Potato spindle tuber disease VIRIOID DISEASE

Potato spindle tuber disease K R.pptx

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. 2

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. 3

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. 4

5. Reference- https://microbiologynote.com/difference-between-virus-and-viroids/ 5

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 6

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 7

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. 8

9. 1 CGGAACUAAA CUCGUGGUUC CUGUGGUUCA CACCUGACCU CCUGAGCAGA AAAGAAAAAA 61 GAAGGCGGCU CGGAGGAGCG CUUCAGGGAU CCCCGGG GAA AC CUGGAGCG 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 ) 10

11. ETIOLOGY 11

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 12