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Page number:184 
Remarks (internal):Stable isolates of A. solani are easily distinguishable from isolates of every other ex-Solanaceae taxon currently recognized. Every culturally stable isolate from potato leaf or tuber that has been examined preliminary to this Manual, beginning in 1995, sporulates readily on potato-carrot agar, V-8 juice agar, and hay-decoction agar under the simple light, temperature, and humidity protocol followed in this work. No extraordinary or additional manipulation of the colony is required -neither wounding of the mycelium nor exposure to radiation other than that present in commonly available fluorescent lamps.
A conclusion stated in the earlier study of wide-spread and destructive A. solani (Simmons 2000, Alt.T&V 258) merits repetition and emphasis: not one of the scores of ex-potato isolates received from colleagues or established personally can be identified by culture characters, sporulation pattern, or conidium morphology as being the commonly encountered pathogen related to “early blight of tomato,” that is, to A. tomatophila. Conversely, among the scores of isolates examined of large-spored Alternaria from tomato plant lesions, not one is identifiable as the pathogen related to “early blight of potato,” that is, to A. solani.
M.B. Ellis (1971) followed the popular tradition of assigning the name A. solani to nearly every relatively large-spored, narrow-beaked Alternaria observed on “potato, tomato, eggplant and other plants belonging to the Solanaceae” (Ellis, l.c., p. 482). Ellis's concept of A. solani was unacceptably broad, in that it included taxa readily distinguishable from each other in their natural pathology as well as in their morphology as field specimens, as isolates in plate culture, and as preparations for examination at microscope levels.
Unfortunately, specialists on the pathology of solanaceous plants but not of their pathogens, especially Rotem (1994), accepted Ellis's taxonomic opinion without testing its application to their own work. The unfortunate result, as indicated here and also in comments on Alternaria tomatophila, has been the publication of confusing opinions on the difficulty of identifying Alternaria taxa and of erroneous accounts of the difficulty of achieving sporulation of “Alternaria solani” in culture. The claim that obtaining sporulation of A. solani in culture is difficult, and that it can be achieved only through use of extraordinary means such as exposure to near-UV light, is demonstrably incorrect. Cultures of A. solani produce conidia prolifically under quite simple culture conditions.
 
Description type:Non-original description 
Description:Alternaria solani Sorauer, Z. Pflanzenkrankh. 6: 6. Taf. I, fig. 2. 1896. - Fig. 069A, B
= Macrosporium solani Ellis & Martin, Amer. Nat. 16: 1003. 1882.
= Alternaria solani (E. & M.) Jones, Bull. Torrey Bot. Club 23: 353. 1896.
= Alternaria solani (E. & M.) Sorauer, in Jones and Grout, Bull. Torrey Bot. Club 24: 257. 1897.
= Alternaria solani (E. & M.) Jones & Grout, in Jones and Orton, 12th Ann. Rept. Vermont Expt. Sta., p. 179. 1899.
= Sporidesmium solani[-]varians Va˱ha, Naturw. Zeits. Land- und Forst. 2: 117. 1904.
= Alternaria americana Sawada, Govt. Res. Inst. Formosa, Dept. Agr., Rept. no. 51, p. 117. 1931; nom. nov. for A. solani (E. & M.) Jones & Grout (1899), non A. solani Sorauer (1896).
= Alternaria porri (Ellis) Neerg. f. sp. solani (E. & M.) Neerg., Danish Species of Alternaria and Stemphylium, p 234. 1945.
= Alternaria dauci (Kühn) Neerg. f .sp. solani (E. & M.) Neerg., op. cit. p. 234. 1945.
= Alternaria porri (Ellis) Sawada f. sp. solani (E. & M.) Neerg., op. cit. p. 560. 1945.
= Alternaria dauci (Kühn) Groves & Skolko f. sp. solani (E. & M.) Neerg., op. cit. Addit. p.2. 1945.
Type (lectotype, designated Simmons 2000): Illustration in Sorauer (1896), loc. cit., Taf. I, fig. 2.
