The chrysanthemum virome in Liguria: a high-throughput sequencing investigation

Chrysanthemum (Chrysanthemum sp.) is one of the major cut flower ornamentals commercialized in the italian market and is considered a notable crop for the Liguria region. The agamic propagation procedure, ordinarily used for chrysanthemum, has led to unintentional accumulation of viral/viroidal infections, causing a meltdown in the crop yield and quality of several notable varieties for the Liguria area. The CRIREC project aimed to recover the Dilana, Snowdon and Turner notable varieties, still cultivated and appreciated in Liguria but unavailable from Dutch and Danish breeder's catalogues, in order to increase their commercial value, both quantitatively and qualitatively. In Italy, there are several viruses reported to infect chrysanthemum: chrysanthemum virus B (CVB), tomato aspermy virus (TAV), and tomato spotted wilt virus (TSWV) among the most spread. A viroid, chrysanthemum stunt viroid (CSVd), is also reported. Plant samples of the varieties under study, showing viral-like symptoms, were collected in Liguria area between 2017 and 2021 in order to shed light on their "virome" through High-Throughput Sequencing (HTS) techniques, and set up specific molecular diagnostic assays. HTS analysis performed on collected samples highlighted the presence of CVB and TSWV infection, already reported; moreover, sequences related to Avsunviroidae, Bromoviridae, Caulimoviridae, Tombusviridae and Virgaviridae families were identified, and are currently under study. The three chrysanthemum varieties were then treated to rescue virus/viroid-free material through application of in vitro plant tissue culture techniques and apical meristems cultivation associated to termotherapy; specific molecular diagnosis will be also used to assess the absence of infective agents. Overall, our study has shown that a combined approach of HTS, molecular assays and in vitro techniques can be successful in supporting the production of virus free propagative material.