Cochliobolus carbonum
| Cochliobolus carbonum | |
|---|---|
| Scientific classification | |
| Kingdom: | Fungi |
| Phylum: | Ascomycota |
| Class: | Dothideomycetes |
| Subclass: | Pleosporomycetidae |
| Order: | Pleosporales |
| Family: | Pleosporaceae |
| Genus: | Cochliobolus |
| Species: | C. carbonum |
| Binomial name | |
|
Cochliobolus carbonum R.R. Nelson, (1959) |
|
| Synonyms | |
|
Bipolaris zeicola (G.L. Stout) Shoemaker, |
|
Bipolaris zeicola (G.L. Stout) Shoemaker,
Drechslera carbonum (Ullstrup) Sivan., (1984)
Drechslera zeicola (G.L. Stout) Subram. & B.L. Jain, (1966)
Helminthosporium carbonum Ullstrup, (1944)
Helminthosporium zeicola G.L. Stout, (1930)
Cochliobolus carbonum (anamorph: Helminthosporium carbonum) is one of more than 40 species of filamentous ascomycetes belonging to the genus Cochliobolus (anamorph: Bipolaris/Curvularia). This pathogen has a worldwide distribution, with reports from Australia, Brazil, Cambodia, Canada, China, Congo, Denmark, Egypt, India, Kenya, New Zealand, Nigeria, Solomon Islands, and the United States. Cochliobolus carbonum is one of the most aggressive members of this genus infecting sorghum (Sorghum spp. [Poaceae]), corn (Zea mays [Poaceae]) and apple (Malus domestica [Rosaceae]). As one of the most devastating pathogens of sweet corn, C. carbonum causes Northern leaf spot and ear rot disease while the asexual stage causes Helminthosporium corn leaf spot.Cochliobolus carbonum is pathogenic to all organs of the corn plant including root, stalk, ear, kernel, and sheath. However, symptoms of infection show distinct manifestations in different plant parts: whole plant - seedling blight affects the whole plant, leaf discoloration and mycelial growth, black fungal spores and lesions appear on inflorescences and glumes, and grain covered with very dark brown to black mycelium which gives a characteristic charcoal appearance due to the production of conidia.
Cochliobolus carbonum is divided into at least five different races based on pathogenicity, particularly lesion types on corn leaves.Cochliobolus carbonum race 0 (CCR0) is essentially non-pathogenic.Cochliobolus carbonum race 1 (CCR1) produces host specific toxins and oval to circular spots on leaves. While infection by C. carbonum race 2 (CCR2) is rare, it is characterized by the production of oblong, chocolate-colored spots.C. carbonum race 3 (CCR3) produces linear and narrow lesions while C. carbonum race 4 (CCR4) is weakly pathogenic, forming oval to concentric circular spots.
The genus Cochliobolus is distinguished by the presence of dark to black ascomata with a unilocular, globose pseudothecium and a short, cylindrical neck. Ascomata also bear hyphae and conidiophores and asci are bitunicate, 2-8 spored, and cylindrical to obclavate. Ascomata are black, globose to ellipsoidal, and setae are present over the upper half of the wall mixed with conidiophores. Pseudoparaphyses are filiform, hyaline, septate, and branched. The shapes of asci are cylindrical to clavate, short-stalked, straight to slightly curved having 1-8 spores, and vestigial bitunicate. Conidia are straight to moderately curved, occasionally cylindrical but usually broad in the middle and tapering towards the rounded ends, distoseptate, and 36-100 X 12-18 µm. The surface of the conidia is often granulose and the hilum is inconspicuous. Conidia are produced from the apex of an unbranched conidiophore. Generally, the conidiophore arises singly or in small groups which are straight or flexuous, mid to dark brown, smooth, septate, cylindrical, and up to 250 μm long, 5-8 μm thick. Variation in mycotoxin production by Cochliobolus species is used to distinguish some taxa and these mycotoxins are host-specific and non-host specific. HC toxin produced by C. carbonum race 1 and T toxin produced by C. heterostrophus are host-specific toxins while ophiobolins produced by C. miyabeanus and carbotoxin produced by C. carbonum are non-host-specific toxins.
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