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[EN] An analysis of incidence of Phytophthora spp. in 732 European nurseries producing forest transplants, larger specimen trees, landscape plants and ornamentals, plus 2525 areas in which trees and shrubs were planted, is presented based on work conducted by 38 research groups in 23 European countries between 1972 and 2013. Forty-nine Phytophthora taxa were recorded in 670 nurseries (91.5%); within these nurseries, 1614 of 1992 nursery stands (81.0%) were infested, although most affected plants appeared healthy. In forest and landscape plantings, 56 Phytophthora taxa were recovered from 1667 of 2525 tested sites (66.0%). Affected plants frequently showed symptoms such as crown thinning, chlorosis and dieback caused by extensive fine root losses and/or collar rot. Many well-known highly damaging host¿Phytophthora combinations were frequently detected but 297 and 407 new Phytophthora¿host associations were also observed in nurseries and plantings, respectively. On average, 1.3 Phytophthora species/taxa per infested nursery stand and planting site were isolated. At least 47 of the 68 Phytophthora species/taxa detected in nurseries and plantings were exotic species several of which are considered well established in both nurseries and plantings in Europe. Seven known Phytophthora species/taxa were found for the first time in Europe, while 10 taxa had not been previously recorded from nurseries or plantings; in addition, 5 taxa were first detections on woody plant species. Seven Phytophthora taxa were previously unknown to science. The reasons for these failures of plant biosecurity in Europe, implications for forest and semi-natural ecosystems and possible ways to improve biosecurity are discused., The authors are grateful to all public and private owners of nurseries and plantings who contributed to this extensive study. T. Jung acknowledges the support by the Regione Autonoma della Sardegna, Visiting Professor Program at the University of Sassari, Italy. The authors also thank the COST Office and the European Council for providing the European COST Actions FP0801 (http://www.cost.eu/domains_actions/fps/Actions/FP0801) and FP 1002 (http://www.cost.eu/domains_actions/fps/Actions/FP1002), the EU projects FOR-THREATS and ISEFOR, and BiodivERsA project RESIPATH as platforms for stimulating discussions on the nursery pathway and possible management solutions.

Summary The composition of the endophytic fungal assemblages in Quercus cerris, Q. pubescens and Q. robur, three oak species most susceptible to decline, was investigated in Fagare ` (Padova), Ulignano (Pisa), and Radda in Chianti (Firenze). The endophytic assemblages were studied as a function of health status of the whole tree and of twigs and leaves. The effect of station altitude was tested on Q. cerris. Samples were gathered from healthy and declining trees. In April (bud opening time) 20 twigs and 10 leaves were collected from each tree. Fungi were isolated from twig segments and leaf portions. A total of 23 fungal genera with 27 different species were isolated, in addition to a few sterile mycelia. Eleven species were found to be common to all three oak species, while other species were found only on one oak species, suggesting host specificity. Among the fungal species isolated, some were known to be pathogenic (Apiognomonia quercina, Colpoma quercinum, Diplodia mutila, Phomopsis quercina). The colonization frequency (CF) of pathogenic species varied between 0.9% for A. quercina in Q. cerris and 60.2% for P. quercina in Q. robur. Analysis of variance showed a statistically significant difference among the oak species tested. The CF was higher in declining trees in comparison with healthy trees, and also in twigs vs. leaves. The CF was found to be higher for Q. cerris trees growing at sea level as compared with those situated at an elevation of 350‐400 m. In stands where, on account of particular ecological conditions, pathogenic behaviour is displayed simultaneously by more than one endophytic fungal species, trees accentuate their decline.

