Abstract:
Syzygium jambos (Myrtales, Myrtaceae) trees in Hawaii are severely affected by a rust disease caused by Austropuccinia psidii (Pucciniales, Sphaerophragmiaceae), but they are commonly co-infected with species of Cryphonectriaceae (Diaporthales). In this study, S. jambos and other trees in the Myrtales were examined on three Hawaiian Islands for the presence of Cryphonectriaceae. Bark samples with fruiting bodies were collected from infected trees and fungi were isolated directly from these structures. Pure cultures were produced and the fungi were identified using DNA sequence data for the internal transcribed spacer (ITS) region, part of the β-tubulin (BT1) gene and the transcription elongation factor-1α (TEF1) gene. Five species in three genera of Cryphonectriaceae were identified from Myrtaceae tree samples. These included Chrysoporthe deuterocubensis, Microthia havanensis and three previously-unknown taxa described here as Celoporthe hauoliensis sp. nov., Cel. hawaiiensis sp. nov. and Cel. paradisiaca sp. nov. Representative isolates of Cel. hauoliensis, Cel. hawaiiensis, Cel. paradisiaca, Chr. deuterocubensis and Mic. havanensis were used in artificial inoculation studies to consider their pathogenicity on S. jambos. Celoporthe hawaiiensis, Cel. paradisiaca and Chr. deuterocubensis produced lesions on young S. jambos trees in inoculation trials, suggesting that, together with A. psidii, they may contribute to the death of trees. Microsatellite markers were subsequently used to consider the diversity of Chr. deuterocubensis on the Islands and thus to gain insights into its possible origin in Hawaii. Isolates of this important Myrtaceae and particularly Eucalyptus pathogen were found to be clonal. This provides evidence that Chr. deuterocubensis was introduced to the Hawaiian Islands as a single introduction, from a currently unknown source.
