Published on October 4, 2007
Exploitation of allelopathic properties for weed control in grain production -: Exploitation of allelopathic properties for weed control in grain production - is that an environmentally sound strategy? Inge S. Fomsgaard, Solvejg Mathiassen, Per Kudsk, Lars M. Hansen History of allelopathy: History of allelopathy 300 BC, Theophrastus: reported inhibitory effects of pigweed on alfalfa 81 BC, Plinius Secundo : desribed allelopathic effects from walnut trees 1832, De Candolle: proposed that exudates from plants could be the reason for soil sickness History of allelopathy: History of allelopathy 1881, Hoy and Stickney: reported deleterious effects of walnut on plants nearby 1907, Screiner and Reed: isolated organic acids released by plant roots that suppressed the growth of other crops History of allelopathy: History of allelopathy 1937, Molisch: coined the word ”allelopathy” from Greek ”allelo” and ”pathy”, meaning ”mutual” and ”suffering” 1966, Muller: defined the phenomenon of plant-plant interaction as ”interference”, involving both competition and allelopathy History of allelopathy: History of allelopathy Research in allelopathy: adverse effects of living plants or their residues upon growth of higher plants and crop yields, interactions among organisms, ecological significance of allelopathy in plant communities, replanting problems, autotoxicity, problems with crop rotations, the production, isolation and identification of allelochemicals in both natural and agroecosystems. Allelopathy - definition: Allelopathy - definition 1996, Torres et al: Allelopathy was defined as: Any process involving secondary metabolites (allelochemicals) produced by plants, microorganisms, viruses, algae and fungi that influence the growth and development of agricultural biological systems Allelochemicals: Allelochemicals secondary plant metabolites alkaloids phenolics flavonoids terpenoids glucosinolates benzoxazinones cyanogenic compounds Allelochemicals: Allelochemicals Reigosa et al, 1999 Use of pesticides in agriculture: Use of pesticides in agriculture Exploitation of allelopathic effects Isolated natural substances Synthetic transformation of natural substances Pure synthetic products Organic crop rotations for grain production - an example: Organic crop rotations for grain production - an example http://www.agrsci.dk/pvj/plant/croprot/indexuk.shtml Allelochemicals in selected cereals: Allelochemicals in selected cereals Wheat, rye and maize contain 4-hydroxy-1,4-benzoxazin-3-ones (hydroxamic acids) as glucosides Wheat: DIMBOA, DIBOA Rye: DIBOA Maize: DIMBOA. DIM2BOA Concentration levels of DIMBOA in wheat: Concentration levels of DIMBOA in wheat From 1.4 to 10.9 mmol DIMBOA/kg fresh weight in 52 Chilean cultivars (young seedlings) Worldwide screening of 37 cultivars: from 0.99 to 8.07 mmol DIMBOA/kg fresh weight Triticum speltoides: 16 mmol DIMBOA /kg fresh weight (10 days seedlings) Biological activity of 4-hydroxy-1,4-benzoxazin-3-ones: Biological activity of 4-hydroxy-1,4-benzoxazin-3-ones Increase the resistance of cereals to insects, fungi and bacteria trigger the reproduction of grass-feeding mammals influence the growth of weeds are involved in the detoxification of pesticides are mutagenic agents Biological activity of 4-hydroxy-1,4-benzoxazin-3-ones, examples: Biological activity of 4-hydroxy-1,4-benzoxazin-3-ones, examples Increase the resistance of maize to the European corn borer increase the resistance of cereals to aphids inhibit root and coleoptile growth of wild oats Molecular structure of 4-hydroxy-1,4-benzoxazin-3-ones: Molecular structure of 4-hydroxy-1,4-benzoxazin-3-ones Mechanism for decomposition of 4-hydroxy-1,4-benzoxazin-3-ones to benzoxazolinones, ex. DIBOA decomposed to BOA: Mechanism for decomposition of 4-hydroxy-1,4-benzoxazin-3-ones to benzoxazolinones, ex. DIBOA decomposed to BOA DIBOA BOA Further decomposition of benzoxazolinones in soil: Further decomposition of benzoxazolinones in soil Kumar et al, 1993: BOA 2-amino-3H-phenoxazin-3-one Nair et al, 1990: BOA 2,2´-oxo-1,1´-azobenzene (AZOB) Further decomposition of benzoxazolinones in soil: Further decomposition of benzoxazolinones in soil R = H DIBOA-glu BOA AZOB Utilization of rye