Correlation Between Nec1 Gene Copy Number Detected in Soils by Quantitative Competitive Quenching Probe PCR and Incidence of Potato Common Scab Disease

We surveyed the soils from 54 potato fields in Nagasaki during the 2003 and 2004 spring croppings, and examined the relationship between the detectable copy number of the nec1 gene at harvest and the incidence of scab disease in each field. The nec1 gene in soil samples was quantified by a quantitative competitive quenching probe PCR (QCQP-PCR) method, using primers specific to the nec1 gene and fluorescence quenching-based probes. A significant positive correlation (r2=0.8195) was observed between the detectable copy number of the nec1 gene and the incidence of disease in tubers from 21 fields in 2003. In 23 of 25 fields where the incidence of disease was >10%, more than 103 copies of nec1 per g-soil were detected. Of the nine fields where the incidence of disease was <10%, eight had fewer than 103 gene copies. The nec1 gene was not detected in 20 fields where no disease was found. These results suggest that scab disease occurs more frequently in fields where more than 103 copies of nec1 per g-dry soil are detected.