Danish species of Alternaria and Stemphylium.
AbstractThe writer's exhaustive study of Alternaria and Stemphylium is described as a continuation of the attempts already made by J. A. Elliott (Amer. J. Bot., iv, pp. 439-476, 1917), P. C. Bolle [R.A.M., iv, p. 60], P. A. Young [ibid., vi, p. Ill], and S. P. Wiltshire [ibid., xviii, p. 141] to provide a rational survey of the taxonomy and parasitism of these genera, and represents a further contribution to a monograph on the subject.
In order to determine the host range of individual species of the genera, mono-spore inoculation experiments were carried out on 36 plant species belonging to 14 families, the ten principal ones being wheat, onion, carnation, cabbage, peas, cucumber, Godetia hybrida, carrot, tomato, and lettuce: van Luyk's method, involving the use of seedlings raised from sterilized seeds on filter paper and distilled water in autoclaved test tubes [ibid., xviii, p. 47], was employed in a large number of the trials. A. tenuis auct. sensu strictu (the name retained as the designation of a group of forms usually described by this name in the mycological literature), syn. Macrosporium caudatwm Cke & Ell. p.p., M. seguerii Allesch., A. rugosa McAlpine, A. mali Roberts, and A. solani (E. & M.) Jones & Grout, f. symphoricarpi Davis [ibid., x, p. 669], is ubiquitous and its presence as a facultative parasite on some 120 species of seeds was established. A. circinans (Berk & Curt.) Bolle (which in an addition to this work the author admits is antedated by A. oleracea Milbrath) is extremely prevalent on cabbage in Denmark [ibid., xxv, p. 378], where barely 10 per cent. of 746 lots of seed grown from 1935 to 1941 were found to be free of infection. The pathogen appreciably reduces seed production both qualitatively and quantitatively [ibid., xiii, p. 204J. Positive results were obtained in inoculation tests on onion, carrot, carnation, peas, and wheat.
A. resedae n. sp., first observed on Reseda odorata seeds in October, 1941 [ibid., xxiii, p. 427], was found to be present between that date and December, 1944, on eight out of 39 lots examined, the incidence of infection ranging from 1 to 28 per cent. Four of the contaminated lots were grown in Denmark, one in Czechoslovakia, one was imported from France, and two from Germany. It is characterized by olive-buff to dark olive-buff, closely septate, non-or sympodially-branching conidiophores, 30 to 50 by 4 to 6 μ ,; smooth, obclavate, conical, oval, or cylindrical, sometimes slightly curved, deep or dark olive-buff to buffy-brown conidia, produced in chains of up to 10 (usually 5 to 6 in agar cultures), furnished with 1 to 10 transverse and up to 3 longitudinal walls, and a beak measuring 2 to 28 by 2 to 4.5 (2 to 6 by 2 to 4.5) μ, almost invariably non-septate, rarely provided with up to 3 septa, the total length of the conidia, including the beak, being 9 to 66 μ and their width 6 to 15 μ. There is a considerable resemblance between the conidia of A. resedae and those of A. circinans, but they may be distinguished, e.g., by the greater symmetry, rather smaller cell dimensions, general absence of a beak, fewness of longitudinal septa, and darker coloration of the latter. The optimum temperature for mycelial growth in both species is 25 ° C. A. resedae retains its virulence in culture for a year, after which there is a steady decline, a 21/2-year-old isolate having been found virtually non-pathogenic. Cabbage and G. hybrida contracted mild infection in inoculation tests with A. resedae.
G. hybrida was the only one of the ten main test plants to be attacked by A. tenuissima [ibid., xiii, p. 326], which is presumably a saprophyte or at most a facultative parasite of a very low order of virulence. However, a new variety of the species, var. godetiae, caused severe depredations in G. hybrida crops in Denmark from 1937 to 1941, reducing the seed yield of susceptible varieties like Kelvedon Glory and Sybil Sherwood to a fraction of the normal. It differs from the type in the larger and more frequent terminal swelling of the beak, the length of which may reach twice that of the conidial body instead of the same length, and in its cultural characters, as well as in its severe pathogenicity to G. hybrida.
