Biological Characteristics And Detection Of Rhizoctonia Root Rot On Cruciferous Vegetables

Cruciferous vegetables are one of the main vegetable plants that people consumed and demanded in daily life.Because of the short growth period,dense crops and annual production,leading to serious continuous cropping obstacles.In recent years,Rhizoctonia root rot have become one of the important factors restricting production,which lead to the decreased of the crop yield and quality,and even more no yields.At present,there are no registered fungicides to control Rhizoctonia root rot of cruciferous vegetables,which makes more difficult to control this disease in the field in China.In this thesis,pathogenic biological characteristics,detection technology and control drugs on Rhizoctonia root rot were studied based on morphological identification,pathogenicity determination and molecular biology methods.The main results were as follows:1.The species of Rhizoctonia spp.on cruciferous vegetables in China,including four anastomosis groups have been identified and they existed differences in biological characteristics.In this study,a total of 278 Rhizoctonia spp.strains were isolated and identified through the investigation and collection of diseased plants from sixteen provinces and thirty-one regions including Hebei,Tianjin,Beijing,Inner Mongolia,Gansu,Jiangxi,Shanxi and so on.Nine hosts included such as Chinese cabbage,rape,mustard,radish,and cabbage.Four anastomosis groups were identified,including AG-2-1,AG-1-IB,AG-4HGII and AG-A by morphological identification,pathogenicity tests and sequence analysis of ITS and TEF-1?.Among the four anastomosis groups,AG-2-1 had the highest separation frequency,which was 62%.2.A multiplex real-time PCR detection system for AG-2-1,AG-1-IB and AG-4HGII of R.solani was built.Based on the comparative analysis of the TEF-1?and LSU sequences,specific primers and probes including Rhs2F/R/P,Rhs1BF/R/P and Rhs4GF/R/P were designed.The recombinant standard plasmids A,B and H carrying the target gene were constructed.A standard curve by plasmid gradient dilution was established and optimized,and the detection limit reached 10^-7 ng/?L.On the second day after inoculation,R.solani could be detected.On the third day after inoculation,the roots began to exhibit symptoms,and the maximum detection amount of R.solani were determinded on the 6th day.R.solani with fluorescence signal could be detected in diseased Chinese cabbage and rhizosphere soils in fields,respectively.3.Iprodione and Dimetachlone with high efficacy against Rhizoctonia root rot was screened.The results of bioassay showed that the fourteen kinds of fungicides could inhibit the mycelial growth of Rhizoctonia spp.in varying degrees.The inhibitory effect of 50%Iprodione WP and 40%Dimetachlone WP were all strong,and the EC₅₀ value was 0.24?g/mL and 5.61?g/mL,respectively.The antifungal effect of 25%Azoxystrobin SC was the most worst,and its EC₅₀ value was 1532.81?g/mL.In addition,the seedling control assays were also carried out in greenhouse,and the results showed that 50%Iprodione WP and 40%Dimetachlone WP had the higher control efficacy,reaching 93.10%and 93.97%,and that of 30%Hymexazol AS was the worst,with the control effect of 27.59%.Other fungicides had also played a certain role in controling Rhizoctonia root rot.