JUNE 5TH

WORLD ENVIRONMENT DAY

WEED

A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place”.

It causes•Yield losses •Low output efficiency •Extra Labor costs•Environmental issues through herbicide usage etc.

THE TIME A WEED SPENDS IN CONTACT WITH A CROPPLANT CAN HAVE A DRAMATIC EFFECT ON YIELD.

ALL WEED PLANTS IN CULTIVATED FIELD GIVING HARM RATHER THAN BENEFITCROP TYPE PRODUCTION LOSSES

CEREALS 433.903 54.349

VEGETABLES 201.691 23.718

FRUITS 66.567 2.462

WINEYARD 50.697 7.909

World wide Production and Losses due to Weeds (Million tons) (Duke et al. 2013)

BIOTECHNOLOGICALINTERVENTIONS ON WEED

MANAGEMENTSHELVY S2011-09-123

INTRODUTIONoTransgene technology has been used to generate herbicide-resistant crops, which have profound effects on the herbicide market.

oSame technology has the potential to make crops better competitors with weeds through improving competitive traits or making the crop more allelopathic. And has wide application in agronomy and horticulture by transgenic bio control agents.

oMolecular Systematics helps to provide information on weed identification and characterisation.

Chemical Method Mechanical Method

Cultural Method Biological Method

CONVENTIONAL

WEED CONTROL

CONVENTIONAL WEED MANAGEMENTMechanical

All common tillage practices before and after planting crops, including frequent cultivation at precise times using specialized implements, deep plowing to bury weed seed banks, hand plucking etc.

CulturalIncludes fallowing land, stale seedbeds, adjusting seeding dates, transplanting instead of seeding, mowing, and smother cover crops, etc.

ChemicalUse of Chemical Herbicides

BiologicalIntroduction of a living organism to control a weed species. (Bio control agents )

WHY BIOTECHNOLOGYA national Research Council report acknowledge “GE Crop technology has produced substantial net environmental and economic benefits to farmers growing GE products over using non GE varieties in conventional production system.Because of concerns of health, safety, and sustainability, there is a growing interest in reducing chemical weed control measures.

BIOTECHNOLOGICAL APPROACHES FOR WEED MANAGEMENT Development of Herbicide resistant crops Improvement of Biocontrol Agents Development of Transgenic Allelopathy in crops Characterization of weeds using Molecular systematics

DEVELOPMENT OF HERBICIDE

RESISTANT CROPS

TYPES OF HERBICIDES BY CHEMICAL FAMILIESChemical Family Affected System Target Proteins Spectrum

Triazines (atrazine, ametryne, cyanazine, prometryn, simazine

Photosystem II, electron transport from QA to QB

D-1 protein, product of psbA gene

Total

Sulfonylurease, imidazolinones, triazolopyrimidines

Amino acid synthesis Acetolactate synthetase (ALS)

Selective

Aryloxypenoxypropionates (AOPP), cyclohexanediones

Lipid Synthesis Acetyl coenzyme Acarboxylase (ACCase)

Selective

Glyphosate (N-phosphonomethyl)glycine

Amino acid Synthesis 5-enolpyruvyl-shikimate-3-phosphate synthetase (EPSPS)

Total

Bromoxynil Photosystem II D-1 protein Total

Phenoxycarboxylic acids (eg: 2,4-D)

Unknown Unknown Selective

Glufosinate (Phosphinothricin, PPT)

Amino acid synthesis Glutamine synthetase Total

Bypiridiliums, praquats, diquats

Photosystem I Electron transfer system

Total

BIOTIC RESISTANCE DEVELOPMENT IN CULTIVATED CROPS IN INDIA

Acharya N. G. Ranga Agricultural University

PROBLEMS IN APPLICATION OF HERBICIDES•Lack of tolerance to the chemical by one or more of the major world crops, e.g. Rice, Maize, Soybean, Wheat etc.

•Use of multiple types of herbicides to broaden the spectrum of the affected weeds, which in turn increase the possibility that the crop is injured also.

•Continuous use of one herbicides leads to the development of super weed.

