中国假尾孢属 (Pseudocercospora) 的系统学研究

Pseudocercospora, one of the most important genera within Mycosphaerellaceae (Capnodiales, Dothideomycetes, Ascomycota), is a large cosmopolitan genus of plant pathogenic fungi that are commonly associated with leaf and fruit spots as well as blights on a wide range of plant hosts. In China, Pseudocercospora had been considered a “Form-Genus”, thus almost no systematic study has been conducted on it. Most recent studies indicated that Pseudocercospora sensu stricto is a monophyletic genus with Mycosphaerella-like teleomorphs. In particular, the distribution of Psuedocercospora has regional barrier, such as species identified basing on host, symptomatology and general morphology between different geographic regions cannot be warranted, which means the application of European and American names to Asian taxa is not practical. The aim of this study is to clarify the biodiversity and interspecies relationships of Pseudocercospora in China based on multi-locus phylogeny. By combining morphology, host spectrum, geographic distribution, disease symptoms as well as the results of molecular phylogeny, more reliable species circumscription criterions and natural classification system will be reached. By evaluating different DNA fragment, proper DNA barcoding loci will be selected for species identification. A large number of specimens and isolates will be collected, and more new species of Pseudocercospora are expected to be found. In addition, this study will provide scientific basis for plant disease surveillance and develop fast diagnosis of quarantine fungi.

假尾孢属是子囊菌门、座囊菌纲、煤炱目、小球壳科内的一个重要类群，分布广、物种多样性丰富，可引起许多经济作物的叶斑、果斑病及枯萎病等病害。然而，我国假尾孢属的分类研究主要以寄主植物科及其形态特征为依据，目前还缺乏分子系统学研究；而国外最新分子系统学研究结果表明假尾孢属的物种分布具有地域性，即欧美与我国的同科寄主上形态相同的种极可能不是同一个物种。因此，为了揭示我国假尾孢属真菌的物种多样性及其系统演化关系，本项目拟以我国假尾孢属为对象，在馆藏标本借阅、标本采集与分离菌株的基础上，进行形态特征描述；通过构建多基因分子系统发育树，并结合形态、寄主、地理分布、病害症状等特征进行多相分析与评价，确定物种分类依据，建立趋于自然的种间系统演化关系；通过多基因片段分析，筛选出适合假尾孢属物种鉴定的DNA条形码。本项目可收集保藏大量假尾孢属的标本和菌株，发现大量新分类单元，为真菌病害的防治和检疫提供科学依据。

假尾孢属(Pseudocercospora Speg.)属于子囊菌门、座囊菌纲、煤炱目、球腔菌科，有性型为球腔菌属(Mycosphaerella Johanson)；假尾孢属真菌在世界范围广泛分布。其寄主范围极广，可侵染植物的叶、茎、花和果实，在林业、农业上都会造成一定的经济损失。目前国内对假尾孢属真菌的研究主要依赖形态学，极少利用DNA序列比较方法研究假尾孢属分类，但分子系统学分析在分类研究中已逐渐成为主要依据。本研究主要采用形态学结合多基因系统发育分析的方法，对我国的假尾孢属真菌进行系统的研究。对野外采集的标本进行形态学观察、显微照相、菌株分离，对分离的菌株进行DNA提取和多基因测序。系统发育分析使用ITS、tef1-α、ACT、RPB1/2 和 TUB基因片段，运用最大简约法(Maximum Parsimony)及最大似然法(Maximum Likelihood)构建系统发育树，结合RAxML和PAUP等生物分析软件对我国的假尾孢属真菌进行细致全面的系统发育学分析。本项目从我国20多个省市采集假尾孢属真菌的标本879份,分离菌株538株，并对采集的标本及菌株进行了DNA提取、序列测定及物种鉴定，共初步鉴定出40科、63属寄主植物上的假尾孢属真菌106种，其中62个新种及44个已知种。ITS、tef1-α、ACT和RPB2在区分假尾孢物种有效性方面从高到低的顺序依次是tef1-α>RPB2>ACT>ITS，而RPB1与TUB对假尾孢属真菌的分辨率较低。对从本项目采集分离的538株假尾孢属真菌的菌株进行了ITS、tef1-α、ACT、RPB1/2 和 TUB等多基因测序及序列分析，构建了该属较完整的系统发育树，并对多个分类地位不明确的分支进行了寄主植物、地理分布、形态特征等多相分类研究，订正了其中部分物种的分类地位，研究结果正在进一步分析整理中。