| With the implementation of Chinese potato staple food strategy,Northern region in China as the main potato producing area has been confronted with great opportunities and challenges.Potato late blight caused by Phytophthora infestans which occurred frequently was particularly defended in this area.The population phenotype of the pathogen and the genetic diversity closely related to the incidence and epidemic of this disease.Therefore,this experiment aims to provide some reference for the prevention and control,as well as scientific breeding cultivars for potato late blight.The main contents of this experiment are as follows:(1)Collecting,isolating and purifying P.infestans strains in five northern provinces(Hebei,Jilin,Liaoning,Heilongjiang and Inner Mongolia)in 2017,and identifying the type,composition and virulence of physiological races,and deteriminating the distribution and dynamic changes of super physiological race,especially;(2)To make the 11 potato differential hosts grow as the same speed for identifying the P.infestans physiological races timely and exactly,the culture conditions of the host tissue culture seedlings were optimized by changing the content of some components in MS medium and selecting different transferring time in this experiment;(3)To know the genetic differences in DNA level among P.infestans isolates collected from northern provinces in 2016 and 2017,the polymorphisms of 197 isolates were detected by two loci,Pi4B and Pi4G of SSR primers,and nominated based on SSR molecular marker;(4)To detect the distribution of mitochondrial DNA haplotypes(MDH)of P.infestans and the relationship between different MDH and their biological characteristics,197 isolates of P.infestans collected from northern provinces in 2016 and 2017 were detected by PCR-RFLP,the relationship between biological characteristics and growth,sporulation quantity and pathogenicity of four MDH of P.infestans strains were elucidated at different temperatures and potato detached leaves,respectively.The main results are as follows in this experiment:1.The number of diseased leaves was 137,the number of isolates was 82,and the total number of strains identified was 82.type of P.infestans physiological racefrom 5 provinces in north China in 2017 was 35.The dominant physiological race was super physiological race(R1.2.3.4.5.6.7.8.9.10.11),and the frequency was 35.37%.The super physiological race was found in 5 provinces.2.The virulence genes(Vir1-Vir11)in P.infestans corresponding to 11 known and major resistance genes in potato existed in strains collected from the five northern provinces.The resistance genes R7,R9,R10,and R11 were overcome by 80%to 88%of the isolated test strains.R1 was overcome by more than 90%of isolates.3.The modified host medium after optimization was:when the amount of agar in MS medium increased from 7g/L to 10g/L,promoted markedly rooting and growing of the plantlets,at the same time,the contamination of 11 differential hosts could be significantly reduced,the pollution rate dropped from 30.56%to 13.89%;that of sucrose decreased from30g/L to 26g/L were appropriate for growth of 7 differential hosts,while the optimal sucrose contents for R1 and R11 hosts which grow slowly were 28g/L and 27g/L,respectively,and that for R3 and R5 hosts which grow quickly was 24 g/L and 23g/L,respectively.4.SSR genotypes were determined for 197 strains of P.infestans in 2016 and 2017.The results showed that 10 allele genes and 14 SSR genotypes were identified.A total of 14 kinds of SSR genotypes were A-03,A-10,B-01,D-03,E-01,F-01,F-02,F-06,G-02,G-03,G-07,K-01,L-01,and N-01,respectively.Of which,A-10 and N-01 were novel genotypes that had not reported in this regions,and F-06 was the dominant genotype,accounting for 24.3%in the measure isolates.5.Through cluster analysis on the results of SSR amplification,there was no relation between cluster and geographical origin.Also,through population genetic diversity analysis by using POPGENE32 software,genetic difference was minimal among all tested P.infestans populations.And from 2016 to 2017,the genetic diversity of the P.infestans population is increasing.6.The species phenotype is controlled by the genotype,so the relationship between the SSR genotype and the physiological race of Phytophthora infestans was studied,and it was clear that there was no corresponding relationship between them.7.P.infestans mt DNA haplotypes in five northern provinces were detected.The results showed that there wereⅡa、Ⅱb andⅠa haplotype,in which Ⅱa was the obvious advantages in two years,with an average frequency of 64.2%.butⅠb was not found in both years.8.The optimal growth temperature for the four MDH strains was 20℃.The Ⅱ a strains had the fastest growth rate(6.43mm/d)and the maximum sporulation,and average sporulation quantity was 3.35×10~5 cells/m L,while the I b had a slowest growth rate(3.41mm/d)and the minimum sporulation,average sporulation quantity was 0.64×10~5 cells/m L.Different mitochondrial haplotype strains could result in lesions on the potato detached leaves,but their pathogenic ability had difference.The virulence from strong to weak was Ⅱa,Ⅱb,Ⅰa,Ⅰb. |
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