between P. cambivora and a species related to P.

Phytophthora inundata sp. nov., a part heterothallic pathogen of trees and shrubs in wet or flooded soils.

A Phytophthora pathogen of trees and shrubs previously designated Phytophthora sp. O-group is formally named as P. inundata sp.

Multiple new phenotypic taxa from trees and riparian ecosystems in Phytophthora gonapodyides-P. megasperma ITS Clade 6, which tend to be high-temperature tolerant and either inbreeding or sterile.

Phytophthora isolates associated with Phytophthora major ITS Clade 6 were grouped into 11 phenotypic taxa. These comprised the described morphospecies P. gonapodyides, P.

Identity and Pathogenicity of Two Phytophthora Taxa Associated with a New Root Disease of Olive Trees.

Fifty-two Phytophthora isolates from necrotic roots of olives were characterized. Colony morphologies on carrot-agar medium led us to separate them into two groups: A (36 isolates) and B (16 isolates). The optimum growth temperature for Group A was about 21°C, with slow growth at 30°C.