What's New

New Plant Pathology article May 2016

Metabarcoding and development of new real-time specific assays reveal Phytophthora species diversity in holm oak forests in eastern Spain

Català, S., Berbegal, M., Pérez-Sierra, A. and Abad-Campos, P. (2016). Plant Pathology. doi: 10.1111/ppa.12541

The evergreen holm oaks (Quercus ilex subsp. ilex and Q. ilex subsp. ballota) are the most representative tree species in the Iberian peninsula and the main tree species in oak-rangeland ecosystems (dehesas). Oak decline in western, central and southern parts of Spain has been associated with root rot caused by Phytophthora cinnamomi for decades. However, Phytophthora species such as P.  quercina and P. psychrophila have recently been found associated with Quercus decline in eastern Spain where calcareous soils are predominant. Soil and root samples from two Quercus forests presenting decline symptoms in two different geographical areas in eastern Spain (Carrascar de la Font Roja and Vallivana) were analysed by amplicon pyrosequencing. Metabarcoding analysis showed Phytophthora species diversity, and revealed that an uncultured Phytophthora taxon, named provisionally Phytophthora taxon ballota, was the predominant species in both areas. In addition, a real-time PCR assay, based on the pyrosequencing results, was developed for the detection of this uncultured Phytophthora taxon, and also for the detection of P. quercina. TaqMan assays were tested on soil and root samples, and on Phytophthora pure cultures. The new assays showed high specificity and were consistent with metabarcoding results. A new real-time PCR protocol is proposed to evaluate the implication of different Phytophthora spp. in oak decline in eastern Spain.

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New Forest Pathology article April 2016

Phytophthora ×alni and Phytophthora lacustris associated with common alder decline in Central Portugal

Kanoun-Boulé, M., Vasconcelos, T., Gaspar, J., Vieira, S., Dias-Ferreira, C., Husson, C. (2016), Phytophthora ×alni and Phytophthora lacustris associated with common alder decline in Central Portugal. Forest Pathology, 46: 174–176. doi: 10.1111/efp.12273

Since the early 1990s, an emerging disease induced by the highly aggressive oomycete Phytophthora ×alni has caused widespread alder decline across Europe. In parallel, P. lacustris, a recently described species associated with riparian habitats, has been subject of increasing interest. A field survey conducted in 2014 showed high mortality rates in alder stands located in the riparian gallery along two rivers in Central Portugal. The pathogens isolated from necrotic alder stem base during this study were identified as P. ×alni and P. lacustris. This paper is the first to report the occurrence of P. lacustris in Portugal and presents the first finding of P. ×alni affecting mature trees in natural ecosystems located in Central Portugal.

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New IMA Fungus article March 2016

An overview of Australia’s Phytophthora species assemblage in natural ecosystems recovered from a survey in Victoria

William A. Dunstan, Kay Howard, Giles E. StJ. Hardy, and Treena I. Burgess, IMA FUNGUS · 7(1): 47–58 (2016)

Although Phytophthora species cause serious diseases worldwide, until recently the main focus on disease in natural ecosystems in southern Australia has been on the distribution and impact of P. cinnamomi. However, new Phytophthora pathogens have emerged from natural ecosystems, and there is a need to better understand the diversity and distribution of these species in our natural forests, woodlands and heathlands. From a survey along a 70 km pipeline easement in Victoria, Phytophthora species were isolated from 249 rhizosphere samples and 25 bait bags deployed in 21 stream, river, or wetland locations. Of the 186 Phytophthora isolates recovered, 130 were identified to species based on ITS sequence data. Ninety-five isolates corresponded to 13 described Phytophthora species while additionally 35 isolates were identified as Clade 6 hybrids. Phytophthora cinnamomi was the most common species isolated (31 %), followed by P. elongata (6 %), both species were only recovered from soil. Samples from sites with the highest soil moisture at the time of sampling had the highest yield of isolates. Consistent with other studies throughout the world, Clade 6 species and their hybrids dominated water samples, although many of these species were also recovered less frequently from soil samples. Many of the species recovered in this study have not previously been reported from eastern Australia, reinforcing that Phytophthora species are widespread, abundant and diverse in natural ecosystems. We have probably been underestimating Phytophthora diversity in Australia.

