Relationship between pathogens of Eucalyptus and native Myrtaceae in Uruguay

Eucalyptus (Myrtaceae) is one of the most important hardwood crops in the world, planted primarily for pulp and timber production. In Uruguay, the area planted to Eucalyptus has tripled in the last 10 years. The explosive increase in the area planted has been associated with increases in disease problems. Despite this, very few investigations have been carried out to study Eucalyptus pathogens and knowledge regarding the etiology, biology and epidemiology of these diseases is limited. Eucalypts are exotics species in Uruguay and pathogens affecting their production could be exotics too. However, it has been demonstrated that different species of native trees could be host to some pathogens affecting eucalypts. Many species belonging to the Myrtaceae have been reported as potential hosts of Eucalyptus pathogens. Since Myrtaceae are dominant species in Uruguayan natural forests, the aim of this study was to determine the relationship between pathogens occurring on Eucalyptus and those occurring on native Myrtaceae. Between 2005 and 2008 several surveys were made to examine fungal infections on both Eucalyptus and native forest trees located geographically close to Eucalyptus plantations. Fungal identification was based on morphological characteristics and confirmed with DNA sequence comparisons. Puccinia psidii, Quambalaria eucalypti, and several species residing in the Botryosphaeriaceae and Mycosphaerellaceae were found occurring in both hosts countrywide. Interestingly, results suggest that most likely host jumps are occurring from native trees to Eucalyptus plantations (eg. P. psidii) and vice versa (eg. Q. eucalypti and N. eucalyptorum ). These results raise concern about the host speciation of these pathogens and illustrate the danger of moving crop plants between countries, together with fungi that are poorly understood. The negative impact of host jumping events in plant pathology has been well documented and many examples have been cited in the literature. Biotic exchanges are expected to increase as the planted area and age of plantation increase. This study provides a better understanding of the biology and ecology of these pathogens in Uruguay and will assist breeding programs in attempts to obtain disease resistant Eucalyptus plantations. The results also establish new concerns for the threat of these pathogens to native trees.