Book Description

Cytospora species and their Valsa teleomorphs are commonly found on Eucalyptus trees and some of these have been associated with stem canker diseases. The taxonomy of these fungi has been confused and has in many cases hindered pathology studies. This study was based on extensive collections of Cytospora species and their teleomorphs from Eucalyptus trees in Africa, Australia, Central and South America, Southeast Asia and California. Sixty-two Cytospora and three Cytospora-like isolates from Eucalyptus, yielding 33 unique ITS-rDNA sequences, were compared for homology to Cytospora species from other hosts. Phylogenetic analysis clustered isolates of Cytospora from Eucalyptus into at least 15 unrelated groups. The Cytospora-like isolates that morphologically resembled Cytospora clustered in a separate group, which is related to Phomopsis. Morphology of the fungi was examined on natural subtrates and in culture in order to identify distinctive characters linked to the phylogenetic lineages emerging from DNA sequence analyses. The specimens from Eucalyptus included morphological features encompassing the Cytospora infrageneric sections Cytospora, Lamyella, Leucocytospora, and Torsellia with the majority residing in sect. Lamyella. Several species exhibited morphological characteristics of more than one section and other species had unique characteristics not represented in the established sections. Phylogenetic inference did not support the sections that have been established based on morphological characteristics. The concepts underlying the establishment of sections in Valsa and Cytospora were, therefore, discarded and descriptive terms have been introduced to distinguish between ascostroma and locule forms. Descriptions of Cytospora australiae, C. eucalyptina, C. eucalypticola, and the anamorphs of Valsa eucalypti and Leucostoma sequoiae have been emended based on morphological studies of cross-sections of holotype and isotype specimens. Teleomorphs associated with Cytospora specimens on Eucalyptus have been described from Australia, California, Chile, Congo, Hawaii, India and Uganda. Each teleomorph had unique morphological characteristics and DNA sequence but several conformed to the broad description of Valsa ceratosperma, even though they resided in separate phylogenetic lineages. Additionally, sequences for V. ceratosperma on hosts other than Eucalyptus resided in separate lineages and were different from all of the isolates from Eucalyptus. One of the lineages, commonly found on Quercus, was recognised as corresponding to the original species concept and was designated as V. ceratosperma sensu stricto (= V. ceratophora). Results of this study have shown that numerous genetically distinct lineages of Cytospora and Cytospora-like fungi occur on Eucalyptus, and that the current description of V. ceratosperma encompases several distinctly different fungi. Leucostoma sequoiae and V. eugeniae were found on Eucalyptus, and V. eucalypti and L. sequoiae have been synonymised. Cultural characteristics including colony colour, pycnidium structure, cardinal temperatures for growth, and tolerance to cycloheximide have been described for the species. Several new species of Valsa and Cytospora from Eucalyptus have also been delimited based on morphological characteristics. This wide-ranging study should contribute to a better understanding of the taxonomy of Cytospora spp. and their teleomoprhs, particularly on Eucalyptus. It is also hoped that this will lead to improved management strategies for diseases associated with these fungi.