| The South China is the main rice planting area in China and also a common area for various rice diseases,posing a threat to the safe production of rice.It is of great significance to clarify the main pathogenic types of the main epidemic strains of Xoo and the disease resistance of rice varieties,as well as the main resistance/susceptibility genes carried by the rice,in guiding the selection and layout of rice varieties in cultivation zoning,gene combinations in breeding of resistant and transformation of rice varieties.In this study Xoo strains were isolated and identified from rice bacterial leaf blight fields in 14 cities of Guangxi in recent year.And the pathogenicity types of Xoo strains were identified while genetic diversity was studied.The genetic features of Xoo isolated from Guangxi were analyzed by sequencing the genomes of representative isolates.Then the resistance of 239 high-quality rice varieties to Xoo was evaluated by the main pathogenic strain GXO2026 and the standard Xoo strain PXO99~A.Finally,some commonly used bactericides in production were used for Xoo resistance analysis.The main results are as follows:1.A total of 84 Xoo epidemic strains were isolated and identified from bacterial leaf blight fields in 14 cities of Guangxi since 2019 to 2022.Physiological and biochemical phenotypic detection showed that most of the isolated strains were basically consistent with the standard Xoo strain PXO99~A.Xoo strains showed diversity in the same detection and the same strain was classified as different levels in different phenotypic detection.2.The Guangxi isolates were identified as type I,IV,IX and the new pathogenic type SSRSR by 5 Chinese identification varieties(Jingang 30,Java14,Nanjing 15,Tetep,and IR26)with the type IX being the dominant pathogenic type in Guangxi accounting for 77.78%.The IRBB2,IRBB3,IRBB5,IRBB13,IRBB14,and IR24 which were selected from near-isogenic lines identified the Guangxi isolates as R1 and R8 physiological races with R8 being the dominant race in Guangxi,accounting for 97.22%.The result showed that most of the isolated Xoo of Guangxi were highly pathogenic.It was found that IRBB5,IRBB7 and CBB23 also showed good resistance to Guangxi Xoo of type IV and type IX.3.An analysis of the genetic diversity of Xoo strains reveals that the genetic diversity of the isolates from Guangxi is rich.The results indicated the rich genetic diversity of Xoo of Guangxi.The clustering analysis of IS-PCR showd that cluster 2 and cluster 3 were the dominant clusters of Guangxi Xoo strains.The RFLP analysis showed that the dominant cluster was cluster one indicating that the dominant clusters revealed by the two methods were composed of similar Xoo isolates.The tal gene analysis conducted by RFLP showed that there were 6 molecular types and molecular type 1 and type 4 carry the highest number of tal bands.The strains in molecular type 1 all belonged to the dominant cluster.4.The whole genome sequencing of the representative strains of Xoo in Guangxi indicates that the Guangxi Xoo strains belongs to the V branch of the Xoo Asian lineage and is closely related to some Philippine strains,as well as strains from other southern China provinces such as Guangdong and Hainan.Other strains from South China were closely related to each other.Several representative strains of Guangxi Xoo sequencing are highly consistent in the genome common structure and genetic content,and the main pathogenic genes are more conservative.Genomic analysis shows that the representative Xoo GXO2026 belongs to the main pathogenic type IX was used for disease resistance detection has a comprehensive pathogenic gene system containing a strain special tal gene and the encoding product belongs to a new TALE.The virulence factor genome of the low virulence Xoo GXO2029 is not significantly different from other Xoo strains but carries a plasmid.5.The pathogenicity of the international standard Xoo PXO99~A and the Guangxi Xoo GXO2026 infected the main cultivated varieties and high-quality germplasm rice in Guangxi were compared.Among the 239 rice materialsm,most of them showed moderate resistant to moderate susceptible to PXO99~A but were high susceptible to GXO2026.In resistance gene test of the rice,the detection rates of Xa1,Xa3 and Xa4were highly reaching over 80%,Xa10 and Xa23 were not detected while xa5 and xa13 were mostly detected as susceptible bands.The chip hybridization results were basically consistent with PCR results.6.The bactericide tolerance of Xoo epidemic strains in Guangxi was detected by the plate method.No strains that have developed super resistance to existing bactericides were found.20%zinc thiazole,20%thiediazole copper and 20%thiamethoxazole copper which were commonly used for the prevention and control of bacterial leaf blight showed unremarkable antibacterial activity of indoor experiments.3%benziothiazolinone has a relatively uniform effect on representative strains of Xoo at different concentrations with a lethal concentration of 1 mg/L that far lower than the recommended concentration.In summary,this study isolated and identified the Xoo epidemic strains from BB field in Guangxi in recent years.The main pathogenic type of Guangxi Xoo epidemic strains was identified as type IX and R8,the main genes of Guangxi Xoo are conserved and regional in genomic feature and have genetic diversity in physiological,biochemical phenotype and molecular typing through pathogenic type analysis,molecular type analysis and whole genome analysis.In addition,no high resistant varieties to the representative strain GXO2026 were found in 239 high-quality rice varieties.Meanwhile,the approved rice varieties have a disease resistance level of susceptible to high susceptible to GXO2026.Fortunately,no Xoo strains that have obvious resistance to bactericides have been found in this study.The indoor bactericidal effect of 3%benziothiazolinone is significant batter than the current leading agent for the prevention and control of bacterial leaf blight.The results of this study can provide a basis and reference for the comprehensive control and disease-resistant breeding of rice bacterial blight in Guangxi. |
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