All biochemical interactions (stimulatory and inhibitory) among plants, including microorganisms (Molisch ,1937) . Derived from two Greek words i.e. Allelon (each other) and Pathos(to suffer) i.e. the injurious effects of one upon another. Allelopathy refers to any process involving secondary metabolites produced by plants, microorganisms, viruses and fungi that influence the growth and development of Agricultural and Biological Systems (International Allelopathy Society )

1. CREDIT SEMINAR
Allelopathy and its effects on vegetable production
Presented By:
Jyoti Prakash Sahoo
2014-AMJ-15
25 May 2021 1

2. Allelopathy???
All biochemical interactions (stimulatory and inhibitory) among
plants, including microorganisms (Molisch ,1937) .
Derived from two Greek words i.e. Allelon (each other) and
Pathos(to suffer) i.e. the injurious effects of one upon another.
Allelopathy refers to any process involving secondary
metabolites produced by plants, microorganisms, viruses and
fungi that influence the growth and development of Agricultural
and Biological Systems (International Allelopathy Society )
25 May 2021 2

3.  First recognised by Democritus(500 B.C.) and
Theophrastus (300 B.C.)( Smith and Secoy,1977) .
 DeCandolle(1832)
 Molish (1937) coined the term “Allelopathy”.
 Since 1960’s – Recognised as important ecological
mechanism.
 Most progress in field carried out by Rice(1984).
 Most allelopathic research has been conducted in
developed countries due to practice of monoculture.
Elroy Leon Rice
Hans Molish
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4. Allelopathy
Chemical interaction among
plants and microbes ,
stimulatory as well as
inhibitory.
Interference
Adverse effect of a neighbouring plant
growing in association. (Muller, 1969).
Both competition and allelopathy are two
mechanisms of Interference.
Competition
One plant utilizes
environmental growth
resources resulting shortage
which is harmful to other
plant
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5. Allelochemicals
 Secondary metabolites
 Includes natural herbicides, phytoalexins
 Allelochemicals are produced in above or below ground plant parts or in both
.
Sources
Roots/
Rhizomes
Stems
Leaves
Flowers/
Pollen
Fruits
Seeds
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6. Types
True
Allelopathy
Auto
Alleopathy
Functional
Allelopathy
Allo
Allelopathy
Allelochemical which are toxic in the form they produced
Allelochemical which are toxic in their transformed/degraded form
Toxicity to the
different species
Toxicity within
the same species
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7. Modes of release
 Plant generally store allelochemicals in the plant cells in a bound
form.
 During enzymatic breakdown or environmental stress, the toxic
chemicals are released into the environment from special glands
on the stems or leaves (Putnam and Duke, 1978)
Volatilization
Leaves/stem
leachates
Decomposition of
plant residues
Root exudates
Modes
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8. Volatilization
Allelochemicals may volatilize and absorbed directly by neighbouring plants from the following
(Muller,1966).
 From Atmosphere
 From Condensate in dew
 Absorbed on the soil particles
 This phenomenon is observed in the arid regions of the world or in drought condition.
 Several terpenoids transfer in these ways such as α-pinene, β-pinene, cineole and camphor
 Examples:Artemisia, Salvia, Parthenium , Eucalyptus (Rice,1984).
 Pulverised leaves of cruciferae species (Brassica juncea, B. nigra, B. napus, B. rapa and B.
oleracea) released volatile substances. The volatiles of B. juncea and B. nigra were most
harmful to germinating seeds of lettuce (Oleszek ,1987)
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9. Leachates
 Removal of water soluble substances by the action of aqueous
solvents such as rain,dew ,mist and fog(Tukey Jr., 1970).
 The degree depends on type of tissue, stage of maturity ,
amount and duration of precipitation (Tukey Jr., 1970).
 Phenolic acids, terpenoids and alkaloids are the chemicals.
(Borner, 1960; Tukey and Mecklenburg, 1964; Tukey Jr., 1970).
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10. Root exudates
 Although their volume is small i.e. 2-12% of the total
phytosynthates (Grodzinsky, 1974), but they play
significant role in allelopathy (Woods, 1960; Rovira,
1969).
 The root exudates of cucumber exerted allelopathic
inhibitions (Putnam and Duke, 1974).
 Kim and Kil (1987) found that the root exudates of
tomato inhibited the growth of lettuce and egg plant.
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11. Decomposition of Residues
More severe and persistent toxicity has been
reported from cold and wet soils (Patrick and Koch,
1958; McCalla and Haskins, 1964).
Penicillium spp. synthesize patulin and pecolinic
acid; Aspergillus spp. synthesize malphermine etc.
these substances produced from the crop residues
inhibited the growth of crops (McCalla, 1971).
Phenolics also released from decomposed plants.
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12. Factors causing allelochemical production(Rice,1984)
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Factors
Temperature
Mineral
deficiency
Water
stress
Radiation
Genetics
Age of
plant
organ
Allelopathic
Agents
Pathogen,
predators

