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Remarks (public):For a complete description including images see www.cababstractsplus.org/dfb 
Remarks (internal):May be distinguished from V. dahliae (CMI Descript. 256) by the absence of microsclerotia or of growth at 30°C and by the production of dark resting mycelium (Isaac, 1949; Skadow, 1969). Also on plant tissue the bases of the conidiophores in V. albo-atrum tend to be brownish (Smith, 1965). In England the Progressive Wilt Disease of Hops Orders of 1941, 1953, 1957 and 1965, made under the Destructive Insects and Pests Acts, have aimed at limiting the spread of a virulent ('progressive') form of V. albo-atrum in hops by requiring removal and destruction of diseased plants and prohibiting (inter alia) the movement of plant material away from farms where the disease is present. Diseases caused by V. albo-atrum have been controlled by development of resistant varieties and by eliminating the pathogen from soil by grassing-down (46, 398) or by fumigation. Development of systemic fungicides offers a further possible means of control.
 
Description type:Non-original description 
Description:Verticillium albo-atrum Reinke & Berthold, Die Zersetzang der Kartoffel durch Pilze p. 75, 1879.
= Verticillium albo-atrum var. caespitosum Wollenw., 1929.
= Verticillium albo-atrum f. pallens Wollenw., 1929.
= Verticillium albo-atrum var. tuberosum Rudolph, 1931.
Cultures growing rapidly on potato dextrose agar and malt agar at 23 °C, the prostrate hyphae first produced hyaline. Mycelium becoming flocculose and white to greyish, rather more densely compacted on PDA than MA, hyaline, whitish to cream in reverse after 1 week; after 2-3 weeks becoming brownish-crearn to black centrally due to the formation of darkresting mycelium; white sectors frequently produced in the generally greyish colonies. Conidiophores abundant, more or less erect, hyaline, verticillately branched, 2-4 phialides arising at each node, phialidessometimes secondarily branched; characteristically darkened at the base when growing on plant tissue. Phialides variable insize, mainly 20-30 (-50) x 1,5-3 µm. Conidia arising singly at the apices of the phialides, ellipsoidal to irregularly sub-cylindrical, hyaline, 0 (-1)-septate, 3,5-10,5 (-12,5) x 2-4 µm.Resting mycelium appearing after 10-15 days, dark brown to blackish but sometimes hyaline in sectors, regularly septate,becoming swollen between the septa so as to appear somewhat torulose in parts, never budding to form microscierotium-likestructures, hyphae 3-7 µm wide; production tending to cease after prolonged subculturing. Chlamydospores absent.Microsclerotia absent.
Hosts: On a wide range of dicotyledonous plants, mostly herbaceous. Engelhard (1957) gives a host index for V. albo-atrum, including V. dahliae, and it is not always evident which species is being reported. Moore (1959) lists British records. Economically important diseases are caused in hop, lucerne and solanaceous crops.
Diseases: Causes so called 'wilt' diseases: diurnal flaccidity followed by permanent wilting commonly occur, but not invariably; in some 'wilts' there is chlorosis leading to marginal and interveinal necrosis and progressive desiccation without flaccidity (e.g. hop wilt). Leaves are generally affected in acropetal succession. Infection of only a few vascular bundles may result in one-sided development of chlorosis and necrosis in a pattern that is related to stem and leaf vascular connections. Infected xylem strands commonly show brown discoloration but this may develop only after considerable delay. See also Talboys (1968).
Geographical distribution: Widespread, but predominantly in temperate regions (CMI Map 365, ed. 2, 1968).
Physiological specialization: Isolates from one host species can frequently cause disease in a wide range of other species and genera and can infect still more without causing obvious symptoms. However, isolates from lucerne evidently show some host-specificity (43, 1681).
Transmission: The fungus persists in the soil in the debris of dead infected plants, and infects roots that come into contact with it. Conidia formed on the debris (39: 502) may also contribute to root infection. Additional infection by air-borne conitia can occur in lucerne through the ends of stems severed during harvesting (37: 176). Spread of disease generally results from dissemination of infectet plant debris by natural agencies or in the processes of cultivation, harvesting, etc. The pathogen may be transferred in cuttings, etc. propagated in infested soils and transmission by superficial infection of seeds occurs in lucerne (41: 393).
Literature: Isaac, Trans. Br. mycol. Soc. 32: 137-157, 1949; Smith, N.Z. Jl agric. Res. 8: 450-478, 1965; Skatow, Arch. PflSchutz 5: I55-166, 1969 (taxonomy); Talboys, Ch. 6. In, Water deficits and plant growth, vol. 2 (ed. T.T. Kozlowski), 1968 (symptom patterns in vascular diseases); Engelhard, Host index of Verticillium albo-atrum Reinke & Berth. (including Verticillium dahliae Kleb.), Pl. Dis. Reptr Suppl. 244, 1957; Moore, British parasitic fungi, 1959 (hosts). Where the text of a paper refers to the presence of microsclerotia it has been assumes that the organism concerned is V. dahliae even though it may have been assigned by the author to V. albo-atrum.
 
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