Dutch elm disease in Austria

Abstract

Dutch elm disease (DED) has first been recorded in Austria in 1928 and subsequently caused severe damage to elms in this country. In the 1990s studies on the incidence and geographical distribution of Ophiostoma ulmi and the subspecies of O. novo-ulmi in Austria have been initiated. Additionally, efforts were made to identify hybrids between these subspecies. In this paper we present a synthesis of this research and review the history and impact of DED in Austria. By the 1990s only O. novo-ulmi was present in Austria and O. ulmi had already disappeared. Based on its unique colony morphology and its female sterility, one isolate is suspected of being a hybrid or introgressant between O. ulmi and O. novo-ulmi. Both subspecies of O. novo-ulmi were detected in Austria, with ssp. novo-ulmi occurring more frequently than ssp. americana, and their ranges overlap, which suggests that they hybridize in this part of Europe. Examination of seven isolates of O. novo-ulmi for their fertility response as donor to authenticated isolates of O. novo- ulmi and by PCR-RFLP of the cerato-ulmin (cu) gene and colony type (col1) gene have unequivocally shown that genetic recombination occurs between ssp. novo-ulmi and ssp. americana and that Austria forms part of a hybrid zone between O. novo-ulmi ssp. novo-ulmi and O. novo-ulmi ssp. americana.