Magnaporthe Grisea is a plant fungus that affects rice. This detrimental rice disease is also known as rice blast fungus, rice rotten neck, rice seedling blight, blast of rice, oval leaf spot of graminea, pitting disease, rye grass blast, and Johnson spot. In this article we will explore the causes, symptoms and treatment of magnaporthe in rice.
Magnaporthe Grisea is an ascomycetous fungus, which means its spores are formed in an ascus, a sexual spore bearing cell. This fungus produces both appressoria ( which infects the rice's aerial tissue) and hyphae ( which manages to infect the plants root systems). It produces these harmful spores via both sexual and asexual reproduction.
The strains of rice that are quite susceptible to the disease Magnaporthe are M-201, M-202, M-204, M-205, M-103, M-104, S-102, L-204, Calmochi-101. When a rice plant becomes infected they will exhibit lesions or spots on the shoot area. This lesions will appear white or gray with darker colors on the outside areas of the spot. Older lesions will be of the same colour as the aforementioned spots, but their outside borders will be necrotic (dead) and inside it will be spindle-shaped. This lesions are known to increase in size, with some even managing to kill the entire leaf. Lesions can also be seen on the leaf collar, culm, culm nodes, and panicle neck node. The infected rice plant will also appear to produce less seeds, this is due to Magnoaporth preventing maturation of the actual grain. Sometimes the colour and shape of the lesion will depend on where it is formed, as described below.
Leaf: These are usually diamond in shape, and their color is gray or white in the center and brown or reddish brown around the border area. Size of the lesion will be on average 0.39 to 0.58 inch long and 0.12 - 0.2 inch wide.
Leaf Collar: This lesion will form at the junction of the leaf blade and sheath, and can sometimes cause the whole leaf to die and fall off.
Node: This is where the node becomes disease, which causes the node to become black or brown. This infection is quite severe causing the complete death of the stem above the infection.
This disease unfortunately has a quick cycle duration, with one lesion being able to produce thousands of spores in one night, and continue to produce for 20 days. This makes Magnaporthe a highly devastating disease to individual rice crops.
Magnaporthe is very devastating in tropical, high humidity, little or no wind and no moisture environments. The amount of spores produced will increase with high relative humidity. Soil conditions can also make a plant more susceptible to Magnaporthe, where there is an increase amount of Nitrogen in the soil the plant can be in a weakened state thus the disease will be more likely to be damaging to the plant's health.
Magnaporthe has been witnessed to grow immune to certain kinds on management techniques, such as chemical treatments and genetic resistance. This is due to the plant mutating to adapt to the new introduced conditions. This feature of Magnaporthe can be avoided by implementing a management strategy that combines a number of different treatment methods in order to avoid overusing a single method, thus limiting the potential for the disease to adapt to its environment and mutate. Examples of different management techniques are listed below:
- To regulate the irrigation of the planed area. This will limit the spores mobility thus dampening the opportunity for spread and infection
- Using a combination of chemical treatments, at different times.
Magnaporthe can also infect wheat, rye, barley, and pearl millet.
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