Identification, Characteristics And Population Genetics Analysis Of Pathogens Causing Poplar Anthracnose In The Beijing Region

Poplar anthracnose occurred seriously in Beijing region where poplars as street or scattered trees were infected extensively. Colletotrichum gloeosporioides has been reported as the pathogen to poplar. But recent researches revealed that on the one hand,’gloeosporioides complex’included several new Colletotrichum species, on the other hand, isolates of C. gloeosporidoies in morphology and virulence were in great difference which increases the difficulty of identification among similar species as well as disease control.To identify the pathogen(s), samples of infected poplar leaves in four districts of Beijing during2009and2010were collected, and the strains were isolated and purified for examining in morphological, cultural characteristics, multi-gene phylogenetic analysis and inoculation test. Detached poplar leaves and live saplings were selected as the host of treatment by spray inoculation to determine the differentiation of pathogenicity/resistant of isolates and poplar species respectively. In addition, genetic diversity and genetic differentiation of4C. gloeosporioides populations causing poplar anthracnose in Beijing region were analyzed by sequence-related amplified polymorphism (SRAP) for further development on disease control and poplar breeding. The main results are as follows:1. Fifty four isolates of Colletotrichum were obtained from those samples from Chang Ping, Yan Qing, Mi Yun and Shi Jingshan, and the poplar samples were Populus×beijingensis, Populus nigra, Populus cathayana and Populus nigra var. italica. All the tested isolates were separated in two groups in term of morphological and culture features in conformity with phylogenetic analysis.The identification results revealed two colletotrichum species were responsible to anthracnose including Colletotrichum gleosporidoies (Penz.) Penz,&Sacc.,,(50isolates) with unconstant cultures and round or oval appressoria and Colletotrichum populi C.M.Tian&Zheng Li sp. nov.from Shi Jingshan district, host of Populus nigra var. italica, recognized as a new species with constant cultures (cottony aerial hyphae and indistintive conidia mass) producing irregular claved appressona.2. Inoculation test illustrated C.populi had weaker pathgenicity to poplar leaves compared with C.gloeosporioides in both leaves and saplings treatments. Disease susceptible species of poplar in descending order were Populus×beijingensis>Populus Canadensis>Populus nigra>Populus tomentosa.3. Four pair primers screened from36pair-primers were applied in the polymerase chain reaction (PCR) of50individuals of C. gloeosporioides.Sixty-one polymorphic loci were observed from total63loci, accounting for96.83%.The population from Yan qing2possessed the highest genetic diversity compared with the other populations, given that Nei’s gene diversity (h) and Shannon’s information index (Ⅰ) were0.1825and0.2799respectively.4. The genetic differentiation coefficient (Gst) among populations was0.2223, and the gene flow (Nm) was1.7497, implying the migration phenomenon. The range of genetic identity of4populations was from0.8960to0.9820, indicating a high level of genetic similarity and a close relationship among populations. The analysis of unweighted pair group method with arithmetic mean (UPGMA) showed that the isolates were clustered on the basis of geographic origin, few of which ran into a separate group.