PCR-based genetic markers for detection and infection frequency analysis of the biocontrol fungus Chondrostereum purpureum on Sitka alder and trembling aspen

Diagnostic molecular genetic markers were developed to estimate the infecti on frequency following the application of the biocontrol fungus Chondroster eum purpureum on two target weed species in a field trial in British Columb ia. Sitka alder (Alnus sinuata) and trembling aspen (Populus tremuloides) s tump sections were sampled 4 months after treatment with the biocontrol fun gus, chemical herbicide, or blank controls and assayed for the presence of C. purpureum. A Chondrostereum-specific PCR primer pair, designed to amplif y the intergenic region of ribosomal DNA (rDNA), allowed for the detection of C. purpureum while a second sequence-characterized, amplified region (SC AR) marker was developed to identify the specific C. purpureum genotypes. S ignificantly, the biocontrol isolates were recovered only from stumps to wh ich they were applied, suggesting that topical application of C. purpureum is highly target specific. The absence of secondary infection on control st umps by biocontrol isolates of C. purpureum indicated that nontarget infect ion was absent. There was a significant difference in the infection frequen cies of the two target weeds. Approximately 90% of biocontrol-treated Sitka alder stems and 40% of trembling aspen stems were successfully infected by C. purpureum. It is expected that this methodology will provide an early i ndication of success of biocontrol using C. purpureum. (C) 1999 Academie Pr ess.