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Allelopathic Interaction

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• Soil oxygen status
• Aerobic and anaerobic decomposition of organic material.
• Under oxygen deficit condition; organic acids, hydrogen sulphide ,
phenolic compounds and many other produced.
Soil
Aeration
Major factors affecting phytotoxin production
Plant spp. Duration of phytotoxicity References
Broccoli 30 days Patric et al.(1963)
Sweet Potato 12 weeks Harrison Jr. and Peterson,
(1986)

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Effect of different method of oat straw disposal on
wheat yield(Source: Lynch et al.,1981)
• Conventional tillage and minimum or
no-tillage
• Crop residues are left on the soil
surface as stubble mulch in soil
erosion area.
• Decomposition of crop residues occur
early, when incorporated into the soil,
than when lying on the soil surface
Straw
treatment
Furrow opener Yield
(t/ha)
Burnt Triple Disc 8.51
Single Disc 8.14
Chopped
and spread
A.Left in situ Triple Disc 3.77
B.Disced Single Disc 5.37
C.Rotavated Single Disc 4.50
Tillage
Practices
Cont…

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Experimental
findings

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Effects of different sources on seed germination and growth of test crops
DONOR CROP RECEIPIENT CROP
REFERENCE
CROP Sources Crop Inhibitory/ stimulatory effect
Sweet
potato
Crop residue Sweet potato
Cowpea
Inhibited plant growth in both and
reduced uptake of P, K, Ca , Mg , S,
Zn, B, Cu in Sweet potato
Walker and Jenkins
(1986)
Walker et.al.(1989)
Chinese
Cabbage
Crop residue
decomposition and
extract
Tomato
Cabbage
Sweet potato
Inhibited seed germination and
seedling growth Kuo et.al.(1981)
Asparagus Root extract Asparagus,
Tomato,
Lettuce,
Cucumber
Reduced germination (tomato,
cucumber) and 0.5 g dry root
tissue/100 ml of water inhibited
radicle growth of lettuce
Hazebroek et al.(1989)
Radish Root extract Pearl millet Ascorbic acid
stimulated growth of seedling
Sharma and
Singhvi(1981)
Alfalfa Root exudates Radish,
Turnip
Reduced germination Tsuzuki and
Kawagoe(1984)

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0
10
20
30
40
50
60
70
80
90
100
Alfalfa Turnip Radish
%
OF
GERMINATION
Control Aquous extract
Effect of aquous extracts of alfalfa on
seed germination of crops(Truzuki and
Kawagoe,1984)
Plant part Shoot weight(gm) Root weight(gm)
Fresh Dry Fresh Dry
Sweet Potato “Jewel”
Vines 22.33 3.22 13.73 2.30
Roots 6.59 1.21 4.64 0.97
Control 33.51 4.74 19.19 2.95
Sweet Potato “Centennial”
Vines 22.35 3.90 15.37 2.37
Roots 8.86 1.30 4.48 0.79
Control 25.81 4.77 20.58 3.07
Cowpea “Brown Crowder”
Vines 4.18 0.69 0.80 ------
Roots 1.61 0.30 0.67 ------
Control 16.21 3.21 3.35 ------
Influence of sweet potato vines and root exudates on growth of
sweet potato vines and cowpea plants( Walker and Jenkins,1986)
Cont..

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Crops Exhibiting autotoxicity and soil sickness in
monoculture
Summer
Squash
Potato Cowpea
Population of fungi Penicillium and Aspergillus increases
Plant parasitic nematode Meloidogyne
incognita population increases
Lechates of summer squash have auto toxicity effect

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Allelopathic effects in crop rotation/crop mixtures
Crop rotation/Crop
Mixture
Donor Crop
Recipient Crop
Reference
Crop Inhibitory/ Stimulatory effects
Watermelon-
Pangola grass
Water
melon Pangola Grass Increased growth(40%)
Chou(1986)
Corn
+
Water melon
Corn
Water
Melon Reduced growth Cruz et al.(1988)
Treatment Head
No of plants/Plot Diameter(cm) Weight(gm) Yield(t/acre)
Brocolli 73 13.55 353.6 4.41
2 mustard plants/m2 + brocolli 89 14.16 332.8 5.02
4 mustard plants/m2 + brocolli 101 14.62 358.35 6.25
8 mustard plants/m2 + brocolli 199 15.83 406.35 6.74
Mustard intercropping on yield attributes and yield of broccoli, (Osorino and Gliessman, 1987)

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Crop-Weed Interaction
Donor Crop Affected Weed Species
Crop Source Weed Inhibitory/
Stimulatory effects
Cucumber
Seed
Leachates
Panicum
miliaceum
Supressed seed germination(46%) and dry weight
(40%),effect persisted upto 9 days of imbibition
Treatment Tissue dry weight of Yellow nutsedge (mg)
Shoot Root Rhizome + Tuber
Control 898 169 187
Sweet Potato 719 99 139
Harrison and Peterson (1986)
Lockerman and Putnam(1981)

