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Blue-green algae are also known asCyanobacteria , blue-green bacteria orCyanophytaDomain: BacteriaPhylum: Cyanobacteria

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C yanobactyeria are prokaryotic organisms.Organells.

DNA & chromosomes.Ribosome.C ell wallThey are unicellular, colonial and filamentousbut lacks flagella.Typical blue colour.

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Cell FormCell Wall

Trichome.Filaments.HeterocystsAkinetesHormogonium

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1 . Asexual reproduction -Ex osporesE

ndospores (baeocytes)AkinetesHormogonium2. S exual reproduction - Unknown

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I t can fix atmospheric nitrogenI t helps in phosphate solubilizationI t synthesize Vit-B 1

2and growth hormone like

au x in and ascorbic acid.Some BGA is used as vegetables in C hina and Japan.

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According to cell structure Cyanobacteria are broadly divided intothree categories-1. Unicellular: e.g. Aphanothece , Chroococcus .2 . Co lo nial: e.g . Mi crocyst i s3 . Filament o us : mainly 2 f o rm

a) Simple filament o us f o rm: e.g. P horom idi um, Osc ill ator i ab ) Heter o cyst o us filament o us f o rm- Composed of 2 cells-

1.Vegetative chlorophyllus cells.2 .Cells lacking chlorophyll.

Different heterocystous filamentous forms are listed below-i. Un b ranched Heter o cyst o us filaments- e.g. Anabena, N ostoc . : ii. Un b ranched Heter o cyst o us sh o rt filaments - e.g. Ca l othr ix.

iii. Falsely b ranched Heter o cyst o us filaments .- e.g. S cytonema .

iv . T ruly b ranched Heter o cyst o us filaments .- e.g. H apa l os i phon .

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(1 ) I ntroduction: In recent years, blue-green algae,have been shown to be agriculturally important,particularly in tropical rice field soils. This is becauseof capacity of some of the algae to synthesize organic

substances and also to fi x atmospheric nitrogen. .This will reduce burden on small and marginalfarmers, especially in developing countries to meetthe demand of important crop nutrient.

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F orms like Anabaena,Nostoc and Calothrixwere found to be widely

distributed throughoutrice growing tracts ofIndiaDifferent forms of BGAfound in different statesare-

STAT E S BGA SPP

Uttar Pradesh Aulosira

Gujarat Mastigocladae

Maharashtra Westiella

Karnataka Cylindrospermum

Punjab Calothrix

Others Anabaena, Nostoc

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Anabaena spp Calothrix spp

Nostoc spp

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S cytonema spp Tolypthrix spp

Cylindrospermum spp

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(1 ) Capacity to fix nitrogen- Heterocyst-formingspecies are specialized for nitrogen fi x ation and areable to fi x nitrogen gas into ammonia (NH3), nitrites(NO2ï) or nitrates (NO3ï) which can be absorbed byplants and converted to protein and nucleic acids.

They can fix

nitrogen-(a) Under aerobic condition(b) Under anaerobic condition

(2)G

rowth promoting effects of blue green algae-

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(3) Helps in reducing iron toxicity- The o x ygenliberated by the blue green algae in the microaerobic

or anaerobic zones of a rice field converts F e++ toF e+++. The later being insoluble gets participitatedand iron content of the water is reduced.

(4) P hosphate solubilization- Many algae have beenfound to solubilize the insoluble phosphate to theex tent of 2.27mg P2O5/ml/ 1 5 days.

(5) O thers- The polysaccharidic sheath presentaround the trichomes of these algae binds the soilparticles and increases the particle size.

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The results of the field trials conducted in India haveindicated about 10 -1 5 % increase in rice yields with

BGA application.Algalization of rice crop has been found tosupplement nitrogenous fertilizers to the e x tent of 3 0 -40 kg N/ha/season.

Application of dried soil-based blue-green algal flakes@10 kg/ha is recommended for rice crops.

The algal inoculant is to be applied 10 days after

transplantation of rice crop.

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The growth of these blue green algae in saline ²alkaline habitats reduces salinity by 25-3 0 %,pH, electrical conductivity and e x changeablesodium.I t also increases aggregation, hydraulicconductivity, soil nitrogen and permeability.

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I t is essential to select N 2 fix ing strains capable of rapidgrowth.C yanobacteria should be selected which can fi x N 2equally well under aerobic, micro aerobic and anaerobicconditions, so that they can tolerate the very wide rangeof ox ygen tension found in rice fields.

I t is important to choose C yanobacteria that fi x N 2 underPhotoautotrophic, Phoheterotrophic and

chemoheterotrophic conditions. These Cyanobacteriainclude species of Anabaena, Anabaenopsis, Nostic andTolypothrix.

Strain that show little or no H 2 evolution should beselected.

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There are four methods of algal production-(a) Trough or tank method.

(b) Pit method.(c) F ield method.(d) Nursery cum algal production method.

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Broadcast the dry algal material over the standing water in the rice field ata rate of 10 -1 5kg/ha one week after transplanting the seedlings.

Addition of e x cess algal material is not harmful and will accelerate themultiplication and establishment in the field.

The sun dried algal material can be stored for a long time in a dry statewithout any loss in viability.

Do not store the algal material in direct contact with chemical fertilizers orother chemicals.

Apply algae for atl east three consecutive seasons so that there will besufficient algal innoculum found in the field.

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n recent years blue-green algae have been shownto be agriculturally important , particularly in tropicalrice field soils. This is because of capacity of some

of the algae to synthesize organic substances andalso to fix atmospheric nitrogen. This has becomenecessary component for alternative sources tomeet at least a part of nitrogen requirement of cropproduction. This has resulted in reducing burdenon small and marginal farmers , especially indeveloping countries.

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