Pathogen Identification Of Corn Gray Leaf Spot In Shaanxi And Screening Effective Fungicides And Resistant Variety For Disease Control

Corn is one of the most important crops in China.It ranks the first position both for its planting area and its output.As a major industrial material,also considerable food resources for human and animals,corn takes a crucial role in Chinese food availability and security.Corn gray leaf spot is a worldwide disease.Although it is comparatively new disease in China,corn gray leaf spot has become one of the most important and devastating foliar disease in corn production because of transforming of corn germplasm resources,transporting of corn varieties and changing of environments including weather.Two species of fungi are identified as the pathogen of corn gray leaf spot in China.One is Cercospora zeae-maydis Tehon Daniels which originally occurs in Northwest of China,and the other is Cercospora zeina Crous&U.Braun sp.nov.that initially happens in southwest of China.They distributed in north or south individually and never occurred together in one place before.Corn gray leaf spot was discovered in Shangluo,Shaanxi province in 2009.Its pathogen has not reported till now.150 diseased samples were collected from 15 counties or districts in Shaanxi?18 strains were isolated and purified from the diseased samples.With morphological observation and molecular biological techniques,the pathogens were identified the 18 strains.In order to provide scientific evidences for disease control,toxicity tests of nine common fungicides for Cercospora zeae-maydis were carried out in laband variety resistance identifications to Cercospora zeina were also conducted in field.All the results were as follows:1.Two species of fungi were identified as the pathogen of corn gray leaf spot in Shaanxi with morphological observation and molecular biological techniques.One is Cercospora zeae-maydis Tehon Daniels and the other is Cercospora zeina Crous&U.Braun sp.nov..2.Toxicity tests of nine common fungicides for Cercospora zeae-maydis in lab showed that three kinds of fungicides had good control effects.80%azoxystrobinWDG ranked first with EC₅₀ of 0.14?g/mL;400g/LpyrimethanilSC took the second position with EC₅₀ of0.53?g/mL;80%mancozebWP occupied the third with EC₅₀of 0.80?g/mL?3.Variety resistance identifications to Cercospora zeina revealed that there was 1highly resistantvariety,4 resistant varieties,3 moderately resistant varieties,8 susceptible varieties and 5 highly susceptible varieties in 2017;and there was 1 highly resistant variety,4 resistant varieties,6 moderately resistant varieties,17 susceptible varieties and 2 highly susceptible varieties in 2018.From the results of two years field tests,resistant varieties occupied less,19 out of 51 tested varieties,making out 37.25%;while susceptible varieties took more,32 out of 51 tested varieties,accounting for 62.75%.