magnaporthe oryzae causes blast disease which is the most destructive disease of rice
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Magnaporthe oryzae or rice blast fungus, causes rice blast, the most important fungal rice disease in the world (3). Taxonomic research indicated that M. oryzae is distinct from M. grisea, a species that is morphologically indistinguishable from M. oryzae, a species that affects crabgrass (Digitaria). M. oryzae, infects millet and other grasses but primarily rice, the most economically important host (1). Leaf blast may result in significant economic loss; however, it is the panicle blast symptom that has the greater economic impact (4).
The biology of M. oryzae has been studied as a model to further understand fungal/plant interactions (2). Rice blast fungus is a hemiobiotrophic pathogen meaning that initially, the fungus establishes a biotrophic relationship with its host (i.e., invades a few cells, steals nutrients, but does not kill host cells). Eventually, the fungus becomes necrotrophic, destroying plant tissue (1). Infection starts when three-celled conidia from the pathogen adhere to the host’s surface. Initial attachment of conidia and other fungal structures is mediated by mucilage. Upon germination of the conidia, an appressorium is produced. This develops a penetration peg that breaks through the cell wall giving rise to proliferation of hyphae. Cell to cell movement is achieved through plasmodesmata. After colonization of the host and infection of aerial parts, lesions are formed and sporulation takes place. The fungus produces new conidia that disperse through the air and serve as secondary inoculum, giving continuity to the epidemic (1). Fungal resting structures, hyphae inside crop residues and conidia, allow the survival of the pathogen off season. These are the source of primary inoculum that enables the disease to reinitiate (4).
Symptoms and Signs
The symptoms of rice blast include lesions that can be found on all parts of the plant, including leaves, leaf collars, necks, panicles, pedicels, and seeds. A recent report shows that even roots can become infected. However, the most common and diagnostic symptom, diamond shaped lesions, of rice blast occur on the leaves, whereas lesions on the sheaths are relatively rare.
Rice leaves. The symptoms on leaves may vary according to the environmental conditions, the age of the plant, and the levels of resistance of the host cultivars (Figure 4). On susceptible cultivars, lesions may initially appear gray-green and water-soaked with a darker green border and they expand rapidly to several centimeters in length. On susceptible cultivars, older lesions often become light tan in color with necrotic borders. On resistant cultivars, lesions often remain small in size (1-2 mm) and brown to dark brown in color.
Rice collars. The collar of a rice plant refers to the junction of the leaf and the stem sheath. Symptoms of infection of the collars consist of a general area of necrosis at the union of the two tissues (Figure 5). Collar infections can kill the entire leaf and may extend a few millimeters into and around the sheath. The fungus may produce spores on these lesions.
Rice necks and panicles. The neck of the rice plant refers to that portion of the stem that rises above the leaves and supports the seed head or panicle. Necks are often infected at the node by the rice blast fungus and infection leads to a condition called rotten neck or neck blast (Figure 6). Infection of the necks can be very destructive, causing failure of the seeds to fill (a condition called blanking) or causing the entire panicle to fall over as if rotted. The rice blast fungus can also infect the panicles as the seeds form (Figure 7). Lesions can be found on the panicle branches, spikes, and spikelets. The lesions are often gray brown discolorations of the branches of the panicle, and, over time, the branches may break at the lesion.
Rice seeds. The fungus has often been isolated from the pedicels of the seeds. Seeds are not produced when pedicels become infected, a condition called blanking. Symptoms of rice blast on seeds themselves consist of brown spots, blotches (Figure 8), and occasionally the classic diamond-shaped lesion often seen on leaves. The process and the time during which infection of seeds by spores of the pathogen occurs has not been fully described but recent information shows that the fungus can infect seeds by infecting the florets as they mature into seeds, and it is believed that this is the main way seed infection develops
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The biology of M. oryzae has been studied as a model to further understand fungal/plant interactions (2). Rice blast fungus is a hemiobiotrophic pathogen meaning that initially, the fungus establishes a biotrophic relationship with its host (i.e., invades a few cells, steals nutrients, but does not kill host cells). Eventually, the fungus becomes necrotrophic, destroying plant tissue (1). Infection starts when three-celled conidia from the pathogen adhere to the host’s surface. Initial attachment of conidia and other fungal structures is mediated by mucilage. Upon germination of the conidia, an appressorium is produced. This develops a penetration peg that breaks through the cell wall giving rise to proliferation of hyphae. Cell to cell movement is achieved through plasmodesmata. After colonization of the host and infection of aerial parts, lesions are formed and sporulation takes place. The fungus produces new conidia that disperse through the air and serve as secondary inoculum, giving continuity to the epidemic (1). Fungal resting structures, hyphae inside crop residues and conidia, allow the survival of the pathogen off season. These are the source of primary inoculum that enables the disease to reinitiate (4).
Symptoms and Signs
The symptoms of rice blast include lesions that can be found on all parts of the plant, including leaves, leaf collars, necks, panicles, pedicels, and seeds. A recent report shows that even roots can become infected. However, the most common and diagnostic symptom, diamond shaped lesions, of rice blast occur on the leaves, whereas lesions on the sheaths are relatively rare.
Rice leaves. The symptoms on leaves may vary according to the environmental conditions, the age of the plant, and the levels of resistance of the host cultivars (Figure 4). On susceptible cultivars, lesions may initially appear gray-green and water-soaked with a darker green border and they expand rapidly to several centimeters in length. On susceptible cultivars, older lesions often become light tan in color with necrotic borders. On resistant cultivars, lesions often remain small in size (1-2 mm) and brown to dark brown in color.
Rice collars. The collar of a rice plant refers to the junction of the leaf and the stem sheath. Symptoms of infection of the collars consist of a general area of necrosis at the union of the two tissues (Figure 5). Collar infections can kill the entire leaf and may extend a few millimeters into and around the sheath. The fungus may produce spores on these lesions.
Rice necks and panicles. The neck of the rice plant refers to that portion of the stem that rises above the leaves and supports the seed head or panicle. Necks are often infected at the node by the rice blast fungus and infection leads to a condition called rotten neck or neck blast (Figure 6). Infection of the necks can be very destructive, causing failure of the seeds to fill (a condition called blanking) or causing the entire panicle to fall over as if rotted. The rice blast fungus can also infect the panicles as the seeds form (Figure 7). Lesions can be found on the panicle branches, spikes, and spikelets. The lesions are often gray brown discolorations of the branches of the panicle, and, over time, the branches may break at the lesion.
Rice seeds. The fungus has often been isolated from the pedicels of the seeds. Seeds are not produced when pedicels become infected, a condition called blanking. Symptoms of rice blast on seeds themselves consist of brown spots, blotches (Figure 8), and occasionally the classic diamond-shaped lesion often seen on leaves. The process and the time during which infection of seeds by spores of the pathogen occurs has not been fully described but recent information shows that the fungus can infect seeds by infecting the florets as they mature into seeds, and it is believed that this is the main way seed infection develops
.....Hope it helps ......
......Please mark as brainliest......
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