Fusarium eumartii is a fungus associated with declining Quercus robur, in which it is found in the vessels. The response of oak species to infection is known to vary: Q. robur is susceptible, but Quercus cerris and Quercus pubescens are resistant. An experiment was carried out in 1996 and repeated in 1997, to examine how F. eumartii colonization differed in oak species that were susceptible or resistant to the fungus by counting the number of vessels with mycelium at various distances from the inoculation site in infected seedlings and by determining the amount of viable fungus in infected tissue. Infected vessels with mycelium were counted on sections (10 μm thick) cut at 0, 2, 4, 6, 8 and 10 cm from the inoculation site on 1-year-old inoculated seedlings as well as on sections cut every 2 cm to the seedling tip. The amount of viable fungus was determined by counting the colony forming units (CFUs) in stem segments from the same seedlings. Quercus robur seedlings had the greatest number of infected vessels and the greatest number of CFUs. Forty days after inoculation, the extent of vertical fungal spread was 28.12 cm in Q. robur, 3.15 cm in Q. cerris and 3.00 cm in Q. pubescens. The greatest number of CFUs was found in Q. robur at day 5 after inoculation. Analysis of variance confirmed the results.

The presence of Discula quercina on dormant buds and twigs of declining Quercus cerris was studied on two test sites. A number of fungi, including some endophytic ones, were isolated in association with D. quercina as part of the total oak mycoflora: Acremonium spp., Diplodia mutila, Phomopsis quercina, Hypoxylon mediterraneum, Cylindrocarpon sp., Phoma cava and Trichoderma viride plus some less frequent species. The distribution of these fungi did not appear to be related to the altitude of the test sites studied: sea level and 600 m a.s.l., nor to the differing composition of the site vegetation. Discula quercina was isolated both from the twigs (18.02% from woody tissue; 5.82% bark tissue) and from the buds (11.62% embryo; 14.55% bud scales). The results indicate that D. quercina is able to live in symbiosis with its host. Although the colonization of the aerial parts of Q. cerris is possible through infection with wind-borne inoculum, leaf infection can also occur through overwintering mycelium migrating to the leaves mainly from the buds, but also to a lesser extent from the twigs. Zusammenfassung Discula quercina als Endophyt absterbender Exemplare von Quercus cerris An zwei Standorten wurde untersucht, ob Discula quercina in ruhenden Knospen und Zweigen absterbender Zerr-Eichen (Quercus cerria) vorkommt. Dabei wurden neben D. quercina verschiedene Pilze isoliert - darunter einige Endophyten -, die ebenfalls zur Eichen-Mykoflora gehoren:Acremonium spp., Diplodia mutila, Phomopsis quercina, Hypoxylon mediterraneum, Cylindrocarpon sp., Phoma cava und Trichoderma viride, auserdem einige seltener vorkommende Arten. Die Verteilung dieser Pilze hing offenbar weder von der Hohenlage der Versuchsstandorte (Meereshohe und 600 m uber N.N.) noch von der unterschiedlichen Zusammensetzung der Vegetation der Versuchsstandorte ab. D. quercina wurde sowohl aus den Zweigen 18,02% aus Holzgewebe; 5,82% aus Rindengewebe als auch aus den Knospen (11,62% Embryo;14,55% Knospenschuppen) isoliert. Die Ergeb- nisse zeigen, dasD. quercina in Symbiose mit der Wirtspflanze leben kann. Die Besiedlung der oberirdischen Teile von Q. cerris ist durch eine Infektion mit windburtigem Inokulum moglich, doch eine Infektion der Blatter kann auch durch uberwinterndes Myzel erfolgen, das hauptsachlich von den Knospen, in geringerem Mase aber auch von den Zweigen zu den Blattern gelangt.