A. dianthi [ibid., xxiii, p. 389] is of rare occurrence in Denmark, where it has been found on Saponaria officinalis, S. vaccaria, carnation, and Dianthus barbatus (seeds only of the two last-named). In inoculation experiments it also attacked Gypsophila elegans. On the other hand, A. dianthicola n. sp. [ibid., xxiii, p. 427] is common and severe on carnation, D. barbatus, and D. plumarius, causing the development of whitish to faintly brownish-yellow, dark-bordered, usually oval spots, 5 to 10 mm. in length, sometimes confluent, forming areas several cm. in length on the stems, leaves, and buds, and producing immediately on the exposure of the petals dense olive-green patches of conidia, which render the flowers unsaleable and may reduce the profits on the crop by 5 to 20 per cent. From 1st April, 1941, to 1st December, 1944, it was isolated from 74 out of 192 lots of carnation and 3 out of 23 D. barbatus seed, originating in France, Holland, Germany, and Hungary. The writer thinks there has been widespread confusion in the past between A. dianthi and A. dianthicola, which may, however, be differentiated on the basis of the following characters. In the former the conidia are broader and shorter than in the latter (13.5 to 66 by 7-5 to 25.5 compared with 12 to 87 by 7.5 to 21μ), the beak is much shorter (1.5 to 69 as against 9 to 99 μ), there are many more longitudinal septa (up to nine) in A. dianthi than in A. dianthicola (maximum of three), the conidia of the former are darker coloured, the cultural features of the two species are quite distinct, and they also differ physiologically, the capacity of A. dianthicola for sporulation in culture persisting much longer than that of A. dianthi. G. elegans was infected by A. dianthicola in inoculation tests.
A. matthiolae n. sp. (antedated by A. raphani Groves & Skolko as noted in the 'addition' to this work, syn. A. brassicae (Berk.) Sacc. var. macrospora Sacc.) [ibid., xvi, p. 103] is extremely common on Matthiola incana and radish seeds of Danish, Dutch, German, and Hungarian origin (one lot of the former also imported from France). The fungus does not appear to be of great economic importance, though it probably impairs the germinative capacity of the seed, judging by the results of experiments on radish. Positive results were obtained in inoculation tests on cabbage, wallflower, Iberis, and lettuce. The principal morphological differences between A. raphani and the nearly related A. brassicae are the longer conidia and beak of the latter (33 to 147 and 9 to 148 μ, compared with 12 to 78 and 3 to 76.5μ.) the rare formation of secondary conidia by A. brassicae, contrasted with the normal development of chains of two to four in A. raphani; the paler colour of the conidia of A. brassicae (deep to dark olive-buff compared with dark olive-buff to buffy-brown in A. raphani); and the absence in the former species of gemma formation, a characteristic feature of the latter. A close morphological similarity further exists between A. raphani and A. dianthi, important differences being the generally smaller and darker-coloured spores of the latter and their conical shape (those of the former are usually oval), and the absence of gemma formation in A. dianthi.
A. porri appears to have been only twice recorded in Denmark, in 1937 on onion seeds [ibid., xvii, p. 654] and in 1942 on leek foliage affected by a purple blotch resulting in a loss of 25 to 30 per cent. of the crop. These are believed to be the first observations of the fungus in Europe. Besides Macrosporium porri[Alternaria porri], the author regards A. allii Nolla [ibid., vi, p. 524] as a synonym of A. porri.
A. porri (Ell.) Saw. [see correction on p. 560] f. sp. dauci (Kuhn.) n, comb., or in view of Groves and Skolko's paper A. dauci (Kuhn) Groves and Skolko f. sp. porri (Ell.) n. comb. (M. [A.] carotae), is the agent of a destructive leaf spot of carrots in the United States [ibid., xxiv, p. 303], but in Europe it appears to be of little practical importance. Inoculation tests gave positive results on parsley, lettuce, celery, cabbage, cucumber, carnation, Godetia hybrida, tomato, radish, and eggplant. The fungus lost its virulence almost entirely in the course of three years' pure culture.
A. porri (Ell.) Neerg. f. sp. solani (E. & M.) n. comb, or A. dauci (Kühn) Groves & Skolko f. sp. solani (E. & M.) n, comb. (syn. A. solani (E. & M.) Jones & Grout, Sporodesmium solani-varians Vanha, etc.), does not ordinarily cause heavy reductions in the Danish potato yield owing to the relatively late development of infection [ibid., xxiv, p. 469], and for the same reason it is of no great importance on tomatoes. Inoculations were successful on chilli, Capsicum globatum, tomato, eggplant, carrot, cabbage, carnation, onion, cucumber, lettuce, G. hybrida, Ageratum hou-stoniarum, Nicotiana sanderae, Papaver paeoniflorum, and Zinnia elegans. In pure culture the virulence of the fungus declined from the second to the fifth year.
Alternaria zinniae Pape [ibid., xxii, p. 389] has been observed annually on Z. elegans in Denmark since 1937, its intensity varying considerably with climatic factors. Other natural hosts include Callistephus chinensis, Chrysanthemum corinatum, Cosmos bipinnatus, Helianthus debilis, and P. alpinum, while among those artificially infected were lettuce, G. hybrida, tomato, and N. sanderae.
