类病毒是单链、共价、闭合环状的非编码RNA分子，是目前已知的最小病原物，能在宿主体内自主复制和系统运输，引起多种园艺作物病害并可能导致重大经济损失。高通量测序技术已成为发现类病毒病原的一条重要手段，而类病毒的致病性鉴定是防控类病毒病害的前提。项目组前期利用该技术结合PFOR软件分析和RT-PCR方法从月季中发现一个迄今未曾报道过的类病毒新种，该新类病毒具有核酶活性，分子大小为485 nt，远超过目前已知的类病毒大小。本研究将分析其序列多样性，确定新类病毒的进化分类地位；通过构建侵染性克隆，接种自然寄主和常见草本指示植物，鉴定新类病毒的寄主范围和致病性；同时调查新类病毒在田间月季种植区的发生分布情况，明确该类病毒和田间病害症状之间的对应关系。这是首次在月季上发现类病毒，对其分类地位和致病性的研究，不仅为月季类病毒病害的诊断和防控奠定基础，而且对进一步研究类病毒的流行传播规律也具有重要意义。

Viroids are single-stranded, covalent, closed circular noncoding RNA and the smallest known infectious agents, which replicate and systemically traffic in plants, and induce lots of severe diseases leading to heavy economic losses of many horticultural crops. Nowadays, next-generation sequencing (NGS) technology has become an important method for the discovery of viroid pathogens, and the identification of viroid pathogenicity is the prerequisite and basis for the prevention and control of the viroid diseases. In the previous, a China rose (Rosa chinensis Jacq.) leaf showing mosaic symptom was analyzed by NGS, wherein a new viroid was discovered using PFOR software and confirmed by RT-PCR. The new viroid consists of 485 nucleotides (nt), which is much larger than the current known viroid. It contains a biologically active hammerhead ribozyme in both polarities. In the present study, sequence diversity will be analyzed to determine the phylogenetic classification status of the new viroid. The determination of host range and pathogenicity will be performed by inoculating natural hosts and common herb indicator plants (rose plants, cucumber, tobacco and tomato) using the constructed infectious clones. In addition, we will investigate the occurrence and distribution of the new viroid in the rose-planting areas to clarify the correspondence between the viroid and the disease symptoms. We discovered a new viroid species, and this is the first time to find a viroid infecting rose plants. The study of its classification status and pathogenicity not only lays the foundation for the diagnosis, and prevention and control of rose viroid, but also has a profound historical significance for the further study on the models of epidemic spreading of the viroid.