Population Genetic Structure Of Puccinia Striiformis F.sp. Tritici In Yunnan Province

Wheat stripe (yellow) rust is one of the most important epidemics which threaten wheat securityseverely. Yunnan is a district where stripe rust breaks out constantly. It is a province where there islargest over-summering and over-wintering areas for Puccinia striiformis f. sp. tritici (Pst), and is one ofthe rare regions where the pathogen is very complex in China. Yunnan has the important characteristicsof the origin of Pst in China and the sufficient and prerequisite conditions for long distance dispersal ofthe pathogen. It’s very important to know the population genetic structure of Pst in Yunnan beforeanswering the relationship of pathogen between Yunnan and other epidemic regions, because it canreveal the origin, evolution and migration of pathogen. Study on the host population resistance andresistance genes based on the results of pathogen virulence monitoring can provide information forrational utilization of varieties and resistance genes deployment in the field. This study obtained themain results as follows:1. Survey on the time course of the stripe rust occurrence and epidemic The step by stepoccurrence, generally directed from southwest to northeast for the beginning and the peak periods of thestripe rust, revealed the direction of dispersal for wheat stripe rust is from southwest to northeast inYunnan Province. The sequential occurrence from fields rotated with dryland farming to fields rotatedwith paddy rice revealed that the primary source of the pathogen was from high altitude areas for thepathogen overwintering. The complicated subenvironment may hide the direction of the dispersal.2. Monitoring of Pst physiological races The monitoring results of Pst during the period of2008–2011years indicated that Pst population was undergoing changes from the population structure withprevailing races, such as CY32, CY33, Hy-8, Hy-6, etc., to a more balanced structure, in whichfrequencies of dominant races lowered year after year and the population became more and morecomplicated in terms of races. The development of Pst virulence in the populations calls for theadjustment of the differential hosts and the reform of the virulence analysis method. It is urgent to use aset of single gene lines or near-isogenic lines (NILs) as differentials to analyse the virulence genes andtheir frequencies of the pathogen to replace physiological races identification method.3. Development of Pst SNP primers SNP primers had been developed of Pst house-keeping genesMapk1, Cdc2and Ef-1α for the first time in the world. The primers have good polymorphism based on149isolates from5provinces. It can be used to analyses Pst population structure.4. Molecular population genetic structure of Pst Concatenated genes Mapk1, Cdc2and Ef-1α wereused to analyse the SNP of Pst populations with297isolates altogether collected in2008and2011. Theresults indicated that Pst population had rich haplotypes. Yunnan and South Gansu population had highfrequencies of shared haplotypes. The two populations had several private haplotypes, respectively.There is great genetic differentiation, lower gene flow and higher population mutation rate withinYunnan population. There was higher genetic diversity and higher recombination events in South Gansu.The ancestral haplotype was discovered in Yunnan population from the results of both years. Yunnan has more ancient and younger haplotypes, longer evolution time, higher heterogenicity and evolutionefficiency than South Gansu. Inaddition, strong gene flow existed between Yunnan and South Gansu.Besides the molecular evidence, we also analyzed the relationship of coevolution between the pathogenand its host wheat, and the migration trajectory of Pst in upper airflow during the peak period of the rustpathogen. These provide us the evidences that Pst pathogen of Yunnan can migrate to South Gansudirectly from different perspectives.5. Resistance assessment of wheat cultivars and gene postulation Adult resistance of125wheatcultivars were assessed by inoculating the main dominant races CY31, CY32, CY33and mixture ofmany races in recent years, respectively. The results indicated that there were66.4%cultivars showeddifferent degrees of resistance from immune to mid-resistance and32%cultivars showed slow-rusting.Only1.6%cultivars showed high-susceptibility. Seedlings of52commercial wheat cultivars fromYunnan were inoculated with25differential isolates of Pst from foreign and home to postulateresistance genes to yellow rust. The results indicated that resistance gene is not rich in cultivars fromYunnan. Only10probable resistance genes were characterized in these cultivars. Yr9among them hadhigh virulence frequency,25%. Genes/combinations Yr2+YrA, Yr6, Yr7, Yr8, Yr17, Yr21, Yr26andYr27, had lower frequency. Twenty-two cultivars could not been characterized in this study.