This document discusses allelopathy, which is the phenomenon where one plant produces chemicals that harm other plants. It provides examples of allelopathy between crops and weeds. Some common allelochemicals produced by plants are phenolic acids, coumarins, terpenoids, and flavonoids. These chemicals are released through leaching, exudation, volatilization, or decomposition. Allelopathy can affect weed suppression and crop yields. The strength of allelopathic effects depends on factors like crop variety, environmental conditions, and soil fertility. Further research on allelopathy could provide natural herbicides and support sustainable agriculture.

1. ALLELOPATHY –A TOOL FOR WEED
MANAGEMENT
Credit Seminar
SEMINAR INCHARGE
& GUIDE
DR. M. L. KEWAT
PROFESSOR
Department of Agronomy, JNKVV ,Jabalpur(M.P.)Department of Agronomy, JNKVV ,Jabalpur(M.P.)
COLLEGE OF AGRICULTURECOLLEGE OF AGRICULTURE
JAWAHARLAL NEHRU KRISHI VISHWA VIDYALAYAJAWAHARLAL NEHRU KRISHI VISHWA VIDYALAYA
JABALPUR(M.P.)JABALPUR(M.P.)
PRESENTED BY
POONAM CHOURASIYA
Enrl. no. 160111009

2. ConceptConceptConceptConcept
• The phenomenon of one plant having detrimental effect on
another through the production and exertion of toxic
chemical compounds is called allelopathy. Allelopathy is
the indirect harmful effect through exertion of chemical
substances.
• Allelopathy is existent in the natural ecosystem and it
occurs widely in the natural plant communities. Allelopathy
is possibly a significant factor in maintaining the present
balance among the various plant communities. Allelopathic
substance was first detected by Davis (1928) in black
walnut tree (Juglans nigra) whose foliar leachate
containing Juglone was found to damage germination and
seedling growth of crops beneath the tree.

3. ALLELOPATHIC PROBLEMS IN AGRICULTURE,
HORTICULTURE AND FORESTRY
1)1)Soil sicknessSoil sickness
2)2)Auto toxicity under same crop monocropping.Auto toxicity under same crop monocropping.
3)3)Increased crop- weed interferenceIncreased crop- weed interference
4)4)Growing susceptibility of plants to disease/ pestsGrowing susceptibility of plants to disease/ pests
5)5)Reduced nitrification and biological nitrogen fixationReduced nitrification and biological nitrogen fixation
6)6)Reduced nutrient uptakeReduced nutrient uptake
7)7)Weed seed decomposition delayed/ preventedWeed seed decomposition delayed/ prevented
8)8)Poor success on replanting of tree cropsPoor success on replanting of tree crops
9)9)Failure of vegetative propagation (e.g. grafting, budding)Failure of vegetative propagation (e.g. grafting, budding)
10)10)Suppression effect from treesSuppression effect from trees

4. INTRODUCTIONINTRODUCTION
• Allelopathy is derived from two Greek words “allelon”Allelopathy is derived from two Greek words “allelon”
means “of each other” and “pathos” means “to suffer”,means “of each other” and “pathos” means “to suffer”,
and means the “injurious effect of one organism uponand means the “injurious effect of one organism upon
the other”the other”
• Hans Molisch (1937)Hans Molisch (1937), plant physiologist, University, plant physiologist, University
of Vienna, Austria, coined the term allelopathyof Vienna, Austria, coined the term allelopathy
• It was first reported in alfa-alfa, and the firstIt was first reported in alfa-alfa, and the first
allelochemical was extracted from walnut.allelochemical was extracted from walnut.
• Actually, it is the process involving secondaryActually, it is the process involving secondary
metabolites, produced by algae, bacteria, plants ,metabolites, produced by algae, bacteria, plants ,
which influence the growth of the other or samewhich influence the growth of the other or same
species.species.

5. • The central principle in Allelopathy arises from the fact that
plants and microorganisms collectively produce thousands of
chemicals, and many of these chemicals are released from the
producing organism by leaching, exudation, volatilization, or
decomposition processes. Subsequently, some of these
compounds (known as allelochemicals) alter the growth or
physiological functions of organisms that encounter them during
growth.
• For example, almost pure droplets of sorgoleone (a quinone)
are exuded from the roots of Sorghum species, which inhibits growth
in plants that contact it by blocking photosynthesis and respiration.
• Cinnamic and benzoic acids, flavonoids , and various terpenes
are the most commonly found allelochemicals,. A few allelo-
chemicals have been developed as herbicides and pesticides.

