Southern corn leaf blight
| Southern corn leaf blight | |
|---|---|
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| Southern corn leaf blight on Maize | |
| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Subdivision: | Pezizomycotina |
| Class: | Dothideomycetes |
| Order: | Pleosporales |
| Family: | Pleosporaceae |
| Genus: | Bipolaris |
| Species: | B. maydis |
| Binomial name | |
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Bipolaris maydis Nisikado & Miyake |
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Southern corn leaf blight (SCLB) is a fungal disease of maize caused by the plant pathogen Bipolaris maydis (also known as Cochliobolus heterostrophus in its teleomorph state).
The fungus is an Ascomycete and can use conidia or ascospores to infect. There are three races of B. maydis: Race O, Race C, and Race T; SCLB symptoms vary depending on the infectious pathogen's race. Race T is infectious to corn plants with the Texas male sterile cytoplasm (cms-T cytoplasm maize) and this vulnerability was the cause of the United States SCLB epidemic of 1969-1970 For this reason, Race T is of particular interest. While SCLB thrives in warm, damp climates, the disease can be found in many of the world's maize-growing areas. Typical management practices include breeding for host resistance, cultural controls and fungicide use.
The primary host for Southern corn leaf blight is Zea mays, or maize, known as corn in the United States.
Various types of corn with normal cytoplasm (N), while vulnerable to Race O, have cytoplasmic resistance to the T-toxin of Bipolaris maydis (produced by Race T). This resistance owes itself to the absence of a gene found only in plants with Texas male sterile cytoplasm. Corn plants with T-cms cytoplasm have maternally inherited the gene T-urf 13, which encodes for a protein component of the inner mitochondrial membrane. This portion of the mitochondria functions as T-toxin's site of action. In a similar manner, Race C is only pathogenic to hosts with cytoplasm male-sterile C.
SCLB can also infect sorghum and teosinte.
Table 1. Race Overview
Symptoms vary depending on which race is present. The telltale symptom of SCLB is the presence of leaf lesions.
Lesions when Race O is present are tan in color with buff to brown borders. They begin as small, diamond-shaped lesions and elongate within the veins to become larger and rectangular. Race O's lesions remain within the leaves of the maize plant. Lesion size ranges from 2 to 6 millimeters wide and 3 to 22 millimeters long.
Lesions caused by Race T are tan with yellow-green or chlorotic halos. Later on, lesions have red to dark brown borders and can spread to all other above-ground parts of the plant including the stem, sheath, and ear. The shape of lesions are elliptical or spindle and can be larger than lesions caused by Race O, at 6 to 12 millimeters wide by 6 to 27 millimeters long. Race T infection causes seedlings to wilt, and they die within three or four weeks.
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