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Pyrenophora tritici-repentis
''Pyrenophora tritici-repentis'' (telomorph) and ''Dreshslera tritici-repentis'' (anamorph) is a necrotrophic plant pathogen of fungal origin Phylum Ascomycota. The pathogen causes a disease commonly called tan spot, yellow leaf spot, yellow leaf blotch or helminthosporiosis. At least eight races of the pathogen are known to occur based on their virulence on a wheat differential set.
The tan spot fungus was first described in 1823 and was identified in Europe, the USA, and Japan in the early 1900s. The disease is one of the most important fungal disease on wheat and the fungal pathogen is found to infect in all parts of the world wherever wheat and other susceptible host crops are found.〔 P. tritici-repentis overwinters on stubble, and due to recent heavily no-till/residue retention cultural practices, increased incidence and yield loss of up to 49% has been witnessed if ideal conditions occur.〔 It forms characteristic, dark, oval-shaped spots of necrotic tissue surrounded by a yellow ring.〔(eumedia.es - Control de enfermedades en cereales de invierno ). Web consulted June 6th, 2008.〕 It is responsible for losses that account for up to 30% of the crop,〔(Manejo de las enfermedades del trigo ). Pérez Fernández, Jesús & Corro Molas, Andrés. Web consulted June 1, 2008.〕 due to its effects reducing photosynthesis. Pathogenesis and toxicity in P. tritici-repentis is controlled by a single gene, transformations of this gene cause the pathogen to become benign when interacting with wheat.〔()〕 This has major implications for those in agriculture seeking to combat the effects of this fungus.
==Hosts and symptoms==
Tan spot is found primarily on wheat, but is also found to infect other cereals and grasses including triticale, barley, and rye, but are less frequently affected.〔Other grass species effected by the pathogen include Siberian wheat grass, sand bluestem, meadow brome, sheep fescue, June grass, little bluestem, green foxtail, needle and thread, and tall wheatgrass.While these are not necessarily agriculture crop hosts such as wheat, the pathogen is able to form and survive on many grass hosts, which can eventually venture into wheat fields. Other important grass susceptible hosts include smooth brome which can be found in pastures, as well as quack grass that is found in the environment and considered a weed in many agricultural crops. Lesions typically appear on both upper and lower leaf surfaces, and initially are tan to brown specks. Eventually, the tan to brown specks expand to larger irregular, oval, lens-shaped, ellipse, tan blotches with a yellow ring around them. The yellow ring is often referred to as a halo, yellow discoloration as chlorosis, and browning/death of leaf tissue as necrosis. The development of a dar brown to black spot in the center the lesion is characteristic of the disease.〔(【引用サイトリンク】url=http://archive.hgca.com/minisite_manager.output/3623/3623/Cereal%20Disease%20Encyclopedia/Diseases/Tan%20Spot%20(DTR).mspx?minisiteId=26 )〕 If warmer temperatures and moist conditions persist, spores known as conidia will move up plant as secondary inoculum and can also infect head/spikes. Symptoms on the head are indistinct, but can cause brownish glumes, and grains can have a reddish appearance similar to the pathogen ''Fusarium''.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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