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Black sigatoka of banana

Scientific Name
Mycosphaerella fijiensis
Scientific Author
M. Morelet
Taxonomy
Ascomycetes, Mycosphaerellales

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Diagnostic Images

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Caption
Conidiophores and conidium (BRIP 21186)
Source
Dr Jose R. Liberato DPI&F
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Diagnostic Images (28)
Diagnostic Notes
Symptoms:

A brief description of the six stages in symptom development according to Meredith & Lawrence (1969) follows:

1. Stage 1 (initial speck stage): Symptoms occurs initially as feint, minute (up to 0.25 mm in diameter), reddish brown specks on the lower surface of the leaf, which first appear on the third, fourth or older leaves and are often more abundant near the margin, particularly towards the tip.

2. Stage 2 (first streak stage): The specks elongate, becoming slightly wider, and form a narrow, reddish brown streak up to 20 x 2 mm, with the long axis parallel to the leaf venation. The streaks are more clearly visible on the lower surface of the leaf than the upper surface and its distribution on the leaf is variable. Streaks can be numerous and coalesce to form larger streaks.

3. Stage 3 (second streak stage): The streaks change colour from reddish brown to dark brown or almost black, sometimes with a purplish tinge, becoming clearly visible on the upper surface of the leaf. When they are numerous and more or less evenly distributed, the entire leaf blackens.

4. Stage 4 (first spot stage): The streak broadens and becomes somewhat fusiform or elliptical and develops a light brown, water-soaked border around the spot.

5. Stage 5 (second spot stage): The dark brown or black central area of the spot becomes slightly depressed and the water-soaked border becomes more pronounced due to darkening. At this stage, a slight yellowing of the leaf tissue immediately surrounding the water-soaked border may occur.

6. Stage 6 (third or mature spot stage): The centre of the spot dries out, becoming light grey or buff-coloured, and further depressed. The spot is surrounded by a narrow, well-defined, dark brown or black border. Between this border and the normal green colour of the leaf, there is often a bright yellow transitional zone. After the leaf has collapsed and withered, spots remain clearly visible with the light-coloured centres and dark borders.

The fungus:

Fruiting amphigenous, predominantly hypophyllous, dark brown, scattered on the lesion. Stroma none or moderately developed, textura angularis, substomatal, erumpent, or on young spermatia, brown. Conidiophores in loose or dense fascicles, continuous or septate, smooth, cylindric, simple, olivaceous brown, up to 25 x 3-4 µm, Conidiogenous cells apical, sometime sessile, straight or geniculate, simple, smooth, olivaceous brown, sympodial; conidial ontogeny holoblastic, proliferation enteroblastic, with 1-3 moderately visible scars on the apices or on geniculations; up to 25 µm long, 3-4 µm wide at the base and 2-4 µm wide at the apex. Conidia solitary, obclavate or cylindric-obclavate, subhyaline, rarely guttulate, base truncate with a moderately visible scar, 1-6 septate, smooth, schizolytic secession, 10-120 x 1.5-2 µm (Pons 1987).

Perithecia amphigenous, submerged, globose, spherical, papillate ostiole, slightly erumpent, dark brown walls, cells polygonal, 42-81 µm. Asci numerous, bitunicate, obclavate, 8-spored, 28-34.5 x 6.5-8 µm. Paraphyses absent. Ascospores hyaline, fusiform, clavate, biseriate, 1-septate, slightly constricted at the septum, 14-20 x 4-6 µm. Spermogonia numerous, amphigenous, pale to medium brown, obpyriform, 31-52 µm in diameter. Spermatia cylindric or bacilliform 3.5-4.5 x 1.5-2.5 µm (Mulder & Stover 1976, as M. fijiensis var. difformis).

Notes

1. Although some authors described the conidial scars as conspicuous, the conidiogenous locus of this species is actually confined to a narrow, thickened rim around the scar (Pons 1987). It was considered a key characteristic for segregation of the genus Paracercospora from Pseudocercospora until recently. However, the differentiation between both genera is often difficult, and there are numerous intermediate taxa. Crous & Braun (2003) have considered these two genera as synonymous based in results of mol
More Information
Specimen Contact
Dr Jose R. Liberato
Author
Liberato JR, Peterson RA, Gasparotto L, Ferrari JT, Grice K, Porchun SC & Shivas RG
Created
22/03/2006 05:28 AEST
Last Updated
19/07/2016 08:40 AEST
Citation
Liberato JR, Peterson RA, Gasparotto L, Ferrari JT, Grice K, Porchun SC & Shivas RG (2006) Black sigatoka of banana (Mycosphaerella fijiensis ) Updated on 7/19/2016 8:40:01 AM Available online: PaDIL - http://www.padil.gov.au.
Image Use
Free for use under the Creative Commons Attribution 3.0 Australia License

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