The Profile And Pathogenic Diversity Of Rhizoctonia Isolates Associated With Maize In Some Regions Of China

Maize sheath blight is one of the major diseases in corn production.With the compact variety of a large area of corn planting, planting density significantly increased the amount of nitrogen fertilizer increased maize sheath blight in favor of the formation of the micro-climate conditions occur, coupled with the promotion of the current resistance of different varieties, dry pattern in recent years, corn against a rapid increase in disease, caused widespread concern.On sheath blight of domestic research on the rice and wheat, corn sheath blight research is lagging behind. Especially the pathogen group that caused corn sheath blight in the main corn-producing areas, differentiation of pathogenic pathogen and pathogenic mechanism were lack of systematic research. In this study, first composition of Rhizoctonia spp about maize and pathogenic types were analysed in part of eastern China's corn-producing areas of corn , virulence analysis of differentiation, and then analyze the pathogenic mechanisms of different pathogens, in order to provide a theoretical basis understanding the pathogenic role of Rhizoctonia solani ,the virulence of the strains were compared, and the relationship between virulence and enzymes related active oxygen metabolism ( SOD and CAT ) were analysised preliminary in order to provide a theoretical basis for understanding the pathogenic role of R.solani .1.Analysis of the composition of Rhizoctonia spp about maize and pathogenic types some regions of ChinaTwo hundreds and four isolates of Rhizoctonia spp. were collected from sheath and leaves of maize showing symptoms like sheath blight disease in Shandong, Anhui,Jiangsu, Hubei and Shanxi provinces. The isolates can be divided into six types of colonies and they belonged to multinucleate Rhizoctonia, binucleate Rhizoctonia and uninucleate Rhizoctonia according to the mycelium nucleates after staining with DAPI. The ratio of different types of Rhizoctonia was 97.55% (multinucleate), 1.47% (binucleate) and 0.98% (uninucleate) respectively.Characterization of anastomosis groups (AGs) was performed using sequencing of the 5.8S rDNA-ITS region. Within the multinucleate isolates, the most prevalent AG was AG1-IA (84.80%), followed by WAG-Z (5.88%), AG-4-HG-I (3.43%) and AG-5(3.43%). The binucleate Rhizoctonia isolates belonged to AG-A. The uninucleate isolates had not been identified yet and this is the first report of uninucleate Rhizoctonia from maize in China.The pathogenicity potential of the Rhizoctonia isolates collected was tested under greenhouse conditions. Isolates of WAG-Z, AG-4-HG-I, AG-5, AG-A and uninucleate Rhizoctonia were pathogenic, but only AG1-IA can cause typical symptoms of sheath blight on maize plants.2. Differentiation of virulences about AG1-IAThe main pathogen related maize sheath blight R.solani anastomosis group AG1-IA were inoculated in the maize seedling stage sheath in greenhouse with embedded method corn Nongda 108, Zhengdan 958, LU Yu 9th. Determination of the pathogenicity of the results using DPS system UPGMA cluster analysis showed that the fusion group, there was a significant differentiation of pathogenicity, and the 74 isolates can be divided into three groups.Most of the pathogenic isolates tested of 58.11% of the total number strains were remained with the medium-pathogenicity group(an average of disease index for 68.69% -54.92%), the strong(an average of disease index for 68.69% -54.92%) and weak(average condition index for the 16.18% -33.57%) pathogenicity strains were less ,respectively, 14 and 17 strains , respectively 18.92% and 22.97% of the total number.3. Analysis of genetic diversity of the Rhizoctonia solani AG1-IA based on the IGS1 length polymorphismThe isolates of Rhizoctonia solani AG1-IA caused corn sheath blight showed significant virtual pathogen. In order to understand genetic differences of different strains, ITS and IGS of 28 AG1-IA strains selected randomly were compared. The results showed that the length of ITS is not significant difference in different strains. But IGS sequence alignment analysis of the test strains showed that the length of the strain IGS1 were significant differences (from 766bp to 826bp).Sequence analysis revealed that IGS1 sequence of the strains were also significant changes. The phylogenetic tree about the sequence of IGS1 was establish using MEGA 3.1 and we found that the test strains with IGS1 was divide into two cluster groups . The two Cluster groups were analysised,found that no apparent relationship were existed between IGS1 and distribution.4. The preliminary analysis on enzymes activity related to active oxygen of R. solani AG1-IAThe enzymes related to scavenge active oxygen of pathogeny were one of the relevant nosogenesis factors.In order to understand the relationship between these enzymes and pathogenic fungi the strong pathogenic strain LY1-3-1 and the weak strain NJ005-1 were choosed, three areas were studied. First of all, the capacity of resistant to reactive oxygen species were compared, we found that the growth of strong pathogenic strain LY1-3-1was normal ,but the weak was inhibited in the 0.4mM concentration of hydrogen peroxide. Second, CAT and SOD activity with the two strains were analysised ,found that CAT the CAT activity of LY1-3-1 increased significantly in high concentration H2O2 (0.8mM), greatest activity was 94.27U / g; while the activity of NJ005-1 increased significantly at a relatively low concentration (0.6mM), and the largest was 82.99U / g, while concentration of H2O2 was 0.8mM, the CAT activity had dropped to 42.98 U / g; SOD activity compared found little change in activity of two strains, but the SOD activity of the strong strain had been higher than the weak strain. Third, CAT and SOD activity after H2O2-induced were compared, found that SOD and CAT activity for the first time increased then decreased dealed with 0.4mM hydrogen peroxide, but SOD and CAT activity of strong pathogenic strains increased more rapidly.