Woodward, Steve

BALTIC FORESTRY

English

Aberdeen University Research

Introduction Part 3: Other Invasive Tree Pathogens STEVE WOODWARD*University of Aberdeen, Institute of Biological and Environmental Sciences, Cruickshank Building, St. Machar Drive, Aberdeen AB24 3UU, Scotland, UK *For correspondence: s.woodward@abdn.ac.uk, tel. +44 1224 272669Woodward, S. 2017. Introduction Part 3: Other Invasive Tree Pathogens. Baltic Forestry 23(1): 253-254. The outbreak of ash dieback, caused by the spread of Hymenoscyphus fraxineus in Europe has caused much excitement in the public and press, rightly so, as yet anoth-er invasive pathogen spreads across the continent threaten-ing the stability of one of our iconic trees and the forest ecosystems it inhabits, from Russia to Northern Spain, from Greece to Finland. As interest focuses to a great ex-tent on this particular problem, however, we must not lose sight of the many other invasive pathogens that are current-ly spreading in Europe (Santini et al. 2013), some of which have long been known, others recognised rather recently. Arguably, we can trace invasions by Phytophthora cin-namomi and P. cambivora back to the early 19th Century, although it is difficult to be precise over this time span, particularly as spontaneous generation remained the per-ceived ‘cause’ of plant problems, amongst others, at that time. After the debunking of spontaneous generation, how-ever, it eventually became clearer that microorganisms cause disease in plants and animals. At the same time, it was recognised that pathogens could be transported around the world by various means, not least of which was through human activities. We now assume, with considerable justification that the arrival of H. fraxineus in Europe – probably in the 1980s – resulted from an inadvertent co-transport of the pathogen on ash tissues, although the precise cause re-mains unclear. Sadly, this mode of arrival of invasive pathogens in regions and continents distant from their evolutionary origins is all too common (Fisher et al. 2012; Santini et al. 2013).  Highlights of this issue The following set of papers is focused on several other invasive pests and pathogens that have entered Eu-rope, some recently, one over 50 years ago. For example,the pathogen causing the current epidemic of Dutch elm disease, Ophiostoma novo-ulmi, first entered Europe though British ports in the early-mid 1960s on consign-ments of elm logs from North America. A previous epi-demic of elm wilt, caused by Ophiostoma ulmi, had swept through Europe in the early-mid 20th Century, but many trees either recovered from the infection, or proved of low susceptibility. The appearance of a second pathogen caus-ing Dutch elm disease, however, led to the deaths of mil-lions of elms, and threatens the genus with extinction in Europe. The disease is still spreading in the northern-most areas of Europe. Pecori et al. (2017), however, highlight the use of selection and breeding in the fight against Dutch elm disease in Italy, where there have been some successes in crossing Asian elms against European Ulmus species to produce hybrids of suitable form and growth rates to utilize in southern Europe.  Dutch elm disease is still causing much destruction of trees in northern Europe, however, as illustrated in the paper by Menkis et al. (2017), in which attempts were made to slow disease spread by applying decay fungi in an attempt to kill stumps of felled elms,thereby preventing resprouting and perpetuation of the presence of host tissues susceptible to beetle attack and, subsequently, infection by O. novo-ulmi. This method was not of particular practical value, although it is clear that choice of fungus to kill the stumps must be considered carefully. Two pathogens causing leaf blights of Buxus sem-pervirens entered Europe (Henricot et al. 2000), probably in the 1990s, and have spread very rapidly through natural and cultivated populations of this valuable understory shrub since then. Buxus sempervirens is the main understo-ry woody species in the forests of north-east Turkey, but is being very badly damaged by Calonectria pseudonavicula-ta and C. henricotiae (Lehtijarvi et al. 2017) in that region. As with many invasive pathogens, the two Calonectria species are proving extremely difficult to manage, and boxwood is now considered endangered. The same prob-lem is also wreaking havoc in the forests of Georgia and Iran. ??? ?????????????????????????????????????????? ? ?????????????????????????????????????????????????????????????????????????? ? ? ? ? ? ?? ? ? ? ? ? ? ? ? ???Pitch canker of pine poses a massive threat to the fu-ture of pine forests in Europe (Bezos et al. 2017). It also attacks Pseudotsuga menziesii. Transmitted via seed, the pathogen is proving extremely difficult to detect in path-ways of introduction, but appears to colonize plants in nurseries, often asymptomatically. The pathogen is then transported to forest sites on the young plants. Although established only in Spain and Portugal (solely in forest