ALLELOPATHY AND WEED MANAGEMENT

SAMEERALI M.

PALB-2186

Presented by:

?????????..... What is allelopathy? When? Who ? Which are the main allelochemicals? Site of production? Mechanism of action? Constraints in using allelopathy as a weed

management tool? Practical applicability of allelopathy in weed

management?

INTRODUCTION Allelopathy refers to all biochemical

interactions,stimulatory or inhibitory,among plants including m.org(Molisch,1937)

Detrimental effect of chem.or exudates produced by one living plant sp.on germn,growth&dev.of other plant or m.org sharing same habitat. (Evenari,1949)

The term allelopathy refers to any direct or indirect inhibitory effect by the production, of chemicals by a plant which can influence the growth and development of another plant.(Rice,1974)

.

For weed management we are interested in the inhibition of one plant (the weed or weeds) by another (usually the crop or weed) through the production of allelochemicals

Allelopathy, from the Latin words allelon ‘of each other’ and pathos ‘to suffer’, refers to the chemical inhibition of one species by another.

The source of allelochemicals in agricultural fields may be the weeds, crops or microorganisms.

HISTORY Democritus (500 BC)and

Theophrastus(300 BC) Pliny-Naturalis Historica Decondole(1832) Molisch(1937)-coined allelopathy Rice (1974)

Elroy L. Rice

WHICH CROPS SHOW ALLELOPATHIC PROPERTIES???

Many crops have been reported as showing allelopathic properties at one time or another …

some crops such as oats seem to clean fields of weeds better than others. The list also includes:

Lucerne Rice SorghumBuckwheat

Red clover

sweet clover

• TrifoliBarley Wheat

FACTORS.. Varieties There can be a great deal of difference

in the strength of allelopathic effects between different crop varieties.

Specificity A crop which is strongly allelopathic against one weed may show little or no

effect against another.

Autotoxicity Allelopathic chemicals may suppress

same sp. Lucerne is particularly known for this

kind of autotoxicity. The toxic effect of wheat straw on

following wheat crops is also well known.

FACTORS AFFECTING PRODUCTION OF ALLELOCHEMICALS

Light Mineral deficiency Drought stress

Environmental factors Several factors impact on the strength

of the allelopathic effect, 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.

TYPES OF ALLELOPATHY

There are two types:

1) True type - the release into the environment of compounds that are toxic in the form in which they are produced.

2) Functional type - the release into the environment of a substance that is toxic as the result of transformation by micro-organisms

TYPES OF ALLELOPATHY

• Instantaneous direct effect

• sorghum

• Lentil residues on wheat

• Maize – on chenopodium album,

• Sorghum on abutylon

• theophrasti

• Wheat,• alfalfa,• cowpea

Auto allelopath

y Allo allelopat

hyConcurrent /direct allelopat

hy

Residual

Forms of allelopathic interactions

Weed again

st weed

Crop again

st crop

Crop again

st weed

Weed again

st crop

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

WEEDS AGAINST WEEDS Parthenium hysterophorus Effect of several waste land weeds on parthenium

suppressionSl.no

Species Extent of suppresssion (%)

1 Cassia auriculata Moderate(26-50 )

2 Sida spinosa Moderate(26-50 )

3 Cassia occidentalis High(51-754)

4 Amaranthus spiinosus High(51-754)

5 Mirabilis jalappa Very high(76-100)

6 Ipomea carnea Very high(76-100)

(Mahadevappa,1997)

SOURCES OF ALLELOCHEMICALS

Sources

Stem

Leaves & Flowers

Fruits& seeds

Roots & Rhizome

CHEMICAL NATURE OF ALLELOCHEMICALS Usually secondary plant

products/metabolites(whittakker and peeny,1971)

Phenyl propones Terpinoides Acetogenins Akaloids Steroides

According to Rice(1984),allelochemicals grouped into:

Tannins Terpinoides

Organic acids

Cinnamic acid deriv.

Flavinoides Sulphides Lactones

Coumarins

Purines Polypeptides Glycosides

Complex quinones

LIBERATION OF ALLELOCHEMICALS

•Volatalization

•Leaching

•Exudation

•Weathering

Volatalization Arid and semi arid environment Mostly terpinoid group. Released from special glands on stems

or leaves Susceptible plants absorbs through

cuticle directly from air or adsorbed on dry soil and taken up.

