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 infection frequency following the application of the biocontrol fungus Chondrostereum purpureum on two target weed species in a field trial in British Columbia. Sitka alder (Alnus sinuata) and trembling aspen (Populus tremuloides) stump sections were sampled 4 months after treatment with the biocontrol fungus, chemical herbicide, or blank controls and assayed for the presence of C. purpureum. A Chondrostereum-specific PCR primer pair, designed to amplify the intergenic region of ribosomal DNA (rDNA), allowed for the detection of C. purpureum while a second sequence-characterized, amplified region (SCAR) marker was developed to identify the specific C. purpureum genotypes. Significantly, the biocontrol isolates were recovered only from stumps to which they were applied, suggesting that topical application of C. purpureum is highly target specific. The absence of secondary infection on control stumps by biocontrol isolates of C. purpureum indicated that nontarget infection was absent. There was a significant difference in the infection frequencies 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 indication of success of biocontrol using C. purpureum. (C) 1999 Academie Press.