Some experiments were conducted (in duplicate) to determine the effects of the osmotic potential on the growth of Diplodia mutila, and the effects of the pre-dawn water potential on the development of cankers by D. mutila on Quercus robur. Mycelium of D. mutila was grown on liquid medium enriched with various amounts of polyethylene glycol so as to give osmotic potential values of -0.35, -1.18, -1.75, -3.00 and -3.98 MPa. At the two lowest MPa values (-3.00 and -3.98 MPa) D. mutila growth was slower in relation to the fresh weight and the dry weight of the mycelium. To determine the pre-dawn water potential 30 3-year-old Q. robur seedlings were inoculated with D. mutila mycelium. Water-stressed seedlings had lower pre-dawn water potential values (MPa -2.92) and longer cankers than the unstressed seedlings (MPa -0.79). It is concluded that Q. robur, a highly hygrophilous oak, suffers from water stress to such an extent that its structural and chemical defences are overcome and the seedlings are seriously damaged. A similar situation is observed in nature, where frequent and prolonged droughts may induce states of water stress that account for the spread and the incidence of D. mutila in Italy. Zusammenfassung Wasserstres und Entwicklung von Diplodiamutila-Rindennekrosen bei Quercus robur Verschiedene Experimente wurden (zweifach) durchgefuhrt, um den Einflus des osmotischen Potentials auf das Wachstum von Diplodia mutila sowie die Wirkungen des vor Tagesanbruch herrschenden Wasserpotentials auf die Entwicklung der durch Diplodia mutila verursachten Rindennekrosen bei Quercus robur zu untersuchen. Myzel von D. mutila wurde auf Flussigmedium angezogen, das unterschiedliche Mengen PEG enthielt, wodurch die Werte des osmotischen Potentials bei –0,35, –1,18, –1,75, –3,00 und –3,98 MPa lagen. Bei den beiden niedrigsten MPa-Werten (–3,00 und –3,98 MPa) wuchs D. mutila langsamer, was anhand des Frischgewichts und des Trockengewichts des Myzels ermittelt wurde. Zur Bestimmung des vor Tagesanbruch herrschenden Wasserpotentials wurden 30 drei Jahre alte Samlinge von Q. robur mit Myzel von D. mutila inokuliert. Unter Wasserstres leidende Samlinge wiesen vor Tagesanbruch niedrigere Wasserpotentiale (MPa –2,92) und langere Rindeneekrosen auf als die nicht gestresten Samlinge (MPa –0,79). Es wird gefolgert, dasQ. robur als Eiche, die viel Feuchtigkeit benotigt, unter Wasserstres so sehr leidet, das ihre strukturellen und chemischen Abwehrmechanismen nicht ausreichend wirksam sind und die Samlinge von D. mutila stark geschadigt werden. Eine ahnliche Situation wird in der freien Natur beobachtet–die Ausbreitung und die Befallshaufigkeit von D. mutila in Italien gehen vermutlich auf haufige und lange andauernde Trockenperioden zuruck.

Ten-year-old field-grown Quercus pubescens Willd. and Quercus cerris L. individuals were inoculated with Diplodia mutila (teleomorph Botryosphaeria stevensii Shoe-maker) to observe symptom evolution over 2 years. The experiments were carried out for the 3 years: 1991, 1992 and 1993. At the same time, the effect of D. mutila on leaf water potential and peroxidase activity was assessed on the leaves of 2-year-old seedlings from the same two species growing under controlled conditions (18 h day, relative humidity 75%), temperature 24/15°C day/night). Quercus pubescens was more susceptible than Q. cerris, and frequently exhibited dieback of the branch above the inoculation site. On the seedlings, the visible symptoms of infection were much more severe than on the older trees. The infected seedlings showed a lower leaf water potential than healthy seedlings, particularly those of Q. pubescens after the third week. The peroxidase activity was increased in infected Q. pubescens seedlings compared with both groups of control seedlings (wounded but not inoculated, and neither wounded nor inoculated) 14 and 21 days after inoculation. Leaf water potential and peroxidase activity are known indicators of stress which appear even before any visible symptoms; they could therefore serve as early indicators of D. mutila infection. Zussamenfassung Zehn Jahre alte, im Feld wachsende Quercus cerris- und Quercus pubescens-Baume wurden mit Diplodia mutila (Teleomorph Botryosphaeria stevensii Shoemaker) inokuliert, um die Befallssymptomentwicklung uber einen Zeitraum von 2 Jahren beobachten zu konnen. Die Versuche wurden in den Jahren 1991, 1992 und 1993 durchgefuhrt. Zur gleichen Zeit wurde der Einflus einer D. mutila-Infektion auf das Wasserpotential sowie die Peroxidasaktivitat in den Blattern von 2 Jahre alten Samlingen der gleichen Quercus-Spezies ermittelt, die unter kontrollierten Bedingungen (18 h Tag, RH75%, Temperature 24/15°C Tag/Nacht) wuchsen. Festgestellt werden konnte, dasQ. pubescens anfalliger als Q. cerris ist, ein Absterben der Zweige oberhalb des Inokulationspunktes wurde haufig beobachtet. Die sichtbaren Befallssymptome waren deutlich starker bei Samlingen als bei den alteren Baumen. Infizierte Samlinge hatten ein niedrigeres Blattwasserpotential als gesunde Samlinge, besonders bei Q. pubescens drei Wochen nach der Inokulation. 14 und 21 Tage nach der Inokulation war die Peroxidaseaktivitat in infizierten Q. pubescens-Samlingen erhoht, verglichen mit den Kontrollen (verletzte aber nicht inokulierte sowie weder verletzte noch inokulierte Samlinge). Anderungen des Blattwasserpotentials und der Peoxidaseaktivitat sind bekannte Stresindikatoren, die mesbar sind, bevor Symptome eines Befalls erscheinen. Von daher konnten sie als ein fruher Nachweis einer D. mutila-Infektion dienen.

