engleski

Characterization of Dutch elm disease pathogen populations affecting Ulmus minor in Croatia

Dutch elm disease (DED) is a vascular wilt disease of elms caused by ascomycetes of the genus Ophiostoma. Two devastating pandemics of the disease have occurred in Europe and North America since the beginning of the 20th century. The first DED pandemic was caused by O. ulmi, which presently has been largely replaced by much more aggressive pathogen, O. novo-ulmi, causal agent of ongoing second DED pandemic. Ophiostoma novo-ulmi is separated into two distinct subspecies, ssp. novo-ulmi and ssp. americana, with weak prezygotic barrier to hybridization and emergence of ssp. novo-ulmi x ssp. americana hybrids was reported in several European countries where ranges of two subspecies overlap. In Croatia, the disease was first recorded in Slavonia in 1929 and since then it is considered to be the most significant cause of the decline of elms in Croatian forests, especially affecting Ulmus minor. Recent investigation indicated that O. novo-ulmi is the only causal agent of DED in Croatia, while O. ulmi has probably completely disappeared. This study was conducted in order to determine distribution of O. novo-ulmi subspecies and estimate incidence of their hybrids in U. minor populations in Croatia. A total of 31 isolates of O. novo-ulmi, previously obtained from infected U. minor samples from three sites across Croatia (Nova Kapela, Đurđevac i Jastrebarsko), were analyzed by PCR-RFLP of cerato-ulmin (cu) and the colony type (col1) gene regions. Presence of both O. novo-ulmi subspecies was proven, but with significantly higher incidence of ssp. novo-ulmi at investigated sites. A twenty-one isolate was assigned to O. novo-ulmi ssp. novo-ulmi and only three isolates were assigned to ssp. americana. Seven isolates were shown to be subspecies hybrids. O. novo-ulmi ssp. novo-ulmi as well as hybrid isolates, were present at all three investigated sites, while O. novo-ulmi ssp. americana was detected only in Nova Kapela and Đurđevac. Results of this study represent significant contribution to understanding of the structure of DED pathogen populations affecting U. minor in Croatia.

Ophiostoma novo-ulmi, hybridization, subspecies hybrids, PCR-RFLP

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