Leaching Through aqueous solutions (rain,dew) Mature leaves are more susceptible

Exudation Metabolites exuded from roots to

surrounding atm. Pottential source of allelopathic effect

Decomposition Leaves and stubbles By weathering and micro organisms.

MECHANISMS OF ACTION

Celldivision and elongation Gibberllin or IAA(growth hormones) Mineral uptake Nitrification (nitrosomonas-furilic acid) Respiration Stomatal opening Protein synthesis and org.acid

metabolism Specific enzymatic activities. Retardation of photosynthesis

INHIBIT

How allelochemicals introduced into plant??

INHIBITION OF PLANT SPECIES THROUGH ALLELOPATHY

Rye, some varieties of barely, oats as well as buckwheat are effective inhibiting the growth habit of a large number of weed species.

Root excudates of wheat and oats contained phenolic acid which has more detrimental effects on wild mustard.

Sunflower crop inhibit the growth of certain weeds.

Cucumber which strongly inhibit the growth of wild mustard Root inhibition of rye grass weed is influenced by wheat seed

density

CONTD..• The leaf litter and root exudates of some Eucalyptus species are

allelopathic for certain soil microbes and plant species.

• The tree of heaven , Ailanthus altissima, produces allelochemicals

in its roots that inhibit the growth of many plants.

• Rice allelopathy depends on variety and origin: Japonica rice is more allelopathic than Indica and Japonica-Indica hybrid. More recently, critical review on rice allelopathy and the possibility for weed management reported that allelopathic characteristics in rice are quantitatively inherited and several allelopathy-involved traits have been identified.

• Continuous cropping of legume crop alfaalfa has been created to auto toxicity in low land weed.

CONTD….• Corn gluten meal (CGM) is a natural preemergence

weed control used in turfgrass, which reduces germination of many broadleaf and grass weeds.

• Garlic mustard is an invasive plant species.Its success may be partly due to its excretion of an unidentified allelochemical that interferes with mutualisms between native tree roots and their mycorrhizal fungi.

• The black walnut (Juglans nigra) produces the allelochemical juglone, which affects some species.

CASE STUDY Dry leaf leachates of female plants of

cannabis sativa caused maximum reduction in bio.activities of Parth.hysterophores.

Aqueous leachate concn(%)

Germination Shoot fresh wt(g)

Fresh leaf leachate

Dry leaf leachate

Fresh leaf leachate

Dry leaf leachate

Control 87(0.0) 89(0.0) 2.50(0.0) 2.32(0.0)

50 80(8.1) 68(23.6) 1.96(21.6) 1.65(28.9)

100 76(12.6) 45(49.4) 1.89(24.4) 1.10(52.66)

(Sing and thapar,2003)

• High amount of all.chem present in dried leaf extract which respiration and metabolic process responsible for biosynth. Of PROTEASE, amylase,IAA and there by inhibit seed germination.

Reduced seed germination

• Reduced biosynthesis of photosynthates

Reduction in fresh wt of shoots

CONSTRAINS IN RESEARCH..1.Difficulty in exudate collection 2.Poor knowledge of conditions under

which exudates are released3.The exact concn in which

allelochemicals are released is unknown.4.Difficulty to identify which weed is

responsible for the observed allelopathy.5.Presence of autoallelopathy. 6.Lab to field gap .

.

6. Information about which crops are effective against which weeds is limited

7. Information about which are the most allelopathic varieties of a particular crop is not available.

Phytotoxins Source

Coumaric acidVanillic acidFerrulic acid

Maize

Vanillic acid,P -hydrobenzoic acid

Wheat

Caffeicclorigenic

sunflower

Ferrulic acid Soybean

Dhurrin Sorghum

caffeine coffee

Acetaldehyde Sugar beat

Sinigrin Mustard

Sources of plant and microbial phytotoxins with promising herbicidal activity

Where do we stand now - Research? Research is ongoing to identify

allelopathic effects and to identify genes responsible for allelopathy.

This should lead, in time, to recommendations for using allelopathy in weed management and to breeding of new varieties.

CONCLUSION As outlined in the previous discussions

there are many potential problems with attempting to use allelopathy as a practical tool still if we overcome them to some extend allalopathy is the best “Natural herbicide”

REFERENCES Weed science,basics and applications (T K das)LA Weston - Agronomy Journal, 1996 -

crops.orgwww.organicweeds.org.in

Thank you…