Utilizing allelopathy in organic crop
production
Nishanth Tharayil, Ph.D.
Agricultural & Environmental Sciences
Clemson University, Clemson SC
Dissecting the appearances
Biology is a synchronous dance between chemicals
Chemical ingredients of “All Natural”
produce
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“All Natural” ingredients
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Aroma in coffee
An egg is chemically more complex than jeans
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Fascinating chemistry of plants
•Primary metabolites
•
essential & evident metabolic function
• carbohydrates, lipids, proteins, and nucleic acids
Carbohydrates
Proteins
Fats
Alkaloids- for pain and pleasure!
• Can permeate through blood-brain barrier
Morphene
Nicotine
Opium poppy
Tobacco
Caffeine
Cocaine
Coffee
Coca
Terpenes- the smell!
Reactive oxygen species and health
http://radiation-remedies.com/inflammation-and-double-break-dna-rupture/
Polyphenols
Sip, Swirl, Swallow!
Antioxidant activities of various beverages
Free Radic Res. 1999 Feb;30(2):153-62.
How much is too much?
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LD50 880 mg/kg
LD50 7300 mg/kg
LD50 590 mg/kg
LD50 5 mg/kg
All plant compounds are not that innocuous
LD50 microgram scale
Why are PSMs produced?
• Cellular, organismal, ecological functions
• Protection from UV damage
• Protection from pest & disease
• Uptake of nutrients
• Quenching reactive radicals
• Tolerance to heat & low temp
• Response to toxic chemicals
• Cellular signaling
• Plant-microbe interaction
Plant-pathogen interactions
Indirect plant-herbivore interaction
Eavesdropping on plant defenses
Armyworm
Cardiac glycoside
Milkweed
Toxicity on blue jay
Monarch caterpillar
Monarch butterfly sequesters cardenolides from milkweed for self defense
Tansy Ragwort and cinnabar moth
Pyrrolizidine alkaloid
Chemical warfare among plants
•Allelopathy
• Allelon – “of each other”
• Pathos – “to suffer”
• Any process involving secondary
metabolites produced by plants,
micro-organisms, viruses and fungi
that influence growth and
development of agricultural and
biological systems (excluding
animals), including positive and
negative effects
Allelopathy & invasion by exotic plants
Peculiar invasion patterns of Centaurea maculosa, which is replacing native plants in the
fields of northwestern USA. (a) Non-invaded area. (b) Same area photographed 20 years
later (Bias et al. 2004)
Epi-catechin
Sinigrin
Mycorrhizal(MR)
Garlic mustard
Invasion through indirect toxicity
Disruption of MR
Invaded forest understory
Multidimensional nature of allelopathy
DOI: 10.5772/56185
Metabolism mediated allelopathy
Japanese Knotweed
Inhibition of soil N mineralization
Tannin
protocatechuic catechin
Toxic degradation products
How can we utilize the allelopathy in
agriculture?
• Cover crops with allelopathic potential
• Use secondary compounds as herbicides
• Breed crops to have higher allelopathic potential
Cover crops with allelopathic potential
• Brassica sp
• Nigra
• Napus
• Juncea
Primary toxic compound in Brassicaceae
• Glucosinolates (GLS)
• Type of GLS vary with
respect to brassica
species and growing
conditions
• LD50 = 100-200 ppm
Cellular trickery of GLS defense
Sinigrin
+
Myrosinase
Isothiocyanate (5 times more toxic)
Current experimental approaches
•
Management of cover crops primarily focused on the GLS production
• GLS to ITC conversion is assumed to be less important
• Theoretical GLS to ITC conversion efficiency
• One mol of GLS = 1 mol of ITC
• Currently observed conversion efficiency is <5 %!!
• How we can increase the pesticidal potential of
cover crops ?
Optimizing for the retention of ITC
Retaining ITC in soils helps!
5%
22%
18%
3%
Optimizing for the GLS-ITC conversion
• Grow or to defend- dilemma in plants
• Plant grown under stress are well defended
• Will biotic/abiotic stress increase the toxic potential
of brassica?
• Nutrient deficiency
• Herbivory
Biotic/abiotic influence of GLS
• Nutrient deficiency and herbivory increases glucosinolate production
Stressed plant might not be well defended
Myrosinase activity
• Plants challenged by herbivore produce more glucosinolate
• However the thiocyanate production is low in these plants due to low myrosinase
activity
Sorghum allelopathy
Sorgoleone is an
allelochemical produced
by sorghum spp.
Netzly and Butler, 1986 Crop Sci. 26, 775-778
Sorgoleone
USDA Natural Products Utilization Research Unit
Pesticide usage (2008)
J. Agric. Food Chem., 2014, 62 pp 11613
Herbicides top the list!
J. Agric. Food Chem., 2014, 62 pp 11613
Trends in pesticides
• EPA Pesticide Registration New Active Ingredients (1997-2010)
• 109 new conventional active
ingredients registered
• 85 synthetic, 7 natural product, 16
synthetic natural-derived, and 1
biological
• Combined impact of natural
products on conventional
pesticides is 20.4 % of new AI
registrations
Natural product-based major pesticides
• Herbicides
• glufosinate– based on phosphinothricin
• triketones – based on leptospermone
• Fungicides
• Strobilurins
• Insecticides
• pyrethroids
• spinosads
• Bt toxins
• neonicotinoids
Bialaphos and glufosinate
• Bialaphos is obtained from the fermentation culture of the
actinomycete Streptomyces hygroscopis. It is marketed in eastern Asia
whereas the synthetic analog glufosinate is sold elsewhere around the
world
phosphinothricin
Chemical ecology clue
O
O
O
O
leptospermone
O
O
NO2
Callistemon spp.
bottlebrush plant
O
O
S
O
mesotrione
USDA Natural Products Utilization Research Unit
Leptospermum spp. (tea tree)
Manuka oil is about 40% natural triketones
p-hydroxyphenylpyruvate dioxygenase inhibitor
USDA Natural Products Utilization Research Unit
Barnyard grass (Echinocloa crus-galli)
USDA Natural Products Utilization Research Unit
Sarmentine
The bioassay-guided fractionation and purification of the
crude extract of Long pepper led to isolation of sarmentine
It is a contact herbicide and
possessed broad-spectrum
herbicidal activity
The phytotoxicity of sarmentine and its analogs matched that
of fatty acids with similar tails, such as sarmentine and
decenoic acid
Huang et al. (2010) Phytotoxicity of sarmentine isolated from long pepper (Piper longum) fruit, J.
Agric. Food Chem. 58, 9994
Macrocidin
Isolated from Phoma macrostoma
Causes bleaching of the foliage of
broadleaf weeds, but not grasses
Possible RNA polymerase inhibitor
Graupner et al. (2003) The macrocidins: novel cyclic tetramic acids with herbicidal activity
produced by Phoma macrostoma, J. Nat. Prod. 66, 1558
Agriculture and Agri-Food Canada
Breeding for weed control
Allelochemicals in rice
Rice allelopathy mediated by microbes
Plant, Cell & Environment
23 JAN 2015 DOI: 10.1111/pce.12492