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New Plant Disease article Feb 2016
C. Morales-Rodríguez, A. M. Vettraino, and A. Vannini, Plant Disease 2016 100:2, 324-330

The efficacy of biofumigation with Brassica carinata pellets (BioFence) to control vegetative and reproductive structures of Phytophthora cinnamomi was investigated in vitro at different doses and temperatures. Biofumigation was effective in inhibiting mycelial growth (culture diameter) and chlamydospore and zoospore germination, and was lethal at 24 mg of pellet per plate (approximately 0.4 mg/liter). The 50% effective concentration values showed that efficacy of B. carinata pellets in inhibiting or killing the vegetative and reproductive structures of P. cinnamomi was maximum at 15°C and decreased as temperature rose to 25°C. However, the fungicide effect was independent of the temperature. In vivo biofumigation of Quercus cerris seedlings with BioFence confirmed efficacy by reducing the inoculum density (CFU/g) of P. cinnamomi, thus protecting the host from root infection. The use of BioFence provides an alternative to synthetic pesticides to control P. cinnamomi within disease management programs in agroforestry systems.

 

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First Look Plant Disease article January 2016

First Report of Phytophthora cinnamomi Causing Root Rot of Castanea mollissima (Chinese chestnut) in China.

Chengzhong Lan, Hongchun Ruan, and Jinai Yao

http://apsjournals.apsnet.org/doi/10.1094/PDIS-09-15-1105-PDN?ai=hcj&ui=1f1&af=T

3-year-old plants of Castanea mollissima were found with leaf discolouration, wilting, and stunted growth associated with severe root rot in several commercial nurseries in Jianou, Fujian, China. Five Phytophthora-like isolates were isolated from necrotic taproots and identified as Phytophthora cinnamomi on the basis of morphological characteristics and molecular analyses. Pathogenicity tests were carried out and Koch's postulates were fulfilled. This is the first report of Phytophthora root rot of C.mollissima caused by P. cinnamomi in China.


New Phytopathology article January 2016

Host Phenology and Leaf Effects on Susceptibility of California Bay Laurel to Phytophthora ramorum

Steven F.Johnston, Michael F.Cohen, TamasTorok, Ross K.Meentemeyer, and Nathan E.Rank
January 2016, Volume 106, Number 1. Pages 47-55. http://dx.doi.org/10.1094/PHYTO-01-15-0016-R
Spread of the plant pathogen Phytophthora ramorum, causal agent of the forest disease sudden oak death, is driven by a few competent hosts that support spore production from foliar lesions. The relationship between traits of a principal foliar host, California bay laurel (Umbellularia californica), and susceptibility to P. ramorum infection were investigated with multiple P. ramorum isolates and leaves collected from multiple trees in leaf-droplet assays. We examined whether susceptibility varies with season, leaf age, or inoculum position. Bay laurel susceptibility was highest during spring and summer and lowest in winter. Older leaves (>1 year) were more susceptible than younger ones (8 to 11 months). Susceptibility was greater at leaf tips and edges than the middle of the leaf. Leaf surfaces wiped with 70% ethanol were more susceptible to P. ramorum infection than untreated leaf surfaces. Our results indicate that seasonal changes in susceptibility of U. californica significantly influence P. ramorum infection levels. Thus, in addition to environmental variables such as temperature and moisture, variability in host plant susceptibility contributes to disease establishment of P. ramorum.

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New Mycologia article

The Phytophthora species assemblage and diversity in riparian alder ecosystems of western Oregon, US.

LL Sims, W. Sutton, P. Reeser, and EM. Hansen. 2015. Mcologia 7:105 pp. 889 - 902 http://www.mycologia.org/cgi/doi/10.3852/14-255

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Phytophthora species were systematically sampled, isolated, identified and compared for presence in streams, soil and roots of alder (Alnus species) dominated riparian ecosystems in western Oregon. We describe the species assemblage and evaluate Phytophthora diversity associated with alder. We recovered 1250 isolates of 20 Phytophthora species. Only three species were recovered from all substrates (streams, soil, alder roots): P. gonapodyides, the informally described “P. taxon Pgchlamydo”, and P. siskiyouensis. P. alni ssp. uniformis along with five other species not previously recovered in Oregon forests are included in the assemblage: P.citricola s.l., P. gregata, P. gallica, P. nicotianae and P. parsiana. Phytophthora species diversity was greatest in down- stream riparian locations. There was no significant difference in species diversity comparing soil and unwashed roots (the rhizosphere) to stream water. There was a difference between the predominating species from the rhizosphere compared to stream water. The most numerous species was the informally described “P. taxon Oaksoil”, which was mainly recovered from, and most predominant in, stream water. The most common species from riparian forest soils and alder root systems was P. gonapodyides.


