Problems in ITS-rDNA taxonomy: Hypervariable ITS sequences among isolates and within single-ascospore strains of Ceratocystis fimbriata sensu stricto
T. HARRINGTON (1). (1) Iowa State University, Ames, IA, U.S.A.
The South American species <i>C. fimbriata ss</i> is homothallic, soilborne, and depends on insects or humans for long-distance dispersal. Thus, natural populations are genetically isolated and may acquire local variations in DNA sequences, especially in ITS-rDNA. Some ITS haplotypes have been introduced from Brazil to other locations and described as new species without distinguishing phenotype. Isolates from introduced populations that appeared to be clonal based on microsatellite markers varied at up to 14 bp in ITS sequence. In four isolates, TA cloning and sequencing of PCR products from single-ascospore strains identified two or more ITS sequences representing different putative species (1 spore = 2 species). Strains of eight ITS haplotypes representing the range of ITS diversity were fully interfertile in sexual crosses. Maximum parsimony (MP) and maximum likelihood (ML) analyses of ITS sequences of 116 isolates of recently described species and Brazilian isolates gave poorly resolved trees. In contrast, analyses of mating type genes (<i>MAT1-1-2</i> and <i>MAT1-2-1</i>) resolved a single MP tree with a topology identical to that of the ML tree, with branches of high bootstrap and posterior probability support. These analyses support three phenotypic species (based on pathogenicity): <i>C. platani</i>, <i>C. cacaofunesta</i> and <i>C. colombiana</i>. However, five ITS species (<i>C. manginecans</i>, <i>C. mangicola</i>, <i>C. mangivora</i>, <i>C. acaciivora</i>, and <i>C. eucalypticola</i>) appear to be synonyms of <i>C. fimbriata ss</i>.
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