Exploitation of allelopathic properties for weed control in grain production -

1
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
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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

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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

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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

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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.

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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

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Allelochemicals

• secondary plant metabolites
• alkaloids
• phenolics
• flavonoids
• terpenoids
• glucosinolates
• benzoxazinones
• cyanogenic compounds

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Allelochemicals
Reigosa et al, 1999
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Use of pesticides in agriculture
Exploitation of allelopathic effects
Synthetic transformation of natural substances
Isolated natural substances
Pure synthetic products
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Organic crop rotations for grain production - an
example
http//www.agrsci.dk/pvj/plant/croprot/indexuk.sht
ml
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Allelochemicals in selected cereals

• Wheat, rye and maize contain 4-hydroxy-1,4-benzoxa
  zin-3-ones (hydroxamic acids) as glucosides

Wheat DIMBOA, DIBOA
Rye DIBOA
Maize DIMBOA. DIM2BOA
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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)

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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

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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

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Molecular structure of 4-hydroxy-1,4-benzoxazin-3-
ones
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Mechanism for decomposition of 4-hydroxy-1,4-benz
oxazin-3-ones to benzoxazolinones, ex. DIBOA
decomposed to BOA
DIBOA
BOA
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Further decomposition of benzoxazolinones in soil
Kumar et al, 1993 BOA ? 2-amino-3H-phenoxaz
in-3-one
Nair et al, 1990 BOA ? 2,2-oxo-1,1-azobenz
ene (AZOB)
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Further decomposition of benzoxazolinones in soil
R H
DIBOA-glu
BOA
AZOB
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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

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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)

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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

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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

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FATEALLCHEM

• Fate and toxicity of allelochemicals in relation
  to environment and consumer

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WP2

• Cultivation of wheat in 2 countries
• Economic evaluation

Isolation and identification of allelochemicals
from plants Isolation and identification of soil
metabolites from allelochemicals

• Quantification of allelochemicals in plantssoil
• Interlaboratory evaluation of analytical results

WP1

• Dev. of analytical method for allelochemicals in
  plants and soil
• Interlaboratory evaluation of analytical results

WP3
Degradation studies of allelochemicalsin soil
Herbicidal effects of soil-incorporated wheat
plant material
Insecticidal effects of whole wheat plants
Ecotoxicology of allelochemicals to soil
organisms
Ecotox of allelochemicals to water organisms
Insecticidal effects of isolated allelochemicals
Herbicidal effects of isolated allelochemicals
Sorption studies of allelochemicals in soil
QSAR modelling of ecotoxicology of
allelochemicals
Germination studies with allelochemical compounds

QSAR modelling of fate of allelochemicals
WP5
WP4
QSAR modelling of human toxicology of
allelochemicals
Fungicidal effects
WP8
Allelochemicals in old Polish wheat varieties
WP6
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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
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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)
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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
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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
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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
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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)
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Conclusion
Toxicity?
Transport to ground water?
Exposure of non-target plants and other living
organisms?
Cheng, 1992
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Future studies

• The holistic approach!