- Dutch elm disease (DED) is a disease of elm trees caused by three species of Ascomycota fungi: Ophiostoma ulmi, Ophiostoma novo-ulmi, and Ophiostoma himal-ulmi. There are also two subspecies of O. novo-ulmi: subsp. americana and subsp. novo-ulmi. The pathogen is spread by bark beetles, which inhabit and traverse different elms. O. novo-ulmi is noted to be more aggressive than O. ulmi, and thus many areas in which O. ulmi had been dominant are being replaced by O. novo-ulmi.
Epidemiology of DED has been studied in areas including Spain, New Zealand, and Austria. Studies of the disease in the United States are not as prevalent. This study attempts to identify to subspecies, 14 fungal strains isolated from diseased elms growing in Portland, Oregon. Goals include determination of the relative abundance of O. novo-ulmi and O. ulmi. Most elm surveys categorize diseased elms as having signs of DED, but do not specify the causal species or subspecies. Another goal is to develop methods that can be used to differentiate between the species and subspecies of Ophiostoma, based on growth rate and polymerase chain reaction (PCR). A final goal of this study is to devise a protocol for Oregon State University’s Plant Clinic to type Ophiostoma by a method other than morphology.
Typing of isolates was done using the mtsr primers (Hafez and Hausner 2011), which target gene sequences specific to O. ulmi and O. novo-ulmi. Subspecies differentiation of O. novo-ulmi was done using the CU primers (Konrad et al. 2002), which target the specific gene sequences needed to differentiate between subsp. americana and subsp. novo-ulmi. A growth rate experiment was also conducted using different optimal growth temperatures for each species.
Results suggest that O. novo-ulmi is more abundant than O. ulmi around Portland, Oregon, and that subsp. americana is more abundant than subsp. novo-ulmi. Growth rates did not appear as useful as the PCR screen to differentiate between O. ulmi and O. novo-ulmi, and cannot differentiate the O. novo-ulmi subspecies. PCR is a more reliable method to differentiate between O. ulmi and O. novo-ulmi, as well as the two subspecies of O. novo-ulmi. These findings could be used to further the knowledge of the DED pandemic that is currently occurring.