HETEROGENEITY IN INTERGENIC REGIONS OF THE RIBOSOMAL REPEAT OF THE PINE-BLISTER RUSTS CRONARTIUM-FLACCIDUM AND PERIDERMIUM-PINI

Mixed aeciospore isolates of Cronartium flaccidum and Peridermium pini were obtained from single-tree infections in Britain, Italy and Greec e. The 5.8s ribosomal RNA gene and flanking intergenic transcribed spa cer regions ITS1 and ITS2 were found to be highly similar between C. f laccidum and P. pini. Within samples heterogeneity was detected at thr ee nucleotide loci in the ITS1 and at four loci in the ITS2 suggesting that several fungal genotypes may occur at a single infection court. The heterogeneity was confirmed by heteroduplex polymorphism analysis of mixed aeciospore products. RFLP of the ribosomal intergenic spacer region 1 (IGS1) amplified from the same templates indicated limited se quence polymorphism in some copies of this repeated locus. Both the se xual and asexual forms of C. flaccidum show evidence of sequence polym orphism in two independent, non-coding regions of the ribosomal gene a rray. Variation appears to be greater in the sexual form C. flaccidum, than in the monoaecious form P. pini.