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In this article we will discuss about the effects of M. grisea on plants.
M. grisea is an ascomycete fungus. It is an extremely effective plant pathogen as it can reproduce both sexually and asexually to produce specialized infectious structures known as appressoria that infect aerial tissues and hyphae that can infect root tissues.
The asexual life cycle begins when the hyphae of the fungus undergo sporulation to produce fruiting structures called conidia which contain many spores. When these spores land on leaves and other aerial tissues of susceptible plants they germinate, developing the appressorium.
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The appressorium penetrates the plant cell by producing a penetration peg. Pressure in the appressorium increases and the structure explodes, forcing the penetration peg through the cell wall and into the cell. The fungus can then grow hyphae within the leaf and form lesions. Once established in the host plant the fungal hyphae can undergo asexual sporulation again.
Sexual reproduction occurs when two strains of opposite mating types meet and form a perithecium in which ascospores develop. Once released, ascospores can develop appressoria and infect host cells. Spores are transmitted between plants by the wind.
In 2004 (unpublished work) it was shown that in addition to infecting plants through the leaf, M. grisea can also infect the plant roots. The mode of root infection is the same as most root infecting fungi; it grows long hyphae that form an infection pad to gain entry to the root’s interior.
Once embedded in the root the fungus can produce resting structures. The blast fungus can also invade the plant’s vascular system, growing inside the xylem and phloem and blocking the transport of nutrients and water from the roots, and produce lesions on aerial plant parts.
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In 2005 (unpublished work) the complete genome of M. grisea was sequenced. The organism is predicted to have over 11,000 genes. It is expected that the genome will reveal the mechanisms of fungal pathogen-plant interaction, in both aerial and root infection.
The fungus can kill or damage the plant in a number of ways. Aerial infection in seedlings is usually lethal because the young plants are unable to photosynthesize. Aerial infection in mature plants does not kill them, but reduced photosynthesis due to lesions on the leaf and use of photosynthetic by the fungus greatly reduces yield.
Infection of root and vascular tissues has the potential to kill the plant by cutting off the supply of water and nutrients to the root.
Systematic Position:
Kingdom: Fungi.
Phylum: Ascomycota.
Class: Sordariomycetes.
Order: Sordariomycetes incertae sedis.
Family: Magnaporthaceae.
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Genus: Magnaporthe.
Species: grisea.
Binomial name: Magnaporthe grisea (Hebert) Barr.
