Cannabis genotypes display differences in the tissue distribution and levels of Hop latent viroid in leaves and roots following inoculation

Hop latent viroid (HLVd) is a destructive pathogen of cannabis (Cannabis sativa L.) plants, in which symptom development is greatly influenced by the cannabis genotype. In the present study, we assessed three commercial genotypes for levels of HLVd following artificial inoculation. Viroid levels were measured in root and leaf tissues by RT-qPCR at 14, 28, 42 and 56 days post-inoculation (dpi) under controlled environmental conditions. The genotype, tissue type and sampling time all significantly (p < 0.05) influenced HLVd levels in these plants. The viroid was consistently present in root tissues of all genotypes at 14 dpi, with varying viroid levels (reflected by Cq values), depending on the genotype. Highest levels were observed in genotype Pennywise (PWE), followed by Pink Kush (PK), and were lowest in genotype Powdered Donuts (PD). In leaves, there were also significant differences in viroid levels between genotypes at 42–56 dpi, with PWE showing the highest levels and PD the lowest. In genotype PK, viroid levels were initially reduced in root and leaf tissues at 28–42 dpi, but resumed at 56 dpi to levels observed at 14 dpi. At all sampling times, HLVd levels were consistently greater in root tissues compared to leaves. The differences in viroid levels, determined by RT-qPCR, suggest that cannabis genotypes may express varying levels of tolerance to HLVd, where tolerance is defined as the ability of the genotype to influence viroid replication and accumulation within infected plants. The effect of these varying tolerance levels on symptom development and viroid spread requires further investigation.