Identification And Genetic Diversity Analysis Of Corn Leaf Spot In Shanxi Province

Corn leaf spot is one of the important factors affecting corn production.With the change of corn planting methods and varieties,the types,occurrence laws and damage degree of corn leaf spot in different regions have changed.In this experiment,the species,distribution of pathogens and the genetic diversity among pathogens in different regions of Shanxi Province were analyzed,and the disease resistance evaluation of corn varieties at seedling stage was carried out.This experiment provides a theoretical basis for clarifying the species of corn leaf spot and the effective prevention and control of this kind of diseases in Shanxi Province.In addition,it also has important theoretical and practical significance for the breeding of corn resistant varieties in Shanxi province.1.Type and distribution of corn leaf spot pathogens in Shanxi ProvinceFrom 2017 to 2018,diseased leaf with corn leaf spot were collected from 36 counties and cities in Shanxi Province.After isolation and purification,a total of six pathogens were obtained,namely Exserohilum turcica,Bipolaris zeicola,Bipolaris maydis,Exserohilum rostratum,Bipolaris zeae,and Curvularia lunata.Among them,corn northern leaf blight are distributed in all parts of Shanxi,and the other five pathogens are only distributed in some areas.For the first time,Exserohilum rostratum was found to be the pathogen of corn leaf spot in China.2.ISSR analysis of maize leaf spot pathogen in ShanxiThe genetic diversity of maize leaf spot pathogens isolated from different corn varieties in different regions of Shanxi Province was analyzed by inter-simple sequence repeat(ISSR)labeling technique.A total of 223 bands were amplified by using 17 polymorphic primers,of which 218 were polymorphic bands,and the polymorphic rate was 97.75 %.The genetic similarity coefficient between the tested strains ranged from 0.333 to 1.00,and the average genetic similarity coefficient was 0.699.The genetic similarity coefficient between different strains in the specie is greater than the genetic similarity coefficient between species.When the genetic distance was 0.71,48 strains were divided into 6 ISSR groups,which belonged to 6 different pathogens.When the genetic distance was 0.823,25 strains of Bipolaris zeicola were divided into 5 BGs subgroups.The results of genetic diversity analysis indicated that there were obvious genetic differentiation among the interspecific and intraspecific of corn leaf spot pathogens in Shanxi Province.The division of ISSR group of pathogens was related to the classification of corn leaf spot,and there was no correlation with the geographical origin of the strains.3.Evaluation of resistance to early-stage and late-maturing corn varieties in Shanxi Province to corn leaf spot caused by Bipolaris zeicola.A total of 100 varieties of early,middle and late mature corn varieties in Shanxi Province were selected for the seedling disease resistance test of round spot disease.The results showed that there were 8 high-resistance varieties,accounting for 8.0% of the tested varieties;7 of the medium resistant varieties,accounting for 7.0% of the tested varieties;68 resistant varieties,accounting for 68.0% of the tested varieties;13 of sensible variety,accounting for 13% of the tested varieties;4 high-sensitivity varieties,accounting for 4.0% of the tested varieties,respectively M3,M5,M12,M18,they are mid late-maturing varieties.In the absence of immune varieties,the incidence of mid-late maturing and late maturing varieties was higher than that of early maturing varieties during the survey.