New Genomics Data article

Genome sequences of six Phytophthora species associated with forests in New Zealand

D.J. Studholme, R.L. McDougal, C. Sambles, E. Hansen, G. Hardy, M. Grant, R.J. Ganley and N.M. Williams. 2016. Genomics Data Vol. 7, pp 54-56.
http://www.sciencedirect.com/science/article/pii/S2213596015300854

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Abstract

In New Zealand there has been a long association of Phytophthora diseases in forests, nurseries, remnant plantings and horticultural crops. However, new Phytophthora diseases of trees have recently emerged. Genome sequencing has been performed for 12 Phytophthora isolates, from six species: Phytophthora pluvialis, Phytophthora kernoviae, Phytophthora cinnamomi, Phytophthora agathidicida, Phytophthora multivora and Phytophthora taxon Totara. These sequences will enable comparative analyses to identify potential virulence strategies and ultimately facilitate better control strategies. This Whole Genome Shotgun data have been deposited in DDBJ/ENA/GenBank under the accession numbers LGTT00000000, LGTU00000000, JPWV00000000, JPWU00000000, LGSK00000000, LGSJ00000000, LGTR00000000, LGTS00000000, LGSM00000000, LGSL00000000, LGSO00000000, and LGSN00000000.

 

Leaf ‘bait’ uncovers dieback crossbreeds

ScienceNetwork Western Australia, Wednesday, 16 September 2015 article by Samille Mitchell

  • Dieback becomes pathogenic as it mixes with other species
  • South-west waterway ‘fishing’ reveals naturally occurring hybrid
  • Discovery raises questions about how species came into contact

MURDOCH University scientists have discovered the first known natural occurrence of hybrids of the plant pathogen Phytophthora, commonly known as the dieback, which has ravaged south-west bushland and forests.

But the Centre of Phytophthora Science and Management (CPSM) research also shows that Phytophthora is not always the ‘baddy’ of the plant world that it is perceived to be.

Murdoch University Associate Professor Treena Burgess says Phytophthora species naturally occur in many areas throughout WA, and not all become damaging pathogens.

She says Phytophthora species tend to become more pathogenic the more they hybridise.

But she says the newly discovered natural hybrids come from relatively low-pathogenic parent species and therefore do not pose a big risk to native vegetation in the short-term.

She cites example of naturally occurring endemic species of Phytophthora in the northern sandplains which are believed to survive on plant roots with little impact.

However, if a seedling from its host plant sprouts nearby, the Phytophthora will kill it, thus ensuring wider spread growth for the host species.

“Everything that’s naturally occurring is here for a reason,” she says.

“Everything is interconnected—we just don’t see what’s going on underneath the earth.”

Before this discovery Phytophthora hybrids had only been known from mixing in nurseries, rather than from the natural environment.

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New Phytopathology article

Winter Conditions Correlate with Phytophthora alni Subspecies Distribution in Southern Sweden

Miguel A. Redondo, Johanna Boberg, Christer H. B. Olsson, and Jonàs Oliva

Phytopathology 2015 105:9, 1191-1197 http://dx.doi.org/10.1094/PHYTO-01-15-0020-R

During the last century, the number of forest pathogen invasions has increased substantially. Environmental variables can play a crucial role in determining the establishment of invasive species. The objective of the present work was to determine the correlation between winter climatic conditions and distribution of two subspecies of the invasive forest pathogen Phytophthora alni: P. alni subspp. alni and uniformis killing black alder (Alnus glutinosa) in southern Sweden. It is known from laboratory experiments that P. alni subsp. alni is more pathogenic than P. alni subsp. uniformis, and that P. alni subsp. alni is sensitive to low temperatures and long frost periods. By studying the distribution of these two subspecies at the northern limit of the host species, we could investigate whether winter conditions can affect the geographical distribution of P. alni subsp. alni spreading northward. Sixteen major river systems of southern Sweden were systematically surveyed and isolations were performed from active cankers. The distribution of the two studied subspecies was highly correlated with winter temperature and duration of periods with heavy frost. While P. alni subsp. uniformis covered the whole range of temperatures of the host, P. alni subsp. alni was recovered in areas subjected to milder winter temperatures and shorter frost periods. Our observations suggest that winter conditions can play an important role in limiting P. alni subsp. alni establishment in cold locations, thus affecting the distribution of the different subspecies of P. alni in boreal regions.

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