Intoduction Harms of weedicides Existent problems What is allelopathy? How does it execute? Examples of allelopathic plants Rice weeds Screening methods Field studies Results Advantages Conclusion

1. POSSIBLE WEED MANAGEMENT
WITHOUT WEEDICIDES
Ms. Venus Haridas Tupate
M. Sc I
Department of Biotechnology,
SGBAU, Amravati

2. CONTENTS
Intoduction
Harms of weedicides
Existent problems
What is allelopathy?
How does it execute?
Examples of allelopathic plants
Rice weeds
Screening methods
Field studies
Results
Advantages
Conclusion

6. Existent problems
• The overuse of agrochemicals has caused
environmental degradation, pest tolerance and
human health concerns.
• Agriculture worldwide is currently using about 3
million tons of herbicides annually, and
herbicide-resistant weeds have become more
prolific, which has further expanded the use of
herbicides.

7. Weeds Are Winning the War against Herbicide Resistance!!!
Herbicides are under evolutionary threat.

8. What is
Allelopathy?

9. Allelopathy is a biological
phenomenon by which an organism;
plant produces one or
more biochemicals that influence or
inhibit the germination, growth,
survival, and reproduction of other
organisms.

10. How?

11. • These biochemicals are known
as allelochemicals and can have beneficial
(positive allelopathy) or detrimental (negative
allelopathy) effects on the target organisms and
the community.
• Through the release of allelochemicals, certain
plants can greatly affect the growth of other
plants either in a good or bad way by leaching,
decomposition, etc.

12. On the other hand, allelopathic plants
may also be considered Mother
Nature’s own weed killer.
(NATURAL WEED KILLERS)

13. • Various parts of plants can have these
allelopathic properties, from the foliage and
flowers to the roots, bark, soil, and mulch.
• Most all allelopathic plants store their protective
chemicals within their leaves, especially during
fall.
• Some plants also release toxins through their
roots, which are then absorbed by other plants
and trees.

14. Asparagus (Asparagus officinalis)
The Asparagus plant inhibits the growth of any other plant and even its
own seedlings from its space by producing certain amino acids,
phenolic acids, ferulic acids and saponins

15. Black Walnuts (Juglans nigra)
The Walnut tree produce a compound called ‘Juglone’ from its buds, leaves, nut
shells and roots. The substance affects growth of adjoining plants such as
tomatoes, peppers, eggplant, potato, pine and birch.

16. Eucalyptus
The Eucalyptus tree too affects the seed germination, growth of
seedlings and root length of cotton and wheat growing in its vicinity.
The foliage and leaves of the tree have compounds that are found to be
having inhibitory effect on other plants.

17. Marigold (Tagetes minuta)
The plant with beautiful flowers not only produces aromatic
compounds but also poisonous substances from its roots. It produces
alpha-terthienyl from the roots which kills nematodes and hinders the
growth of adjoining plants.

18. Pine (Pinus roxburghii)
The pine tree produces phenols and esters which get transferred to the ground
through its foliage. Through leaching and decomposition, the compounds get
mixed with soil making it acidic which helps the tree to check the growth of its
competitors in the area

19. EXAMPLE: Rice allelopathy and the
possibility for weed management
Rice (Oryza sativa L.)
It is the principal food crop in Asia and the staple
food of the majority of the population in many
regions of the world.

20. Major paddy weed seeds such as:
1. Barnyardgrass (Echinochloa crus-galli)
2. Monochoria (Monochoria vaginalis)
3. Indian jointvetch (Aeschynomene indica)

21. SCREENING METHODS
1. Relay seedling
2. Bioassay-guided isolation by GC-MS
3. HPLC screening
4. Field screening
5. Sandwich
6. Rice straw meal and soil mixture
7. Leaf, straw and hull aqueous extract
8. Interplanted in fields

22. Some commonly tested plants
• Lettuce (Lactuca sativa L.)
• Radish (Raphanus sativus)
• Cress (Lepidium sativum L.) etc can be used in
the screenings as indicator plants.

23. FIELD STUDIES
• Dilday et al. (1992, 1994, 1989, 2000)
• 412 among 12 000 rice cultivars exhibited
allelopathic activity against Ducksalad in field
assessment
• In another trial, 94 and 145 out of 5000 tested
rice cultivars were allelopathic against
Barnyardgrass and Redstem, respectively.
• Some rice cultivars with strong weed
suppression ability were selected, such as
PI321777 and PI338046.

24. Cont…
• Olofsdotter et al. (1997)
45 out of 1000 screened rice cultivars were
allelopathic against either barnyardgrass or
monochori
• About 20–40% of 1000 rice cultivars in Egypt
were allelopathic against indicator plants
including 45 that showed strong allelopathic
activity (Hassan et al., 1998)a and five
inhibited both species.

25. RESULTS
• Among detected phenolic acids, p-hydroxybenzoic,
vanillic, p-coumaric and ferulic acids may be the
most common allelochemicals in rice (Rice, 1984;
Mattice et al., 1998; Chung et al., 2001a; Rimando et
al., 2001; Seal et al., 2004a,b).
• Modern analytical instruments, such as GC-MS, LC-
MS, NMR and IR, have helped to either identify or
confirm various allelochemicals as cytokinins,
phenols, indoles, terpenic acid, phenylalkanoic acids,
sterols, benzaldehydes, benzene derivatives and
long-chain fatty acids and their esters and ketones.

26. ADVANTAGES:
• Weed management using allelopathy may effect
a yield improvement without environmental
cost, which is one of the most important
considerations for scientists working to secure
the world’s food supply for future generations.

27. Conclusion
• Success in breeding new rice cultivars having
good weed-suppressing ability would benefit
farmers in rice-cultivating countries and play an
important role in sustainable agricultural
production.

28. Thank you!!