COMPARISON OF THE 5.8S RDNA AND INTERNAL TRANSCRIBED SPACER SEQUENCESOF ISOLATES OF LEPTOSPHAERIA-MACULANS FROM DIFFERENT PATHOGENICITY GROUPS

The regions coding for the 5.8s rRNA and the flanking internal transcr ibed spacers (ITS1 and ITS2) from nine isolates of the blackleg pathog en Leptosphaeria maculans and one isolate of Sclerotinia sclerotiorum were amplified by the polymerase chain reaction and sequenced. Five of the L. maculans isolates were highly virulent to Brassica plants, two were weakly virulent and two were isolated from the cruciferous weed Thlaspi arvense. The 5.8s DNA sequences of all L. maculans isolates we re identical. However, there were major differences in both ITS1 and I TS2 sequences that correlated with the pathogenicity grouping. Phyloge netic analysis of the ITS sequences by both parsimony and maximum-like lihood methods indicated that each pathogenicity group was statistical ly different from each other with the weakly-virulent isolates being m ore closely related to the Thlaspi than to the highly-virulent isolate s. The relationships of L. maculans to other fungi, based on a compari son of the 5.8s rDNA sequences, are discussed.