Viroid

Viroid Structure and Function
Plant Pathology
Transmission of Viroid

1. MOHAMMAD BILAL KAKAR DEPARTMENT OF MICROBIOLOGY UNIVERSITY OF BALOCHISTAN QUETTA Viroid

2. TABEL OF CONTENT Brief intro to viroid Discovery / History Origin Structure Classification Viroid disease Host-range & Transmission Host Resistance Control of viroid disease Plants that are affected from viroid

3. Viroid Viriods are the smallest known agents of infectious disease. They are composed of short strand of circular, single-stranded RNA that has no protein coating. They are capable of self-replicating which use host machinery to replicate itself (Genome). Viroids are the infectious agent of plants that mainly cause disease in plants. Viriods only infect the plants. They are known as plant Pathogens.

4. DISCOVERY/ HISTORY In 1971, Theodor Diener, a pathologist working at the Agriculture Research Service, discovered an acellular particle that he named a viroid, meaning “virus-like.”   Viroids  consist only of a short strand of circular RNA capable of self-replication. The first viroid discovered was found to cause potato tuber spindle disease, which causes slower sprouting and various deformities in potato plants.

5. ORIGIN OF VIROID The origin of viriods remains unknown, although Diener Speculated that: viriods may be derived from host cellular RNAs Transposable Elements. Plasmids or Introns and may be relics of pre-cellular RNA evolution.

6. STRUCTURE OF VIROID Composed of small covalently closed, circular single-stranded RNA molecule. Range in size from 239 to 401 Nucleotides. Viroids have unique, thermodynamically stable structures that are composed of a series of helices and loops due to intra-molecular base pairing which results that they are partially double stranded and although they are circular molecules . Viroids have two different types of structures. Rod-like Multibranched

7. Structure of viroid ROD TYPE VIROID STRUCTURE BRANCHED VIROID STRUCTURE

8. CLASSIFICATION OF VIROIDS There are 30 known viroid species that are taxonomically divided into two families. Pospiviroidae ( PSTVd ) Avsunvirioidae ( ASBVd ) That are further divided into 3 subfamilies and 7 genus.

9. Viroid diseases Potato-spindle Tuber Viroid ( PSTVd ) Hope Stunt Viroid ( HSVd ) Hope Latent Viroid ( HLVd ) Coconut codang-codang Viroid ( CCCVd ) Avacado Sun-blotch Viroid ( ASBVd ) Chrysanthemum Stunt Viroid. ( CSVd ) Peach latent Mossaic Viroid ( PLMVd )

10. Potato-spindle tuber viroid

11. Hope stunt viroid Mainly cause disease in citrus trees.

12. COCONUT CODANG-CODANG VIROID Every year one million coconut palms are killed by CCCVd and over 30 million coconut palms have been killed since Cadang-cadang was discovered .

13. Avacado sunblotch viroid viroid for sunblotch avocado is a disease that affects avocado trees. Infections result in lower yields and poorer quality fruit.

14. Peach latent viroid Peach latent mosaic  viroid  is the type species of the genus  Pelamoviroid , which belongs to the family  Avsunviroidae . This family is characterized as having chloroplastic viroids with  hammerhead ribozymes . Peach latent mosaic viroid is a 336-351 nt   circular RNA  which has a branched formation. The symptoms of the disease include  necrosis  of buds, delayed shoot development, necrotic branches, premature ageing of trees, flower streaking, ripening deformations, enlarged rounded stones, circular discoloured areas on the fruit skin and in some cases mosaic, blotch, vein banding or calico appearance on infected leaves

15. Apple scar skin viroid Scarcity of apple skin Discoloration Non Ripened Irregular shape