Southern
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
blight |
| Other Names |
The agent causes a wide
variety of blights, cankers and rots. Southern blight is the name given
to its infection of cucurbits (pumpkins and squash). |
Causative Agent
|
Sclerotium rolfsii |
| Synonyms |
- Athelia rolfsii
- Corticium rolfsii
- Pellicularia rolfsii
- Sclerotia delphinii
|
| Crops Affected |
Major crops affected include:
- Crucifers (cabbage, cauliflower, broccoli, rape)
- Cucurbits (melon, pumpkin, gourds, squashes)
- Legumes (beans, peas and lentils)
S. rolfsii has an extraordinary host range with up to 500 species
in over 100 families known to fall victim to it. Greatest economic damage
worldwide is done to peanut crops.
|
| Description of the Agent |
S. rolfsii is a basidiomycete or club fungus. It grows on plants
and culture media as a dense, downy, white mass. Plants are usually
infected at or near the soil surface and grow rapidly up the stem and
even more rapidly into the root system where it can cause root or tuber
rot.
The agent is soil-borne and survives in soils as spore bodies called
sclerotia.The mycelium can survive in acid soils, but not in alkaline
ones and can grow at soil temperatures of >10°-35°C.The
mycelium is killed by freezing but the sclerotia can survive -10°C.
However, distribution is limited to outside areas where the soil temperature
regularly reaches freezing, typically temperate and tropical zones.
Spores are distributed in contaminated soil or in water, typically in
irrigation.
|
| Symptoms |
The commonest diagnostic
indicators are yellowing and wilting of leaves followed by the appearance
of a white fluffy mass of hyphae on the stem of the plant, usually near
the soil line. It may also show some sclerotia, asexual reproductive structures
that resemble mustard seed. A dark brown lesion on a plant stem near the
soil line is a very early indicator that is difficult to spot.. |
| Prevention and Treatment |
Despite its aggressive nature, S. rolfsii can be controlled
by good cultural practices including deep ploughing and the use of soil
amendments that stimulate the growth of microorganisms that inhibit
growth of the fungus. A number of microorganisms have been found to
limit its growth, including:
- Bacillus subtilis,
- Gliocladium virens,
- Penicillium,
- Trichoderma harzianum,
- Trichoderma viride.
A relatively cheap and effective method of killing the fungus is by
soil solarization. This involves covering the soil with plastic and
allowing the sun to heat the trapped air. Temperatures high enough to
kill the microorganism in surface layers of soil can be attained. Similarly,
black plastic mulch is also effective. The fungus can also be controlled
by liming soil to make it alkaline. Fungicidal treatments appear to
be limited in effectiveness and need to be applied to seed before planting.
The most effective are seed and field fumigants.
|
| Other Comments |
S. rolfsii appears
on lists of potential biological agents considered by the United States
in the 1950's and 1960's. Its broad host range and rapid action make it
attractive, but the lack of straightforward protective measures, such
as a simple fungicidal spray that can be applied after it is detected,
suggest that it could turned upon the user as easily upon the target.. |
|