The Analysis Of Population Genetic Structure Of Effector Pi06087 And Pi02860 And The Adaptability Of Temperature Of Phytophthora Infestans

Late blight caused by Phytophthora infestans is a devastating disease of potato,causing serious economic losses to the potato production industry.Breeding and planting of resistant varieties is the most cost-effective and efficient control measure for potato late blight.However,due to the rapid evolution of P.infestans,many highly resistant varieties was overcome in a short period of time.During the transformation processes of potato resistance towards susceptibility,the virulent mutation of the effector gene of P.infestans played a very important role.Therefore,understanding the population genetic structure and mutation mechanisms of P.infestans effector genes in fields is of great significance for the layout of fieldresistant varieties as well as selecting of resistant potato varieties.To this end,the first part of this thesis analyzed the population genetic structure and mutation mechanisms of the two core effectors Pi02860 and Pi06087,which provided the scientific basis for the layout and breeding of potato resistant varieties.In addition,the frequent occurrence of extreme weather had a huge effect on the host-plant pathogen interaction.In order to understand the effect of extreme temperature on the interaction between P.infestans and potato,the second part of this thesis focused on the influence of temperature on P.infestans pathogenicity.Through these two studies,we hope to clarify the genetic diversity of Pi02860 and Pi06087 effectors and the temperature adaptability of P.infestans,and provide theoretical basis for ecological sustainable control of potato late blight in the future climatic condition.The findings were as follows:The study conducted on 510 strains from the four major potato cultivation areas in China showed that the types of mutation found on effectors Pi02860 and Pi06087 were point mutation.The mutation sites of effector Pi02860 were mainly concentrated at the 30 th,143th,and 295 th sites,while the mutation sites of effector Pi06087 were not concentrated and distributed throughout the sequence.Both the two effectors Pi02860 and Pi06087 had relatively lower genetic diversity.The haplotype diversity of effector Pi02860 was 0.74844,and the nucleotide diversity was 0.00307.Furthermore,the haplotype diversity and nucleotide diversity of the effector Pi06087 were 0.55904 and 0.00188,respectively.The genetic variation of the two effectors in the haplotype network diagram was relatively simple,and the haplotype was generated by one or two step mutations.Moreover,the analysis of selective stress showed that only effector Pi06087 in the first northern production area and southern winter production area was negatively selected.Genetic differentiation between the two effectors showed that Pi02860 was higher than Pi06087,and their genetic differentiation in the different farming areas were mainly come from individual strains.The above results showed that the genetic diversity of the two effectors were low.Thus,we concluded this might because there was low selection pressure due to no corresponding large-scale planting of resistant varieties grown in fields yet.Based on the results of the first part of this study,we selected 55 strains with the same Pi02860 and Pi06087 haplotypes from the four cultivation areas,and conducted a pathogenicity experiment under five temperatures 13 °C,16 °C,19 °C,22 °C,and 25 °C.The results showed significant differences in the incubation period of the strains in different cultivation areas at different temperatures(P < 0.01),likewise,the incidence rate of different farming areas differs significantly.The incidence rate at 13 °C was 81 %,while at 22 °C and 25 °C were both 100 %.There was a clear negative correlation between temperature and incubation period(P < 0.01).Moreover,there was a significant positive correlation between the experimental temperatures and lesion area(P < 0.01).At the temperature of 13 °C and 16 °C,the pathogenic area of the strains in the first northern production area was higher than the other three areas.The pathogenic area of the strains in the southern winter production area was higher than the other three farming areas at the experimental temperatures of 22 °C and 25 °C this showed that temperature adaptability existed in pathogenicity of P.infestans.