Mycological findings

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Mycological findings

Introduction

The list of powdery mildews (Ascomycota, Erysiphales) of Europe is constantly updated with species originating from other regions, mainly from North America and East Asia. The North American species penetrate into Belarus and Ukraine mainly via Western Europe. Thus, for the past two decades, such species as Erysiphe azaleae (U. Braun) U. Braun & S. Takam., E. elevata (Burrill) U. Braun & S. Takam., E. flexuosa (Peck) U. Braun & S. Takam., E. platani (Howe) U. Braun & S. Takam., and Golovinomyces greeneanus (U. Braun) V.P. Heluta entered Ukraine and naturalized there (Heluta, Vrytyuk, 2004; Heluta et al., 2004, 2009, 2013; Heluta, Korytnianska, 2011). Of these, E. azaleae and E. flexuosa are also widely distributed in Belarus (Hirylovich, Lemeza, 2008). This process continues, as it is evidenced by the powdery mildew on Amelanchier alnifolia Nutt. and A. spicata (Lam.) K. Koch (Rosaceae) (Fig. 1, a-c, f, h, j-m; Fig. 2) found in Belarus and Ukraine and identified as Podosphaera amelanchieris Maurizio. This brief article is devoted to the characterization of the fungus and its spread in the mentioned countries.

Materials and methods

Samples of powdery mildew infecting A. alnifolia and A. spicata were collected in Belarus in 2000-2014 and in Ukraine in 2012 and 2015. They are listed below, following the species characteristics. The specimens are deposited in the National Herbarium of M.G. Kholodny Institute of Botany of the National Academy of Sciences of Ukraine (KW) and in the Herbarium of the Belarusian State University (MSKU). The fungus was studied and photographed under a light microscope «Primo Star» (Carl Zeiss, Germany) using the camera «Canon A 300» and the software «AxioVision 4.7». Only herbarium specimens were used. The mycelium, conidiophores and conidia removed from the surface of infected leaves by a transparent adhesive tape. To restore shape and size, a piece of tape with these fungus structures was put in a droplet of 40 % lactic acid solution on a microscope slide (sticky side up), covered with a cover glass, gently heated to boiling point, then examined under the light microscope. Chasmothecia were prepared and studied in a drop of distilled water. For scanning electron microscopy (SEM), small dried pieces of serviceberry leaves affected by the fungus were glued on to the metal stubs, then coated with gold and studied under the scanning microscope Jeol 6060LA (Japan). Digital data were treated statistically when n was > 30 for each character.

Results and discussion

In Belarus and Ukraine, Amelanchier alnifolia and A. spicata are introduced plants. The species originate from North America and are widely cultivated as important ornamental plants and a rootstock material for undersized apples and pears (Kokhno et al., 1986). According to our observations, the seeds of A. spicata are spread by birds, therefore young serviceberry plants in the wild state are quite common in the pine forests around settlements. In the recent monograph by Braun and Cook (2012), only two powdery mildews are mentioned on the representatives of the genus Amelanchier, Phyllactinia mali (Duby) U. Braun and Podosphaera amelanchieris. In our report, the former species is not a subject of discussion, since it was not found on serviceberry in our countries. As for the latter one, the Belarusian and Ukrainian samples largely correspond to this species, especially to the European specimens that are discussed in detail in the aforementioned monograph by Braun and Cook. Below is an illustrated description of our materials.

Podosphaera amelanchieris Maurizio, Zentralbl. Bakt. Parasitenk., Abt. 2, 72: 145. 1927 (Fig. 1, a--c, f, h, j-m; Fig. 2; Journal cover, Page 4)

