herbicide resistance in weeds

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HERBICIDE RESISTANCE

IN WEEDS


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INTRODUCTION

Herbicides are the most effective and economic among

the weed management practices.

The advent of selective herbicides in agriculture

proved a boon for weed management in various cropsbut soon posed the problem of spread of the natural

tolerant or resistant weed species.

These resistant weed population pose today the biggestchallenge to the weed scientists, the world over


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MEANING

Herbicide Resistance

Weed


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What is Herbicide Resistance?

(official WSSA definition)

Inherited ability of a plant to survive

and reproduce following exposure toa dose of herbicide normally lethal to

the wild type.


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DEFINITION

It is the evolved capacity of a previously herbicide

susceptible weed population to withstand an

intended herbicide complete its life cycle when

the herbicide was used at its normal rates in an

agricultural situation ( Gupta ,1998) .

It is defined as the inherited ability of weed to

survive a rate of herbicide which would normally

give effective control( Walia ,2010).


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Resistance vs Tolerance

Herbicide tolerance: It is the ability of a

species to survive and reproduce afterherbicide treatment. It is the ability to

compensate the damaging effect of herbicides

with No physiological mechanisms involved

(Menalled and Dyer ,2006).


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Herbicide resistance: Refers to the inherited abilityof a weed or crop biotype to survive a herbicide application to which

the original population was susceptible herbicide resistance is simply

an altered response to a herbicide by a species which was earlier

susceptible and it is the naturally occurring, irreversible and

inheritable ability of some weed biotypes within a population (Duary

and Yaduraju , 1999).

The resistance is considered as an extreme

case which occurs less frequently than the

herbicide tolerance. (Prado & Franco-2004)


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HISTORY

Resistance of weeds to herbicides is not a unique

phenomenon. Although herbicide resistance was reported as

early as 1957 against 2, 4-D from Hawaii (Hilton 1957), thefirst confirmed report of herbicide resistance was against

triazine herbicide in common groundsel (Senecio vulgaris)

and was reported in 1968 from U.S.A. (Ryan 1970).


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Consequently, several other reports confirmed

resistance developed against dozens of other herbicides

in five decades The number of resistant weed biotypes

against various herbicides is on the rise since its first

report .Till July 10, 2008, 319 biotypes belonging to 185 species

(111 dicots and 74 monocots) have been reported

resistance against various herbicides(Das,2008).

CONT.


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CURRENT SCENARIO

There are currently 403 unique cases (species x site

action) of herbicide resistant weeds globally, with 21

species (129 dicots and 89 monocots). Weeds hav

evolved resistance to21 of the 25 known herbicide sitof action and to 148 different herbicides. Herbicid

resistant weeds have been reported in 66 crops in 6

countries.(www.weedscience.org)


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T bl 1 li t f i t t d


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Table.1 list of resistant weeds

C t


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Cont

Source;www.weedscience.org


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TYPES OF RESISTANCE

SINGLE HERBICIDE RESISTANCE/SIMPLE RESISTANC

Simple resistance is the resistance of a weed species

due to its continuous exposure to a herbicide.

it is of two kinds

a)COMPLETE/FULL RESISTANCE

b) PARTIAL RESISTANCE (Rubin, 1991)


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CROSS RESISTANCE

Cross resistance evolves when a weed species alreadresistant to a herbicide shows resistance to othe

herbicides of same chemical class to which it had neve

been exposed or it shows resistance to two or morherbicides due to single resistance mechanism.e.g; Avena fatua resistant to triallate is cross resistant

difenzoquat(reported in canada)

It is also two kinds.


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1.TARGET SITE BASED RESISTANCEResistance to two or more herbicides of similar

dissimilargroups inhibiting the same target site due to simil

target site alteration.it may occurs across herbicides of triazine

,triazinones,phenyl urea,uracils etc which inhibit photosynthesis

PSII.

2.METABOLIC RESISTANCEResistance to two or more herbicides of similar

dissimilargroups inhibiting the same target site due to simil

metabolic/degradative process and similar rate of degradation

the herbicides.e.g;phalaris minorshowing resistance to isoproturon and diclofo

methyl.


