Abstract: Rust fungus of Melampsora larici-populina (abbr. MLP) is a great enemy of poplar industry in China, and it threatened short rotation forest seriously, including poplars of Sect. Tacamachacae, and Sect. Aigerios, and their hybrids. [Objective]To understand the genetics of avirulence genes in their family, and to detect the phylogenic relationship of avirulence gene sequences between Chinese MLP and the other races in European and USA.[Method] Population of F₁ aecia of MLP was harvested by cross-fertilization with spermogonia of physiologic race 2 (MLP₂) collected from Houzhengzi (in which, isolate HZ3542 as a male maternal,incompatible with Populus purdomii) and Huoditang (in which, isolate HF2369 as a female maternal, compatible with purdomii poplar) in Qinling Mountain, and segregation pattern of avirulence genes in MLP₂ family as detected and inoculating aciospores and urediospores on P.purdomii leaves in vitro. Primers were designed and selected by referring to AvrL5671-8;9-16;17-26;27-37;38-45;46-56;57-67;68-74;75-81;82-88;89-94;95-105;106-112;113-123;124-130;131-137;138-144;145-152;153-183;160-167;168-176;177-183;184-191;192-197;198-203;204-211;212-224(accession: AAS66952) in Melampsora lini. Avirulence genes were amplified by PCR homogenized technology and then sequenced. All putative sequences were revised and aligned with other avirulence genes in the related public molecular information data, and a maximum likehood (abbr.,ML) phylogeny tree was then constructed. [Result] Segregation of avirulence genes in MLP₂ was coincident to the Mendel's law, and showed a single dominant heterozygous phenotype (Aa) in the incompatible isolate, and homozygote phenotype (aa) in the compatible isolate. Their F₁ population in both aeciospores (P=0.01) and urediospores (P=0.05) segregated by following 1∶1 with dominant to recessive phenotype. The certification for dominant avr phenotype is revised and confirmed by combination with quality traits of necrosis and chlorosis, quantitative trait loci (QTLs) including latent days, both diameter size and density of uredinia. PCR productions were also used to test and confirm avirulence phenotype under annealing by selected primer pair AvrPr1 (5'-TAATCCTCGTTGACATCAGTC-3',5'-AAGCTTGAGAGCTCCGCTC-3'). ML phylogeny tree differentiated two groups from all tested sequences at a low bootstrap data. Among them, all Melampsora sequences were grouped together with a relatively high homology, and five of six AvrL567 sequences from China MLP₂ isolates grouped into a sub-clad together with two Canada MLP sequences, and another one was grouped into another sub-clad with French MLP, USA M. lini, etc.[Conclusion] Incompatible race 2 of MLP in China was a phenotype of Aa, and its avirulence gene sequences showed a high homology with that of tested Canada isolates.

Key words: Melampsora larici-populina, avirulence gene, segregation law, phylogeny tree