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Alternaria dauci
''Alternaria dauci'' is a plant pathogen. The English name of the disease it incites is "carrot leaf blight".
== Hosts and Symptoms ==
Alternaria Leaf Blight is a foliar disease of carrots caused by the fungus ''Alternaria dauci''. ''Alternaria dauci'' is included in the porri species group of ''Alternaria'', which is classified for having large conidium and a long, slender filiform beak. Because many of the members of this group have similar morphology, ''Alternaria dauci'' has also been classified as formae specialis of carrots, or ''A. porri f. sp. dauci''.〔 It has been well established that the host range of this disease is on cultivated and wild carrot, but it has also been claimed that ''Alternaria dauci'' has the ability to infect wild parsnip, celery, and parsley.〔 A study in 2011 by Boedo et al. evaluated the host range of ''Alternaria dauci'' in a controlled environment and concluded that several non-carrot species could constitute alternate hosts, such as ''Ridolfia segetum'' (corn parsley) and ''Caucalis tenet'' (hedge parsley). Despite their findings, reports of ''A. dauci'' colonization on non-carrot hosts continues to be debated because the use of Koch's Postulates on recovered isolates of ''A. dauci'' is challenging and is rarely reported; in addition, few reports are often made of such infections in field settings.〔
Symptoms of ''A. dauci'' appear first as greenish-brown, then water-soaked, and finally necrotic lesions 8–10 days following an infection event.〔 These lesions will appear on carrot leaflets and petioles, and have a characteristic chlorotic, yellow halo. The lesions can be irregularly shaped, and will often appear on older leaves first. Older leaves are the most susceptible to infection; when approximately 40% of the leaf surface area has become infected by ''Alternaria dauci'', the leaf will completely yellow, collapse, and die. It is during extended conditions of warm, moist weather that lesions can coalesce and cause entire tops of carrot plants to die off, a phenomenon that is sometimes mistaken for frost damage. The symptoms of this disease are also commonly confused with Cercospora Leaf Blight of carrots as well as bacterial blight, and microscopic analysis is frequently needed to accurately diagnose the pathogen. ''A. dauci'' produces characteristically dark to olive-brown hyphae and elongated conidiophores, with conidia typically borne singly.〔 Petiole infection can also occur without any lesion development on leaflets, and ''A. dauci'' can additionally result in damping-off of seedlings, seed stalk blight, and inflorescence infections.〔 These symptoms can significantly reduce yield due to lost photosynthetic activity, prevention of mechanical harvest, and infection of commercial carrot seeds.〔
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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