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NEGATIVE CROSS RESISTANCE/COLLATERAL

SENTITYVITY

It is the mechanism by which an individual weedresistant to one herbicide or a chemical family of

herbicides shows higher susceptibility to other

herbicides than its natural wild type susceptible

population.This happens very frequently due tochange in target enzyme.

e.g;atrazine resistant biotype of Echinochloa

crusagallishows 33 & 2 times more sensitivity to

fluazifop-butyl and sethoxydim respectively

(Gadamaski et.al.2000).


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MULTIPLE RESISTANCE

It is the resistance through which a weed species shows

resistance to herbicides of different chemical classes

having different mode of action by two or more distinct

resistance mechanisms.e.g; Lolium rigidum against various groups of herbicides

like triazines, phenyl urea, sulfonylureas,

carbamate,glyphosateetc in Australia(Das,2008).


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REVERSE RESISTANCE

It is the phenomenon in which weed biotypes

resistant to a herbicide fall susceptible to the

same herbicide if not used for a period of 7-10years.


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CO- RESISTANCE/COMPOUND

RESISTANCE

It is the phenomenon in which a weed develops

resistance to both mixing partner herbicides of a

mixture applied concurrently.e.g; Lolium rigidum resistant to amitrole and

atrazine applied concomitantly.(Yadav &

Malik,2003).


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DEVELOPMENT OF RESISTANCEContinuous and repeated use of a herbicide or herbicide

having same mechanism of action in intensive agriculture

or horticultural system involving crop monoculture and

minimum tillage have been the major causes o

occurrence of herbicide resistance.

It is not due to the mutation caused by the herbicideas chemical, rather resistance appears from the

selection of natural mutation that exist as smal

fraction of population of resistant plants. . Such a

minute number of resistant plants continue to growand expand by generation over time and seasons.


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RESISTANT BIOTYPE


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Year 1


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Year 2

3


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Year 3

Y 4


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Year 4

Y 5


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Year 5

MECHANISMS OF


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MECHANISMS OF

HERBICIDE RESISTANCE

Dekker and Duke (1995) broadly grouped mechanisms oherbicide in to the following two categories:

EXCLUSIONARY RESISTANCE

SITE OF ACTION OF RESISTANCE



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This refers to those mechanism that exclude the herbicid

molecule from the site of action in plants where they induc

toxic response.

Such exclusion of herbicide from the site of action ca

be due to several reasons. such as


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(a) Differential herbicide uptake:

In resistant biotypes the herbicides are not taken

up readily due to morphological uniqueness

like over production of waxes, reduced lea

area etc. It can be differential herbicide uptake

due to the morphological barrier on leave

such as extraordinarily increased waxy coating

on the cuticle, hairy epidermis and low foliagenumber and size etc.

(b) Differential translocation


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(b) Differential translocation:

In resistant biotypes the apoplastic (cell wal

xylem) and symplastic (plasma lemma, phloemtransport of herbicide is reduced due to differen

modifications. It can also be due to differentia

translocation whereby apoplastic (xylem tubes) osymplastic path (phloem cells) restrict or dela

movement of right concentration of herbicide a

the site of action. (Ozair et al. 1987).


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(c) Sequestration and compartmentation

Herbicides are sequestered in many location

before it reaches the site of action. e.g. somlipophilic herbicide may become immobilized b

partitioning into lipid rich glands or oil bodie

(Stegink and Vaughn 1988). Compartmentatiomay be either by storage of the herbicide or it

metabolites in the cell vacuole or thei

sequestration in cells or tissue, far from the site o

action.


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(d) Metabolic detoxification:

Herbicide is detoxified before it reaches the

site of action at a rate sufficiently rapid that

the plant is not killed. The biochemica

process that detoxifies herbicides can be

grouped into four major categories:

oxidation, reduction, hydrolysis, and

conjugation. Three enzyme systems are

known to be involved in resistance due to

increased herbicide detoxification.


