Allelopathy

1. ALLELOPATHY AND WEED MANAGEMENT SAMEERALI M. PALB-2186 Presented by:

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. 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)

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) .

5. 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.

6. History Democritus (500 BC)and Theophrastus(300 BC) Pliny- Naturalis Historica Decondole (1832) Molisch (1937)-coined allelopathy Rice (1974) Elroy L. Rice

7. 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:

8. 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.

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. Factors affecting production of allelochemicals

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. Types of allelopathy There are two types: True type - the release into the environment of compounds that are toxic in the form in which they are produced. Functional type - the release into the environment of a substance that is toxic as the result of transformation by micro-organisms

13. Types of allelopathy

14. 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

15. Weeds against weeds Parthenium hysterophorus Effect of several waste land weeds on parthenium suppression Sl.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)

16. Sources of allelochemicals

17. Chemical nature of allelochemicals Usually secondary plant products/metabolites( whittakker and peeny,1971)

18. According to Rice(1984), allelochemicals grouped into:

19. Liberation of allelochemicals

20. 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.

21. Leaching Through aqueous solutions ( rain,dew ) Mature leaves are more susceptible Exudation Metabolites exuded from roots to surrounding atm. Pottential source of allelopathic effect

22. Decomposition Leaves and stubbles By weathering and micro organisms.

23. 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 I N H I B I T

24. How allelochemicals introduced into plant??

25. 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

26. 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.

27. 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.

28. 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)

29. constrains in research.. 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 . .

30. 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.

31. 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 Sources of plant and microbial phytotoxins with promising herbicidal activity

32. 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.

33. 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”

34. references Weed science,basics and applications (T K das) LA Weston - Agronomy Journal, 1996 - crops.org www.organicweeds.org.in

35. Thank you…