A real-time PCR assay for Erysiphe betae and its effectiveness when used with different spore trapping methods

Powdery mildew caused by the fungus Erysiphe betae can cause sugar yield losses of up to 35% in sugar beet ( Beta vulgaris ). The timing of fungicide applications is typically based on visual symptom onset or past history, rather than when conidia of E. betae first enter the field. Therefore, fungicide timing could be optimized if growers know when conidia are present. Spore traps, when used with a sensitive and specific qPCR assay, could be used for the detection of spores/conidia prior to infection. In this study we developed a real-time qPCR assay based on TaqMan chemistry for E. betae and evaluated it with five different spore trapping technologies to determine the feasibility of their use in disease forecasting. The qPCR assay was designed to the rDNA ITS region and was specific to E. betae when tested with other powdery mildew species and sugar beet pathogens. The assay was capable of detecting E. betae DNA in asymptomatic sugar beet leaves and from as little as one conidia. From 2018 to 2020 the assay, when used in conjunction with a Burkard multi-vial cyclone spore trap, detected DNA from spores of E. betae at least 15 days before visual symptoms were observed in southwest Idaho. This study shows that spore trapping used in conjunction with a sensitive real-time PCR assay is possible for the early detection of E. betae .