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SITE OF ACTION OF RESISTANCE

(a) Altered site of action:

Site of action is altered in such a way that it is no

longer susceptible to the herbicide .

e.g. In Lactuca sativa biotypes which are resistan

to sulfonylurea herbicides, the ALS enzymwhich is the site of action of herbicide i

modified in such a way that herbicide can n

longer bind with the enzyme and inactivate (Eberlein et al. 1999).

(b) d i f i f i


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(b) Overproduction of site of action:

It also happens in some cases that the site of action

enlarged or overproduced as a result dilution effect o

herbicide occurs. The applied normal rate of herbicide i

unable to inactivate the entire amount of enzymprotein produced. Therefore, the extra amount o

enzyme produced by the plant biotype can allow it carr

on its normal metabolic activities surmounting thlethal effect of the herbicide.

Factors controlling the development of


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g pherbicide

Resistance in weeds(A)WEED FACTORS

a) Initial frequency of the resistant individuals

b) Selection pressure for evolution of resistan

populationc) Ecological/Biological fitness: Fitness measures th

potential evolutionary success

d) Weed reproduction, seed production, seed dormancand germination and seed bank in the soil


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SELECTION PRESSURE

Selection pressure is any mechanism whicencourage dominance of one particular type o

individual in a mixed population.


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SELECTION FOR HERBICIDE

RESISTANCE

Ch i W d P l ti Aft E t i U


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Change in Weed Population After Extensive Use

of Herbicide Effective on Weeds A and B

but Weak on Weed C

Year 1 Year 2 Year 3 Year 4 Year 5

0

20

40

60

80

Year 1 Year 2 Year 3 Year 4 Year 5

Weed A

Weed B

Weed C

%o

fpop

ulation


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HERBICIDE CHARACTERISTIC

(a) Herbicides with highly specific mode of actio

(b) Herbicides metabolism

(c) Long residual activity

(d) Over dependence on single herbicide

(e) Type of herbicide and its time and dose of

application

CROPPING PRACTICE


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CROPPING PRACTICE

(a) Tillage

(b) Cropping system


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Think

Resistance

Management

HERBICIDE MANAGEMENT


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HERBICIDE MANAGEMENT

a) Stop use of herbicide to whichresistant developed

b) Use of alternative herbicides

c) Herbicide mixture and rotation

d) Herbicide selection and application

e) Use of herbicides with short

residual life


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PREVENTIVE METHOD

Crop rotation

Tillage practices

Biological control o

resistant weed

Oth lt l ti


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Other cultural practices :

Selection of weed competitive crop cultivar

Use of clean seed and certified seed

Stale seed bed technique

Closer row spacing Timely sowing and rate of seeding

Good crop husbandry

Soil solarization

farmers Awareness, training and


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, g

Participatory approach

farmers may be provided adequate traininon how to monitor manage weed resistanc

.farmers participatory approach mean

farmers participation in problem solvinactivities planned and designed by th

scientists and extension personnel

Monitoring of herbicide resistance if


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g

any:

The field must be visited regularly and

weeds surviving the treatments

particularly after spraying thealternative herbicides should be

identified

Integrated Weed Management


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Integrated Weed Management

(IWM)IWM strategies involving physical, chemical an

biological in a integrated fashion without excessiv

reliance on any single method can help in successful

managing herbicide resistance while maintaining farprofitability and sustainability.

Integrated weed management is a viable strategy as it

based on the principle of using a wide range of contr

methods in appropriate combinations

CONCLUSIONH bi id i t i ld id h d


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Herbicide resistance is worldwide phenomenon and

number of resistant biotypes of weeds is increasing at an

alarming rate.To overcome thisOver-reliance on herbicide should be

minimized and herbicide should be used integrated

with other practices.

Herbicide should be used in rotation or as mixture. We

must keep available all other alternative tools we ever

had, including the manual, cultural and other practices

which should be used in an integrated manner.


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herbicide resistance in weeds

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