Symptoms: Foliar symptoms vary as brown flecks, fine linear streaks, small oval spots, large irregular oval, oblong, or almost rectangular spots measuring 1-10 × 0.5-3 mm. Large fusiform lesions are sometimes produced. Lesions may expand and coalesce. Lesions may be solid dark brown but usually become tan or greyish brown with a more or less distinct dark-brown border (Luttrell 1954).
Pathogen and disease characteristics: Pigmented conidia are fusoid to obclavate fusoid, straight to usually slightly curved, thin walled but becoming moderately thick walled at maturity, pale or moderately dark olivaceous brown, and 44-151 × 10.6-19.6 µm, with 4 to 13 septa (Luttrell 1954).
The pathogen causes seed decay, seedling blight, leaf spot, and head mold of pearl millet. Young plants and maturing plants are most susceptible to foliar blight (Wells and Burton 1967). Seedling blight is more pronounced at temperatures of 25 °C and less (Wells 1967).
Host range: Pearl millet, napiergrass, browntop millet (Panicum fasciculatum Swartz) [sic], Arundinella nepalensis (Bhowmik 1972), sugarcane, teosinte, maize (Nishihara 1967), sorghum, Paspalum scrobiculatum,Panicum miliaceum, barley (Hordeum vulgare), wheat (Triticum aestivum), oat (Avena sativa), cogongrass (Imperata arundinacea, old nomenclature, now I. cylindrica), bermudagrass (Cynodon dactylon) (Misra et al. 1974).
Nomenclature discrepancies:Synonyms or similar pathogens: Several "Helminthosporium" species differ only slightly in the thickness of conidial walls and size of the conidia (Luttrell 1954,Luttrell et al. 1974). Some confusion and possible controversy exists in regards to description, taxonomy, and host range of this and other potentially very similar fungi, including:
Bipolaris urochloae (Putterill) Shoem (Singh et al. 1990) [has been implicated in causing "brown leaf spot"]
Drechslera setariae Saw.
Helminthosporium australiense Bugnicourt (Chand and Singh 1966)
Helminthosporium sacchari (van Breda de Haan) Butl. (Misra et al. 1974)
Helminthosporium setariae Saw.
See table 2 for additional Bipolaris species pathogenic to Pennisetum.
Primary citations: As indicated above.
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Original posting: June 5, 1999.