| Wheat sharp eyespot,also known as wheat pointy eye spot(spot)disease,is a soilborne fungal disease caused by Rhizoctonia cerealis(Rc)and Rhizoctonia solani(Rs),which occurs widely in China.With the climate warming,straw return,and the large-scale planting of susceptible varieties,wheat sharp eyespot has become more and more serious in China in recent years,rapidly spreading from south to north,and now it has become one of the five major diseases threatening wheat production in Huang-Huai wheat region.To widely understand China’s wheat sharp eyespot composition,distribution,the virulence of the main pathogenic bacteria,and on China’s huanghuai wheat sharp eyespot resistant germplasm resources appraisal,selection,we successively identified the wheat sharp eyespot by using the main pathogenic bacteria of 242 strains sharp eyespot from Henan,Shandong,Anhui and other 12 provinces(autonomous regions and municipalities directly under the central government)in different years,the main results were as follows:1.A total of 335 isolates related to wheat sharp eyespot were successfully isolated and purified from 1683 stem isolates,of which 321 ITS sequences were obtained.Blast analysis showed that Rc accounted 83.2% of the 321 sharp eyespot pathogens,followed by Fusarium pseudograminearu(Fpg)and Alternaria alternate(Aa),which accounted 3.4% and 2.5%,respectively.There were 17 other types of pathogens,their proportions were lower than 1%.The identification results of the above isolates also showed that almost all isolates of Rc type could produce obvious moire spots in wheat stalks.In conclusion,it can be seen that Rc is the main pathogen of wheat sharp eyespot in China.2.321 of separation to sharp eyespot related isolates of pathogenicity identification show that different types of isolates on wheat seedling infection phenotypic difference is bigger,the Rc types can produce typical grain dry spots,and other types of pathogenic bacteria although can cause varying degrees of leaf sheath the symptom such as Browning,stem rot,but not observed significant moire shape grain dry spots.The pathogenicity of all isolates was analyzed by using the pathogenicity identification method of wheat sharp eyespot at seedling stage established by our group.The results showed that the highest pathogenicity isolates were(Fusarium graminearum,Fg),and the least pathogenicity isolates were Chaetomium cochliodes(Cco),and most of Rc isolates were at the medium pathogenicity level.In general,the pathogenicity of most Rc isolates were tested by moderate(mean disease index was 30.1~59.9),accounting for 89.1% of the total isolates.16 isolates with high pathogenicity and 13 isolates with weak pathogenicity were found to have a mean pathogenicity of more than 60,a mean pathogenicity of less than 30.There were significant differences in the pathogenicity of Rc isolates from different provinces.The average pathogenicity of Rc isolates from Shanxi Province was the highest,and the average pathogenicity of Rc isolates from Hubei Province was the weakest.In terms of pathogenicity of Rc isolates from different years,the proportion of high pathogenicity types of Rc isolates obtained in 2019 and2020 increased.Comparison of the combined pathogenicity of isolated Rc BLAST results showed that QD1-2-4 isolates and D32 isolates showed relatively strong pathogenicity,and D32 was also the highest proportion of Rc pathogen isolated in our study.3.The ITS sequences of 266 Rc isolates showed that 167 isolates had a single ITS sequence,while the other 100 isolates had several different ITS sequences.Polymorphism analysis of all ITS sequences with single sequence types showed that there were 28 polymorphisms in all ITS sequences,including 13 polymorphisms in ITS1 region and 15 polymorphisms in ITS2 region.In terms of variation types,the polymorphism in ITS1 region was dominated by T type mutations,while the polymorphism in ITS2 was dominated by T type and A type mutations.In addition,the phylogenetic tree of Rc isolates was constructed by using the single ITS sequences obtained above.The results showed that the isolates could be divided into two branches at the similarity level,most of which were clustered in AG-D Ⅰ(93.3%),and a few clustered in the vicinity of AG-D Ⅲ(6.7%).In addition,an isolate from Shaanxi was different from other isolates,but it was closely related to Rc isolate from Japan.Strains from all the tested areas intersected with each other and showed rich genetic diversity.4.The results showed that most of the strains were moderately to highly susceptible to R0301,indicating that the high virulent strains isolated in this study were generally highly pathogenic to wheat materials in the Huang-Huai wheat area.In addition,three resistant materials with moderate resistance to sharp eyespot were identified,which were Yanfeng 712(RDI 0.6),Xinmai 68(RDI 0.6)and Yongfengnong 2(RDI 0.6).These materials can be used to construct cross progeny of resistance to wheat sharp eyespot and lay a foundation for resistance breeding of wheat sharp eyespot.5.In addition,in order to facilitate the early identification of sharp eyespot and stem rot,so as to facilitate the effective control of the two main soil-borne wheat diseases.In this study,three specific molecular markers were developed based on the different sequences of ITS regions of Rc,Rs and three Fusarium isolates.The results showed that Rc-F/R marker could amplify bands in Rc,but no bands in Rs and four Fusarium isolates.Rs-F/R markers can amplify bands in Rs,but no bands in Rc.FCR-F/R marker could only amplify bands in Fusarium,but no bands in Rc and Rs.These markers can be used for the early identification and control of these two wheat diseases. |