Mycelium foliicolous, amphigenous, effuse or in irregular confluent patches, evanescent to more or less persistent, greyish white. Conidiophores straight, 98--146 qm, foot-cells subcylindrical, usually slightly thickened toward the top, about 36--60 x 5.5--9.0 qm at the base and x 7.0--9.5 qm at the top, followed by 2--3(--4) shorter cells, forming catenescent conidia. Conidia ellipsoid to doliiform-subcylindrical, 23--31 x 11.5--15.5 qm. Chasmothecia scattered to gregarious, hemispherical, depressed below, (70--)75--92(--100) qm diam. Peridium cells not very distinct, irregularly polygonal, 11--20 qm diam. Appendages equatorially arising, frequently also erect from the upper half of the ascoma, rather stiff, straight to slightly arcuate, 6--16, unequal in length on the same chasmothecium, 1--3(--3.5) times as long as the chasmothecial diam., 95--250 qm, 8--10 qm wide at the base, mostly narrower towards the tip, stalk septate, with 3--5 septa, wall smooth to verruculose-rugose, simple, rarely forked near the middle of the stalk, about 75 % or even more of the stalk pigmented, brown below, paler towards the hyaline apex. Apices 3--5 times tightly dichotomously branched, sometimes primary branches elongated, branched part flat, up to 48.5 qm wide, tips more or less knoblike, wide, occasionally somewhat recurved. Ascus subglobose to broadly ovoid, (6-)8-spored, 75--82 x 65--73 qm, ascus wall 2--3 qm wide, terminal oculus 16.5--23.5 qm diam. Ascospores oblong-ovate, mostly slightly asymmetric, recurved, with 1--2(--3) oil drops, colourless, 22--30 x 12--15 qm.

Specimens examined

On Amelanchier alnifolia Nutt. (Rosaceae). Ukraine: Kyiv, Pivdenna Borshchahivka, Symyrenko Str.,V.P. Heluta (KW70093F).

On Amelanchier spicata (Lam.) K. Koch. Belarus: Brest Region: Brest, city square, 14.09.2001, I.S.Hirylovich (MSKU 4432); Drahichyn District, near the urban village Antopal', 06.09.2006, I.S.Hirylovich (anamorph; MSKU 4736). Gomel Region: Rahachov District, village Haradziec, park, 28.08.2005, I.S. Hirylovich (MSKU 4735); Zlobin District: village Chornaya Virnia, 26.08.2005, I.S.Hirylovich (MSKU 4737); near the village Maiskwye, 12.08.2013, I.S. Hirylovich (KW 60652F). Minsk Region: Barisaw District, Barisaw, city square, 10.09.2002, I.S. Hirylovich (anamorph; MSKU 4427); Dzyarzynsk District, near the village Byareza, 22.08.2008, I.S. Hirylovich (MSKU 5769); Minsk, city square, 15.09.2000, I.S. Hirylovich (KW60653F); ibid, 16.08.2003, I.S. Hirylovich (KW 60661F); Minsk District, near the village Barauliany, forest park, 28.08.2014, I.S. Hirylovich (MSKU 6283); near the village Hliebkavichy, military training area, 10.08.2009,

I.S.Hirylovich (MSKU 5770); Pukhavichy District, Pukhavichy, park, 06.09.2014, I.S. Hirylovich (MSKU 6282); Valozyn District, near the village Kaldyki, clearing in pine forest, 27.07.2013, I.S. Hirylovich (KW60654F); near the village Sakabscyna, at the edge of pine forest, 18.07.2011, I.S. Hirylovich (MSKU 5766); village Zhamoid', 20.07.2003, mossy pine forest with Frangula, I.S. Hirylovich (MSKU 4431). Mogilev Region: near Asipovichy, in plantations along the railroad, 28.07.2003, I.S. Hirylovich (MSKU 4430). Ukraine: Cherkasy Region, Uman', Sophiivka arboretum, green ornamental plantings, 10.10.2012,

Fig. 1. Podosphaera amelanchieris on Amelanchierspicata (a--c, f, h, j--m) and P. clandestina on Crataegus sp. (d, i) and Mespilus germanica (e, g): a -- infected young plant, b--g -- chasmothecia, h--i -- appendage apices, j -- ascus, k -- ascospores, l -- conidiophore and conidium, m -- conidia. Bars: b--e -- 100 дт, g--m -- 20 дт

Fig. 2. Podosphaera amelanchieris on Amelanchierspicata (KW60655F; SEM): a--c -- chasmothecia (c -- bottom view), d--f-- dichotomously branched appendage apices, g -- appressorium. Bars: a -- 100 дт, b--c -- 50 дт, d--f -- 10 дт, g -- 5 дт

