Plant Pathology & Quarantine Observations on Erysiphe platani in Germany

Kirschner R*

Department of Life Sciences, National Central University, Jhongli City, 320 Taoyuan County, Taiwan R.O.C.

Kirschner R. 2011 – Observations on Erysiphe platani in Germany. Plant Pathology & Quarantine 1(2), 115–119.

The powdery mildew Erysiphe platani was recorded on London plane ( × acerifolia) in Germany. Ascomata and conidia were found on a leaf of a tree at an avenue in the city of Frankfurt am Main, which had also been colonized by the invasive Sycamore Lace Bug ciliata. The spread of both invasive species from south Europe towards the north might be correlated with global warming. Difficulties in detecting and identifying the mildew as the causative agent of the symptoms are presented. Information relevant for the diagnosis and prognosis is compiled and discussed.

Key words – – Erysiphales – invasive and fungi – Oidium

Article Information Received 15 September 2011 Accepted 22 September 2011 Published online 2 October 2011 *Corresponding author: Roland Kirschner – e-mail – [email protected]

Introduction America, has been introduced to South Ame- London plane (Platanus × acerifolia rica, South Africa, Australia, New Zealand, (Ait.) Willd.) is a very common ornamental Asia, and also to several European countries tree planted in public places and along avenues (Braun 1987, Pastirčáková & Pastirčák 2006). in Germany. It is considered hybrid between P. In Europe, the has been recorded main- occidentalis and P. orientalis (Carpenter et al. ly from countries in the south and southeast 2005), for which different scientific names are (ISC 2011), beginning in Italy in the 1960s commonly used (Santamour & McArdle 1986). according to the historical outline by A major reason for preferring the hybrid Pastirčáková & Pastirčák (2006), but not from as an ornamental as compared to its parent spe- Germany. This powdery mildew is reported cies is the larger resistance to anthracnose cau- here from Frankfurt am Main and remarks on sed by the ascomycete veneta difficulties encountered in differentiating the (Sacc. & Speg.) Höhn. (, as Gno- symptoms caused by this pathogen from those monia platani, Santamour & McArdle 1986). caused by other reasons are noted. A detailed Platanus species also suffer from para- account of the species with focus on the epi- sitic organisms, such as the invasive Sycamore demic spread in Germany, the morphology of Lace Bug (Say) which has the anamorph and the phylogenetic position spread to London planes in Germany (Fig. 1). using rDNA sequence data will be presented in The was first introduced from North another publication considered for Andrias, a America to Italy in the 1960s and has been re- journal of Staatliches Naturkundemuseum ported from Germany since the 1980s. Karlsruhe, Germany (Scholler et al. in prep., M. The powdery mildew Erysiphe platani Scholler, pers. comm.). The phytopathological (Howe) U. Braun and S. Takam., also a patho- focus with emphasis on the teleomorph justifies gen restricted to species of Platanus in North a separate publication here.

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Fig. 1 – Exuvia of nymph of Corythucha ciliata and insect droppings on lower side of leaf of Platanus × acerifolia.

