In 2007, hop growers in Slovenia reported the appearance of severely stunted hop plants, a phenomenon that spread rapidly within hop gardens and among farms. Classical diagnostic methods were unable to detect a new pathogen; therefore, single step high-throughput parallel sequencing of total RNA and small RNAs from plants with and without symptoms was employed to identify a novel pathogen. The sequences were assembled de novo and also mapped to reference genomes, resulting in identification of a novel sequence of Citrus bark cracking viroid (CBCVd) in the stunted hop plants. Furthermore, the presence of this novel pathogen on hop was confirmed by RT-PCR analysis of 59 plants with symptoms from 15 hop gardens, representing the main outbreak locations identified by systematic disease monitoring, and small RNA Illumina sequencing of the bulked RNA sample. The high infectivity of the newly identified CBCVd was also confirmed by biolistic inoculation of two hop cultivars, which developed aggressive symptoms in controlled conditions. This study shows the feasibility of deep sequencing for the identification of causative agents of new diseases in hop and other plants.
COBISS.SI-ID: 8056185
Viroids are the smallest plant pathogens; their genome is short, single-stranded, non-coding, circular RNA molecule. They can infect cultural and ornamental plants and cause diseases that have a major economical impact. The plants defence against viroid pathogens is based on the mechanism of RNA silencing. Viroids can avoid this mechanism due to compact secondary structure and localization in organelles. Furthermore they can turn mechanism of RNA silencing in their favour, therefore they are able to silence selected host genes. By using the RNA silencing mechanism viroids can silence genes associated with plant defence, signal transmission, cell wall structure and many others. This leads to the development of symptoms such as dwarfing, leaf curling, stem and leaves necrosis, distortion of the fruits, in some cases, plants may also die. The manuscript presents mechanism of viroid infection process in plants and basic characteristics of viroids.
COBISS.SI-ID: 8084089