Diversity And Pathogenic Relations Research Of DsRNA In Rhizoctonia Solani

Rhizoctonia solani is widely distributed at cultivated soil and non-cultivated soil, whichis easily dissociated from infected plants and the soil. The host range of Rhizoctonia isextensive, infecting more than100crops and making them show symptom. Double-strandedRNA (dsRNA) is the genome of dsRNA viruses existed in higher plants or originates fromplasmid-like factors whose function is unknown. The reason that people’s interest in thesefactors is increasing is that dsRNA can be used as the mark of diagnosing viruses in the higherplants. Besides, the evidence that dsRNA can dominate the virulence in the plant pathogenicfungi is more and more.In the country, the research of the relationship between the diversity of dsRNA in theRhizoctonia Solani and pathogenicity is less, which is more concentrated in the anastomosisgroup identification and genetic diversity research. This study tries to explore the relationshipbetween dsRNA and Rhizoctonia solani’s pathogenicity and the diversity of Rhizoctoniasolani that comes from different host, different regions and different anastomosis group, themeans of which is to detach dsRNA from nearly100Rhizoctonia solani strains isolated fromdifferent host, different regions and different pathogenicity but same host by this laboratory.The main results are as follows:1. Culture strong virulent strains including YWK-100, YWK-196.YWK-176and weaklyvirulent strains including YWK-211, YWK-62which isolated from maize sheath blight andunder the AG1-IA on the cellophane. From the second culturing day, scrape mycelium forcontinuous7days and accommodate them in the sampling bags and be stored at-20degrees.After7days, extract dsRNA. YWK-211—the weakly virulent strain—and YWK-176—thestrong virulent strain—have dsRNA strip, and these dsRNA bands produce after the culturingfourth day. The dsRNA bands are not detached in the other strains. Experiments show thatdsRNA in the Rhizoctonia Solani do not exist in all strains, and cannot be detached in the newmycelium. Therefore, during the dsRNA detection, the tested strains should be cultured in anincubator for more than four days.2. To have conducted the dsRNA of Rhizoctonia solani diversity analysis which hasdistinct pathogenicity and is classified to Rhizoctonia solani AG1-IA that is isolated by thislaboratory. The results show that there are three Rhizoctonia solani strains which havingdsRNA fragments in the ten tested virulent strains, and there are two dsRNA fragments typesof23000bp and15000bp. Besides, among the fourteen weakly pathogenic strains, nine strainshave dsRNA fragments, and there are three dsRNA fragments types of23000bp,15000bp and 2000bp. Therefore, dsRNA exists in both virulent strains and weakly pathogenic strains ofRhizoctonia solani AG1-IA, and the presence of rate of dsRNA in the weakly pathogenicstrains is higher than that in the virulent strains. However, the type of dsRNA bands in thevirulent and weakly pathogenic strains is more consistent (Although there is a2000bp strip inthe weakly pathogenic strains, it does not exist in the virulent strains), which shows that thepresence of dsRNA has no significant correlation with the pathogenicity of Rhizoctonia solaniAG1-IA.3. Analyzing the diversity of dsRNA of strains of Rhizoctonia solani AG1-IA isolatedfrom the Northeast China and the Huang-Huai-Hai region, the results show that dsRNA existsmore commonly both in the Rhizoctonia solani AG1-IA from the Huang-Huai-Hai region andin the Rhizoctonia solani AG1-IA from the Northeast China and its presence of rate is allabove50%. There are three types of dsRNA fragments involving23000bp,15000bpand2000bp existed in the Rhizoctonia solani AG1-IA from the Huang-Huai-Hai region. Thereare four types of dsRNA fragments including23000bp,15000bp,11000bp and2000bp existedin the Rhizoctonia solani AG1-IA from the Northeast China. The dsRNA fragments whosemolecular sizes are23000bp and15000bp exist more commonly in the Huang-Huai-Hairegion than in the Northeast China, but dsRNA fragment whose molecular size is15000bpexists more commonly in the Northeast China than in the Huang-Huai-Hai region, whichshows that tency between the different regions, but each type of dsRNA fragments isdistributed between distinct regions but slightly different.4. Analyzing the diversity of dsRNA of strains of advantage pathogenic group AG1-IA,AG-3and AG-4of different Rhizoctonia diseases which are isolated from corn sheath blight,potato mole disease and cotton damping-off, the results show that the rate of dsRNA detectionand the type of dsRNA fragmenrs and its distribution differ significantly between differentanastomosis groups. The presence of rate of AG-3is highest (100%), followed by AG1-IA(about70%), the last is AG-4(about50%). AG1-IA has4types of dsRNA bands, which are23000bp,15000bp,11000bp and2000bp. AG-3has3types, which are23000bp,15000bp and2000bp. AG-4has7types, which are15000bp,6500bp,3500bp,3000bp,2100bp,2000bp and1900bp.5. Evaluating the growth and development indicators of the strains that have dsRNA andthe ones that do not have dsRNA which are under the AG1-IA and AG-4, the results show thatthe strains with dsRNA fragments have no significant difference in the rate of growth anddevelopment of the colonies with the strains which do not have dsRNA fragments.6. In order to know about the Trichoderma biocontrol of Rhizoctonia, select efficient antagonistic Trichoderma T21which is separated in the laboratory to have the indoorconfrontation experiments to the representative strains of AG1-IA, AG-3and AG-4. Theresults show that the Trichoderma T21’s inhibition of Rhizoctonia differs according to thedifferent groups of anastomosis groups, the rate of inhibition for AG-3is highest, reachingabout81%; followed by AG1-IA group strains, and the average rate of inhibition is about71.1%; the last is AG-4group strains, and the average rate of inhibition is about62%. Thisindicates that the T21for AG1-IA, AG-3and AG-4all have great biocontrol potential.