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Clypeus amphigenous, developing in epidermis, generally circular, 0.5-2.0 mm diameter, dark-brown to black, glossy. Ascomata perithecial subglobose, ostiolate, aggregated or scattered, subepidermal beneath clypeus, 170-350 µm diameter. Paraphyses numerous, filiform, longer than asci, to 125 µm. Asci narrowly cylindrical, 8-10 x 80-100 µm, pedicel short. Ascospores uniseriate in ascus, hyaline, aseptate, broadly ellipsoid, 5.5-8.5 x (8-)10-14 µm (often 13-14 µm). Conidiomata pycnidial, subepidermal beneath clypeus, often in younger lesions. Conidiophores branched at two or three levels, branches tapering, 11-16 x 1.0-1.5 µm. Conidia filiform, hyaline, 10-15 x 0.5 µm, gradually tapering to apex. For additional descriptions see Dalby (1917), Orton (1944), Parbery (1967), and Liu (1973).

Recoginition

Lower leaves should be examined for small, raised, glossy, dark, circular, or oval to irregular, spots, or for brown lesions, often with a dark border, having a dark ascomata at the centres (CIMMYT, 2003).

Related invasive species

  • Phyllachora maydis

Related Farm Practice

  • Development
Impact

P. maydis, a perithecial ascomycete, causes a tar spot disease of maize that is usually a minor problem. More significant damage to leaves and yield is caused by the fungus Monographella maydis whose infection follows that of the tar-spot fungus, at least where studied in Mexico (Hock et al., 1992;1995). The source of initial inoculum for both fungi is not determined. The disease they cause occurs in the cooler and higher elevations of Mexico, and Central and South America, and the West Indies, so their ability to spread over land through other climatic zones may be limited. Not known to be seedborne or to infect other species, P. maydis could be transported on fresh or dry maize leaves or husks, or products made from them, from which ascospores would have to be produced and carried by wind or rain splash to maize [ Zea mays ].

Has Cabi datasheet ID
40876
Symptons

Initial symptoms are small, yellow-brown spots on either side of the leaf. The raised glossy black clypeus covering the ascomata, surrounded by a narrow chlorotic border, develops in the spot. Spots are circular, oval, sometimes angular or irregular, and may coalesce to form stripes up to 10 mm long (Liu, 1973).
Some spots enlarge around the ascomata, with an initially water-soaked area becoming necrotic, to form circular-oval brown lesions 3-8 mm diameter with a dark outer edge (Bajet et al., 1994);this is called the “fish-eye” symptom (Hock et al., 1992). These larger lesions coalesce after 7-14 days;areas between spots become water-soaked and dry out. When conditions favour disease, leaves may be fully dead in 21-30 days. The fungus spreads from the lowest leaves to upper leaves, leaf sheathes and the husks of developing ears (Bajet et al., 1994).
As many as 4000 lesions may form on a leaf, and, in susceptible genotypes, 80% or more of the leaf area is affected, leaving little green tissue or killing the plant (Ceballos and Deutsch, 1992). Affected ears have reduced weight and loose kernels, and kernels at the ear tip may germinate prematurely (CIMMYT, 2003).

Hosts

P. maydis is restricted to Zea mays (maize) (Parbery, 1967), and was not found on other grasses, including other Zea species, in Mexico (Hock et al., 1995).

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