6.  Allelopathic ChemicalsAllelopathic Chemicals
• Phenolic acid
• Coumarins – block mitosis in onion by forming
multinucleate cells
• Terpinoids
• Flavinoids
• Scopulatens – inhibits photosynthesis without
significant effect on respiration

7. Ways of releasing allelochemicalsWays of releasing allelochemicals
Allelopathic chemicals are released from the plants as:
• Vapour – from root and leaf (through stomata)
• Foliar leachate
• Root exudate
• Breakdown/ decomposition product of dead plant parts
• Seed extract

8. SOURCES OF ALLELOPATHY

9. . TYPES OF ALLELOPATHY
 True allelopathy
 Functional allelopathy

10.  Crop against other crops:
Examples:Examples:
• Sunflower has been foundSunflower has been found
allelopathic to groundnut underallelopathic to groundnut under
intercropping situationintercropping situation
• Tree crops likeTree crops like EucalyptusEucalyptus also shows some allelopathicalso shows some allelopathic
interactions to vegetables and some field crops growninteractions to vegetables and some field crops grown
as intercrop with it.as intercrop with it.
• Crop residues of lentil are phytotoxic to wheat and ofCrop residues of lentil are phytotoxic to wheat and of
sunflower and mustard to several cropssunflower and mustard to several crops
• Sorghum is allelopathic to wheat and sweet potato toSorghum is allelopathic to wheat and sweet potato to
cowpea.cowpea.
• Mung/ green gram and cowpea are stimulatory to theMung/ green gram and cowpea are stimulatory to the
FORMS OF ALLELOPATHIC INTERACTIONS

11. Crop against weeds:Crop against weeds:
Examples:Examples:
• Sorghum releases hydrocynic acid (HCN) and suppresses manySorghum releases hydrocynic acid (HCN) and suppresses many
weeds growing in vicinity.weeds growing in vicinity.
• Barley produces “gramine” an alkaloid, which inhibits weed growthBarley produces “gramine” an alkaloid, which inhibits weed growth
S.No. Crops Weed species
1 Maize Chenopodium album, Amaranthus retroflexus
2 Sorghum Setaris viridis, Bromus pectinatus, Amaranthus hybridus
3 Cucumber Echinochloa crusgalli
4 Sweet potato Cyperus rotundus, Cyperus esculentus

12. Crops Weeds Cause/source
released from
crop plant
Effect on
weeds
Coffea arabica
(Coffee)
Amaranthus
spinosus
(Spiny amaranth)
1,3,7-
trimethylxanthin
Inhibit germination
Zea mays (Maize) Agropyron repens
Setaria viridis
Increased Catalase
and Peroxidase
activity by root
extract
Inhibit growth
Oat, pea, wheat Chenopodium
album
(Lamsquarter)
Root exudates Suppress growth

13. Weed against crops:Weed against crops:
S.No. Weeds Crops
1 Cyperus rotundus Sorghum , soybean
2 Imperata cylindrical Severalcrops
3 Chinopodium album Alfalfa, cucumber, oat, maize
4 Cirsium arvense Severalcrops
5 Avena fatua Severalcrops

14. •
Weeds Crops Cause/source
released from
weeds
Effect on crops
Agropyron repens
(Quack grass)
Maize, potato Ethylene produced
by the activity of
microorganism on
rhizomes of weeds
Decrease uptake
of manures (N,K)
followed by yield
reduction of crop
Avena fatua
(Wild oat)
Wheat, barley, oat Root exudates Growth of leaves
and roots of wheat
Cynodon dactylon
(Bermuda grass)
Barley Decayed grass
residues of weeds
Seed germination,
root and top
growth of crop
Cyperus
esculentus (Yellow
Nut sedge)
Grain crops,
soybean, orchard
Vanillic acid,
Hydrobenzoic acid
in sedge extract
Root and shoot
growth of maize
and soybean

15. Weeds Weeds Cause/source
released from
weeds
Effect on
weeds
Impereta cylindrica
(Cogon grass)
Borreria hispada
(Button weed)
Exudates of
inhibitory
substances
through rhizomes
Inhibits the
emergence and
growth
Sorghum
halepense
(Johnson grass)
Setaria viridis
(Giant foxtail),
D. sanguinalis
(Large crabgrass)
Living and
decaying rhizomes
and leaves
Inhibit growth
WEEDS AGAINST WEEDS

