Spore PCR and qPCR Methods for Rapid Detection of Five Colletotrichum Species Responsible for Pepper Anthracnose in Korea

Pepper anthracnose, caused by Colletotrichum spp., leads to a decrease in the quantity of pepper fruit production. Molecular diagnosis is crucial for rapid identification of pathogens and determination of fungicide resistance. However, the traditional process of isolating the pathogen, extracting genomic DNA, and analyzing the gene sequence is time-consuming, which delays rapid diagnosis. In this study, we introduced a method using conidia of Colletotrichum spp. instead of genomic DNA, eliminating the need for DNA extraction or special processing for diagnosis. To elucidate this method, sensitivity was assessed through polymerase chain reaction (PCR) and quantitative real-time PCR (qPCR) tests using internal transcribed spacer-based primer pairs. Both PCR and qPCR tests showed that detection is feasible with just one conidia, with over 1,000 conidia yielding results comparable to approximately 1 pg of genomic DNA. For amplifying the cytochrome b gene for quinone-outside inhibitor fungicide susceptibility testing, detection from a single conidium is achievable, but a stable PCR product is obtained by increasing the number of cycles to 35. Additionally, the addition of 10% grinding fresh chili pepper paste to V8-Juicea gar medium, which is known for inducing conidia rapidly from the isolates, resulted in 3.2 to 6.0 times more conidia compared to the commonly used potato dextrose agar medium, enhancing the potential for swift testing. Taken together, this study presents a direct utilization of pepper anthracnose conidia through PCR or qPCR, offering a valuable technique for amplifying target genes, such as the minimum conidial amount and barcode genes, for molecular identification of anthracnose disease in pepper through PCR and qPCR analysis.