Variability in pathotype, aggressiveness, RAPD profile, and rDNA ITS1 sequences of UK isolates of Rhynchosporium secalis

A local population of Rhynchosporium secalis was sampled and the race struc ture, pathogenicity, RAPD profile and rDNA ITS sequence examined. RAPDs wer e also used to compare this population with a larger sample of isolates inc luding some isolated more than 30 years ago. Both the local population and the wide sample revealed much variation for all characteristics with no two isolates identical. The reliability of detached leaf pathogenicity tests w as improved over previous studies by pre-washing spores and brushing the le aves prior to inoculation. Isolate aggressiveness was highly correlated wit h lesion number but not lesion size. There was no correlation between race and aggressiveness. RAPD profiles showed high levels of variability but mor e similarity was observed within a site than between sites. Clusters of sim ilarity were primarily associated with samples from the same locality but s amples taken 8 years apart from within the same field were not closely rela ted. ITS2 sequences were all identical whereas ITS I sequences showed 0.8 % polymorphism, ITS polymorphisms fell mostly within one RAPD cluster. ITS s equence comparisons with the EMBL. database gave sonic indications of the t axonomic placement of R. secalis.