Cryphonectria Canker on Eucalyptus in Florida Reconsidered

Abstract

Cryphonectria canker is one of the most important diseases of plantation-grown Eucalyptus spp. in the tropics and Southern Hemisphere. The disease has been known in Florida, USA, for many years, and the causal agents are attributed to two known canker pathogens, Chrysoporthe cubensis (≡ Cryphonectria cubensis) and Microthia havanensis (≡ Endothia havanensis). These identifications were based on morphological characteristics, which are inadequate to recognise cryptic species in the Cryphonectriaceae. In this study, we visited various sites in Florida where Eucalyptus grandis and E. amplifolia trees are cultivated and investigated the presence of cankers. Isolations were made from fungal structures on symptomatic tissues associated with cankers. A total of 41 cultures resembling Cryphonectriaceae spp. were isolated. The isolates were identified based on DNA sequences for the ITS region of the rRNA and sections of the β-tubulin gene, and confirmed as the three species of Cryphonectriaceae, namely Microthia havanensis, Chrysoporthe cubensis and Chrysoporthe doradensis. Of these, Chrysoporthe doradensis was discovered for the first time in the USA. In addition, this study represents the first record of any Cryphonectriaceae on E. amplifolia , a Eucalyptus species that is poorly studied in terms of disease. Pathogenicity trials on Eucalyptus showed that all three Cryphonectriaceae species could cause disease on these trees, with Chrysoporthe spp. being more aggressive. These findings highlight the importance of continuous monitoring and surveillance to detect emerging pathogens and safeguard the sustainability of Eucalyptus in non-native forestry systems.