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Maize (Zea mays L.) is important food, forage, industrial and energy crop taking apivotal place in agriculture. Northern corn leaf spot(NCLS) has occurred and become moreseverely in Yunnan in recent years, but few understanding of pathogenic diversity is knownabout the pathogen. This study focused on the causal agent, and analysis in its morphology,races, mating-types and mating capacity.The pathogen was firstly identified as Bipolaris zeicola (G．L．Stout) in Yunnan,Cochliobolus carbonum R.R. Nelson (perfect stage), and divided into3physiological races,Race1, Race2and Race3, based on its morphology, ITS sequence and pathogenicity onmaize Cultivars.Among169single spore isolates collected from13prefectures of Yunnan, Race3prevailed, accounting for73.96%, Race2took the second place, and Race1was rare,accounting for lower than1%. The races varied in distribution and frequency in Yunnan.Race1was only found in Dehong City, Race2was about30%and Race3about70%inthe most regions of Yunnan except for Lincang City where Race3was observed only. Race2was47.62%in Yuxi City. Among the isolates, most of them were weakly or moderatelypathogenic, and only were3%strongly pathogenic to maize.C. carbonum varied in cultural traits and spore morphology. It secreted5types ofpigments, azure, grayish-green, light red, reddish violet and puce and most of the pigmentswere grayish-green and light red. The spore size was30.19~76.86×8.46~14.27μm（av.53.52×11.37μm）with2.90~6.53（av.4.72）ratio of length to width, the longest one was119μm, the widest19μm with3~9（av.6）septa according to15,629spores. Race2andRace3were significantly different in sporulation, the former sporulated fewer than thelatter on PSA. The experiment also identified the specific isolates, such as CC054sporulating a lot but low pathogenic, CC131and CC133sporulating very few and CC023,CC084, CC087, CC115, CC161and CC171differing from the typical isolates inmorphology.C. carbonum had two mating types, MAT1-1and MAT1-2, no hermaphrodite isolates were found in Yunnan Province and83:85for both types with1:1segregate ratio. For Race2of43isolates, MAT1-1accounted for23.26%. Both of types could be found in a region,even in the same maize field. Race2and Race3could make crosses inside and betweenraces, however, the mating ability varied with isolates.When the169isolates were clustered with Q type average method，they were includedinside2.5distance coefficient. They belonged to11and27genetic groups at0.5and0.25distance coefficients.
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