Detection and Quantification of<i>Plectosphaerella cucumerina</i>, a Potential Biological Control Agent of Potato Cyst Nematodes, by Using Conventional PCR, Real-Time PCR, Selective Media, and Baiting

<jats:title>ABSTRACT</jats:title><jats:p>Potato cyst nematodes (PCN) are serious pests in commercial potato production, causing yield losses valued at approximately $300 million in the European Community. The nematophagous fungus<jats:italic>Plectosphaerella cucumerina</jats:italic>has demonstrated its potential as a biological control agent against PCN populations by reducing field populations by up to 60% in trials. The use of biological control agents in the field requires the development of specific techniques to monitor the release, population size, spread or decline, and pathogenicity against its host. A range of methods have therefore been developed to monitor<jats:italic>P. cucumerina</jats:italic>. A species-specific PCR primer set (PcCF1-PcCR1) was designed that was able to detect the presence of<jats:italic>P. cucumerina</jats:italic>in soil, root, and nematode samples. PCR was combined with a bait method to identify<jats:italic>P. cucumerina</jats:italic>from infected nematode eggs, confirming the parasitic ability of the fungus. A selective medium was adapted to isolate the fungus from root and soil samples and was used to quantify the fungus from field sites. A second<jats:italic>P</jats:italic>.<jats:italic>cucumerina</jats:italic>-specific primer set (PcRTF1-PcRTR1) and a Taqman probe (PcRTP1) were designed for real-time PCR quantification of the fungus and provided a very sensitive means of detecting the fungus from soil. PCR, bait, and culture methods were combined to investigate the presence and abundance of<jats:italic>P. cucumerina</jats:italic>from two field sites in the United Kingdom where PCN populations were naturally declining. All methods enabled differences in the activity of<jats:italic>P. cucumerina</jats:italic>to be detected, and the results demonstrated the importance of using a combination of methods to investigate population size and activity of fungi.</jats:p>