Probe-Based Multiplex Real-Time PCR as a Diagnostic Tool to Distinguish Distinct Fungal Symbionts Associated With and in California.

California has been invaded by two distinct spp. that vector unique plant pathogenic symbiotic fungi on multiple hosts and cause Fusarium dieback. The objective of this study was to develop multiplex real-time quantitative PCR assays using hydrolysis probes targeting the β-tubulin gene to detect, distinguish, and quantify fungi associated with the polyphagous shot hole borer (PSHB; , , , and ) as well as the Kuroshio shot hole borer (KSHB; , , and ) from various sample types. Absolute quantification reaction efficiencies ranged from 88.2 to 104.3%, with a coefficient of determination >0.992 and a limit of detection of 100 copies µl for all targets across both assays. Qualitative detection using the real-time assays on artificially inoculated avocado shoot extracts showed more sensitivity compared with conventional fungal isolation from wood. All symbiotic fungi, except , from PSHB and KSHB female heads were detectable and quantified. Field samples from symptomatic , spp., and spp. across 17 of 26 city parks were positively identified as PSHB and KSHB through detection of their symbiotic fungi, and both were found occurring together on five trees from three different park locations. The molecular assays presented here can be utilized to accurately identify fungi associated with these invasive pests in California.