B.Sc. Ag Final YEAR
• Allelopathy is derived from two greek words “allelon or
allele” means “mutual or each other” and “pathos”
means “suffering or to suffer.”
• Hans Molisch (1937), plant physiologist, University
of Vienna, Austria, coined the term allelopathy
• It was first reported in alfa-alfa, and the first
allelochemical was extracted from walnut.
• Actually, it is the process involving secondary
metabolites, produced by algae, bacteria, plants ,
which influence the growth of the other or same
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
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, and it may
be possible to genetically engineer a crop to
produce its own herbicides.
TYPES OF ALLELOPATHY
a) Alloallelopathy and Autoallelopathy
b) True allelopathy and Functional allelopathy
FORMS OF ALLELOPATHIC
Crop against other crops:
• Sunflower has been found allelopathic to groundnut
under intercropping situation
• Tree crops like Eucalyptus also shows some allelopathic
interactions to vegetables and some field crops grown
as intercrop with it.
• Crop residues of lentil are phytotoxic to wheat and of
sunflower and mustard to several crops
• Sorghum is allelopathic to wheat and sweet potato to
• Mung/ green gram and cowpea are stimulatory to the
growth of wheat.
• Crop against weeds:
Sorghum releases hydrocynic acid (HCN) and suppresses many
weeds growing in vicinity.
Barley produces “gramine” an alkaloid, which inhibits weed growth
Chenopodium album, Amaranthus retroflexus
Setaris viridis, Bromus pectinatus, Amaranthus hybridus
Cyperus rotundus, Cyperus esculentus
Weed against crops:
Sorghum , soybean
Alfalfa, cucumber, oat, maize
Weed against other weeds
Cassi sericea, has shown encouraging result to oust parthenium in Karnataka
Secale cereal L.
Barnes & Putnam (1987)
Avena sativa L.
L. P-cumaric acid
L. 2,4- Dihydroxy- 7- methoxy-1, 4benzoxazin-3-one (DIMBOA)
Perez ( 1990)
Liu and Lovett (1993)
Corcurea et al. (1992)
Medicago sativa L.
Krol et al. (1995)
Corcurea et al. (1992)
Cucumis sativus L. (Cucumber)
Benzoic and Cinnamic acids
Yu and Matsui, 1994
The Glucoside which is present in wheat, rice, maize
can have many aspects:
• Influence growth of weed
• Involve in detoxification of pesticides,
• Increase the resistance of insects, fungi and
bacteria, in cereals.
• Trigger the reproduction of grass-feeding mammals,
• Are mutagenic agents
ALLELOPATHIC PROBLEMS IN AGRICULTURE,
HORTICULTURE AND FORESTRY
1) Soil sickness
2) Auto toxicity under same crop monocropping.
3) Increased crop- weed interference
4) Growing susceptibility of plants to disease/ pests
5) Reduced nitrification and biological nitrogen fixation
6) Reduced nutrient uptake
7) Weed seed decomposition delayed/ prevented
8) Poor success on replanting of tree crops
9) Failure of vegetative propagation (e.g. grafting, budding)
10)Suppression effect from trees
INFLUENCES OF ALLELOPATHY IN CONTROLLED OR
Modern crops have been selected by
desirable agricultural characteristics,
removed allelopathic properties.
a) Rapid seed germination achieved by selecting lines
with reduced seed coat inhibitors. Some germination
inhibitors also act as antibiotics/fungicides.
b) Increase production of edible parts, allelopathic
compounds and all other secondary (defensive
metabolites) require energy. Cultivated crops are
developed for either high sugar content or larger heads
of grain or bigger storage roots.
• c) Other numerous selections for desirable
plant virtues must of necessity reduced
levels of bitterness or other chemical which
wild forms make use of for defense.
2. Using allelopathy in agriculture.
• a) In new forests or in reforestation make use
of allelopathy by planting a mix of species that
speed up succession thus preparing the soil for
long term support of tree crops.
• b) For nematode and soil born disease control
use rotations with ground covers shown to
strongly reduce these problems.
• Rhodes grass useful for reniform nematodes
and soybeans for potato scab.
Helianthus tuberosus, a staple food crop in Europe in
past, which has now become a weed, can be used as
method to control weeds, especially monocot weeds.
• Soil+HT @ 25 tonne/ha,
• Soil+HT @ 50 tonne/ha.
• After 25 days, there is severe impact on weeds both
during growth period and germination period., e.g.,
Oxalis spp., Phalaris minor, Avena spp.
Chopped radish along with manure have also controlling
effect on weeds up to 60% in crops like cotton,