Southern leaf blight:essential data |
Disease Name,
Other Names, Crops
Affected Causative Agent, Synonyms,
Description of the Agent Symptoms,
Prevention and Treatment
Other
Comments |
| Disease name |
Southern
leaf blight |
| Other Names |
Southern corn leaf blight |
Causative Agent
|
Bipolaris maydis |
| Synonyms |
- Helminthosporium maydi
- Cochliobolus heterostrophus
|
| Crops Affected |
- Corn (Zea mays)
- Sorghum
- Teosinte
|
| Description of the Agent |
Bipolaris maydis
is a member of the ascomycetes, the sac fungi. Mycelium and spores can
overwinter in soil and crop debris. Spores are blown by wind or in water
droplets onto the surface of leaves and after they have germinated they
enter the plant through the stomata. The fungus produces a toxin that
attacks the mitochondria and destroys the plants ability to capture energy
from metabolism. There are very important differences in the type of toxins
produced by different races of the agent. Under optimal conditions (20-30°C
and moist weather), the fungus can complete its life cycle in 2-3 days, |
| Symptoms |
The exact symptoms depend
upon the race of the agent and the strain of corn affected. As a general
rule, tan lesions are seen on leaves with the number and size depending
upon the fungal race and the strain of corn. In the worst case the lesions
are numerous and can be several centimeters long and have dark red or
purple edges. Ears are also infected with a black substance that is actually
masses of conidia (asexual spores) on kernels that can lead to ear and
cob rot. Stalks may also be damaged. |
| Prevention and Treatment |
The genetic basis of susceptibilty to leaf blight is well known and
plants resistant to it are widely available and constitute the first
line of defense. If necessary, fungicides can also be used. A large
number are approved for use and these include:
More than one application may be needed.
|
| Other Comments |
Southern leaf blight did
not become a serious threat to the corn crop until the 1970's. Corn breeders
tried to control the cost of labor-intensive steps in hybrid seed corn
production such as detasseling which is important in controlling pollination.
They tried to use the phenomenon of cytoplasmic male sterility to control
cross-pollination. However, when they did this, they introduced a weakness
into the plants. Plants carrying the "Texas cytoplasm" were
very susceptible to infection by the destructive race T of the fungus.
As seed carrying the Texas cytoplasm was widely planted, there were devastating
outbreaks of the blight and large parts of the crop were lost. It now
appears that there may be strains of the pathogen that are cytoplasm-specific
and any attempt to use cytoplasmic male sterility creates a risk of another
outbreak of Southern leaf blight. |