CLONING AND CHARACTERIZATION OF THE RIBOSOMAL-RNA GENE-COMPLEX FROM THE PLANT PATHOGEN VERTICILLIUM ALBO-ATRUM

The DNA coding for the ribosomal RNA gene complex (rDNA) has been clon ed from isolate 621P(PV1) of Verticillium albo-atrum which is pathogen ic for hops (Humulus lupulus). The rDNA was mapped using a range of re striction enzymes. The functional units of the intergenic spacer (IGS) , 18S, 5.8S and 25S regions were located by hybridization to specific gene probes from the rDNA complex of Aspergillus nidulans. The start p oints of the 18S and 5.8S regions were confirmed by partial sequencing . A genomic restriction enzyme map was found to be identical with the map of the cloned DNA. The rDNA repeat was 7.6 kb in length and this w as used as an homologous probe to analyse the size of the repeat in 18 hop isolates of V. albo-atrum strains and in one isolate from alfalfa (Luc2). All of the isolates had a repeat size of 7.6 kb except for Lu c2 where the rDNA complex was 8.4 kb.