Viroids are small, highly infective, single-stranded RNA molecules with profound secondary structure. Research on their infections in plants has been focused on single viroid infections. Currently there are four different viroids able to infect hop plants (Humulus lupulus L.) however, in our work we focused on studying polarity and accumulation levels of HLVd, CBCVd and HSVd in multiple infected hop plants. Based on RT-qPCR results and RNA-seq data, obtained from a project »Plant response analysis in multiple viroid infections and identification of plant resistance – L4-6809« we concluded, that viroids amplify in hop till saturation is reached, probably limited by host's resources. Antagonism amongst viroids also seems to be present in multiple infections, especially between CBCVd and HSVd. RT-qPCR data shows that HSVd is the most sensitive, whereas CBCVd is the least sensitive to the presence of another viroid. Interestingly, in cases of HLVd and CBCVd RNA-seq data indicates that (?) strand is prevailing over (+), which contradicts to some data from the literature. On the other hand, RT-qPCR results are inconsistent regarding viroid polarity. Furthermore, there seems to be a certain degree of biological variability present, suggesting the analysis of several biological replicates in similar experiments. We encourage the use of alternative approaches to studying viroid polarity and viroid-plant interactions.
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