HERBICIDE RESISTANCE IN PLANTS

Herbicide resistance is the ability, trait or quality of a population of plants within a species or larger taxon, to withstand a particular herbicide at a dosage that is substantially greater than the wild type of that plant is able to withstand.

Normal Crop

Herbicide resistant Crop

WHY HERBICIDE RESISTANT PLANTS ?

Total herbicides, when applied, kills all the plants in the field including culture plantSelectivity of a herbicide is an important criteria.Increase selectivity•Maximum effect on herbs•Minimum effect on culture plant

HERBICIDE RESISTANT CROPS Gene for herbicide resistance can be inserted into crop plant’s chromosomal DNA.

GLYPHOSATE

Glyphosate (N-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide used to kill weeds. Such as broad leaf weeds and grasses.

It was discovered to be an herbicide by Monsanto chemist John E. Franz in 1970.

Monsanto brought it to market in the 1970s under the trade name Roundup and Monsanto's last commercially relevant United States patent.

Glyphosate's mode of action is to inhibit a plant enzyme involved in the synthesis of the aromatic amino acids.

It inhibits a critical enzyme of the shikimate pathway, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS).

GLYPHOSATE RESISTANT CROPS

Presently, glyphosate-resistant and glufosinate-resistant crops are the only two transgenic HRCs commercially grown.

Glyphosate-resistant (GR) crops represent more than 80% of the 120 million ha of transgenic crops grown annually worldwide. (Duke et al. 2012)

One to two timely applications of glyphosate, pre-emergence herbicides can provide effective control of a broad spectrum of weeds.

The gene encoding an enzyme that cleaves the C-N bond of glyphosate (glyphosate oxidase; GOX) was isolated from E. coli.

Molecular Approach for the development of Glyphosate Resistant Crops

ADOPTION RATE OF GLYPHOSATE-RESISTANT CROPS IN THE UNITED STATES.

GLUFOSINATE

Glufosinate or its ammonium salt DL-phosphinothricin is an active ingredient in several nonselective herbicides such as Basta, Rely, Finale, Ignite, Challenge, and Liberty.

It interferes with the biosynthetic pathway of the amino acid glutamine and with ammonia detoxification.

Phosphinothricin is an glutamine synthetase inhibitor that binds to the glutamate site. Glufosinate-treated plants die due to a buildup of ammonia and corresponding decrease in pH in the thylakoid lumen, leading to the uncoupling of photophosphorylation.

GLUFOSINATE RESISTANCE

Glufosinate-detoxifying genes bar and pat were isolated and characterized from Streptomyces hygroscopicus and S. viridichromogenes, respectively (Thomson et al. 1987)

Both bar and pat were demonstrated to code for a 21-kDa phosphinothricin acetyltransferase (PAT)

is required for the production of an essential intermediate (N- acetyldemethylbialaphos) in the biosynthesis of the tripeptide bialaphos.

Acetylation of the free amine on glufosinate makes the molecule too bulky to fit in the active site of Glutamine Synthetase.

CROP PLANTS TRANSFORMED WITH THE BAR OR PAT GENE CONFERRING TOLERANCE TO GLUFOSINATE

Crop Species

Alfalfa Medicago sativa

Broccoli Brassica oleracea

Canola Brassica napus

Carrot Daucus carota

Corn Zea mays

Cotton Gossypium hirsutum

Lettuce Lactuca sativa

Melon Cucumis melo

Potato Solanum tuberosum

Rice Oryza sativa

Sugarbeet Beta vulgaris

Sugarcane Saccharum officinarum

Tobacco Nicotiana tabacum

Tomato Lycopersicum esculentum

Wheat Triticum aestivium

BROMOXYNIL

Bromoxynil is a nitrile herbicide, trade names include Brominal, Bromotril, Bronate, Buctril, Certrol B, Litarol, M&B 10064, Merit, Pardner, Sabre, and Torch.

It is used for post-emergent control of annual broadleaf weeds.

It works by inhibiting photosystem II of photosynthesis.

BROMOXYNIL RESISTANCEGene encoding broxynil resistance was isolated from Rhodococcus species with nitrilase enzyme production.

