Allelopathy is the chemical inhibition of one plant (or other organism) by another, due to the release into the environment of substances acting as germination or growth inhibitors.

1. ALLELOPATHY
Department of Agronomy BZU Multan
Presented By:
Malik Ghulam Asghar

2. Outline
1) Background
2) Allelopathy
3) Allelopathic interactions
4) Allelopathic Chemicals
5) Mode of Action of Allelochemicals
6) Effects of Allelochemicals
7) Types of Allelopathy
8) Ways of releasing Allelochemicals
9) Factors affecting the Allelopathy
10) Allelopathy and Competition
11) Allelopathy and weeds management

3. Background
Harmful
effects of
Herbicides

4. ALLELOPATHY
Definition
Greek words
allelon which means "of each other“
pathos which means "to suffer".
“Allelopathy refers chemicals
released into the environment
where it affects the development
and growth of neighboring plants”

5. Forms of Allelopathic Interactions
Forms of Allelopathy
Weed on
Crop
Weed on
Weed
Crop on weed

6. Allelopathic Interaction
1) Weed on Crop
Jungli pallak affect the wheat plant growth and development
Inhibits

7. Allelopathic Interaction
2) Weed on Weed
Impereta cylindrica (Cogon grass) inhibits the emergence and growth
of an annual broadleaf weed i.e. Borreria hispada (Button weed) by
exudation inhibitory substances through rhizomes.
Inhibits

8. Allelopathic Interaction
3) Crop on Weed
Oat, pea, wheat suppress the growth of Chenopodium album
(Lamsquarter)
Inhibits

9. Allelopathic effects of crops on weeds
Crop Weed sp. Source of inhibitors
Maize Chenopodium album,
Amaranthus retroflexus
Roots
Sorghum Abutylontheophrasti,
Amaranthus hybridus
Shoots and foliages
Rye Digitaria sanguinalis,
Ambrosia artimisifolia
Shoots and foliages

10. Allelopathic Chemicals
Phenolic acid
Coumarins
Terpinoids
Flavinoids
Scopulatens

11. Mode of Action of Allelochemicals

12. Extract preparation of Allelochemicals
Washing
Drying
70 ˚c
Chopping
Grinding
Mixing
1:20
Extract

13. Types of allelopathy
1. True Allelopathy
The true allelopathy is the release of substances that are toxic in the form
in which they are produced in the plant.
2. Functional Allelopathy
Functional allelopathy is the release of substances that are toxic or a
result of transformation by micro-organism .

14. Ways of releasing Allelochemicals
Allelopathic chemicals are released from
the plants as:
Vapour – from root and leaf (through
stomata)
Foliar
Root
Breakdown/ decomposition product of
dead plant parts
Seed extract

15. Factors affecting Allelopathic effect
Allelopathic effects might also depend on a number of other factors that might be
important in any given situation:
Varieties
Specificity
Auto-toxicity
Crop on crop effects
Environmental factors

16. Advantages of Allelopathy
1) Limit competition for space,
light, nutrients, water
2) Autotoxity (Chemical produced
inhibits germination of it's own
seeds)
3) Allelopathic Weed Suppression
Through the Use of Cover Crops

17. Allelopathy and Weed Management
Allelopathic extracts have been successfully
used for organic weed management.
Allelochemicals are diverse in nature and
structure and thus lack common mode of
action.
This phytotoxic activity of Allelochemicals is
responsible for growth suppression of weeds.

18. Allelopathy and competition
Plants will compete for sunlight, water
and nutrients.
Allelopathic plants prevent other plants
from using the available resources and
thus influence the evolution and
distribution of other species.

19. Management of Plant Allelopathy
Arrangement of Cropping Systems
Crop allelopathy can be effectively used to
control weeds in the field.
By intercropping those field crops which can
suppress weeds of next crops

20. Management of Plant Allelopathy
Straw Mulching
Allelopathic applications, such as straw
mulching, provide sustainable weed
management
The allelochemicals from decomposed
straw can suppress weed growth in
farmlands, and reduce the incidence of
pests and diseases.

21. Thank you !