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 Fats Proteins

Alkaloids- for pain and pleasure!

• Can permeate through blood-brain barrier

Opium poppy Tobacco

Coffee

Nico

tine

Coca

Co

caine

Caf

fein

e

Mo

rph

ene

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?

LD50 880 mg/kg LD50 7300 mg/kg LD50 590 mg/kg LD50 5 mg/kg

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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

Monarch butterfly sequesters cardenolides from milkweed for self defense

Cardiac glycoside

Milkweed

Armyworm

Monarch caterpillar Toxicity on blue jay

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

Invasion through indirect toxicity

Sinigrin Gar

lic m

ust

ard

M

ycorrh

izal(MR

) D

isrup

tion

of M

R

Invaded forest understory

Multidimensional nature of allelopathy

DOI: 10.5772/56185

Metabolism mediated allelopathy

Tannin protocatechuic catechin

Inhibition of soil N mineralization

Toxic degradation products

Japan

ese Kn

otw

eed

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%

18%

22% 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

• Plants challenged by herbivore produce more glucosinolate

• However the thiocyanate production is low in these plants due to low myrosinase activity

Myrosinase activity

Sorgoleone is an

allelochemical produced

by sorghum spp.

Netzly and Butler, 1986 Crop Sci. 26, 775-778

Sorghum allelopathy

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

Callistemon spp. bottlebrush plant

leptospermone

mesotrione

OO

O O

O

O O NO2

S

O

O

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

Huang et al. (2010) Phytotoxicity of sarmentine isolated from long pepper (Piper longum) fruit, J. Agric. Food Chem. 58, 9994

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

Macrocidin

Graupner et al. (2003) The macrocidins: novel cyclic tetramic acids with herbicidal activity produced by Phoma macrostoma, J. Nat. Prod. 66, 1558

Isolated from Phoma macrostoma

Causes bleaching of the foliage of broadleaf weeds, but not grasses

Possible RNA polymerase inhibitor

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