Molecular detection of plant viroids

• Published in: Biotechnology and plant disease management pp. 277 - 300
• Main Author: Singh, R. P
• Format: Book Chapter
• Language: English
• Published: Wallingford, UK CAB International 2007
• Subjects: America; APEC countries; Commonwealth of Nations; crop plants; detection; Developed Countries; eukaryotes; methodology; methods; North America; OECD Countries; ornamental plants; ornamentals; pathogens; phytopathogens; plant diseases; plant pathogens; plant viruses; plants; Pospiviroid; Pospiviroidae; potato spindle tuber viroid; ribonucleic acid; RNA; techniques; viroids; viruses; viruses of plants; Canada
• ISBN: 1845932889; 9781845932886
• DOI: 10.1079/9781845932886.0277

Viroids were discovered as novel plant pathogens in the early 1970s, and consist solely of single-stranded RNA covalently closed as a circular molecule. Viroids are the smallest known plant pathogen, ranging from 247 to 463 nucleotides (nt) in length. About 30 viroids infecting agricultural, horticultural and ornamental plants are known. Most of the reported viroids cause disease symptoms and economic losses, but many more are present in plants without exhibiting symptoms. The unique molecular composition and structure of viroids has demanded the development of many innovative detection protocols. The need for routine viroid detection methodology first resulted in the development of polyacrylamide gel electrophoresis (PAGE). Novel innovations in the form of 'return'-PAGE (R-PAGE), 'sequential'-PAGE (S-PAGE), temperature gradient gel electrophoresis (TGGE) and PAGE-'mobile laboratory' increased the efficiency and effectiveness of viroid detection. Viroids were also the subject matter in the first application of both molecular hybridization (MH) (solid support) and reverse transcription-polymerase chain reaction (RT-PCR) for plant pathogen detection. Although reports of new viroid species have diminished, new outbreaks of existing spp. have increased in many countries, largely as a result of symptomless viroid carriers. Detection procedures have played an important role in the eradication of potato spindle tuber viroid (PSTVd) from Canada and it is theorized that new outbreaks of viroids on crop plants can be better explained by understanding the role of ornamental plants in the evolution of viroids. Consequently, procedures to facilitate large-scale survey of symptomless ornamental or crop plants for spp. have recently been developed.