Summary Forty isolates of Diplodia mutila, a dieback agent on oaks were characterized by their capacity to produce heterokaryons, by their vegetative compatibility, and by their pathogenicity tests on Quercus cerris. The forty isolates were collected from Quercus cerris, Quercus frainetto, Quercus ilex, Quercus pubescens, Quercus robur and Quercus suber in different regions in Italy. Three nit mutants (nitt, nit and nitM) were identified with different nitrogen sources: sodium nitrite, sodium nitrate, uric acid, ammonium tartrate and hypoxanthine. On the two nutrient media employed, a potato dextrose agar (PDA) medium with chlorate (PDC), and a minimal agar medium with chlorate (MMC), isolates obtained from Q. cerris yielded the greatest number of mutants: 254 on PDC (out of a total of 583) and 190 on MMC (out of a total of 440). Nine vegetative compatibility groups (VCGs) were identified. There was a strong association between these VCGs and host species. All isolates tested except one from Q. cerris were pathogenic.

Summary Tests in vitro and in situ showed that both mycelial and conidial suspensions of Acremonium mucronatum were antagonistic for Diplodia mutila, a common pathogen on the apical twigs of declining Quercus cerris, Quercus frainetto, Quercus pubescens and Quercus robur. Antagonism was greater with the mycelium than with the conidial suspensions, and was strongest at a test temperature of 20°C. The results suggest that pathogenicity of D. mutila on declining trees may be significantly reduced by the presence of A. mucronatum.

Summary The callus-fungal method was employed to test the response to C. flaccidum of the highly susceptible P. nigra var. laricio and the resistant P. sylvestris, and to ascertain whether results obtained with this method matched in planta observations. Calli were inoculated with axenie cultures of C. flaccidum obtained by incubating basidiospores on modified Schenk and Hildebrandt medium. Several parameters were evaluated. Colony growth was more rapid on P. nigra var. laricio. Colonies were dense on P. nigra var. laricio, but sparse on P. sylvestris. Aerial hyphae growth was abundant on P. nigra var. laricio, but less frequent on P. sylvestris. Hyphal branching began after 18 h on P. nigra var. laricio and after 45 h on P. sylvestris. Necrosis of the host cells set in after 24 h on P. nigra var. laricio, and after 70 h on P. sylvestris. The number of cells with plasmolysis was much larger in P. nigra var. laricio than in P. sylvestris. These results were consistent with the known resistance of the two species on whole plants.

Severe damage was caused to coastal forest vegetation by the Libeccio, a sea wind blowing against the Italian coast from W-SW. The behaviour of common cypress (Cupressus sempervirens), smooth cypress (C. glabra) and Monterey cypress (C. macrocarpa) in response to the Libeccio windstorms of 1990 was compared with that due to treatments with the surfactant ABS (sodium dodecylbenzenesulphonate). As regards both the nature and the intensity of the damage to the leaf waxes, the surge damage caused by the windstorms differed little from that produced artifi-cially by ABS sprays.