V.P. Heluta (KW60658F-60660F). Kharkiv, city square, N.B. Saidakhmedova (KW60664F); ibid., 26.08.15, N.B. Saidakhmedova (KW60691F, 60692F). Kyiv, Academician Palladin Avenue, 7, ornamental planting, 09.08.2015, V.P. Hayova (KW 60662F). Volhynian Region: Liubeshiv District, north-western neighborhood of the village Lyubyaz', forest road, V.P. Heluta (KW60655F-60657F).

The species status of powdery mildew belonging to the genus Podosphaera Kunze and parasitizing Amelanchier representatives was discussed in detail in the monograph by Braun and Cook (2012, pp. 100 and 103). The authors have shown that this fungus is a separate American species morphologically close to other parasites of plants of the family Rosaceae such as P. clandestina (Wallr.) Lev. known on species of genera Crataegus L., Cydonia Mill., Mespilus L. and Pyrus L. (Pyreae), Podosphaera prunicola U. Braun (on species of the genus Prunus L., Amygdaleae) and P. spiraeicola U. Braun (on Spiraea japonica L.f., Spiraeeae). However, the fungus ex Amelanchier differs from the first one by more numerous (up to 30, except for European specimens) and longer appendages, from the second -- by thin-walled asci, from the third -- by more cleft and smaller apical parts of the appendages. Note, however, that the European samples of P. amelanchieris described by Braun and Cook (2012) have a relatively small number of appendages (6--15), i.e., on this basis, the fungus rather looks like P. clandestina. Judging by this description, our materials are similar to the European specimens.

In order to confirm identification of the fungus collected on Amelanchier, we conducted a morphological comparison of its fruiting bodies (Fig. 1, b, c, f) with chasmotecia of P. clandestina on Crataegus sp. (Fig. 1, d) and Mespilus germanica L. (Fig. 1, e, g). These are definitely closely related species, however they differ in some characters. Firstly, the appendages of the fungus ex A. spicata are much longer (cf. Figs 1, c and 1, d, e; 1, f and 1, g), up to three times of the chasmothecial diameter or even more (Fig. 2, b). Another difference is in the structure of the apical part of the appendage. Although this feature is quite variable, however, the apices of the fungus ex Amelanchier are mainly dense, with much enlarged, knob-like tips (Fig. 1, f, h; Fig 2, d, e). In P. clandestina ex Crataegus sp. and M. germanica, the tips are generally thinner, so that apices look relatively loose (Fig. 1, g, i). Therefore, we conclude that the specimens of powdery mildew collected on Amelanchier do not belong to P. clandestina.

Thus, we subscribe to the view of Braun and Cook (2012) that the fungus found on serviceberry in Europe, including our countries, belongs to P. amelanchieris, the species introduced from North America.

Up to now, P. amelanchieris was unknown in Belarus and Ukraine. Distributed in North America (Canada, USA), it has been introduced in Europe and already reported from Germany, Lithuania, and Switzerland (Braun, 2012; Braun, Cook, 2012; Kruse, 2014). Furthermore, it is possible that Oidium sp., P. clandestina and P. oxycanthae (DC.) de Bary recorded on representatives of the genus Amelanchier in several European countries (Belarus, France, Great Britain, Lithuania, Norway, Switzerland) (Blumer, 1967; Amano, 1986; Grigaliunaite, 1990; Hirylovich, 2000; Bolay, 2005; Talg0 et al., 2011) also belong to this species.

Acknowledgements

Authors are grateful to Dr. Vera Hayova and Mrs. Natalia Saidakhmedova for kindly providing specimens of serviceberry leaves infected with powdery mildew and to Mr. Vitaly Sapsai for his help with scanning electron microscopy. We also thank Dr. Vera Hayova for her help with the English and valuable comments on the manuscript.

References

invasive mildew fungus

1. Amano K. Host range and geographical distribution of the powdery mildew fungi, Tokyo: Japan Scientific Societies Press, 1986, 741 pp.