Population Structure And Genetic Diversity Of Fungi Causing Rice Seedling Blight In Heilongjiang

Rice is one of the most important and the commonest crops in the world.Heilongjiang Province is one of the main rice producing areas in Northeast China.Because of the special cold condition,the rice seedling blight which is caused by diverse pathogenic microorganisms,occurs worldwide and is the most serious disease in rice seedling stage in Northeast China.It is the premise and foundation of the disease control to make clear the species and distribution of pathogens causing rice seedling blight in Heilongjiang Province.Therefore,we collected and isolated samples from the main rice producing areas in Heilongjiang Province.To further characterize the population structure and genetic diversity of the fungi responsible for rice seedling blight and guide the field production pertinently.Diseased plants of rice seedlings were collected from10 locations of rice-producing areas in Heilongjiang Province,included Harbin,Qiqihar,Jixi,Shuangyashan,Mudanjiang,Yichun,Heihe,Jiamusi,Suihua,and Daqing.A total of 225 fungal strains were isolated from diseased rice seedlings collected from 10 various rice-producing areas.Nine pathogenic fungi were identified by morphology and molecular biology,included Fusarium oxysporum?48.0%?,F.verticillioides?11.6%?,F.tricinctum?8.0%?,F.redolens?6.7%?,F.equiseti?6.2%?,F.solani?6.2%?,R.solani?6.7%?,A.alternata?4.0%?,and C.coatesiae?2.6%?.F.oxysporum causing rice seedling blight was dominant strain in Heilongjiang province.To the best of our knowledge,this is the first report of A.alternata and C.coatesiae as causal agents causing rice seedling blight in Northeast China.After identifying the dominant strains,the pathogenicity of 74 dominant strains of F.oxysporum and their susceptivity to carbendazim,prochloraz and flupronil were determined.The results showed that most of the F.oxysporum isolates causing rice seedling blight had moderate pathogenicity.When the effective dose of carbendazim was 10?g/m L,the strains were all above medium resistance and there were no sensitive strains,indicating that the dominant pathogen populations causing rice seedling blight had developed resistance to carbendazim in Heilongjiang.And carbendazim was not suitable for the control of rice seedling blight in this area.The average EC₅₀ value of prochloraz to F.oxysporum isolates was 13.4562?g/m L;the average EC₅₀ value of flupronil was 0.3393?g/m L,which was far less than the average EC₅₀ value of prochloraz.In other words,both prochloraz and flupronil can inhibit the occurrence of rice seedling blight,but flupronil is more suitable for popularization in the area as an effective agent for the control of rice seedling blight.Simple Repeat Sequence?SSR?analysis was used to assess the genetic diversity of 74 single-spore isolates of F.oxysporum collected from 10 rice growing areas of Heilongjiang.The results show that the F.oxysporum isolates were divided into nine groups based on an SSR analysis involving 14 primer pairs,selecting from 22 SSR primers with the genetic similarity coefficient was0.79.Analysis of molecular variance?AMOVA?results revealed that there was a significant correlation between F.oxysporum population and geographical origin,between the population and pathogenicity,and between the population and susceptibility tocarbendazim?10?g/m L?.There was a great genetic differentiation among populations with different geographical origins?Fsp=0.374?in Heilongjiang province.And,that meant that different geographical origins had significant influence on population differentiation of dominant strains causing rice seedling blight.