This document discusses viroids and the potato spindle tuber viroid. It begins by defining viruses and viroids, noting that viroids are the smallest known infectious agents and consist only of naked RNA. It then describes the discovery and effects of the potato spindle tuber viroid, which was first found in 1971 and causes potato crop failures and economic losses. The document provides details on the structure, transmission, and symptoms of the potato spindle tuber viroid, the causal agent of potato spindle tuber disease.

1. VIRIOID DISEASE
POTATO SPINDLE TUBER
VIRIOD
K R MICRO NOTES 1

2. VIRUSES
➔ A virus is an infectious microbe consisting of a segment of nucleic acid
(either DNA or RNA) surrounded by a protein coat.
➔A virus cannot replicate alone; instead, it must infect cells and use
components of the host cell to make copies of itself.
➔Often, a virus ends up killing the host cell in the process, causing
damage to the host organism.
➔Well-known examples of viruses causing human disease include
AIDS, COVID-19, measles and smallpox.
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3. VIROIDS
➔ Viorids are infectious agent that consists only of naked RNA without
any protective layer such as protein coat,
➔ These are infectious pathogens that only affect plants, hence they are
called as plant pathogens and are replicated at the expense of host cell.
➔ Viorid genomes are small single stranded circular RNA that are only
250-400 bases long.
➔ Viruses are tiny infectious agent that can only multiply within the
living cells and can have either DNA or RNA as nucleic acid, whereas
Viroids are tiniest infectious agent that only attack plants and have
RNA as nucleic acid.
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4. VIROIDS
➔ Viroids were first discovered by T.O. Diener in the year 1971.
➔ It was first examined in the potato spindle tuber viroid that caused a huge
loss to the potato industry.
➔ The plants that are infected by viroids are responsible for the crop failures
and also causes loss of millions of dollars in the agricultural revenue every
year.
➔ Some of the plants that are affected by these pathogens are potatoes,
tomatoes, cucumbers, chrysanthemums, coconut palms, avocados, etc.
➔ Viroids replicate by the process of RNA–RNA transcription. They mainly
infect the epidermis of the hosts after causing mechanical damage to the
cell wall of the plant.
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5. Reference-https://microbiologynote.com/difference-between-virus-and-viroids/
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6. POTATO SPINDLE TUBER DISEASE
➢ Pathogen- Potato spindle tuber
viroid
➢ Primary Host- Solanum
tuberosum(potato) , Solanum
lycopersicum L. (tomato) - both
belong to Solanaceae family
➢ Secondary Host- Ipomoea
batatas (sweet potato)-
Convolvulaceae family and
Solanum melongena (eggplant)-
Solanaceae family
SCIENTIFIC
CLASSIFICATION:
Domain-Virus
Group- Viroids
Family-Pospiviroidae
Genus- Pospiviroid
Species- Potato spindle
tuber viroid
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7. Reference-
https://www.researchgate.net/figure/Typical-
symptoms-of-potato-spindle-tuber-disease-
observed-in-the-field_fig2_282667476
Reference-
https://apsjournals.apsnet.org/doi/10.1094/
PDIS-02-19-0312-RE
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8. STRUCTURE OF PSTVd
➔ Potato spindle tuber viroid (PSTVd) is the first recognized viroid.
➔ Molecular weight of RNA is approximately 100,000 daltons.
➔ SSRNA molecule comprises 359 nucleotides with extensive
regions of base pairing.
➔ Under electron microscope purified but apparently denatured
PSTVd appears as short strands, about 50 nm long.
➔ Sap from infected plants is still infective after dilution 1:1,000 to
10,000 and after heating for 10 min at 75-80° c.
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9. 1 CGGAACUAAA CUCGUGGUUC CUGUGGUUCA CACCUGACCU CCUGAGCAGA AAAGAAAAAA
61 GAAGGCGGCU CGGAGGAGCG CUUCAGGGAU CCCCGGGGAA ACCUGGAGCG AACUGGCAAA
121 AAAGGACGGU GGGGAGUGCC CAGCGGCCGA CAGGAGUAAU UCCCGCCGAA ACAGGGUUUU
181 CACCCUUCCU UUCUUCGGGU GUCCUUCCUC GCGCCCGCAG GACCACCCCU CGCCCCCUUU
241 GCGCUGUCGC UUCGGCUACU ACCCGGUGGA AACAACUGAA GCUCCCGAGA ACCGCUUUUU
301 CUCUAUCUUA CUUGCUUCGG GGCGAGGGUG UUUAGCCCUU GGAACCGCAG UUGGUUCCU
PRIMARY STRUCTURE
SECONDARY STRUCTURE
Putative secondary structure of the PSTVd viroid. The highlighted nucleotides are found in most other
viroids.
Reference-https://en.wikipedia.org/wiki/Potato_spindle_tuber_viroid 9

10. TRANSMISSION
➔ The pathogen is mechanically transmitted and is spread mainly by
knives tools used to cut healthy and infected potato ‘seed’ tubers and
during handling and planting of the crop.
➔ PSTV is also transmitted by several insects including aphids,
grasshoppers, beetles.
➔ About 50% transmission is through contact of bruised sprouts and 80-
100% infection by rubbing of healthy and diseased leaves.
➔ According to Singh(1970) in potato and tomato, the viroid is
transmitted by true seed. It also transmitted through pollen (Singh et
al., 1992)
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11. ETIOLOGY
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12. References
➔ David P. Clark, Nanette J. Pazdernik, Michelle R. McGehee,Chapter 24 -
Viruses, Viroids, and Prions,Editor(s): David P. Clark, Nanette J. Pazdernik,
Michelle R. McGehee,Molecular Biology (Third Edition),Academic
Cell,2019,Pages 749-792,ISBN 9780128132883.
https://doi.org/10.1016/B978-0-12-813288-3.00024-0
➔ https://byjus.com/biology/viroids/
➔ https://www.genome.gov/genetics-glossary/Virus
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