Assessment of Viroid Transmission Risk From Citrus Essential Oils

ABSTRACT Germany is the world's second largest producer of hops, with a long history of producing high‐quality hops for beer brewing purposes. Citrus bark cracking viroid (CBCVd) is a well‐known pathogen of citrus plants, causing mild and often tolerated infections in various citrus species, while causing massive damage to hop plants. In addition to CBCVd infection, hop production is threatened by many pests and pathogens, which can severely reduce hop yield and quality. These threats require the use of crop protection products. However, the increasing demand for high agricultural yields, coupled with restrictions on synthetic pesticides in the European Union, has led to the search for sustainable alternatives. Citrus‐based plant‐strengthening products have emerged as promising alternatives. The purpose of this study was to investigate whether CBCVd would be present in citrus essential oils (CEOs) and therefore function as an infectious agent, thus posing a potential risk for viroid transmission associated with the use of CEO products. A comprehensive testing workflow was established to evaluate various commercially available citrus essential oils, assessing their effects on RNA extraction and any inhibitory effects on real‐time reverse transcription (RT)‐PCR. Initial validation of this workflow was performed by testing the stability of viroid RNA spiked with CEOs stored at room temperature. The outcome of this study indicates a low risk of viroid transmission from CEO products and provides useful insight into the integration of CEO products into sustainable hop production.