|Macrophomina phaseolina spores growing on Pinus|
(Tassi) Goid., (1947)
Botryodiplodia phaseoli (Maubl.) Thirum., (1953)
Occurrence, distribution and symptoms
Macrophomina phaseolina (Tassi) Goidanich causes seedling blight, root rot, and charcoal rot of more than 500 crop and non-crop species (Smith and Carvil 1977). It has a very wide distribution covering most of the tropics and subtropics, extending well into temperate zones having occurrence as far north as the United Kingdom and as far south as New Zealand (Songa 1995). It is an important pathogen of crops particularly where high temperatures and water stress occurs during the growing season. The typical symptoms of the disease are like those described by Smith and Carvil (1977) for soybean: “In soybean, charcoal rot disease symptoms appear in midsummer during high temperature and low soil moisture when the plant is stressed. Initial infections occur at seedling stage but remain latent until the soybean plant approaches maturity. Plants may wilt and die. Sloughing of cortical and tap root tissues occur with characteristic black speckled appearance due to the presence of sclerotia.” Necrotic spots may also appear on the leaves of some plants due to a translocatable toxin (Chan and Sackston 1973, Day 1993) that may be responsible for the rot symptoms sometimes without being able to see other signs. Such toxins from cultures and diseased plants have been shown to produce typical rot symptoms (Dhingra and Sinclair 1974, Day 1993).
Signs of the disease
The disease is well characterised by the presence of numerous black microsclerotia varying from 100 μm to 1 mm in stems, leaves and roots and 50 μm -300 μm in culture (Holliday 1980). Under the microscope they appear as round to ovate black dots which, when lighted from above, have relatively large, smooth, rounded bumps on their surface, a bit like an artichoke. Clear images of microsclerotia were obtained by using optical and electron microscopes.
The mature sclerotia (sclerotia are a special type of spore) are jet black and do not transmit light, hence the SEM.
Pycnidia may also sometimes be seen. These are black and globose varying from 100 μm to 250 μm in length with a truncate ostiole (Dhingra and Sinclair 1978, Mihail 1992), the spores of which are pointed at one end. The hyphae are septate, usually containing numerous vesicles.
The Nomenclature already given looks good it similar apart from a few prefixes . This work was done in 1997 and the changes will be as a result of updates. These changes need to be verified. What follows is an explanation of how it goes. M. phaseolina is of the deuteromycetes, the ‘fungi imperfecti’ normally being without an observable sexual stage, but many such fungi have been shown to be anamorphs with sexual teleomorphs so they are generally grouped as mitosporic fungi (Hawksworth et al. 1995). In the case of M. phaseolina a teleomorph has been described as Orbilia obscura by Ghosh, Muckerji & Basak 1964 (Holliday 1980) but this has not been confirmed (Mihail 1992). Mitosporic fungi are Coelomycetes (enclosed conidia) so for M. phaseolina it goes something like this:
Fungi; Mitosporic fungi (Coelomycetes); Sphaeropsidales (pycnidial); Sphaerioidaceae; Macrophomina Petrak; Macrophomina phaseolina (Tassi) Goid. Synonyms historically are: Macrophoma phaseolina Tassi (1901), Macrophoma phaseoli Maubl. (1905), Sclerotium bataticola Taub (1913), Rhizoctonia bataticola (Taub) Briton-Jones (1925), Macrophomina phaseoli (Maubl.) Ashby (1927), Macrophomina phaseolina (Tassi) Goid. (1947). (From Day 1993). Some of these are still in use along with the present convention of Macrophomina phaseolina (Tassi) Goid. (1947) but are more likely to be seen in some of the older literature on the subject.
Decoding the genome
The genome of Macrophomina phaseolina has been sequenced.
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- Day, P. (1993) In-vitro Studies into Host-pathogen Interactions of Sunflower and Macrophomina phaseolina. P. Day. PhD thesis. pp. 5-10, 257-264. University of Cambridge 1993.
- Dhingra, O.D.and Sinclair, J.B.(1978) Biology and Pathology of Macrophomina phaseolina. Universidade Federal de Vicosa. 1978. 166 pp.
- Hawksworth et al. (1995) Ainsworth and Bisby’s Dictionary of the Fungi. Eds. D.L. Hawksworth, P.M. Kirk, B.C. Sutton, D.N. Peggler. pp 98-99, 604. CAB International 1995. Wallingford.
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- Microscopy resin. TAAB Laboratories Equipment Ltd.
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- Rush et al. (1992) Introduction. In: Methods for Research on Soilborne Phytopathogenic Fungi. Ed. Larry L. Singleton, Jeanne D. Mihail, Charles M. Rush. pp 5. APS Press. The American Phytopathological Society. 2nd edition 1993. St. Paul Minnesota
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Songa, A.(1995). Variation and Survival of Macrophomina phaseolina in Relation to Screening Common Bean (Phaseolus vulgaris L.) for Resistance. A. Songa. PhD thesis. pp 7-32, 89-90. University of Reading 1995.
- Willetts, H.J. (1978). The filamentous fungi Vol 3. Eds. J.E. Smith and D.R. Berry. pp 197-213. Edward Arnold. 1978 London.
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- Young et al. (1982) A new Record For the Longevity of Macrophomina phaseolina sclerotia. D.J. Young, R.L. Gilbertson, S.M. Alcorn. Mycologia. (74).3. pp 504-505 1982.
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