2869482 Agricultural Biotechnology Biofertilizers

8/12/2019 2869482 Agricultural Biotechnology Biofertilizers

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Soil health: Biological, Chemical and Physicalfeatures to long term, sustainable

agricultural productivity withminimal environmental impact

(Arias, 2005).

Soil Fertility:Are: soil organic matter (includingmicrobial Biomass), Soil texture, soil

structure, soil depth, content ofnutrients, storage capacity

(adsorption capacity), soil reactions& absence of toxic elements

(FAO, 2000).


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FERTILIZERS:1. Soils may be naturally low in nutrients2. Deficient due to nutrient removal by crops3. When high yielding varieties are grown

(In order to obtain high yields, Fertilizers are needed).

FERTILIZERS

Chemical Fertilizers(Conventional Farming)

Biological Fertilizers(Organic Farming)


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The threat of chemical Fertilizers:1. Threaten Human Health.

2. Threaten Agricultural soils,Food safety and Waterways.

Soil quality Plant uptake Water quality

The threat of chemical pesticides:*Health & Environmental Problems.WHO-3million acute sever cases of poisoning

20,000 unintentional Deaths each year in D.C.


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Although, during last 50 years, farmershave dramatically increased crop yieldsthrough the use of chemical fertilizers &

pesticides, and improved varieties, today,the rising costs of chemical inputs and a

host environmental concerns have

caused farmers to consider alternativeagri-industrial managements (e.g.OrganicFarming) to reduce costs, protect humanhealth, and conserve the resource base.

(Kritcher, 1993)


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Importance of Biofertilizers:1.Eco friendly.

2.In addition to N2 ,Provide certain PGPsubstances like hormones , vitamins, .

3.Supplying N2 , continuously throughout the

entire period of crop growth in the fieldunder favorable conditions.

4.Without toxic effects.

5.When applied to soil improve the soilstructure.

6. Low production cost.


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Plant GrowthRhizobacteria

1. Endophytic

Bacteria

2. Exophytic

Bacteria


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Bacterial Endophytes:Why Are They There?

Opportunists? Some have no apparent effect

on plant performance Mutualists?

Evidence is accumulating tosupport this possibility


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Bacterial Endophytes: AnotherMutualistic Symbiosis

Benefit to microorganism: Provides an environment buffered from external

stresses Steady source of nutrients and water

Benefit to the plant host: Nitrogen fixation Biological control of plant pathogens and pests Enhanced uptake of nutrients and water


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Bacterial Genera WithEndophytes:

Achromobac te rAcidovoraxAcetobacter

Agrobac t e r iumA c t i n o m y c e sAcine tobacter

AzoarcusAr th robac te rAlca l igenes

Bac i l lusAzosp i r i l lumAzorh izob ium

ClavibacterChryseobacter i u m

Bordetel la

Curtobac ter iumCorynebac ter iumComamonas


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EscherichiaEnterobacterDeleya

Herbaspi r i l lumFlavobacter iumErwinia

Lac tobac i l lusKlebsie l laKingel la

Mic rococcusMethylobacteriumL e u c o n o s t o c

Pasteurel laPantoeaMoraxellaProvidenciaPhyl lobac ter iumPhotobac ter ium

RahnellaPsychrobac te rPseudomonas

SerratiaR h o d o c o c c u sRhizob ium

Staphy lococcusSph ingomonasShewanella

YersiniaXanthomonasVibr io


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* Production of Plant hormones*Antibiosis

* Phosphorous solubilization *Induced resistance* Enhanced iron availability *Iron scavenging* Nitrogen Fixation * Competition for nutrients/niche* Etcetera * Parasitism & Predation

*Etcetera

PGPR affect plant growth

Directly Indirectly


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Well known PGPRs: Arthrobacter Acetobacter Azotobacter Azosperillum Bacillus Enterobacteria

