Viroid Structure and Function Plant Pathology Transmission of Viroid

1. MOHAMMAD BILAL KAKAR
DEPARTMENT OF
MICROBIOLOGY
UNIVERSITY OF
BALOCHISTAN QUETTA
VIROI
D

2.  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.  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.  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. 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.  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.
1) Rod-like
2) Multibranched

7.  ROD TYPE VIROID
STRUCTURE
 BRANCHED VIROID
STRUCTURE

8.  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.  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)

11. Mainly cause disease in citrus trees.

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

14.  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 336-351nt 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.  Scarcity of apple skin
 Discoloration
 Non Ripened
 Irregular shape