A Quantitative PCR System for Measuring Sclerotinia sclerotiorum in Canola (Brassica napus)

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is an economically important disease of canola (Brassica napus) commonly managed by routine application of fungicides. Petal infestation has been demonstrated to be an important stage of the disease cycle in canola and has been the focus of previously developed Sclerotinia stem rot risk assessment methods. Quantitative polymerase chain reaction (qPCR) analysis can provide a more rapid and accurate assessment of petal infestation levels. Primers and a hydrolysis probe were designed to amplify a 70-bp region of an S. sclerotiorum-specific gene, SS1G_00263. A hydrolysis probe-based qPCR assay was developed that had a detection limit of 8.0 × 10^-4 ng of S. sclerotiorum DNA and only amplified S. sclerotiorum DNA. Evaluation of petals collected at five sampling points in each of 10 commercial canola fields on each of two sampling dates (corresponding to 20 to 30% bloom and 40 to 50% bloom) revealed S. sclerotiorum DNA infestation levels of 0 to 3.3 × 10^-1 ng/petal. This qPCR assay can be used to reliably quantify petal infestation and, with further research, has the potential to serve as the basis for a Sclerotinia stem rot risk assessment tool or as a means to study Sclerotinia stem rot epidemiology.