Comparison Of Pathogenicity And Culture Characters For Exserohilum Turcicum Isolates From Different Regions Of Shaanxi Province

Northern corn leaf blight,caused by Exserohilum turcicum,is an important leaf disease of maize occurs at middle and late growing season.It occurs sporadically in most areas of Shaanxi where maize is grown.Average disease incidence is about 10 %to 30%.And it can be up to 70% when rainfall is abundant in summer.If the disease is established before silking,corp will be died and losses in grain yield up to 50% may occur.It takes big threaten to grain safety of Shaanxi.Growing resistant varieties is the most useful and effective way to control this disease.Different pathogenicity for corp pathogens could push corp distribution in an area.northern corn leaf blight develops differentially in Shaanxi along with different landform,climatic feature and farming system of Shaanxi province.Comparison of pathogenicity and Culture characters for Exserohilum turcicum isolates from different regions of Shaanxi were carried out in this study.The main results were as follows.With method of picking a single spore under microscope 38 pure isolates were obtained from 113 diseased leaf samples.Among them 13 were from north Shaanxi,21 from Guanzhong district and 4 from south Shaanxi.Disease severity was investigated when 38 Exserohilum turcicum isolates were inoculated on maize variety Pioneer 335 using spraying their spores on corn leaves.Disease severities were from 1to 9 with average of 6.53.The isolates caused disease severity above 7,taking up about 42.11%,held a major percent.According to disease severity the Exserohilum turcicum isolates were divided into Strong,moderate and weak types.The pathogenicity of the isolates shown great difference and isolates with strong pathogenicity occupied half of them.Pathogenicities of the isolates had strong characters of territoriality.Major of the isolates from north Shaanxi were with strong or moderate pathogenicity and strong type were with frequency of 61.54%.Three types were taken place in Guanzhong areas however strong type occupied themajority with frequency of 47.62%.Moderate and weak type held major role in south Shaanxi and weak type was with about 75.00%.Two isolates were chose from the three types isolates individually for biological characteristics study on mediums of PDA,PSA,OA,Czapek,SNA and WA cultured for7 days.The results indicated that there were significant differences among the six isolates in growth rate of mycelium.There were some but not significant differences in colony colour.There were no difference in shape and texture of colony.Growth rates were determined on Czapek medium with different carbon resource,replacing sucrose with glucose,sorbitol,maltose,fructose,galactose,xylose,and soluble starch under carbon equivalence principle.The results shown that isolates with different pathogenicity had not significant difference ability to use different carbon resources.At the same time,Growth rates were determined on Czapek medium with different nitrogen resource,replacing sodium nitrate with yeast extract,beef extract,peptone,glycine,calcium nitrate,ammonium chloride,ammonium nitrate and urea under nitrogen equivalence principle.The results shown that growth rate of the isolates with different pathogenicity changed significantly with different nitrogen resource.