Host/substrate: Solanum tuberosum L (Solanaceae)
Manual basis: Simmons 2000, Alt.T&V 258 (Fig. 181-182); representative isol. E.G.S. 44-098, 45.020, respectively CBS 109157, 116651; also E.G.S. 45.053
Culture at 50X, 5-7d, V-8: colony 6 cm diam, with concentric rings with diffuse margins; sporulation on cut agar surface, 2 d: V-8 +++
The sporulation pattern of A. solani is striking on V-8 agar, where conidiophore production and an initial flush of conidia are excellent and crowded on surface and aerial hyphae by the 4th day of colony development. By the 6th day, conidiophores have become remarkably branched and geniculate, bearing as many as 3-9 large, rostrate conidia in tufts that are clearly discernible at 50X magnification. The sporulation pattern on PCA is the same as that on V-8, although fewer (though still abundant) tufts are formed. Even on Hay, the conidial tuft character predominates at 7-10 d, with small uncrowded conidial clumps arising wherever the sparse radial surface hyphae develop. A non-routine trial on cornmeal agar has given results identical with those on PCA: a close stand of conidiophores and conidia on young 2-day colonies; masses (many thousands) of conidia at 4 d; and at 9d the characteristic tufts of conidia near the colony margin, where the agar gradually loses moisture.
Representative stable isolates of A. solani- under quite simple controlled conditions of culture, as defined above- produce tens of thousands of well-formed conidia on V-8 agar in unsealed plastic Petri dishes within 7 days. The population is dominated by conidia with a single tapering beak. Also present are large numbers of conidia with two beaks. Conidia with three beaks are present but rare; these latter actually are spores with two beaks, one of which has produced a short branch.
Production of chains of two conidia occurs rarely in A. solani. Examples can be found both in field samples and in cultures on PCA and V-8- practically never in most strains but readily in a few isolates. As examples, an isolate from New Zealand (E.G.S. 45.053) has a decided tendency to produce conidia whose initial beak can become converted into a secondary conidiophore with 1-4 geniculate conidiogenous sites; and an isolate from a potato tuber in California (E.G.S. 45.020) frequently has conidia that generate a secondary conidiophore from a lateral body cell or at the tip of a beak extension. Instead of multiplying through chain production, enormous numbers of conidia arise due to the ability of individual primary conidiophores to branch and to proliferate through series of geniculate conidiogenous extensions.
Primary conidiophores are quite variable in length when they produce an initial apical conidium. Ordinary examples include lengths of ca 150-200 µm, after which geniculation and branching of the conidiophore itself typically take place. Subsequent 3-9+ conidiogenous sites give rise to a radiate cluster of conidia. The branching conidiophore apparatus of A. solani in culture has a sturdy, angular appearance; diameters of the branches and extensions are ca 9-11 µm. The brown pigmentation of the conidiogenous site, the hilum, contrasts with the dilute yellow-brown of the septate conidiophores themselves.
Conidia of A. solani are basically ovoid, but in variations of long, short, broad, and narrow. In general, conidia with a single beak are comparatively long-ovoid or long-ellipsoid whereas those with 2-3 beaks are shorter. Using one excellent isolate as representative (E.G.S. 44.098), conidia with one beak commonly reach a size range of 109-115 x 18-26 µm plus beak lengths of 80-118 µm (noting that beaks may be as long as their spore bodies but usually are shorter in culture); beak width tapers gradually from 5-8 µm to a tip ca 2.5 µm in diameter. Conidia with two beaks reach sizes of 80-106 x 16-21 µm plus an initial beak 58-88 µm long and a second beak 64-88 µm long. Conidium septation commonly reaches 7-11 transverse, with 1(-2) longitudinal in a few of the transverse compartments. The 4-5 primary transepta of large conidia are slightly darker than the secondary ones, which, like the longisepta, often are inconspicuous and obscured by a surface layer of punctulate to strongly punctate ornamentation. Conidium bodies are a dilute, translucent straw color.
 
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