plant microbe interaction

1. Plant diseases
Why study them ?

2. Sustaining sufficient agricultural
production to feed the world
while preserving a clean, safe and
a healthy environment for
the very people we are trying to feed.

3. • About 3000 plants are used by humans as food source
• 30 plant species make up 90% of our food supply
• Plants provide feed for animals
• Lumber for shelter, furniture
• Fibre for cloth, fabrics, rope and paper
• Medicine, beverages, chocolates
• Aesthetic appeal, relaxation and recreation

4. Plant Diseases – yield loss- famine
Bacterial wilt
Chestnut blight
Coffee rust
Downy mildew
Ergot of rye
Phytophthora root rot
Potato late blight
Rice blast
Root Knot
Smuts of cereals
Rusts of wheat
Tobacco mosaic

7. British rule : 85 million deaths due to famines.

8. Plant disease statistics

10. What is a plant disease?
•Visible effects of disease on plants are called
symptoms. Any detectable changes in color,
shape, and/or functions of the plant in response
to a pathogen or disease-causing agent is a
symptom.
•Signs of plant disease are physical evidence of
the pathogen, for example, fungal fruiting bodies,
bacterial ooze, or nematode cysts. Signs also can
help with plant disease identification

11. What causes Plant Disease
a. Micro organisms and parasitic Plants
b. Environmental factors, faulty nutrition, chemical substance

13. Identifying the agent of a Plant Disease
Kochs Postulates
a. Consistent association with disease
b. Isolated in pure culture/abiotic agent identified
c. Healthy plants inoculated with pure culture of
pathogen / treated with abiotic agents/ conditions should develop same symptoms
d. Same pathogen/ agent must be isolated or identified

14. • Atmospheric CO2 concentration has increased
from 280 p.p.m. in 1750 to 368 p.p.m. in 2000
• Temperature is projected to increase by
3·4°C and CO2 concentration to increase to
1250 p.p.m. by ∼2095

15. Climate change, plant diseases and food security: an
overview
Plant Pathology
Volume 60, Issue 1, pages 2-14, 10 JAN 2011 DOI: 10.1111/j.1365-3059.2010.02411.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3059.2010.02411.x/full#f1

16. Plant Virus
700 known plant viruses
Barley yellow dwarf virus- 150 spp .of poaceae
15-38% reduction in yield
Cassava mosaic- UgV
recombinant strain of ACMV and EACMV
•Transmitted by insects which are called vectors

18. Genome of BYDV

19. Plant Bacteria
Xanthomonas 350 different plants
Basmati rice is highly susceptible to bacterial blight
Bacterial blight of rice
Bacterial blight of banana
Ralstonia solanacearum ; infects 200 different plants
Bacterial wilt of ginger
Bacterial wilt of chilli

21. PXO99A KACC MAFF
Length (bp) 5,240,075 4,941,439 4,940,217
GC content
(%)
63.6 63.7 63.7
Annotated
genes
5,083 4,637 4,372
IS elements
(complete/fra
gment)
267 (683) 252 (714) 251 (712)
TAL effector
genes
19 15 17

23. Plant Nematodes

26. Secondary cycles
•Some diseases have only one cycle during the
growing season (often root rots)
•Some diseases develop secondary or repeating
cycles during the growing season (often foliar
diseases)
•Number of cycles depends on the pathogen,
susceptibility of the host, and environmental
conditions

27. Summary
•Understanding the difference between a sign and
a symptom is key in identifying a plant disease
•A plant disease cannot develop if a susceptible
host, pathogen, and favorable environment do not
occur simultaneously
•The major plant pathogens responsible for
disease development in plants are fungi, bacteria,
viruses, and nematodes
•The disease cycle describes the interaction of the
pathogen with the host