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Weed Sources
Recipient Crop
Reference
Crop Inhibitory effects
Parthenium
hysterophorus
root, stem, leaf
and inflorescence
extracts
pea, radish,
cabbage and
cauliflower
reduced the seed germination and
seedling growth
Rao et. al., 1977;
Dube et al., 1979;
Mall and Dagar,
1979
Amaranthus
palmeri
weed residues
onion
carrot
Inhibit growth of carrot(49%), and
onion(68%),germination persisted
upto 62 days in onion
Bradow and
Connick Jr., I987
Digera spp Aquous leaf
extracts(1:250)
tomato,
brinjal , onion
and chillies
Inhibit germination of tomato(46%),
brinjal(58%) , onion(62%) and
chillies(60%)
Dubey, 1973
Weed-Crop Interaction

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Management of insect pests
 The antibiotics may be utilized to breed resistant
varieties or strains against insect-pests of field, fruit
and vegetable crops.

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Antibiotic allelochemicals effects on insect biology
Class Chemical species Source plant Insect species Effects Reference
Protease
inhibitor
Trypsin inhibitor-I Cowpea Callosobruchus
maculatus
Larval mortality Gatehouse and
Boulter(1983)
phenols Phenols Tomato Helicoverpa zea Inhibit larval
growth
Isman and Duffery(1982)
Saponins Ca-precipitable
saponin
Pea Callosobruchus
chinensis
Inhibited growth Applebaum et al.(1969)
Alkaloids Solanin,Demissine Solanum Spp. Leptinotarsa
spp
Inhibited growth Kuhn and Gauhe(1947)
Gluco-
sinolate
Sinigrin
Sinalbin,
Isothiocynate
Brassica spp.
Papilio polyxenes
Myzus persicae
Drosophila spp
Inhibited growth
Killed adult
Kogan(1986)
Lichtenstein et al.(1962)

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Management of phytonematodes
 Plant extracts and crop residues also have nematicidal
property.
 Root exudates of marigold inhibits most plant parasitic
nematodes.
 Neem, Leucaena leucocephala like plants have effective
against nematodes like Heterodera cajani , Heterodera
avenae.

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Case Study

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Hot pepper (Capsicun annuum)
Cucumber (Cucumis sativus)
Lettuce (Lactuca sativa)
Cabbage (Brassica oleracea var. capitata)
Chinese cabbage (Brassica campastris)
Tomato (Lycopersicon esculentum)
Radish (Raphanus sativus)
Cowpea (Vigna unguiculata)
Corn (Zea mays)
Obtained from the Horticultural Laboratory of Sichuan Agriculture University.
Plant Materials

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Preparation of Root Exudates
Hot pepper seeds surface sterilized with 70% alcohol for 5 min and soaked at 55.8 °C for 30 min
Rinsed four times with distilled water and kept for germination on wet filter paper in Petri dishes at 29 °C.
After 4 days seeds were planted into plastic pots.
60 thirty-day-old seedlings transplanted into glass cups containing 200 ml Hoagland’s nutrient solution
Root exudates collected every 3 days (5 times) and then the nutrient solution was changed
Collected liquid filtrated through a column (diameter 20 mm)
Solution with a total volume of 25 ml then refrigerated at “-20°C” until use

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Bioassay
20ml methanol solution diluted with sterile
distilled water to a volume of 250 ml
0, 2 and 5 ml of diluted solution of root exudates obtained and added
with distilled water to a volume of 10 ml
30 seeds of each vegetable surface sterilized with 70% alcohol for 5 min and rinsed
with distilled water
Number of germinated seeds was recorded daily and the germination rate was counted over a
1 week period
Treatment solution (10 ml) added to a filter paper placed in petri dishes
containing the tested seeds
placed on filter papers in a petri dish and kept in a dark chamber at 25°C

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Effect of Hot Pepper Root Exudates on Seed Germination Rate
Results

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Effect of Hot Pepper Root Exudates on Seed Germination Index

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Effect of Hot Pepper Root Exudates on Seedling Growth
S
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Synthetical Effects of Root Extracts from Hot Pepper on the Tested Vegetables
Stimulatory effect Inhibitory effect

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Improvement
of water
drainage
Water
Flooding
Application
of nutrients
Phytotoxin
adsorbents
Removal of phytotoxins from agricultural field

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Mandava(1985) listed some of the following problems:
 Inability to transfer laboratory results into field situations.
 Complexity in allelochemical mixtures and improper assessment of their concentration.
 Failure to detect biologically active chemical in presence of other chemicals.
Besides , the following problems also observed:
 Difficulty in exudate collection
 Information about the most allelopathic varieties of a particular crop is not available.

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Future prospects of research
Weed
Control
Develop
Biotechnology
Antagonistic
effects
Threshold
Concentration

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Conclusion
Weed
control by
Natural
Herbicide
Management
of phyto-
nematodes
Insect-Pest
Management
Selection
of plants
for
Cropping
system
To breed
new
varieties

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