Methods days, only one leaf carrying the powdery mil- dew Erysiphe platani was found. Specimen and morphology Leaves of Platanus × acerifolia were Erysiphe platani (Howe) U. Braun and S. Ta- collected in an avenue with several mature kam., Schlechtendalia 4: 12 (2000). Figs 3–4 individuals. Because the trees were high, leaves Hyphae 2–3 μm wide, appressoria lobed. could be collected by hand only exceptionally Ascomata and conidia formed on lower side of from lowermost branches. The leaves were leaf. Ascomata yellow when young and becom- examined with a hand-lens for the presence of ing black during maturation. Mature ascomata mildew symptoms and studied with a dissec- 107–130 μm diam., cells of ascoma wall irre- ting microscope. Fungal material on a fallen gular, 9–20 × 6–13 μm, covered by 7–19 up to leaf was mounted in 5–10% aqueous KOH for 4 times dichotomously branched appendages study with a light microscope. Because of the with brown base and 0–3-septa, ca. 140–250 sparse material, only ten ascomata and few co- μm long and 6–8 μm wide. Asci 4–8, saccate, nidiophores and conidia were measured with- 48–65 × 29–45, with 2–5 ascospores. Asco- out statistical treatment. The specimen was de- spores ovoid or oblong, 21–23 × 13–14 μm. posited at the fungal collection of National Conidiophores verrucose, 120–215 × 6–12 μm, Museum of Natural Science, Taichung, Taiwan 3-septate. Conidia reticulate, 30–38 × 16–21 (TNM). μm, germinating at one end with a hypha; ger- mination with appressoria formation not found. Results Known distribution (according to ISC Young leaves and leaves infected by pa- 2011) – America, Asia, Australia, Europe: Bul- rasitic show conspicuous white patches garia, France, Germany, Greece, Italy, Monte- composed of plant trichomes (Fig. 2). Several negro, Portugal, Romania, Serbia, Slovakia, leaves were strongly affected by the Sycamore Spain, Switzerland, Ukraine, United Kingdom. Lace Bug Corythucha ciliata, which could be Material examined – Germany, Hessen, concluded by the presence of many black ho- Frankfurt am Main, Miquelallee with planta- neydew droplets and exuviae of the larvae tions of Platanus × acerifolia, on lower side of (Figs 1, 3). Though the same site was investi- fallen leaf of P. × acerifolia, 3 August 2011, R. gated for ca. ten min each of three subsequent Kirschner 3530 (TNM).

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Fig. 2 – Leaves of Platanus × acerifolia with white patches formed by leaf trichomes resembling powdery mildew colonies.

Fig. 3 – Ascomata of Erysiphe platani in different stages of development from yellow to black on lower side of leaf. Note white patches formed by leaf trichomes (lower left corner) and the black dropping of Corythucha ciliata (arrow) resembling a mature ascoma.

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Fig. 4 – Mature, slightly squashed ascoma of Erysiphe platani in the light microscope. Note the brown bases of appendages and presence of septa (arrowheads). Scale Bar = 200 µm.