The gene doesnot impart resistance to other classes of PS ii inhibiting herbicides, thus linking the transgenic crop to a specific herbicide.

The first introduced commercial herbicide-resistant crop (HRC) was bromoxynil-resistant cotton.

Bromoxynil-resistant canola became available to Canadian farmers in 1999 but has had only limited success.

SULFONYLUREA AND IMIDAZOLINONE RESISTANCE They are very potent inhibitors of the acetolactate synthase (ALS), a key enzyme of branched chain amino acid synthesis.

Commercially available ALS inhibitor-Resistant crops have been produced by mutation.

Commercially available Herbicide crops in world

ROUNDUP READY® CANOLA CROP MANAGEMENT PLAN (CMP)

Objective : The Roundup Ready canola Crop Management Plan details, strategies that can be implemented on-farm to manage risks to the integrity of grain supply-chains and the sustainability of agricultural production.

Understanding glyphosate resistance riskResistance management principles for Roundup Ready canolaPre planting, In crop and Post harvest activitiesWeed control rating etc.

ADVANTAGES OF TRANSGENIC HERBICIDE RESISTANCEoIncreased yield performance

oBroader spectrum of weeds controlled

oReduced crop injury

oReduced herbicide carry-over

oUse of herbicides that are more environmentally friendly

oNew mode of action for resistance management

oCrop management flexibility and simplicity

DISADVANTAGES OF TRANSGENIC HERBICIDE RESISTANCE

*Single selection pressure and weed resistance

*Shifts in weed species

*Gene flow and contamination of organic crops

IMPROVEMENT OF BIOCONTROL AGENTS

NEED OF BIOTECHNOLOGY

A host-specific hypervirulent pathogen that controls a major row-crop weed to the extent that farmers require, (i.e. similar to control achieved with a chemical herbicide)

The ecological balance achieved with classical agents in an extensive pasture or forestry situation cannot suffice in intensive agriculture.

A wide variety of transgenic viruses, bacteria, and fungi have been successful in controlling many of weed sps. (Vurro et al. 2001a).

MYCOHERBICIDE Many fungi of native origin are pathogrnic to specific species of weeds. Such fungi are used to kill the weeds selectively and eliminate them from the area. These weed-killing fungi are called mycoherbicides.

Eg : Alternaria alternata is used to control the weed Water hyacinth developed by india

BIOTECHNOLOGICALLY UPGRADING MYCOHERBICIDES

Organisms can potentially be modified to increase pathogenicity by transformation with genes for virulence from other species, by increasing the endogenous expression of genes, or by transfer from other organisms by protoplast fusion (Gressel 2002; Harman and Stasz 1991; Harman and Donzelli 2001; Kistler 1991).

Biocontrol agents could also be engineered to convey genes that convert pro-herbicides to herbicides.This would then allow the mycoherbicide to be applied together with the pro-herbicides.This would have distinct advantages with weeds with underground propagules such as Cyperus that regrow after foliar killing.As the biocontrol agent is specific to the weed, it would not cause the conversion of pro-herbicide to herbicide in crops cultivation

Another approach to enhancing the efficacy of a mycoherbicide is to introduce genes that will affect phytohormone levels in the target plant.

Cohen et al. (2002) introduced two genes encoding enzymes of the auxin pathway into the plant pathogens Fusarium oxysporum and F. arthrosporioides, resulting in transformants that synthesized high levels of auxin.

These transformants were more virulent to the parasitic weed Orobanche aegyptiaca than wild-type pathovars, presumably because the high auxin levels produced effects like 2,4-D.

A weakly mycoherbicidal strain of Colletotrichum coccodes, Virulence was increased nine fold and was more rapidly effected. By introducing NEP 1 encoding a phytotoxic protein.

DEVELOPMENT OF TRANSGENIC ALLELOPATHY

IN CROPS

ALLELOPATHY

Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. or “Plant-produced herbicides”

Three methods for using allelopathy in weed management:

–As a winter cover crop, with residue providing allelopathic compounds

–As a living mulch during the cropping season

–As an isolated compound from an allelopathic plant, applied as an herbicide

METHOD OF APPLICATIONIn most cases where phytotoxic allelochemicals have been identified, and there is limited knowledge about their biosynthetic pathways.

