citrophthora on a selective media and the corresponding DNA CH5424802 quantities evaluated by qPCR. A lower correlation between conventional and molecular methods was found by analysing naturally infected soils because, as speculated by the same authors, the two methods detected different

propagules of the pathogen (mycelia, zoospores, oospores, etc.) with differing efficiency. It should also be taken into account that different propagules often determine single CFU on a medium, but their DNA content can be significantly different. The CFU of F. solani f.sp. phaseoli in soil did not correlate with qPCR data, which was probably due to variation of mechanical strength applied to dislodge and break Fusarium propagules

from soils for subsequent CFU enumeration (Filion et al. 2003). A possible approach to correlate qPCR data with the actual number of fungal propagules per unit of soil is the construction of standard curves by adding known concentrations of inoculum (i.e. conidia or sclerotia) to soils prior to DNA extraction (Schena et al. 2013). Even in this case, however, it must be kept in mind that naturally infested soils are different from the artificially inoculated ones, and the standard curve will not be equally appropriate for different pathogen organs (mycelia, spores, conidia, conidiophores, sclerotia, etc.). The possible correlation of qPCR data with fungal Adriamycin biomass determined by image analysis of the in vitro hyphal length has also been reported (López-Mondéjar et al. 2010). In this study, conducted with Trichoderma harzianum, the authors speculated

that the extrapolation of qPCR data in quantities of fungal biomass potentially provides a more accurate value of the quantity of soil fungi. A major limitation of molecular detection methods applied to soilborne pathogens is the lack of discrimination between living and dead material. Because both traditional and qPCR assays detect nucleic acids rather than living cells, there is a risk that nucleic acids relinquished from dead SPTLC1 and unviable cells may lead to positive PCR signals. Nucleases are widely diffused in the environment and can degrade DNA after the death of microorganisms, but the degradation rate strongly depends on environmental conditions. Schena and Ippolito (2003) found that DNA of R. necatrix is degraded rapidly in soil minimizing the risks of false positives. However, further research is necessary to assess the persistence of the DNA in different environmental conditions and in relation to the structures produced by the pathogens. Indeed, quantitative studies of DNA degradation kinetics by qPCR have shown that the rate of degradation of DNA after cell death is variable, according to DNA-binding potential of the substrate (Wolffs et al. 2005).