Plant Viruses

1. Barley Yellow Dwarf
Virus
Prepared by:
Saleem Sulaiman
BS Microbiology
Kohat University of Science and Technology,
Kohat

2. Barley Yellow Dwarf Virus
Contents
 Introduction
 History
 Taxonomy
 Genome
 Pathogenesis
 Signs and symptoms
 Economic significance
 control

3. Introduction
Barley yellow dwarf virus (BYDV) is an important pathogen of cereal crops
It causes barley yellow dwarf disease in
Wheat
Maize
Barley
Oat
Rice

4. Introduction
BYDV is a single-stranded positive sense RNA
It has an icosahedral shape, approximately 25-30 nm in diameter
The virion is not enveloped in lipid coating
The virus is transmitted by aphids

5. Morphology of BYDV

6. History
In 1890, a mysterious disease of oats was seen in South England, Georgia and
USA
The oats were stunted, sometimes red and often set little seed
The next epidemic struck the U.S oat crop in 1907
T.F. Manns study the possible relationship between aphids and the disease

7. History
Oswald and Houston study the role of insects in the disease
They found that five aphid species were capable of transmitting the disease
Transmission by aphids and lack of transmission by rubbing differentiated it from
other plant viruses
In 1953, Barley yellow dwarf virus was first recognized in California in Barley by
Oswald and Houston

8. Taxonomy
Group: Group IV ss +(ive) sense RNA
Family: Luteoviridae
Genus: Luteovirus
Species: Barley yellow dwarf virus

9. Taxonomy
Barley yellow dwarf virus comprises three subspecies based on
differences in vector specificity
1. Barley yellow dwarf virus-PAV (BYDV-PAV)
2. Barley yellow dwarf virus-MAV (BYDV-MAV)
3. Barley yellow dwarf virus-PAS (BYDV-PAS)

10. Genome
 BYDV has a single stranded RNA of positive polarity
Its genome is linear and non-segmented
In 1988, the nucleotide sequence of entire barley yellow dwarf virus, PAV
serotype (BYDV-PAV) genome was completed by Miller
Its genomic RNA consists of 5677 nucleotides
In the genome, there are six open reading frames (ORFs)

11. Genome

12. Genome
ORF1 and ORF2 encode proteins that are required for virus replication
The product of ORF1 (39 kDa protein) was suggested to be a helicase
It contains several amino acid motifs conserved in most known helicases
A different study suggested that BYDV, as well as the majority of RNA viruses
with genomes smaller that 6 kb, does not contain a helicase
The product of ORF2 (60 kDa protein) is RNA-dependent RNA polymerase
(RdRp)

13. Genome
The BYDV coat protein (22 kDa protein) is encoded by ORF3
The product of ORF4 (17 kDa protein) was suggested to be movement protein
Product of ORF5 (50 kDa protein) has been involved in aphid transmission
 The function of the 6.7 kDa protein encoded by ORF6 is unknown, but it is not
required for virus replication
It has no amino acid sequence homology to any known proteins.

14. Pathogenesis
Barley yellow dwarf virus is transmitted by aphids
Viruliferous aphids transmit the virus to plant phloem when saliva is injected
during feeding
The virus replication cycle begins when the ssRNA is released from the virion
This ssRNA is positive sense that serves as messenger RNA
Early gene products (proteins) are translated from the ssRNA

15. Pathogenesis
These early gene products are believed to be the part of the complex required to
make copies of viral RNA
Complementary negative sense RNA strands are produced from the positive sense
ssRNA
The negative sense RNA strands are then used as templates for the production of
many copies of positive sense ssRNA

16. Pathogenesis
It is believed that these new positive sense RNA strands are transported from cell
to cell in the host, initiating more replication cycles and thus spreading replication
within the plant
Late gene products are produced which include structural proteins of the virions
 Positive sense ssRNA and structural proteins are assembled into virions, which
can be ingested by an aphid vector that transmits the virus to new cell

18. Transmission
BYDV is transmitted from plant to plant by aphids species.
Aphids acquire barley yellow dwarf virus by feeding on infected plant and
transmit the virus in subsequent feeding.
These aphid can pass the disease within 15 min of feeding.

19. Transmission
BYDV is transmitted by more than 20 aphids species but the most imported are;
1. Rhopalosiphum padi (oat-bird cherry aphids)
2. Rhopalosiphum maidis (corn leaf aphid)
3. Schizaphis graminum ( the greenbug)=wheat, oat
4. Macrosiphum avenea (English grain aphid)

20. Vectors

21. Vectors

22. Transmission

23. Signs and Symptoms
Symptoms appear approximately 14 days after infection
BYDV infection can lead to phloem degradation and collapse of sieve elements
The most common symptom is stunting (dwarf appearance) due to reduced
internode length
Root mass of infected plants is often reduced

24. Signs and Symptoms
The most conspicuous symptom on infected host is the loss of green color in
leaves
Barley leaves often turns bright yellow; oat leaves may become orange, red or
purple; rice and wheat leaves typically turns yellow or red; edges of corn leaves
turn red, purple or yellow

25. Signs and Symptoms

26. Signs and Symptoms

27. Economic Significance
Barley yellow dwarf is one of the most widespread and serious viral diseases in
the world
It causes a significant reduction in cereal grain production
The yield losses in cereal crops are estimated to be 13–25 kg/ha
 Up to 80% yield loss of cereal crops due to barley yellow dwarf virus (BYDV)
infection has been reported

28. Control
Due to the mandatory aphid transmission, one of the most effective methods to
control BYDV epidemics has been insecticide applications targeting aphid vectors
However, chemical control is costly and potentially harmful to the environment
Conventional breeding for resistance to luteoviruses has not been able to provide
high levels of crop protection

29. Control
 Genetic engineering is a promising new approach, which potentially combines
high effectiveness and low cost
 Several research groups have developed transgenic plants with increased
resistance to BYDV
Because of the constant evolution of the virus populations in the field, none of the
plant protection methods can be used indefinitely

30. Control
Therefore, continuous research efforts need to be undertaken that are aimed at
better understanding of virus replication and interaction with the host
Such efforts will help to identify new targets for antiviral agents, which may
become the bases of new control strategies.