Evolutionary trait‐based approaches for predicting future global impacts of plant pathogens in the genus Phytophthora

Plant pathogens are introduced to new geographical regions ever more frequently as global connectivity increases. Predicting the threat they pose to plant health can be difficult without in‐depth knowledge of behaviour, distribution and spread. Here, we evaluate the potential for using biological traits and phylogeny to predict global threats from emerging pathogens. We use a species‐level trait database and phylogeny for 179 Phytophthora species: oomycete pathogens impacting natural, agricultural, horticultural and forestry settings. We compile host and distribution reports for Phytophthora species across 178 countries and evaluate the power of traits, phylogeny and time since description (reflecting species‐level knowledge) to explain and predict their international transport, maximum latitude and host breadth using Bayesian phylogenetic generalised linear mixed models. In the best‐performing models, traits, phylogeny and time since description together explained up to 90%, 97% and 87% of variance in number of countries reached, latitudinal limits and host range, respectively. Traits and phylogeny together explained up to 26%, 41% and 34% of variance in the number of countries reached, maximum latitude and host plant families affected, respectively, but time since description had the strongest effect. Root‐attacking species were reported in more countries, and on more host plant families than foliar‐attacking species. Host generalist pathogens had thicker‐walled resting structures (stress‐tolerant oospores) and faster growth rates at their optima. Cold‐tolerant species are reported in more countries and at higher latitudes, though more accurate interspecific empirical data are needed to confirm this finding. Policy implications. We evaluate the potential of an evolutionary trait‐based framework to support horizon‐scanning approaches for identifying pathogens with greater potential for global‐scale impacts. Potential future threats from Phytophthora include Phytophthora x heterohybrida, P. lactucae, P. glovera, P. x incrassata, P. amnicola and P. aquimorbida, which are recently described, possibly under‐reported species, with similar traits and/or phylogenetic proximity to other high‐impact species. Priority traits to measure for emerging species may be thermal minima, oospore wall index and growth rate at optimum temperature. Trait‐based horizon‐scanning approaches would benefit from the development of international and cross‐sectoral collaborations to deliver centralised databases incorporating pathogen distributions, traits and phylogeny

Evaluation of Foliar Fungicide Sprays for the Control of Boxwood Blight, Caused by the Fungus <i>Cylindrocladium buxicola</i>

Cylindrocladium buxicola causes a damaging blight disease on boxwood which has spread rapidly throughout Europe since introduction of the pathogen in England in the mid 1990s. The pathogen has also been recently identified in the USA and British Columbia. The disease is difficult to control using cultural methods and information about chemical control is lacking. To address this, preventative and curative foliar fungicide sprays previously shown in laboratory tests to have efficacy were evaluated over two autumn/winter seasons in the UK. Results from the first autumn/winter season showed that the premix product Opponent (epoxiconazole + kresoxim-methyl + pyraclostrobin) was the best treatment when applied preventatively 3 days before inoculation. In the second autumn/winter season, curative treatment of diseased plants was best achieved with a weekly program of fungicides starting 3 days before inoculation and alternating with two or three products including Bravo (chlorothalonil), Signum (boscalid + pyraclostrobin), and Octave (prochloraz). The only fungicide tested and available to amateur growers in the UK, Fungus Clear (penconazole), was found to give moderate control of boxwood blight. Accepted for publication 7 August 2012. Published 24 October 2013. </jats:p

First Record of Oidium Anamorph of Podosphaera Xanthii on Medusagyne Oppositifolia

Powdery mildew first appeared on mature 3-year-old bushes of ‘jellyfish tree’, Medusagyne oppositifolia (Medusagynaceae), grown from seed at Eden Project, Cornwall, England, in collaborative conservation work with the Seychelles Government. Initially, young leaves showed distortion and patches of mycelium bearing conidia. Later, light brown lesions developed and badly affected plants showed extensive leaf-drop, especially destructive in seedlings. This is the first report of powdery mildew on Medusagyne. Conidia are catenate, elliptical to doliiform, (19) 24–34(47Æ5) · (13Æ5) 15–18 lm with fibrosin bodies and a sinuous wrinkling pattern. Conidiophores erect with a long cylindrical straight or twisted foot-cell, 41–86Æ5 (140) · (7) 9–14 (16) lm, arising towards one end of its hyphal mother cell, the lower septum occasionally raised up to 10 lm, followed by a generative cell and 2–5 maturing conidial units. Superficial hyphal cells, 25–105 · 4Æ5–11Æ5 lm, branched at right angles, bearing inconspicuous or slightly nipple-shaped appressoria. No chasmothecia were present, but characteristics are consistent with Oidium subgenus Fibroidium, the anamorph of Podosphaera. The short, broad germ tubes typical of the fibroidium type, brevitubus subtype narrowed the identification to Podosphaera section Sphaerotheca subsect. Magnicellulatae (Cook & Braun, 2009) with the morphology close to that of Podosphaera (syn. Sphaerotheca) fusca, apparently a ubiquitous species with a broad host range