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*Kaunas Botanical Garden of Vytautas Magnus University, Kaunas, Lithuania **Chemistry Institute, Vilnius, Lithuania

ERYSIPHE FLEXUOSA – THE NEW PATHOGEN OF HIPPOCASTANUM IN LITHUANIA

*A. Stankeviciene, *V. Snieskiene and **A. Lugauskas

Key words: flexuosa, Aesculus hippocastanum, powdery mildew, horse chest- nut, occurrence, Lithuania

Introduction of plant species results in migration of pathogenic microorgan- isms, which in big part manage to adapt to environmental conditions in new re- gions and spread quickly. The spread of new pathogen species can be prompt and threat local flora, so that they may be considered invasive species. For a long time invasive fungi have not been considered dangerous organisms (Palm 2001, Ross- man 2001)and their spread and threat to new ecosystems have not been studied. Yet, the epidemic spread of Ophiostoma novo-ulmi, Gymnosporangium sabinae or Monilia laxa were described in many countries (Raudonis et al. 2008). In recent years the interest in invasive species, including fungi, is growing (Carlton 1999, Biological... 2004). are obligatory parasites causing powdery mildew on plants from 169 families (Hirata 1986). Some species of Erysiphales are known to cause epidem- ics on cultivated plants: grape powdery mildew, spread in Europe in 19th century and American gooseberry mildew, spread in Europe and Asia in 20th century (Weltzien 1978). Their causing agents, Erysiphe necator and Podosphaera mors-uvae (synonim of Sphaerotheca mors-uvae), respectively, have features typical of invasive species. New powdery mildew species, E. flexuosa – causing agent of chestnut powdery mildew, came from North America in 1987 and spread quickly over Europe (Braun 1987, Ale-Agha et al. 2000). It first appeared in Germany around 1999 (Butin and Kehr 2002)and quickly spread over Switzerland (Bolay 2000),England (Ing and Spooner 2002), Slovakia (2002), Slovenia (2004) and Hungary (Kiss et al. 2004). At present the mildew occurs in most European countries (Zimmermanno- va-Pastircakova and Pastircak 2002, Heluta and Voytyuk 2004, Kiss et al. 2004,

Phytopathologia 56: 67–71 © The Polish Phytopathological Society, Poznań 2010 ISSN 2081-1756 68 Short communication

Milevoj 2004). Among Lithuanian neighbour countries the horse chestnut mildew was first registered in Poland in 2000 (Adamska 2002). The pathogen was first described as Uncinula flexuosa but after genetic examina- tion was classified to Erysiphe genus (Braun and Takamatsu 2000). The has greyish white mycelium. Ascomata are abundant, on the lower leaf surfaces, 80 × 128 m. Asci 6–10 per ascoma, are ellipsoidal, with a short stalk, 33–51 × 27–33 m, whereas ascospores ellipsoid-ovoid (according to Butin and Kehr 2002). It af- fects Aesculus hippocastanum by decreasing leaf assimilation, covering the surface and contributing to water loss, thus affecting photosynthesis and transpiration, as well as plant ornamental value. Aesculus hippocastanum was introduced to Lithuania several hundred years ago and neither diseases nor pests have threatened the species seriously. The state of green plantations of Lithuanian cities have been observed and investigated for years and from 1994 on the status of horse chestnut is being assessed in all of the biggest cities of the country (Vilnius, Kaunas, Panevezys, Siauliai, Klaipeda, Marijampole). The health status of horse chestnut is being deteriorating from 2004–2006, when chestnut powdery mildew and horse chestnut leaf miner have spread in the country. In July 2004 the new horse chestnut disease – powdery mil- dew was established in Kaunas, whereas in October the disease was discovered in Siauliai and in September – in Vilnius (Grigali nait et al. 2005). The degree of tree damage was estimated according to the method set by Žiogas et al. (2007)and adapted to our work. The categories of tree condition were esti- mated with a 5-degree scale. After tree condition assessment, the average damage degree was estimated, with a modified method applied in forestry (Žiogas et al. 2007) according to the formula:

VnbN=⋅∑()/ where: V – average damage degree, n – number of plants damaged to the same degree, b – the degree of damage, N – number of plants investigated. Since 2004, when the powdery mildew first appeared in Kaunas, Vilnius and Siauliai the degree of tree infestation stays constant – the degree of damage ca 1–1.5 (Fig. 1), while the damage caused by the leaf miner is increasing on the hole territory of Lithuania – from the degree of damage below 0.5 in 2005 to almost 4 in 2008 and 2009 (Fig. 1). During 2008–2009, chestnut powdery mildew was detected all over the terri- tory of Lithuania, in areas where horse chestnuts were grown: in cities, towns, set- tlements and villages, and roadsides (Snieškien and Stankevicien 2009). It was noticed that A. hippocastanum trees growing nearby, under the same conditions, were not equally resistant to E. flexuosa. A question arises whether this is influ- enced by individual morphological (thickness of leaf covering tissue, etc.)or other (biochemical)tree features. Trees growing under more favourable conditions, also Short communication 69

Fig. 1. The spread of powdery mildew and leaf miner (average degree of damage) on horse chestnut in Lithuania in 2003–2009 luxuriant trees as well as pruned, which produced larger sprouts, were noticed to be more injured by the pathogen. From 2005 on, when massive spread of horse chestnut leaf miner began in Lith- uania, the two invasive organisms (E. flexuosa and Cameraria ohridella)occur to - gether on horse chestnuts (Fig. 1). Leaf blotch disease, which used to spread a few years ago (agent Guignardia aesculi), is rarely detected now. In Germany investiga- tions are carried out on the co-infection of G. aesculi and E. flexuosa together with C. ohridella: the impact of these organisms on each other and the response of horse chestnut to them are being explored (Johne et al. 2006, 2008), yet, the interaction among the host-plant, the insect and fungi is not yet detected. Considering the fact that the spread of powdery mildew agents as well as other invasive pathogens can be possibly related with climatic changes (Glawe 2008), further investigation on the E. flexuosa spread in new areas and on new cultivars and species of horse chestnut is required. 70 Short communication

Streszczenie

ERYSIPHE FLEXUOSA – NOWY PATOGEN AESCULUS HIPPOCASTANUM NA LITWIE

Występowanie mączniaka prawdziwego na kasztanowcach (Aesculus hippocasta- num)w większych miastach Litwy badano w latach 2004–2009. Erysiphe flexuosa za- obserwowano w 2004 roku w Kownie, w tym samym roku także w Wilnie i Siau- liai. Gatunek ten szeroko rozpowszechnił się na terytorium Litwy i występuje razem ze szrotówkiem kasztanowcowiaczkiem (Cameraria ohridella), który wydaje się bardziej szkodliwy dla drzew.

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Authors’ addresses: Dr. Antanina Stankeviciene, Dr. Vilija Snieskiene, Kaunas Botanical Garden of Vytautas Magnus University, Z. E. Zilibero 6, LT-46324 Kaunas, Lithuania, e-mail: [email protected] Prof. Dr. hab. Albinas Lugauskas, Chemistry Institute, Gostauto 9, LT-01108 Vilnius, Lithuania

Accepted for publication: 18.06.2010