Klebsiella Proteus Pseudomonas Rhizobium


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Pseudomonas spp. & related genera: Although a range of different bacterial genera and

species have been studied, the overwhelmingnumber of papers have involved the use ofPseudomonas species. Its so because Pseudomonas and related genera are characteristically:

Fast growing Easy to culture

Manipulate genetically in the laboratory Able to utilize a range of organic compounds Produce many different metabolites which

some are Plant Growth Promoting Substances


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ther rhizobacte ria

Since other rhizobacteria are also

found in the rhizosphere ofmany crop plants Like wheat and there werelittle detailed studies on them from plantrhizosphere:

It becomes interesting to find out theprobable role of others in rhizosphere ofwheat other crop plants.


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DirectPlant Growth Promotion


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1.Microbial Production of Plant Hormones: Plants themselves synthesize Auxin, Gibberellins, Cytokinins,

Ethylene, and Abscisic acid, but under less than ideal climatic

and environmental conditions, Plants may not synthesizesufficient endogenous concentrations to sustain optimalgrowth and development .

Scientists have shown recently That Plant Growth can beimproved when specific microbial strains are used to

inoculate seeds or roots of agricultural crops due tomicrobes production of Plant Growth Hormones (Regulators).

Exogenous Supplementation of PGPHs to plant roots isreletively new approach to maximize crop yield .


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Signals from under ground:Bacterial volatiles

promote plant growth


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1.1.Auxins:


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xproduction:

Some strains of Acinetobacter isolated and characterized fromrhizosphere of wheat were showed indole-3-acetic acid (IAA)production. Pot experiments showed significant increase in plantgrowth inoculated with eight Acinetobacter genospecies ascompared to control plants. IAA production was found to beencoded by plasmid PUP1126 and this is the first report of plasmid-encoded IAA production in the genus Acinetobacter.

The rhizobacterium Pseudomonas putida GR 12-2 is a strongcandidate for development as a soil inoculant to enhance crop

yields. Inoculation of canola, tomato and other agriculturallyimportant plants with this strain results in substantial promotion ofseedling root growth. Characteristics that may contribute to theability of P.Putida to enhance plant growth include the capacity tosynthesize siderophores and thereby provide iron for the plant, thecapacity to lower growth inhibiting levels of ethylene in planttissues by production of 1-aminocyclopropane-1-carboxylic acid(ACC) deaminase , and capacity to secrete IAA .


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1.2.Gibberellic acids: Azospirillum spp. are considered to be important

plant growth promoting rhizobacteria that can

improve the growth and yield of at least several plant species (Labandera-Gonzalez, 1994).

Phytohormone production, including gibberellins(Bottini et al., 1989), is one mechanism that has

been proposed ( Cassan et al., 2001).Other Gibberellin producing bacteria inrhizosphere are as follows:

1. Acetobacter diazotropicus

2. Azosperillum lipoferum 3. Herbosperillum seropedicae 4. Rhizobium phaseoli


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1.3.Ethylene:The effects of C2H4 have been observed inpractically all aspects of plant growth anddevelopment, including seed germination(Ketring et al., 1972), seedling growth (Burg etal., 1968), root growth (Chadwick et al., 1970),growth of leaves (Primrose, 1979), and ripening,

aging (Biale, 1960).Agronomically, microbial production of C2H4

could have an impact on crop production undercertain management conditions. Ethylene

concentrations as low as 10 ,ug liter-' can evokeplant responses, and concentrations of 25 pugliter-' result in decreased fruit and flower

development (Primrose et al., 1979).


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1.4. Cytokinins:the presence of micro-organisms capableof producing cytokinins, can be expectedto raise the amounts of cytokinins in both the soilsolution and in plants growing there. In turn, this

may have an impact on the growth of these plants.In support of this there are numerous reports thatcertain micro-organisms affect plant growth through

their ability to produce phytohormones (Arshad andfrankenberger, 1991, 1998; Steenhoudt andVanderleyden, 2000).


