Study the adverse effects of different viruses and other fungal diseases on the plants and their growth. Discuss the methods e.g. plant disease resistant and genetic engineering to protect the plants.

1. Genetic
Engineering

2. PLANT DISEASE RESISTANCE
AND GENETIC ENGINEERING

3. What is a plant disease?
 A plant disease is any abnormal condition
that alters the abnormal growth or function
of a plant. Disease may also reduce yield and
quality of harvested product.
 Plant diseases are classified in 2 categories:
a) Abiotic
b) Biotic

4. Abiotic Diseases
 Are caused by (non-living) environmental
conditions such as frost, hail, and
chemical burn.
 Damage caused by chronic exposure to
air pollutants such as nitrogen dioxide,
sulfur dioxide etc.

5. Biotic Diseases
 Are caused by living organisms such as
fungi, bacteria, viruses, nematodes, etc.
 Pathogens may infect all types of plant
tissues to include leaves, shoots, roots,
fruit, seeds etc.

6. The Disease Triangle
 For a biotic disease to occur there must be
a susceptible host plant, the pathogen,
optimum environmental conditions.

7. The Disease Cycle
 The development of visual disease
symptoms on a plant requires that the
pathogen must
(a) come into contact with a susceptible
host
(b) gain entrance or penetrate the host
through either a wound, a natural opening
or via direct penetration of the host
(c) establish itself within the host
(d) grow and reproduce within or on the
host

8. Biotic Components
Fungi:-
 They damage plants by killing cells or causing
plant stress.
 Sources are infected seed, soil, crop debris,
nearby crops and weed, which spread by
wind and water splash, and through the
movement of contaminated soil etc.
 They enter plants through natural openings
such as stomata and through wounds caused
by pruning, harvesting, hail, insects, other
diseases, and mechanical damage.

9. Common fungal diseases
 White blister/White rust
 Clubroot
 Botrytis rots
 Anthracnose
 Tuber diseases

10. Viral Infections
 Viruses cause many plant diseases.
The spread of most viruses is very
difficult to control.
 Viruses are often transmitted from
plant to plant by insects.
 Normally, when a RNA virus attacks a
cell, it will produce enormous number
of copies of itself. The copies, in turn,
produce viral protein, which can help
to disable the cells defenses to the
virus.

11.  One way of preventing viral infections is
by giving a plant a viral gene encoding
the virus' 'coat protein'. The plant then
produces this viral protein before
the virus infects the plant. If the
virus arrives, it is not able to reproduce.
 This is called co-suppression. When a
foreign viral DNA enters the plant cell,
viral coat protein is produced, and it
eventually shuts down the viral protein's
expression. When the virus tries to infect
the plant, the production of its
essential coat protein is already blocked.

12.  VCPs encapsulate the viral nucleic
acid and are thought to be important in
nearly every stage of viral infection
including replication, movement
throughout an infected plant, and
transport from plant to plant

13.  Alternatively, apical or axillary
meristems are generally free from viral
particles, which has helped the
scientists to produce virus free plants,
by culturing small meristems collected
from virus infected plants.

14. Gene Transfer in plants
 Vector used: Ti plasmid of
Agrobacterium Tumefaciens.
 Ti Plasmid- Tumor Inducing Plasmid
with Transfer DNA.
 Strategy:
Collect leaf discs
 Infect the tissue with Agrobacterium
carrying recombinant Ti plasmid.

15.  The infected tissue is then raised in Shoot
regeneration medium for 2-3 days, so that
transfer of T-DNA along with gene of
interest takes place.
 Then the transformed tissues are
transferred onto selection cum plant
regeneration medium supplemented with
usually lethal concentration of an antibiotic.
 This medium also contains a bacteriostatic
agent, which suppresses the
Agrobacterium present with the
transformed tissues.

16.  After 3-5 weeks, the regenerated shoots
are transferred to root inducing medium.
 After another 3-4 weeks, complete plants
are obtained, which are transferred to soil,
following the hardening of regenerated
plants.

17. Late Blight in Potato
 produce millions of spores from infected
plants under the wet weather conditions
that favor the disease.
 Spores produced on infected potatoes can
travel through the air, land on infected
plants, and if the weather is sufficiently
wet, cause new infections.

18.  Late blight is caused by the oomycete
Phytophthora infestans.
 Several R genes originating from
introgressions of S. demissum have been
mapped to potato chromosomes using DNA
markers.
 the molecular cloning of R1 gene for
resistance to late blight that is located in the
resistance hot spot on potato chromosome V.
 R1 among plant resistance genes containing
a conserved nucleotide binding domain
(NBS), a leucine-rich repeat domain (LRR)
and a leucine zipper motif.

19.  300 Restriction fragment length
polymorphism(RFLP markers)
 Race specific and hyper sensitive to
p.infectants
 Those groups were R1, R3, R4, R10 and
groups with a larger amount of
accumulated R alleles and 90 different
clones belonging to the species S.
demissum, S. tuberosum ssp. andigena,
S. phureja, S. bulbocastanum and S.
stoloni

21.  Remaining clones in the physical map are
BACs with lengths between 70 and 100
kb.
 Grey bars: BACs from the chromosome
carrying r1.
 Solid black bars: BACs from the
chromosome carrying R1.
 Mapped BAC ends are indicated by the
number of recombinants separating the
BAC end from R1.

22. References
 http://ohioline.osu.edu/hyg-
fact/3000/pdf/PP401_01.pdf
 The%20R1%20gene%20for%20potato%20
resistance%20to%20late%20blight%20(Phy
tophthora%20infestans)%20belongs%20to
%20the%20leucine%20zipper,NBS,LRR%2
0class%20of%20plant%20resistance%20g
enes.%20(4).pdf
 http://www.gmeducation.org/environment/p
190974-thirsty-plants-rely-on-fungus-for-
help.html