Published on

Published in: Education, Technology
1 Comment
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide


  1. 1. Presented by: SAMEERA LI M.
  2. 2.  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?
  3. 3.  Allelopathy refers to all biochemical interactions,stimulatory or inhibitory,among plants including,1937)  Detrimental effect of chem.or exudates produced by one living plant sp.on germn,growth&dev.of other plant or sharing same habitat. (Evenari,1949)
  4. 4.  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
  5. 5. from the Latin words allelon ‘of each other’ and pathos ‘to suffer’, refers to the chemical inhibition of one species by another.  Allelopathy,  The source of allelochemicals in agricultural fields may be the weeds, crops or microorganisms.
  6. 6.  Democritus (500 BC)and Theophrastus(300 BC)  Pliny-Naturalis Historica  Decondole(1832)  Molisch(1937)-coined allelopathy  Rice (1974) Elroy L. Rice
  7. 7.  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 Sorghu m Buckwh eat Red clover sweet clover Barley Wheat • Trifoli
  8. 8.  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.
  9. 9.  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.
  10. 10. Light Mineral deficiency Drought stress
  11. 11.  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.
  12. 12. 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
  13. 13. • Wheat, • alfalfa, • cowpea Auto Allo allelopathy • Lentil residues on wheat allelopathy Residual • Maize – on chenopodium album, • Sorghum on abutylon • theophrasti Concurrent /direct allelopathy • Instantane ous direct effect • sorghum
  14. 14. Forms of allelopathic interactions Weed Crop Crop Weed against against against against weed crop weed crop
  15. 15. Crop Weed sp Source of inhibitors Maize Chenopodium album, Roots Amaranthus retroflexus Sorghum Abutylontheophrasti, Shoots and foliages Amaranthus hybridus Rye Digitaria sanguinalis, Ambrosia artimisifolia Shoots and foliages
  16. 16.  Parthenium  hysterophorus Effect of several waste land weeds on parthenium suppression 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)
  17. 17. Stem Roots & Rhizome Sources Fruits& seeds Leaves & Flowers
  18. 18.  Usually secondary plant products/metabolites(whittakker and peeny,1971) Phenyl propones Terpinoides Acetogenins Akaloids Steroides
  19. 19.  According to Rice(1984),allelochemicals grouped into: Tannins Cinnamic acid deriv. Flavinoides Purines Terpinoides Organic acids Complex quinones Coumarins Sulphides Polypeptides Lactones Glycosides
  20. 20. •Volatalization •Leaching •Exudation •Weathering
  21. 21.  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.
  22. 22.  Leaching  Through aqueous solutions (rain,dew)  Mature leaves are more susceptible  Exudation  Metabolites exuded from roots to surrounding atm.  Pottential source of allelopathic effect
  23. 23.  Decomposition  Leaves and stubbles  By weathering and micro organisms.
  24. 24. I N H I B I T  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
  25. 25. How allelochemicals introduced into plant??
  26. 26. 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 
  27. 27. • 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.
  28. 28. • 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.
  29. 29.  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)
  30. 30. Reduction in fresh wt of shoots • Reduced biosynthesis of photosynthates Reduced seed germination • 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.
  31. 31. 1.Difficulty in exudate collection 2.Poor knowledge of conditions under which exudates are released 3.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 . .
  32. 32. 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.
  33. 33. Sources of plant and microbial phytotoxins with promising herbicidal activity Phytotoxins Source Coumaric acid Vanillic acid Ferrulic acid Maize Vanillic acid, P -hydrobenzoic acid Wheat Caffeic clorigenic sunflower Ferrulic acid Soybean Dhurrin Sorghum caffeine coffee Acetaldehyde Sugar beat Sinigrin Mustard
  34. 34.  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.
  35. 35.  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”
  36. 36.  Weed science,basics and applications (T K das) LA Weston - Agronomy Journal, 1996