Phylogeny, taxonomy and the ecology of Calonectria species

Abstract

Calonectria is a genus of fungi with a global distribution and with species having a wide range of hosts. Many of the species also cause serious diseases of important crop plants. During the last two decades, there have been numerous and increasing numbers of taxonomic studies on Calonectria. However, the taxonomic criteria used to identify Calonectria species have been inconsistent in these studies. For this reason, an important aim of the research in this thesis was to re-evaluate and clarify the phylogenetic relationships of all the published Calonectria species, and to propose a set of credible and stable criteria for species identification. In this thesis, I re-sequenced eight gene regions (act, cmdA, his3, ITS, LSU, rpb2, tef1 and tub2) for all Calonectria species and analyzed the data. Based on these results, combined with the morphological features, I re-evaluated the species boundaries for Calonectria. The result was 51 species reduced to synonymy, two novel species being described, and one species validated. The overall result was an of 120 Calonectria species reduced from an original 169 species. The results revealed that six loci (act, cmdA, his3, rpb2, tef1 and tub2) can be used as robust DNA barcodes for species identification in Calonectria. To explore the diversity and distribution of Calonectria species in FuJian Province soils, a larger number of Calonectria isolates were retrieved from the soil samples collected from Eucalyptus plantations, natural forests and other related hosts. Employing the multigene phylogenetic analyses as well as the morphological characteristics, seven Calonectria species were discovered of which one represented novel taxon. To have a better understanding regarding the connections between Calonectria species on diseased Eucalyptus tissues and in soil samples, a larger number of Calonectria isolates were obtained from the diseased Eucalyptus leaves and soil samples in YunNan Province, southwestern China, overall, the results revealed some species are predominantly soil inhabitants and the pathogens causing Eucalyptus leaf blight mainly originated from leaves. This study revealed that Calonectria species will pose long-term challenges to the development of Eucalyptus forestry in southern China.