16. PLANT CHEMICALS REFERENCES
Secale cereal L.
(Rye)
Avena sativa L.
Sorghum bicolor L.
(Sorghum),
Barley
Mungbean
Medicago sativa L.
Chenopodium
Cucumis sativus L. (Cucumber)
2,4-dihydroxy-1,4(2H)benzoxazin-3-
one (DIBOA) 2(3H)-
benzoxazolinone (BOA)
Ferulic acid
P-cumaric acid
Hydroxamic acid
Saponins
Ascaridole, alpha-terpinene
Gamma-linolenic acid,
Alpha-asarone
Benzoic and Cinnamic acids
Barnes & Putnam (1987)
Rice (1984)
Perez ( 1990)
Corcurea et al. (1992)
Krol et al. (1995)
Corcurea et al. (1992)
Yu and Matsui, 1994

17. Crops Weeds Allelochemicals Referrences
Rice Echinochloa
colona
Phenolic acids Rimando et al.,
2001
Wheat Avena fatua Hydroxamic acids Niemeyer, 1988
Cucumber Impereta cylindrica Benzoic and
Cinnamic acids
Yu and Matsui,
1994
Black mustard Phalaris paradoxa Allyl isothiocyanate Weston, 1996
Buck wheat Canada thistle Fatty acids Weston, 1996
Clovers and
Sweet clover
Echinochloa
crusgalli
Isoflavonoids and
Phenolics
Weston, 1996
Oat Chenopodium
album
Phenolic acids
& Scopoletin
Weston, 1996
Cereals Hydroxamic acids Weston, 1996
Sudangrass - Phenolic acids
and Dhurrin
Weston, 1996
Sorghum Echinochloa
colona
Sorgoleone Netzley and Butler
(1986)
AJEA,2010

18. Factors affecting Allelopathic effectFactors affecting Allelopathic effect
• Allelopathic effects might also depend on a number of
other factors that might be important in any given situation:
• VarietiesVarieties:: There can be a great deal of difference in the
strength of allelopathic effects between different crop
varieties.
• SpecificitySpecificity: There is a significant degree of specificity in
allelopathic effects. Thus, a crop which is strongly
allelopathic against one weed may show little or no effect
against another.
• AutotoxicityAutotoxicity:: Allelopathic chemicals may not only
suppress the growth of other plant species, they can also
suppress the germination or growth of seeds and plants of
the same species. Lucerne is particularly well known for
this and has been well researched. The toxic effect of
wheat straw on following wheat crops is also well known

19. • Crop on crop effectsCrop on crop effects: Residues from allelopathic crops
can hinder germination and growth of following crops as
well as weeds. A sufficient gap must be left before the
following crop is sown. Larger seeded crops are effected
less and transplants are not affected.
• Environmental factorsEnvironmental factors: Several factors impact on the
strength of the allelopathic effect. These include pests and
disease and especially soil fertility. Low fertility increases
the production of allelochemicals. After incorporation the
alleopathic effect declines fastest in warm wet conditions
and slowest in cold wet conditions.

20. CONCLUSION
• Allelopathy plays an important role in investigations of appropriate
farming systems as well as in the control of weeds, diseases and
insects, the alleviation of continuous cropping obstacles, and
allelopathic cultivar breeding.
• Furthermore, allelochemicals can act as environmentally friendly
herbicides, fungicides, insecticides and plant growth regulators, and
can have great value in sustainable agriculture.
• With increasing emphasis on organic agriculture and environmental
protection, increasing attention has been paid to allelopathy research,
and the physiological and ecological mechanisms of allelopathy are
gradually being elucidated. It is obvious that allelopathy requires
further research for widespread application in agricultural production
worldwide.

21. ReferencesReferences
• Abrahim D., Takahashi L., Kelmer-Bracht A. M., Ishii-Iwamoto E. L.
(2003b). Effects of phenolic acids and monoterpenes on the
mitochondrial respiration of soybean hypocotyl axes. Allelopathy J. 11,
21–30
• Anaya A. L. (1999). Allelopathy as a tool in the management of biotic
resources in agroecosystems. Crit. Rev. Plant Sci. 18, 697–739.
10.1080/07352689991309450
• Belz R. G. (2007). Allelopathy in crop/weed interactions–an update.
Pest. Manag. Sci. 63, 308–326. 10.1002/ps.1320
• Bhadoria P. (2011). Allelopathy: a natural way towards weed
management. Am. J. Exp. Agric. 1, 7–20