Development of a Droplet Digital PCR Assay for Detection and Quantification of Stubby Root Nematode, , in Soil.

The stubby root nematode is an important plant-parasitic nematode species within the Trichodoridae family. It can directly harm the plants by feeding on the roots or indirectly by transmitting . These nematodes are mostly diagnosed either by traditional microscopic methods or a polymerase chain reaction (PCR)-based method. Droplet digital PCR (ddPCR) is a novel PCR technique which is sensitive and precise in quantifying DNA templates of the test samples. In this study, we developed a ddPCR assay to detect and quantify in soil. The specificity and sensitivity of the assay was first determined using nematode DNA or DNA from sterilized soil artificially inoculated with , and the assay was used to quantify populations in field soils. The assay did not detect nematodes other than , thus showing high specificity. It was able to detect equivalent to a 0.01 and 0.02 portion of a single nematode in soil DNA and nematode DNA extracts, respectively. Highly linear relationships between DNA copy numbers from ddPCR and serial dilutions of known concentrations were observed with DNA from nematodes ( = 0.9842) and from artificially infested soil ( = 0.9464). The populations from field soils determined by ddPCR were highly correlated with traditional microscopic counts ( = 0.7963). To our knowledge, this is the first report of applying ddPCR to detect and quantify stubby root nematode in soil. The results of this study support the potentiality of a ddPCR assay as a new research tool in diagnostics of plant-parasitic nematodes.