Analysis of Spanish populations ofOphiostoma ulmiandO. novo‐ulmiusing phenotypic characteristics and RAPD markers

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Abstract
One hundred and six isolates of the Dutch elm disease (DED) fungiOphiostoma ulmiandOphiostoma novo‐ulmiwere collected from elm trees with symptoms in 15 regions of Spain. Isolates were compared with eight reference strains belonging toO. ulmiand the two subspecies ofO. novo‐ulmi.The purpose of this study was to assign Spanish isolates to species and subspecies of the DED fungi and to analyse the genetic variability within the Spanish populations of these pathogens. Isolates were examined for their growth rates, colony morphologies and fertility responses and by using random amplified polymorphic DNA (RAPD) markers. Six isolates were identified asO. ulmi, 16 asO. novo‐ulmissp.novo‐ulmiand 78 asO. novo‐ulmissp.americana. Nei's and Shannon's diversity indices and theupgmadendrogram from RAPD profiles indicated a high level of variation among isolates, probably reflecting post‐epidemic status of DED in Spain. Although most isolates were separated into three major clusters representing the three taxa of DED fungi in the RAPD analysis, two isolates from central Spain clustered betweenO. novo‐ulmissp.americanaandO. novo‐ulmissp.novo‐ulmi, and four isolates from Mallorca clustered betweenO. ulmiand the group representingO. novo‐ulmissp.novo‐ulmi. Mating tests conducted with these isolates revealed a variety of fertility responses. The novel combinations between molecular profile and fertility reaction suggest that three isolates from Mallorca may be interspecific hybrids of the DED fungi.

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