Department of Microbiology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria 0002, South Africa.
Stud Mycol. 2006;55:147-61. doi: 10.3114/sim.55.1.147.
Species of the ascomycete genus Mycosphaerella are regarded as some of the most destructive leaf pathogens of a large number of economically important crop plants. Amongst these, approximately 60 Mycosphaerella spp. have been identified from various Eucalyptus spp. where they cause leaf diseases collectively known as Mycosphaerella Leaf Disease (MLD). Species concepts for this group of fungi remain confused, and hence their species identification is notoriously difficult. Thus, the introduction of DNA sequence comparisons has become the definitive characteristic used to distinguish species of Mycosphaerella. Sequences of the Internal Transcribed Spacer (ITS) region of the ribosomal RNA operon have most commonly been used to consider species boundaries in Mycosphaerella. However, sequences for this gene region do not always provide sufficient resolution for cryptic taxa. The aim of this study was, therefore, to use DNA sequences for three loci, ITS, Elongation factor 1-alpha (EF-1alpha) and Actin (ACT) to reconsider species boundaries for Mycosphaerella spp. from Eucalyptus. A further aim was to study the anamorph concepts and resolve the deeper nodes of Mycosphaerella, for which part of the Large Subunit (LSU) of the nuclear rRNA operon was sequenced. The ITS and EF-1alpha gene regions were found to be useful, but the ACT gene region did not provide species-level resolution in Mycosphaerella. A phylogeny of the combined DNA datasets showed that species of Mycosphaerella from Eucalyptus cluster in two distinct groups, which might ultimately represent discrete genera.
子囊菌属的种被认为是许多重要经济作物的最具破坏性的叶病原菌之一。在这些病原菌中，约有 60 种被鉴定为来自各种桉树，它们引起的叶病统称为球腔菌叶病（MLD）。该真菌群的种概念仍然存在混淆，因此其种的鉴定非常困难。因此，DNA 序列比较的引入已成为区分球腔菌属种的决定性特征。核糖体 RNA 操纵子的内部转录间隔区（ITS）的序列最常用于考虑球腔菌的种界。然而，该基因区域的序列并不总是为隐生分类单元提供足够的分辨率。因此，本研究的目的是使用三个基因座（ITS、延伸因子 1-α（EF-1α）和肌动蛋白（ACT）的 DNA 序列来重新考虑来自桉树的球腔菌种的种界。另一个目的是研究无性型概念并解决球腔菌的更深节点，为此，对核 rRNA 操纵子的大亚基（LSU）的一部分进行了测序。发现 ITS 和 EF-1α基因区域是有用的，但 ACT 基因区域在球腔菌中没有提供种水平的分辨率。组合 DNA 数据集的系统发育表明，来自桉树的球腔菌种聚类为两个不同的组，这可能最终代表不同的属。
