Restriction fragment length polymorphisms (RFLPs) of the ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) of isolates of Cylindrocarpon heteronema were analysed using rDNA from Saccharomyces carlsbergensis and mtDNA from C. heteronema as probes. These analyses revealed intraspecific heterogeneity; four rDNA and six mtDNA restriction pattern categories were observed among the isolates tested. The two main rDNA RFLP categories, both of which subdivided into two mtDNA categories, detected within the UK isolates could not be associated with the localities from which they were obtained, but the majority of isolates originating from trees produced in the same nursery, irrespective of where they were finally planted, belonged to the same category.

Relatively rapid, highly specific monoclonal antibody‐based enzyme‐linked immunosorbent and immunofluorescent assays have been developed to detect and visualize Nectria galligena in woody tissue. Hybridoma cell lines were raised by co‐immunization of mice with extracts from freeze‐dried cultures of N. galligena and murine polyclonal antiserum to a related pathogen, N. haematococca. This method appeared to reduce the number of hybridoma cell lines that secreted cross‐reactive antibodies. From two fusions, ten cell lines that recognized N. galligena and not N. cinnabarina were raised. Hybridoma supernatants were screened by ELISA using antigen‐coated wells. Monoclonal antibodies from one cell line, NG‐IE4, proved useful in the detection of the pathogen in woody tissue by ELISA and antibodies from another cell line, NG‐DF11, have been used to immunolocalize the fungus in woody tissue by immunofluorescence. Further applications are ongoing.