Molecular phylogenetic and taxonomic studies in the Ascomycetes

DNA was extracted from xylariaceous fungi. The nuclear small (NS) transcribed ribosomal DNA (rDNA), internal transcribed spacer (ITS), and mitochondrial small (MS) rDNA were amplified using the polymerase chain reaction (PCR). The length of the nuclear NS 5-6 rDNA region is highly variable in the Xylariaceae. More than half of the taxa studied had lengths ranging from 650 bp to 1,320 bp, different from the most common size of 310 bp. Data showed that the xylariaceous fungi had mitochondrial small rDNA of 630 bp, shorter than the common size of 716 bp of most fungi.;Restriction analyses of NS rDNA and MS rDNA were performed. The mitochondrial rDNA exhibited more variability than the nuclear rDNA. Results from cluster analysis of a mitochondrial riboprinting data set indicated some possible intergeneric and interspecific relationships of Xylariaceae. In Xylaria, four groups with the same restriction profiles, respectively, clustered in the dendrogram. They are: (1) X. arbuscula and X. atrosphaerica; (2) X. hypoxylon, X. longiana, and X. magnoliae; (3) X. cubensis and X. enteroleuca; and (4) X. carpophila, X. cornu-damae, and X. persicaria. Based upon length variation and restriction fragment length polymorphism (RFLP) analyses of nuclear and mitochondrial small rDNAs, and random amplified polymorphic DNA (RAPD) assay, it is indicated that X. laevis is a comparatively primitive species and might be related to X. corniformis and X. cubensis.;Genetic variations within known and putative taxa of Xylaria cubensis, X. hypoxylon, and X. polymorpha were assessed by characterizing RAPD markers. The results of this study suggest that X. hypoxylon is a complex species and/or that some taxa represented as that species were misidentified. Xylaria polymorpha probably has at least two biotypes that correlated with their conidial morphologies. Molecular data indicated that X. cubensis might have at least two subtaxa in accordance with geographical isolation.;The pathogenicity tests, morphological characteristics, and RAPD markers indicate that Ascochyta fabae and A. lentis represent distinct taxa. The results of RAPD assay show that an Ascochyta isolated from faba bean in Lebanon has a similar or almost identical banding pattern to known A. rabiei isolates. Faba bean seems to be the twelfth host of A. rabiei.