| In recent years,Northern corn leaf blight has frequently occurred in various production areas in Shanxi Province,which seriously affected the local corn production.At present,the most economical and effective way to control the northern corn leaf blight is to select resistant varieties.Since the physiological differentiation of Northern corn leaf blight pathogen is obvious,the race changes are complex,and the increase in the xx frequency of toxic race easily leads to the loss of resistance of disease-resistant varieties,it is of important scientific significance to clarify the type,distribution and diversity of pathogen for breeding of resistant varieties and effective control of the disease.In addition,the identification of variety resistance is a key step in the selection of resistant varieties,whereas the long identification cycle and large environmental impact of the current field resistance identification method has greatly affected the scientificity and accuracy of variety resistance identification.Therefore,the establishment of a simple,fast and accurate method for disease resistance identification in indoor seedling stage is a technical problem that needs to be solved urgently in disease resistance identification of maize variety.To this end,this study mainly studied the physiological races and genetic diversity of Exserohilum turcicum pathogens in Shanxi,and explored the indoor seedling resistance identification methods of maize,aiming to clarify the physiological race types,distribution and genetic polymorphism of Exserohilum turcicum in Shanxi Province,and the establishment of effective seedling resistance identification evaluation standards,provide the theoretical basis and scientific basis for breeding disease-resistant varieties,resistance identification and effective control of the northern corn leaf blight.The main findings are as follows:1.Physiological race types and distribution of Exserohilum turcicum in Shanxi ProvinceIn this study,a total of 15 physiological races,including 0,1,2,3,N,12,13,1N,2N,3N,123,12 N,13N,23 N and 123 N,was identified by the race-specific single Ht resistance gene identification host method from 185 strains of Northern corn leaf blight pathogen(Exserohilum turcicum)isolated from diseased leaves of corn collected from 32 counties and cities in Shanxi Province from 2017 to 2018.The 123 N was the dominant race in Shanxi Province,accounting for16.22%.Among them,the physiological races No.1,N and 123 N were mainly distributed in Xinzhou,accounting for 60.00%,45.83% and 46.67% of the total respectively;The physiological race No.23 N was mainly distributed in Yuncheng,accounting for 44.00% of the total.The virulence frequencies of the 185 strains against the four single Ht resistance gene Ht1,Ht2,Ht3,Ht N,and combinations of double,triple and quadruple resistance genes were 51.89%,51.35%,51.89%,71.89%,69.73%,43.24% and 16.22%,respectively.In summary,the physiological differentiation of Exserohilum turcicum in various areas of Shanxi Province is obvious,and the distribution of various races in different areas of Shanxi is quite different.The disease resistance of the variety with a single Ht resistance gene has been significantly reduced,and the disease resistance varieties that rely on these four single Ht resistance genes have been unable to effectively control the occurrence and harm of the disease.2.Optimization of ISSR-PCR amplification system and ISSR genetic diversity analysis of Exserohilum turcicum in Shanxi ProvinceIn this experiment,the ISSR-PCR amplification system and program of Exserohilum turcicum were optimized.Using the optimized amplification system and program,the PCR amplification results of 24 strains of Exserohilum turcicum from different regions of Shanxi Province using seven ISSR primers showed that a total of 89 bands were amplified with a polymorphism of 95.51 %.The genetic similarity coefficients of 24 Exserohilum turcicum ranged from 0.326 to 0.955,the average genetic similarity coefficient was 0.725,and were divided into six groups with 0.82,indicating that there are abundant genetic polymorphisms among Exserohilum turcicum in different areas of Shanxi Province.In addition,the polymorphism of the strain was related to the geographical origin and physiological differentiation of the strain,but there was no positive correlation.3.Establishment of indoor seedling resistance evaluation systemIn this experiment,the single factor analysis method was used to compare four inoculation methods.Then,the consistency analysis of resistance identification results obtained at indoor and field was used to compare and analyze three resistance evaluation indexes at the seedling stage and their classification standards.The results showed that the disease index of seedling inoculated through mushroom cake method and cotton liquid spraying method,spraying method and smearing method were 40.00,52.59,62.92 and 86.67,respectively.Among them,the disease index of spraying method was relatively high and easy to operate,which was the best method of inoculation at seedling stage.Three evaluation standards of resistance identification based on the number of disease spots,the area of disease spots and the area ratio were established.According to these evaluation standards,the results of the indoor seedling test and field test were 43.33%,60% and 73.33%,respectively.Among them,the evaluation results of the indoor seedling stage using the area ratio as the indicator of evaluation index has the best coincidence with the field test,which is the best evaluation standard of resistance evaluation at the indoor seedling stage.Therefore,the best inoculation method for resistance identification at the seedling stage is the spray method,and the best resistance evaluation index for the indoor seedling stage is the area ratio. |