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2.Phosphate solublization:The ability of microorganisms to solubilize and mineralizep in soils is vital. Phosphate availability in soil is greatlyenhanced through microbial production of metabolitesleading to lowering of PH and release of phosphate fromorganic and inorganic complexes.The species ofPseudomonas,Micrococcus, Bacillus, Aerobacter,

Xanthomonas, brevibacterium, Alcaligenes, Rhizobium have been reported to be active in phosphatesolubilization (Srivastav, 2004).

Although these PGPRs occur in soil, usually their numbers

are not high enough to compete with other bacteriacommonly established in the rhizosphere. So, foragronomic utility, inoculation of plants by target withsuch microorganisms at higher concentration than thosenormally found in soil is necessary to take advantage oftheir beneficial properties for plant yield enhancement


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for example in this subject, the solubilization ofphosphatic compounds, one of the importantmechanisms of plant growth promotion shown by PGPR

Acinetobacter , increases its potential in the developmentof future bioinoculum for crop plants. In thisinvestigation the phosphate solubilization by

Acinetobacter spp. was also compared with otherrhizosphere isolates like Moraxella sp., Pesudomonas sp.,Serratia sp., and Pseudomonas putida NCIM1313,Escherichia coli NCIM2810.

All the phosphate solubilizing Acinetobacter strains hadzone diameter of dissolution in the range 1-5cm while ascontrol P. putida had average zone diameter in the range

1-3.5cm. Solubilization of insoluble phosphates startedalong with the growth of strains and maximumsolubilization was achieved at logarithmic to latestationary phase. Some cultures showed reprecipitationof solubilized phosphate after prolonged incubation

(Chopade, 2003).


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3. N 2 Fixation:


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N2 Fixation

Asymbiotic Symbiotic

Azotobacter Rhizobium

Azosperillum BradyrhizobiumBacillus Cyanobacteria

Klebsiella AnabaenaClostridiumP.vulgaris


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In Direct

Plant Growth Promotion


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Biocontrol PGPR

According to the United StatesDepartment of Agriculture, biologicalcontrol of plant disease is defined as "

the involvement of the use ofbeneficial microorganisms, such asspecialized fungi and bacteria, toattack and control plant pathogens andthe diseases they cause.

These "specialized" fungi and bacteriaare microorganisms that normallyinhabit most soils.

1 Direct Competition with th T g t O g i


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1. Direct Competition with the Target Organism.

In this case the biocontrol agent out competes the target

organisms for nutrients and space.

Example : Iron competition in Pseudomonads has been intensively studied and

the role of the pyoverdine siderophore has been intensively studiedand the role of the pyoverdine siderophore produced by manypseudomonas species has been clearly demonstrated in control ofPy th ium and fusar ium species.

2 A tibi i


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2. Antibiosis:The biocontrol agent produces an chemical compound suchas an antibiotic or some type of toxin that kills or has some

sort of detrimental effect on the target organism.

Example:phenyazine-1-carboxylic acid (PCA) from Pseudomonas aureofaciens kuyver tx-1 has even been used as a direct fieldtreatment of the control of dollar spot on creeping bent grass

(Powell et al., 2000).

3 Ind ced Resistance of the Host Plant


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3. Induced Resistance of the Host Plant.

It has been know for decades that once a plant is infectedwith a pathogen, that infection triggers some sort of reactionin the infected host plant that helps keep it from beinginfected with other pathogens. The infected plant becomes

more "resistant" to other infections.

Changing that have been observed in plant roots exhibiting


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Changing that have been observed in plant roots exhibiting

Induced systemic resistance (ISR) include :

1. strengthening of epidermal and cortical cell walls anddeposition of newly formed barriers beyond infectionsites including callose, lignin and phenolics.

2. increased levels of enzymes such as chitinase,peroxidase, polyphenol oxidase, and phenylalanineammonia lyase.

3. enhanced phytoalexin production.

4. enhanced expression of stress- related genes.

However, not all of these biochemical changes found in

all bacterial-plant combinations.


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2869482 Agricultural Biotechnology Biofertilizers