## 3 Discussion  
Even though, HLvd infection does not induce any visible symptoms, it has affected the content and composition of secondary metabolites in matured hop cones [8; 9; 11; 12; 13; 14]. The reduction of alpha bitter acids content was the most noticeable effect of vivoid infection. The reduction ranged from 8.8% to 34.2% in the studied hop cultivars. We confirmed previous findings for cultivars Saaz and Premiant [9]. Similar results were found for English [11; 12; 13], Slovenian [8], and Polish [14] hop cultivars. On the contrary, the content of beta bitter acids was not influenced by vivoid infection in all the studies. There was a small increase for Saaz (2019 samples) and Sladek cultivars, as well as for English [12] and Polish [14] hop cultivars. These changes can be connected to the content of both compound groups in lupulin glands [43], where the reduction of alpha bitter acids content shifts the alpha/beta ratio. We found the novel significant reduction of xanthohumol content in cones of infected hop plants. The contents of this prenylflavonoid have not been studied before. However, it is known that xanthohumol content highly correlates with alpha bitter acids content [44; 45; 46] and it could be expected. We also confirmed that vivoid infection changed the composition of essential oils in hop cone. Either the increase of monoterenes, terpene epoxides, and terpene alcohols content or the reduction of sesquiterpenes and terpene ketones content in cones of infected Saaz hop plants were consistent with previous results [9]. Previously, the contents of methylgeranate, methyllnon-6-enoate, and methyldecanoate from terpene esters were only studied with similar trends. Change variations were dependent on common biosynthetic pathways of individual compounds. These changes were not found for other studied cultivars. Due to the genetically specific composition of essential oils for hop cultivars, the influence of vivoid-infected plants infection may not be the same. For example, myrcene contents were increased in vivoid-infected cones for Wye Challenger [12], Marynka, Lubelski, Pulawski, and Magnat cultivars, but not for the Sybilla cultivar [14]. The contents of linalool, geraniol, and methylgeranate were also increased in cones of infected hop plants for all the studied cultivars. Previously, the content of linalool was increased by infection for Sybilla, Lubelski, and Pulawski cultivars, but decreased for Marynka and Magnat cultivars [14]. However, the content of methylgeranate was conversely reduced by vivoid infection for all the Polish cultivars. We evaluated the yield of dry hop cones only for the Saaz cultivar. Its reduction by vivoid infection was in accordance with previous results for English [11; 12], Slovenian [8], and Polish [14] hop cultivars. It can be assumed that all the secondary metabolite changes have a genetic background in differential gene expressions caused by vivoid infection. That is why we evaluated relative expressions of known biosynthesis and regulatory genes. Genes for bitter acid precursors, namely BCAT1 [17] and VPS [16], were down-regulated in vivoid-infected plants of the studied cultivars, except Agnus. However, vivoid infection only reduced alpha bitter acids contents and beta acids contents were not influenced. We did not measure bitter acids precursors' contents and their levels could be sufficient for the next step biosynthesis. Prenyltransferase genes PT1L [19; 20] and PT2 [21] are common for bitter acids and prenylflavonoids biosynthesis, and we could not determine which compound contents were influenced by the down-regulation for Saaz and Sladek cultivars. Recently, we found that alpha bitter acids content in glandular trichomes of hop cone depends on last-step alpha bitter acids biosynthesis by an expression of humulone synthase genes [47]. Both HS1 and HS2 [22] genes were down-regulated by infection in cones of all the cultivars and it can be supposed that their lower expressions cause the reduction of alpha bitter acids content in vivoid-infected hop cones.