Rice Brown Spot:
essential data |
Disease Name, Other
Names, Crops Affected Causative
Agent, Synonyms,
Description
of the Agent Symptoms Prevention
and Treatment
Other Comments |
| Disease name |
Rice Brown Spot |
| Other Names |
Blight Disease of Rice |
Causative Agent
|
Cochliobolus miyabeanus |
| Synonyms |
- Ophiobolus sativus,
- Helminthosporium oryzae
|
| Crops Affected |
Rice |
| Description of the Agent |
C. miyabeanus is an ascomycete, a member of the sac fungi.
It is a member of a group of pathogens that attack members of the
grass family, including important cereal species such as wheat, maize,
barley, oats and rye.
One of the features of these fungi is that they generate spores,
called conidia, that can be easily dispersed by the wind and do
not need insects or other animals to spread them. These spores are
asexual, they do not arise from sexual crosses, but rather act as
a method of dispersing the organism as an infected plant is drained
of its value to the fungus. A consequence of this is that the pathogen
can spread rapidly in devastating epidemics. Rice blight and two
diseases caused by related fungi (Southern corn leaf blight and
Helminthosporium blight of oats) are known for their devastating
outbreaks. |
| Symptoms |
The disease is first seen as brownish spots on the leaves and glumes
of the plant. The spots enlarge and become grey at the center and
brown at the edge. The affected tissues take on a velvety feel as
the fungus begins to develop aerial structures that produce the spores
by which it spreads.
The spores are carried in the rice seed and when it germinates,
the burden imposed by the growing fungus on the developing plants
that the seedlings are weakened and crop yields are drastically
reduced. |
| Prevention and Treatment |
Plants growing in good nutritional conditions are generally
resistant to the disease. The defining weakness for susceptibility
to infection appears to be a deficiency in available silicon. Preventive
treatment of fields with calcium silicate would be indicated if a
threat was present. |
| Other Comments |
There was a major outbreak of rice brown spot in Bengal
in India in 1942. The loss of the crop led to a famine that claimed
two million lives. Bengal is in the eastern part of the subcontinent
close to Indo-China and would have been an important staging area
for operations against the Japanese as they approached India during
their early successes in World war II. The famine must have diverted
resources from military operations, demonstrating how biological weapons
can have indirect effects. |