P-244 - From citrus to collapse: The emergence of CBCVd in hops and the path toward resistance

Until 2014, Citrus bark cracking viroid (CBCVd, Cocadviroid rimocitri) was known as a minor pathogen in citrus, causing no economic damage. However, its transmission to hop (Humulus lupulus) has led to severe disease symptoms, resulting in plant death within five years. The viroid was first identified in hops in Slovenia, marking its emergence in a new host and a non-citrus-growing region. Introduction likely occurred via infected citrus waste, with rapid spread driven by mechanical transmission and vegetative propagation.

To mitigate the infection, various research initiatives have been undertaken and will be presented. Field observations identified potential resistance and tolerance to CBCVd in hop cultivars Styrian Wolf and Styrian Cardinal, respectively. Building on these findings, we evaluated the susceptibility of multiple hop cultivars under controlled tissue culture conditions, with additional field evaluations currently in progress. Complementary pot experiments involved grafting CBCVd-infected Celeia scions onto rootstocks of Styrian Wolf, Styrian Cardinal, and the susceptible Celeia to investigate the genetic basis of resistance. RNA sequencing and differential gene expression analyses revealed key resistance-related genes, particularly those distinguishing tolerant and susceptible cultivars. In parallel, epigenomic profiling uncovered distinct CBCVd-induced methylation changes, providing new insights into the role of DNA methylation in hop–viroid interactions.