There are several ways to do expression profiling, two major approaches are:

mRNA is isolated from tissues that are and are not expressing the trait of interest. These pools of mRNAs are then compared.

An expressed sequence tag (EST) database is created for the tissue/organ where the allelochemicals is highly expressed.

The identified gene of interest for the production of allelochemicals are transferred to the desired crop plant.

A regulation of the biosynthesis occurs and the release rate to enhance the release of allelochemicals or to prolong the period of release of allelochemicals has been suggested

Use of biotechnological transfer of allelopathic traits between cultivars of the same species or between species has also been proposed.

Genetic engineering offers the possibility of generating crop varieties with enhanced allelopathy by enhancing gene expression of existing allelochemicals pathways or introducing genes for synthesis of new allelochemicals into crops efficient.

Identified nine QTL(Quantitative trait loci)s controlling allelopathic effects of rice on  E. crusgalli on chromosomes 1, 2, 3, 4, 5, 8, 9 and 12

CLASSIFICATION OF ORYZA SPS. Classification of wild Oryza sps. and the feral forms of cultivated rice was difficult.

Cultivated Rice Weedy Rice

MOLECULAR SYSTEMATICS

Molecular systematics has been of great assistance and has often provided the decisive data in many cases on whether two similar species were actually one, or were separate, or were hybrids.

PROBLEMS WITH MORPHOLOGICAL DATAo Convergence and parallelismso Phenotypic vs. genotypic differenceso Evaluation of homologyo Misinterpretation of change or polarityo Limitation on number of characters

ADVANTAGES OF MOLECULAR SYSTEMATICS o Can obtain phylogenetically informative characters from any genome of theorganism

o Assumes that genomes accumulate molecular changes by lineage, as morphological characters do

o Possibly greater assurance of homology with molecular data (less likely to misinterpret characters.

o Principal advantages are the much greater number of molecular characters available & greater comparability across lineages

The classical taxonomy is so complicated that It was found using molecular techniques such as phylogenetic analysis etc., many accessions of wild rice species were corrected in the collection of International Rice research (Martin et al., 1997)

TYPES OF MOLECULAR DATADNA Sequences

DNA Restriction Sites : RFLPs

Allozymes : Different forms of proteins

Microsatellites : DNA regions with tandem repeats.

RAPDs : Random amplification of polymorphic DNA

AFLPs : Amplification Fragment Length polymorphism

CONCLUSION

Transgenic crops are strongly impacting weed management choices. They offer the farmer a powerful new tool that, if used wisely, can be incorporated into an integrated pest management strategy that can be used for many years to more economically and effectively manage weeds.

REFERENCE

Amsellem, Z., Cohen, B.A., and Gressel, J. 2002. Engineering hypervirulence in a mycoherbicidal fungus for efficient weed control. Nat. Biotechnol. 20: 1035-1039

Gressel, J. 2000. Molecular biology of weed control. Transgenic Res. 9: 355-382

Khanh, T.D., Linh, L.H., Linh, T.H., Quan, N.T., Cuong, D.M., Hien, V.T.T., Ham, L.H., Trung, K.H. and Xuan, T.D. 2013. Integration of Allelopathy to Control Weeds in Rice. Herbicides – Curr. Res. and Case Studies in Use. 10: 57-112

Roush, T. R. 2012. Biotechnology and weed management. In: Rowe, B., Donaghy, D. and Mendham, N. (eds), Science and Technology: Delivering Results for Agriculture. Proceedings of the 10th Australian Agronomy Conference, Hobart, Tasmania, pp. 15-19

Song, Z.J., Wang, Z., Feng, Y., Yao, N., Yang, J. and Lu, B.R. 2015. Genetic divergence of weedy rice populations associated with their geographic location and coexisting conspecific crop: Implications on adaptive evolution of agricultural weeds. J. of Systematics and Evol. 10: 111 - 129

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