| Melampsora larici-populina Kleb. is one of the important pathogens occurred in the Sect.Tacamachacae, Sect. Aigerios and their hybrids poplars in the world. There has distinguished pathogenic division found within species, and the genetic background is complex. 5 races had been reported in European and North America. To understand the occurrence condition and the genetic background of the pathogen in China, this dissertation focused on studying the rust fungus from 13 areas in China and different years in the way of pathogenic determination, SSR molecular markers, and achieved results bellowing:(1) Pathogenic determination: Through the respective reaction distinction test on host distinction as well as observation of incubation period and sporulation to further confirm physiological race differentiation of Melampsora larici-populina Kleb. in our country. The result displayed 14 belonged to 4 physiological races respectively: Yl071, Wh081, Wh083 and Yl2008 went to No.1 physiological race, CMLP1; Yl073 and Phl081 fell into No.2 physiological race, CMLP2; Gd2008, Gf2008, Phl083 and Hh2008 into No.4 physiological race, CMLP4; By2008, Hd2008, Th2008 and Ts2008 to No.5 physiologic-al race, CMLP5.(2) This dissertation had improved DNA extraction method and silver-staining method. We used magnet to substitute punching a hole to take out steel ball. This method saved time, but also made operation more convenient. The more important was that this method avoid DNA losses. Our silver-staining method which emphasized on specific operation and time controling. The result showed this method is high performance, sensitivity, reproducibility and feasibility.(3) DNA polymorphisms analysis: The genetic diversity of 91 isolates of Melampsora larici-popolina(MLP), from different regions and different years of eight provinces in China, were analysed with SSR molecular markers. The results showed that 62 alleles of all isolates were detected at SSR five loci, of which, MLP12 allele to reach 19. The average observed number of alleles (Na) was 12.400,effective number of alleles (Ne) ranged from 5.4230 to 9.8196, with an average of 7.0464. The polymorphism information content (PIC) of 5 loci changed in the range of 0.64 to 0.89, with an average of 0.79.(4) The genetic diversity analysis show that average observed heterozygosity (Ho), average expected heterozygosity (He) and Shannon's information index (I) of all strains assayed were 0.3588, 0.8564 and 2.1206,respectively. The ratio of gene diversities of heterozygosities (Fst) ranged between 0.2226 and 0.3866, with an average of 0.3424, and the gene flow (Nm) was 0.4800. This revealed that the genetic diversity of MLP in China was very rich, and appeared mainly in populations internally (67.65%), but also existed a certain degree of genetic differentiation between populations of different regions, which could be initially divided into four taxa based Nei's genetic distance. These SSR pattern showed high degree polymorphisms, and it had more to do with geographical origins. The host selectivity plays a very important role. This is not consistent with previous conclutions.The study using the Melampsora larici-poplina rust physiological races, provide a reliable and new division means. It provided more effectively and reliable theoretical basis for the follow-up studies of the strain and treatment of the disease in future.
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