What's New

New Phytophthora alni article in Journal of Maps

Potential risk of occurrence of Phytophthora alni in forests of the Czech Republic

Phytophthora alni is an invasive organism that causes root and collar rot in alders, which significantly damages the forest and riparian vegetation of alder trees in Central and Western Europe. In the Czech Republic, this pathogen was first confirmed in 2001, and since then it has been gradually spreading from the west to the east. Here, we applied a model of potential distribution that estimates the level and spatial variability of the pathogen occurrence and spread risk for Czech Republic forests to target the early detection and control the further invasion of P. alni in this region. Our predictions are based on a rigorous statistical analysis of data obtained from field survey as well as available geodatabases. We used two sets of predictor variables describing (i) the forest stands and (ii) neighbourhood of the stands, and generalized linear modelling with forward stepwise selection of predictors. The results of statistical analysis showed the significant effect of the area of the forest stand, forest vegetation zone, presence of watercourse and area of alder stands in the neighbourhood on the probability of occurrence of P. alni in the study region. The map derived based on the final model shows the potential risk of occurrence and impact of P. alni in forests of the Czech Republic as classified on a five-point scale ranging from very low risk for alder stands with a low level of likely invasion to very sensitive alder stands with high probability of pathogen occurrence and high levels of damage. This is a unique output not only for the Czech Republic but also throughout Europe.

New Plant Disease article

Endemic and Emerging Pathogens Threatening Cork Oak Trees: Management Options for Conserving a Unique Forest Ecosystem.

Moricca S, Linaldeddu BT, Ginetti B, Scanu B, Franceschini A, Ragazzi A. Endemic and Emerging Pathogens Threatening Cork Oak Trees: Management Options for Conserving a Unique Forest Ecosystem. Plant Disease [Internet]. 2016  ;100(11):2184 - 2193. Available from: http://apsjournals.apsnet.org/doi/10.1094/PDIS-03-16-0408-FE

Cork oak (Quercus suber) forests are economically and culturally intertwined with the inhabitants of the Mediterranean basin and characterize its rural landscape. These forests cover over two million hectares in the western Mediterranean basin and sustain a rich biodiversity of endemisms as well as representing an important source of income derived from cork production. Currently cork oak forests are threatened by several factors including human-mediated disturbances such as poor or inappropriate management practices, adverse environmental conditions (irregular water regime with prolonged drought periods), and attacks of pathogens and pests. All these adverse factors can interact, causing a complex disease commonly known as “oak decline.” Despite the numerous investigations carried out so far, decline continues to be the main pathological problem of cork oak forests because of its complex etiology and the resulting difficulties in defining suitable control strategies. An overview of the literature indicates that several pathogenic fungi and oomycota can play a primary role in the etiology of this syndrome. Therefore, the aim of this review is to analyze the recent advances achieved regarding the bio-ecology of the endemic and emerging pathogens that threaten cork oak trees with particular emphasis on the species more directly involved in oak decline. Moreover, the effect of climate change on the host-pathogen interactions, a task fundamental for making useful decisions and managing cork oak forests properly, is considered.

Early view article in Global Change Biology journal

Current and projected global distribution of Phytophthora cinnamomi, one of the world's worst plant pathogens.

Burgess, T. I., Scott, J. K., McDougall, K. L., Stukely, M. J. C., Crane, C., Dunstan, W. A., Brigg, F., Andjic, V., White, D., Rudman, T., Arentz, F., Ota, N. and Hardy, G. E. St.J.

Glob Change Biol. Accepted Author Manuscript. doi:10.1111/gcb.13492

Globally, Phytophthora cinnamomi is listed as one of the 100 worst invasive alien species and active management is required to reduce impact and prevent spread in both horticulture and natural ecosystems. Conversely, there are regions thought to be suitable for the pathogen where no disease is observed. We developed a CLIMEX model for the global distribution of P. cinnamomi based on the pathogen's response to temperature and moisture and by incorporating extensive empirical evidence on the presence and absence of the pathogen. The CLIMEX model captured areas of climatic suitability where P. cinnamomi occurs that is congruent with all available records. The model was validated by the collection of soil samples from asymptomatic vegetation in areas projected to be suitable by the model for which there were few records. DNA was extracted and the presence or absence of P. cinnamomi determined by high throughput sequencing (HTS). While not detected using traditional isolation methods, HTS detected P. cinnamomi at higher elevations in eastern Australia and central Tasmania as projected by the CLIMEX model. Further support for the CLIMEX model was obtained by using the large dataset from southwest Australia where the proportion of positive records in an area is related to the Ecoclimatic Index value for the same area. We provide for the first time a comprehensive global map of the current P. cinnamomi distribution, an improved CLIMEX model of the distribution, and a projection to 2080 of the distribution with predicted climate change. This information provides the basis for more detailed regional scale modelling and supports risk assessment for governments to plan management of this important soil-borne plant pathogen.


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.



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.


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.



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.



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


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.


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


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.