A. anagallidis, described by Raabe from the vicinity of Tubingen, Germany [ibid., xviii, p. 140], was found by the writer on Anagallis arvensis and its var. coerulea in the Copenhagen Botanical Garden in 1942. The conidia of the fungus are very similar to those of A. porri, but the spore body of A. anagallidis is considerably shorter (13.5 to 81 μ).
A. anagallidis var. linariae n. var., was found attacking Linaria maroccana and Antirrhinum majus seeds in the germinator and was weakly pathogenic in inoculation tests on cabbage, G. hybrida, lettuce, tomato, N. sanderae, and P. paeoniflorum. It differs from the type in its conidial dimensions (37.5 to 289.5, inclusive of beak, by 9 to 21 μ). One of the five isolates was still virulent after three years' culture.
Alternaria linicola n. sp. (antedated by A. linicola Groves & Skolko) was first detected in 1940 on non-germinating seeds of Linum grandiflorum rubrum imported from France, and subsequently reported by Miss Johansen under the designation of A. (?) solani [ibid., xxiv, p. 451]. It is distinguishable from A. anagallidis by its longer conidia (39 to 292.5 μ, inclusive of beak), from A. porri by its smaller conidial dimensions, and from A. lini Dey [ibid., xiii, p. 239] by its single conidia, those of the Indian species being concatenate.
The percentage of infection in seven lots of cineraria seeds by A. senedonis n. sp. ranged from 1.3 to 29.5 per cent. Two of the lots were imported from France and Germany, respectively, while the others were home-grown. A. senecionis differs from A. raphani in its conidial dimensions (40.5 to 187.5, inclusive of beak, by 10.5 to 48 μ,) and absence of a tendency to gemma formation, and from another closely similar species, A. brassicae, in the greater width of its conidia and shorter beak (10.5 to 85.5 μ). Inoculation experiments gave positive results on lettuce, cucumber, G. hybrida, and tomato, only the first-named, however, reacting to any extent.
A. gypsophilae n. sp. was first detected in 1938 on Gypsophila elegans seeds and seedlings suffering from damping-off in the germinator, since when it was repeatedly isolated from seeds of the same species and from three lots of G. paniculata, two imported from Holland and one from France. In 1944 it was found in 19 lots of G. elegans seed, including one imported from Germany. Differences between A. gypsophilae and the allied A. dianthi include the modes of conidial production single in the former and concatenate in the latter-and the narrower conidia with longer beaks of A. dianthi. In A. gypsophilae the buffy-, olive-, or natal-brown conidia measure 22.5 to 118.5 (inclusive of beak) by 9 to 27 μ. The virulence of two isolates persisted in culture for four years. Carnations were artificially infected by A. gypsophilae.M. nobile Vize apud Cooke sensu E. Rostrup (1902) is probably identical with this species. A. cheiranthi (Fr.) Bolle sensu Wiltshire [ibid., xiii, p. 326] was isolated from 45 samples of wallflower seed between 1st April, 1936, and 1st January, 1944, of which 26 were grown in Denmark, 12 imported from Holland, five from Germany, and one each from England and France. A. gypsophilae resembles this species, but the conidia of the latter tend to be considerably wider and more irregular in form. A. cheiranthi was successfully inoculated into white cabbage, I. amara, radish, and M. incana. It was still sporulating after 21/2 years in pure culture.
Stemphylium ilicis Tengwall [ibid., iv, p. 60] (M. abietis Tengw., S. congestum Newton [ibid., vii, p. 789], S. dendriticum de Souza da Camara [ibid., ix, p. 687]) is a common saprophyte or facultative parasite which was found by the author in Denmark on 45 species of seeds: it is also prevalent in the same country as the agent of a cucumber leaf spot, in which form it is known as Sporodesmium pluriseptatum (Karst. & Har.) Peck (S. mucosum Sacc. var. pluriseptatum Karst. & Har.) [ibid., xvi, p. 652], a name it is considered advisable to retain pending further clarification of the taxonomic problems involved in its designation. The fungus showed no perceptible impairment of its sporulating capacity after 20 years' pure culture. Cabbage, Godetia hybrida, lettuce, and tomato were among the plants attacked in inoculation tests.
M. daucinum Yatel (J. Microbiol, Ukraine, v, 2, pp. 195-214, 1938) is stated to be identical with Stemphylium radicinum[Alternaria radicina], and M. arnicae Rostrup 1905 with S. botryosum.
The distribution, economic importance, physiology, pathogenicity, duration of virulence, and control of the various species of Alternaria and Stemphylium are also discussed.