Note – The presence of the powdery septa per appendage (0–1 reported in Braun mildew was obscured because the symptoms 1987, Pastirčáková & Pastirčák 2008) and of caused by the bug Corythucha ciliata and leaf up to 8 asci per ascoma (up to 6 reported in areas covered by dense white trichomes pro- Braun 1987, Pastirčáková & Pastirčák 2008). duced by the plant (Fig. 3). The spread of E. platani to Germany might be related to climate change, because in Discussion Europe the fungus has hitherto been known Ascomata and conidia can be dispersed from countries south of Germany, mainly south by wind and accumulate on non-host substrates and southeast Europe (ISC 2011). This situa- (Takamatsu 2004). Records concerning mil- tion is comparable to that of the invasive bug dews of very heterogeneous reliability in the also introduced first in south Europe and internet without investigation of the origin of gradually migrating towards the north. In con- propagules can, therefore, not be considered trast to the fungus, however, experimental evi- here. Though only one leaf with few material dence for preference of higher temperatures of the powdery mildew was found, accidental exists only for the bug (Ju et al. 2009). Similar- wind-spread of mature ascomata and conidia of ly to several other invasive species of Erysi- similar Erysiphe species from other hosts onto phales that often reproduce only asexually for a the leaf of P. × acerifolia (where they might period of several years after being introduced have been caught by the trichomas) can be ex- (Kirschner 2010), E. platani in Europe was cluded, because young yellow ascomata were first known to reproduce by conidia only also found on the leaf and because of the asso- (Braun 1987, Bolay 2005, Pastirčáková & ciated conidiophores. For detailed morphologi- Pastirčák 2006), and also by ascospores for the cal descriptions of the species in Europe see for first time in 2003 in Montenegro, then 2008 in the teleomorph Pastirčáková & Pastirčák Hungary (Pastirčáková & Pastirčák 2008), and (2008) and for the anamorph Bolay (2005) and now in Germany. Due to the presence of the Pastirčáková & Pastirčák (2006). The range of sexual stage which is more adapted to overwin- the few measurements possible with the sparse tering than the asexual stage, more and seaso- material fits generally into the ranges given in nally earlier inoculum of the pathogen can be the literature, except for the slightly larger up- predicted for the following years. Because of per range of the ascomata (up to 130 μm). the continued spread of E. platani in Europe, in Other differences are the presence of up to 3 new plantations of P. × acerifolia attention 118 Plant Pathology & Quarantine should be given to select cultivars with higher Weisenborn is thanked for providing the name resistance against E. platani. Such cultivars of the bug and Markus Scholler for the infor- already exist, such as “Yarwood” (Santamour mation on the parallel preparation of a manu- & McArdle 1986). script about detailed records from Germany. The bug C. ciliata produces conspicuous symptoms in form of numerous minute black, References shiny droplets of honeydew on the lower side of leaves. Though being generally larger than Bolay A. 2005 – Les oïdiums de Suisse (Ery- the ascomata of E. platani, these droplets over- siphacées). Cryptogamica Helvetica 20, lap in size and obscure the presence of the as- 1–176. comata. Braun U. 1987 – A monograph of the Erysi- Young leaves of Platanus spp. are cove- phales (powdery mildews). Beihefte zur red by a white layer formed by dense trichomes Nova Hedwigia 89, 1–700. that gradually disappear during maturation Carpenter RJ, Hill GS, Jordan JS. 2005 – Leaf (Yarwood & Gardner 1970, Carpenter et al. cuticular morphology links Platanaceae 2005). Hairs on both sides are equal in length and Proteaceae. International Journal of in P. × acerifolia, being about 500 µm, Plant Science 166, 843–855. whereas the conidiophores of E. platani (as ISC. 2011 – Invasive Species Compendium, Microspharea alni) are about 100–200 µm, i.e. CABI. http://www.cabi.org/isc/ more than 20% shorter than the hairs (Yarwood Ju RT, Wang F, Li B. 2009 – Effects of tem- & Gardner 1970). Mycelium and conidiophores perature on the development and popula- growing between trichomes, therefore, cannot tion growth of the sycamore lace bug, be differentiated from the trichomes macrosco- Corythucha ciliata. Journal of Insect pically. Shedding off of the trichomes is often Science, 16. Available online: insect delayed in sunken leaf areas which may par- science.org/11.16 ticularly remain even after leaf maturation due Kirschner R. 2010 – First record of Erysiphe to contortion induced by parasitic . magnifica on lotus, a host outside the These white layers on leaves can easily been Magnoliales. Mycological Progress 9, mistaken as colonies of the powdery mildew. 417–424. A further problem is concluded from the Pastirčáková K, Pastirčák M. 2006 – The ana- fact that E. platani was found on only one morph of Erysiphe platani on Platanus fallen leaf. Perhaps the heavy impact of the bug hispanica in Slovakia. Mycotaxon 97, prevents the fungus from rich development. 189–194. Many potential host trees could be checked for Pastirčáková K, Pastirčák M. 2008 – Erysiphe the presence of the fungus, but have a consi- platani causing powdery mildew of derable height so that the leaves of the crown London Plane in Hungary. Acta Phytopa- cannot be investigated without any additional thologica et Entomologica Hungarica 43, tools. 31–36. Gathering specimens from high tree Santamour FS, McArdle AJ. 1986 – Checklist crowns, excluding identification of merely of cultivated Platanus (planetree). Jour- wind-blown propagules, and disguise of asco- nal of Arboriculture 12, 78–83. mata by insect droppings and of conidiophores Takamatsu S. 2004 – Phylogeny and evolution by trichomes all need to be taken into account of the powdery mildew fungi (Erysi- in detecting this powdery mildew. phales, Ascomycota) inferred from nu- clear ribosomal DNA sequences. Myco- Acknowledgements science 45, 147–157. Laboratory facilities were kindly pro- Yarwood CE, Gardner MW. 1970 – Leaf sur- vided by Meike Piepenbring, Goethe Univer- face and leaf hairs affect length of coni- sity Frankfurt am Main, Germany. This work diophores of Erysiphaceae. Mycologia was financed by the National Science Council 62, 707–713. of Taiwan (100-2621-B-008-001-MY3). Jascha

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