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Remarks (public):For a complete description including images see 
Remarks (internal):At present there is some doubt about the application of the name Leptodothiorella aesculicola (Sacc.) Sivan. (=Phyllosticta aesculicola Sacc. = Asteromella aesculicola (Sacc.) Petrak) for the synanamorph microconidial ('spermagonial') state of G. aesculi because van der Aa (1973) considers P. aesculicola as the Asteromella state of a Mycosphaerella species on the basis of the original description provided by Saccardo (1878). According to the current concept the microconidial state of G. aesculi belongs in Leptodothiorella and therefore the identity of P. aesculicola has to be established by examining the type material before an epithet can be confidently applied to the microconidial state. Leaf blotch has been reported to be widespread resulting in severe, premature defoliation in fully grown horse chestnut trees in the field and nursery stock (35, 247; 37, 316; 42, 577). Pathogenicity has been confirmed by inoculating leaves of horse chestnut with ascospores and conidia (67, 5172). It has been reported that Aesculus arguta and A. parviflora were not affected by G. aesculi (42, 496). Since several Aesculus species have been found to be susceptible to G. aesculi chemical control measures have been tested and those recommended include spraying with lime sulphur 1 in 40, or three applications of Bordeaux mixture, (a) when leaves are unfolding, (b) when the leaves are full-sized and (c) 2 weeks after the second (12, 251; 28, 38). Other chemicals reported to be effective are benomyl hydraulically injected into soil around plants (54, 5558; 57, 794), Manzate 200 (mancozeb) (59, 2346), prochloraz followed by bitertanol (64, 4521), zerlate 1·5-100, parzate 1·5-100 (28, 38).
Description type:Non-original description 
Description:Guignardia aesculi (Peck) V.B. Stewart, Phytopathology 6: 5 (1916).
Laestadia aesculi Peck, Rep. N.Y. Mus. 39: 51 (1885).
Botryosphaeria aesculi (Peck) Barr, Contrib. Univ. Michigan Herb. 2: 561 (1972).
Anamorph (synanamorph or macroconidial state): Phyllosticta sphaeropsoidea Ell. & Everh., Bull. Torrey Bot. Club 10: 97 (1883).
Phyllostictina sphaeropsoidea (Ell. & Everh.) Petrak, Sydowia 10: 265 (1957).
Synanamorph or microconidial state ('spermogonial'): Leptodothiorella ?aesculicola (Sacc.) Sivan., The Bitunicate
Ascomycetes: 165, (1984). Phyllosticta aesculicola Sacc., Michelia 1: 134 (1878).
Asteromella aesculicola Petrak, Sydowia 10: 266 (1957).
Leaf blotches on living leaves, reddish brown, with darker centres, coalescing, variable in size and shape often involving the major part of the leaf. Anamorph (synanamorph or macroconidial state): Conidiomata epiphyllous, immersed, becoming partially erumpent, pycnidial, subglobose, 80-165 µm diam., ostiolate; pycnidial wall pseudoparenchymatous, composed of 2-3 cell layers (texture angularis), the outermost layer chestnut brown the innermost layer hyaline. Ostiole circular, 15-20 µm surrounded by conspicuous dark brown cells. Conidiogenous cells hyaline, cylindrical, 5-10 x 2-4 µm, holoblastic, arising from the innermost layer of cells lining the pycnidial cavity. Conidia hyaline, obovoid to subglobose or globose, 10-18 x 6-10 µm, aseptate, guttulate, surrounded by a mucilaginous sheath in fresh material and provided with a hyaline apical appendage, 5-8 µm long. Anamorph (synanamorph or microconidial state): Conidiomata pycnidial, similar in morphology to those produced by the Phyllosticta state. Conidiophores branched at base and septate, arising from the innermost layer of cells lining the pycnidial cavity. Conidiogenous cells cylindrical, phialidic. Microconidia hyaline, dumbbell-shaped, 3-9 x 0,5-1,0 µm. Teleomorph: Ascomata on fallen leaves, immersed, dark brown, 90-160 µm, ostiolate; ascomatal wall psedudoparenchymatous, composed of 2-4 cell layers, the outer cell layers thick-walled, dark brown, the inner layers gradually becoming less pigmented towards the ascomatal cavity. Asci cylindrical to subclavate, 50-70 x 14-18 µm, 8-spored; ascus wall bitunicate. Ascospores hyaline, straight or slightly curved, subellipsoid, wider in the mid region, 12-18 x 7-9 µm.
Hosts: Aesculus glabra, A. hippocastanum (main host) (Hippocastanaceae). Several other species of Aesculus and subspecies including A. ambigua, A. arnoldiana, A. bushii, A. carnea, A. discolor, A. dupontii, A. hybrida, A. mississippiensis, A. mutabilis, A. neglecta, A. octandra, A. pavia, A. splendens, A. turbinata and A. woerlitzensis have been reported to be susceptible (Neely & Himelick, 1963; 50, 2509).
Disease: Leaf blotch or black rot of Aesculus hippocastanum (horse chestnut) and other Aesculus species (5, 706; 28, 38; 64, 4521).
Geographical distribution: Europe (Austria, Belgium, France, Germany, Italy, Netherlands, Portugal, Romania, Switzerland, U.K., Yugoslavia); North America (Canada: Manitoba, New Brunswick, Nova Scotia, Ontario, Quebec; U.S.A.: Eastern U.S.A).
Transmission: Presumably by water-borne conidia during wet conditions. Ascomata are produced on leaves left to over winter outside and both conidia and ascospores discharged from over wintered leaves have been reported to infect leaves of seedlings and produce blotch symptoms (Hudson, 1987).
Literature: Bissett, J. & Darbyshire, S.J., Fungi Canadensis No. 280, 1984; Hudson, H.J., Transactions of the British Mycological Society 89: 400-401, 1987; Neely, D., Plant Disease Reporter 55: 37-38, 1971; Neely, D. & Himelick, E.B., Plant Disease Reporter 47: 170, 1963; Stewart, V.B., Phytopathology 6: 5-19, 1916; Van Der Aa, H.A., Studies in Mycology 5: 1-110, 1973.

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