as cover crop or green mulch: Utilization of rye as cover crop or green mulch Barnes & Putnam, 1986 Barnes & Putnam, 1987 Mwaja et al, 1995 Chase et al, 1991 recent trials in organic crop rotation: rye is sown in a density 3 times normal prcatice, young seedlings ploughed down, and winter crop sown afterwards Slide20: Concentration levels of DIMBOA in wheat From 1.4 to 10.9 mmol DIMBOA/kg fresh weight in 52 Chilean cultivars (young seedlings) Worldwide screening of 37 cultivars: from 0.99 to 8.07 mmol DIMBOA/kg fresh weight Triticum speltoides: 16 mmol DIMBOA /kg fresh weight (10 days seedlings) Slide21: Theoretical concentration levels of DIMBOA in soil 0.99-16 mmol/kg in young seedlings 400 plants per m2 weight of each seedling 0.25 g 190-3078 g DIMBOA per hectare 105-1701 g AZOB per hectare Literature search: Literature search DIMBOA or DIBOA or hydroxa* or benzoxaz* or (allelo* and (wheat or rye or maize)) 2159 records since 1972 195 records since 1999 FATEALLCHEM: FATEALLCHEM Fate and toxicity of allelochemicals in relation to environment and consumer Slide24: Isolation and identification of allelochemicals from plants Isolation and identification of soil metabolites from allelochemicals Cultivation of wheat in 2 countries Economic evaluation Quantification of allelochemicals in plants+soil Interlaboratory evaluation of analytical results Dev. of analytical method for allelochemicals in plants and soil Interlaboratory evaluation of analytical results Herbicidal effects of soil-incorporated wheat plant material Insecticidal effects of whole wheat plants Herbicidal effects of isolated allelochemicals Insecticidal effects of isolated allelochemicals Germination studies with allelochemical compounds Degradation studies of allelochemicalsin soil Sorption studies of allelochemicals in soil QSAR modelling of fate of allelochemicals Ecotoxicology of allelochemicals to soil organisms Ecotox of allelochemicals to water organisms QSAR modelling of ecotoxicology of allelochemicals QSAR modelling of human toxicology of allelochemicals WP2 WP1 WP3 WP5 WP6 WP4 WP8 Fungicidal effects Allelochemicals in old Polish wheat varieties Expected achievements I:: Expected achievements I: IF wheat varieties with well described and efficient allelopathic properties against one or or more of the most important weeds and /or pests are identified and the allelochemicals have low environmental toxicity Expected achievements I:: Expected achievements I: THEN commercial exploitation of isolated allelochemicals is possible and/or exploitation of the identified wheat varieties by plant breeders for production of new varieties for use in both conventional and organic farming is possible and/or exploitation of the adquired knowledge in genetic engineering is possible and/or exploitation by farmers using the known varieties with high concentrations is possible (depending on costs for production and/or obtainable yields) Expected achievements II:: Expected achievements II: IF the evaluation of risks to environment and humans show that the allelochemicals have a risk equal to or higher than synthetic pesticides Danish Institute of Agricultural Sciences, Sept 7-8, 2001 Expected achievements II:: Expected achievements II: THEN new views must be put on the exploitation of allelochemicals crops and/or plant breeders must look for varieties with low concentrations and/or public authorities regulating environmental and health standards must focus on allelochemicals and/or definitions of ”organic farming” must be discussed Expected achievements III:: Expected achievements III: IF none of the tested varieties have well described and efficient allelopathic properties but some allelopathic effect less the the effect of synthetic pesticides and risk to environment and humans is low Expected achievements III:: Expected achievements III: THEN growing of the varities with ”highest” allelopathic properties might still be useful to organic farmers and development by breeding of new varities for use in organic farming is still useful (depending on economy) Conclusion: Conclusion Cheng, 1992 Toxicity? Exposure of non-target plants and other living organisms? Transport to ground water? Future studies: Future studies The holistic approach!