| Disease Name, Other
Names, Crops Affected Causative
of the Agent Symptoms Prevention
- Panicle blast
- Rotten neck
- Magnaporthe grisea
- Magnaporthe poae
- Pyricularia oryzae
- Trichothecium griseum
- Rice blast fungus
||Rice and some other grasses
|Description of the Agent
P. grisea is an ascomycete fungus, a member of the sac
fungi. One of the features of these fungi is that they generate
spores, called conidia or conidiospores, that can be easily dispersed
by the wind and splashing rain. These spores can overwinter in rice
grains and rice stubble and can infect new crops the following year.
Conidia generated in the diseased plant can further spread the infection.
Magnaporthe is the sexual or perfect form of the fungus
and it is not seen in the wild although the name is used in the
academic literature when the genetics of the pathogen are investigated.
||The disease is first seen as elliptical gray-white lesions with
reddish edges on the leaves (leaf blast) and stems of the plant. The
lesions run parallel to the long axis of the leaf or stem. Most damage
occurs when the fungus spreads to the area below the seed head of
the plant, causing it to break off (rotten neck). Otherwise, the disease
prevents the maturation of the rice grains (panicle blast). Crop losses
can reach 50%.
|| Cultural practices including the destruction
of diseased crop residue, careful use of nitrogen fertilizer (high
levels increase the likelihood of disease), the use of water seeding
rather than drill seeding and ensuring that plants remain flooded
all seem to help control the disease. Planting of resistant varieties
of rice may also be helpful.
Effective fungicides include Benlate,
although this is not certified for use in all areas. Guidelines
for use are supplied by the manufacturer. Pyroquilon and tricyclazole
are new fungicides that are showing effectiveness in treatment of
||Infection is most likely after long periods of rain or
high humidity with little or no wind movement and relatively warm
nights (63-73°F or 18-23°C). These conditions favor spore
germination and formation. Ensuring that the plants are flooded and
avoiding drought stress are effective in controlling the fungus.
Resistant strains of rice are known and planting of such strains
may be helpful.
P. grisea is the most important pathogen of rice worldwide.
As rice is the most important starch source, rice blast is arguably
the most important plant pathogen of those considered as anticrop