nurseries so far in Portugal), given the massive area of various pine species in Europe, the disease is clearly a ma-jor threat, particularly to coastal pine forests, where relative humidity is conducive to disease development. Again, this disease is proving rather recalcitrant to mitigation measures. Over the past 20-25 years, Dothistroma needle blight (DNB), caused by Dothistroma septosporum and, in more limited locations, D. pini, have increased massively in overall importance, also threatening the integrity of pine forests and plantations throughout Europe (and beyond). It appears to infect most pines (if not all), along with several Picea spp. and Cedrus. The paper herein, by Lazarevic et al. (2017), extends the number of known host species varie-ties on which DNB occurs, and increases the knowledge of the pines affected in Montenegro. Pests discussed in this collection of papers include the ash black sawfly, Tomostethus nigritus (Meshkova et al.2017) and the emerald ash borer, Agrilus planipennis.Tomostethus nigritus has spread greatly in Europe recently, although populations fluctuate over years. Although not usually a lethal pest to European ash, the sawfly adds an-other layer to the woes faced in Europe by Fraxinus excel-sior. In contrast, the emerald ash borer (Selikhovin et al. 2017, Musolin et al. 2017) is highly destructive, as wit-nessed in invaded regions in North America and around Moscow. As with H. fraxineus, A. planipennis is native to Far East Asia, including the far east of Russia itself. It is, nevertheless, not native in the European parts of Russia, from where the problem is now spreading westwards. Al-ready recorded on the borders of Belarus and Ukraine, it is highly likely that the insect will continue to migrate west-wards, where it will decimate the populations of Fraxinus excelsior remaining after ash dieback. It is essential, there-fore, that any attempts to develop ash resistant to H. frax-ineus also take the emerald ash borer into account. References Bezos, D., Martínez-Alvarez, P., Fernández, M. and Diez, J.J. 2017. Epidemiology and Management of Pine Pitch Canker Disease in Europe - a Review. ??????? ????????23(1): 279-293.Fisher, M.C., Henk, D.A., Briggs, C.J., Brownstein, J.S., Madoff, L.C., McCraw, S.L. and Gurr, S.J. 2012. Emerging fungal threats to animal, plant and ecosystem health. Nature 484:186–194. Henricot, B., Perez-Sierra, A. and Prior, C. 2000. A new blight disease on Buxus in the UK caused by the fungus Cylin-drocladium. Plant Pathology 49:805. Lazarević, J., Davydenko, K. and Millberg, H. 2017. Dothistroma Needle Blight on High Altitude Pine Forests in Montenegro. Baltic Forestry 23(1): 294-302. Lehtijärvi, A., Doğmuş-Lehtijärvi, H.T. and Oskay, F. 2016. Boxwood Blight in Turkey: Impact on Natural Boxwood Populations and Management Challenges. ???????????????23(1): 274-278. Menkis, A., Vasaitis, R., Östbrant, I.-L., Pliūra, A. and Stenlid, J. 2017. Tests with Wood-Decay Fungi to Con-trol Sprouting from Cut Stumps Infected by Dutch Elm Disease. Baltic Forestry 23(1): 270-273. Meshkova, V., Kukina, O., Zinchenko, O., Davydenko, K., 2016. Three-year dynamics of common ash defoliation and crown condition in the focus of black sawfly Tomoste-thus nigritus F. (Hymenoptera: Tenthredinidae). Baltic Forestry 23(1): 303-308.Musolin, D.L., Selikhovkin, A.V., Shabunin, D.A., Zviagintsev, V.B. and Baranchikov, Y.N. 2017. Be-tween Ash Die-back and Emerald Ash Borer: Two Asian Invaders in Rus-sia and the Future of Ash in Europe. Baltic Forestry 23(1):316-333.Pecori, F., Ghelardini, L., Luchi, N., Pepori, A.L. and Santini, A. 2017. Lights and Shadows of a Possible Strategy toCope with Alien and Destructive Forest Pathogens: theExample of Breeding for Resistance to Dutch Elm Diseasein Italy. Baltic Forestry 23(1): 255-263.Santini, A., Ghelardini, L., De Pace, C., Desprez-Loustau, M-L., Capretti, P., Chandelier, A., Cech, T., Chira, D., Diamandis, S., Gaitnieks, T., Hantula, J., Holdenried-er, O., Jankovsky, L., Jung, T., Jurc, D., Kirisits, T., Kunca, A., Lygis, V., Malecka, M., Marçais, B., Schmitz, S., Schumacher, J., Solheim, H., Solla, A., Szabò, I., Tsopelas, P., Vannini, A., Vettraino, A.M., Webber, J., Woodward, S. and Stenlid, J. 2013. Bioge-ographic patterns and determinants of invasion by alien forest pathogenic fungi in Europe. New Phytologist 197: 238–250. Selikhovkin, A.V., Popovichev, B.G., Mandelshtam, M.Yu., Vasaitis, R. and Musolin, D.L. 2017. The frontline of in-vasion: the current northern limit of the invasive range of Emerald ash borer, Agrilus planipennis Fairmaire (Cole-opter: Bu-prestidae), in European Russia. Baltic Forestry 23(1): 309-315. ??? ?????????????????????????????????????????? ? ?????????????????????????????????????????????????????????????????????????? ? ? ? ? ? ?? ? ? ? ? ? ? ? ? ???

Introduction part 3 : Other invasive tree pathogens

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Introduction part 3 : Other invasive tree pathogens

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