Population Genetics Of Rice Sheath Blight And Its Resistance To Several Commonly Used Pesticides

Sheath blight,caused by Rhizoctonia solani Kuhn,is one of the rice’s "three major diseases" worldwide.The disease will cause rice to fail to heading,produce more scurf grain and the low yield.Changes of genetic structure and resistance to fungicides of the pathogen of rice sheath blight are positively associated with the occurrence and the field’s control of the disease.In order to analyze the population genetic structure of R.solani,we investigated the current status of its resistance to common fungicide productions,and these will provide theoretical basis for the prevention and control of the disease.In this paper,10 pairs of SSR markers were used to analyze the genetic structure of 293 R.solani isolates collected from 13 cities of Jiangsu province and 5 regions(Central,South,North,East and Southwest)of China.The resistance of these strains to thiadiazole,tebuconazole,propiconazole and Jinggangmycin were determined.The main conclusions were as follows:1.A total of 293 strains were isolated from the rice sheath blight samples of Jiangsu province and other regions of China,of which 265 from Jiangsu province and 28 from other provinces.The genetic diversity of R,solani populations were analyzed using 10 pairs of SSR primers(TC01,TC02,TC03,TC05,TC06,TC07,TC10,TC11,TC12 and TC13).The results showed that 74 bands could be amplified by 10 pairs of primers,while the amplified product of TC02 primer pair did not be detected polymorphic bands.On average,8.2 bands were amplified by each pair of primers.The most abundant genetic diversity of R.solani population was found in central Jiangsu,and the Nei gene diversity index and Shannon diversity index were the highest with the value 0.1932 and 0.2928 respectively.A total of 78 genotypes were detected in the 293 strains,of which central Jiangsu had the most genotypes,possessed 26 genotypes.DA was the dominant genotype of R.solani populations in central Jiangsu.Among the national strains,the most genotypes were detected in east China with 23 genotypes and the least in southwest China,only 9 genotypes were detected.The genetic diversity of the strain populations in 13 cities of Jiangsu province was significantly different.The strains could be divided into three categories.However,genetic diversity of strains from northern Jiangsu,central Jiangsu,and southern had no consistency with the geography.The strains from 9 provinces crosss the country could be divided into five categories.The strains from the three eastern provinces of Shandong,Jiangsu,and Zhejiang are completely clustered.Although other several provinces geographically closed,but the genetic diversity of strains had greatly difference,especially in Hunan and Hubei.Although both belong to central China,the genetic distance of strains in the two provinces were genetically distant.This result also shows that there is no correlation between the genetic diversity of the strains and its geographical location.2.The resistance of 39 R.solani isolates from Jiangsu province to thiadiazole,tebuconazole,propiconazole and validamycin A was determined by using cross crossing method.The results showed that the sensitivity of different strains to thiadiazole,tebuconazole and propiconazole was quite different,and the EC50 values were 3.83,16.16 and 7.46 times difference,respectively.Based on the EC50 value of the tested strains,the sensitive baselines for thielafuran,tebuconazole and propiconazole were 0.1566μg/mL,1.3393μg/mL and 0.933μg/mL,respectively.Using a 5-fold sensitivity baseline value to determine the frequency of resistance to thiadiazole,tebuconazole and propiconazole in R.solani,the results showed that the vast majority of strains against thiadiazole,tebuconazole and propiconazole have developed drug resistance.The frequency of resistance of some strains even reaches 100%.The frequency of resistance to the thifluzamide was lowest in Yangzhou region,which was 29.17%.The frequency of resistance to thifluzamide in the seven regions of Nanjing,Huaian,Lianyungang,Suqian,Xuzhou,Nantong and Taizhou reached up to 100%.The frequency of resistance to tebuconazole in all regions was greater than 50%,and the frequency of resistance in the eight regions of Nanjing,Yancheng,Huaian,Lianyungang,Suqian,Zhenjiang,Nantong,and Taizhou also reached 100%.The lowest frequency of resistance to propiconazole in all regions reached 62.5%,and the frequency of resistance to propiconazole in the three regions of Lianyungang,Zhenjiang and Taizhou reached 100%.This showed that in recent years,with vast and widespread use of these three fungicides in Jiangsu province,a large range of R.solani isolates have produced resistance.3.To clarify the relationship between SSR markers genetic diversity,growth rate and drug resistance of R.solani.The strains types,strains growth rate,and strains susceptibility to tebuconazole were analyzed through cluster analysis respectively.Cluster analysis showed that there was no correlation between the SSR markers and the strains growth rate and sensitivity to tebuconazole.There was no significant correlation between the growth rate of the strains and the resistance of the tebuconazole.In this study,the genetic diversity of R.solani isolates from Jiangsu province and China was analyzed by using SSR marker technology.The resistance status of R.solani in Jiangsu province to several common fungicides was elucidated.The relationship between the genetic diversity of strains and the growth rate of strains and the resistance to tebuconazole had illuminated too.These results provide a theoretical basis for the scientific control of rice R.solani in production.