INTRODUCTION

Rhizobium, a root nodule bacterium, has the ability to fix atmospheric nitrogen in symbiotic association with host legumes. It was estimated that a total of 175 million metric tones of N is fixed per year globally through biological nitrogen fixation involving Legume Rhizobium symbiosis. Rhizobia invade the roots of legume plants through root hairs, form effective pink colored nodules in the tap or lateral roots and lives symbiotically inside the nodules to fix nitrogen to plant accessible forms.

Rhizobium as component of INM Rhizobium as component of INM

Rhizobium, a root nodule bacterium,

has the ability to fix atmospheric

nitrogen in symbiotic association with

host legumes.It was estimated that a

total of 175 million metric tones of N is

fixed per year globally through

biological nitrogen fixation involving

Legume Rhizobium symbiosis

Curling of root hair

Invagination point

Infection thread develop

Bacteria released

Nodular tissue develop

HOW RHIZOBIA INFECT LEGUME ??

HOW RHIZOBIA INFECT LEGUME ??

Selection of legume cropsSelection of legume crops Collection of nodulesCollection of nodules

ISOLATION AND MAINTENANCE OF RHIZOBIUM

Rhizobium isolation in mediaRhizobium isolation in media Preservation in slantPreservation in slant

Purified rhizobial cellsPurified rhizobial cells Nodulation testsNodulation tests

CHARACTERISTICS OF RHIZOBIUM

Rhizobia invade legume roots through root hairs

Form effective pink colored nodules in the roots

Lives symbiotically inside the nodules and fix nitrogen

Converts atmospheric nitrogen to plant accessible forms

Most rhizobia are host specific in nature

Rhizobia invade legume roots through root hairs

Form effective pink colored nodules in the roots

Lives symbiotically inside the nodules and fix nitrogen

Converts atmospheric nitrogen to plant accessible forms

Most rhizobia are host specific in nature

50 – 200 KG NITROGEN PER HECTARE PER CROP

50 – 200 KG NITROGEN PER HECTARE PER CROP

Rhizobium Inoculation and Crop Response

Inoculation Method

Nitrogen

Fixation

Rhizobium culture

Crop Response

Contribution of Rhizobium in biological N fixation

  CropCrop

  RhizobiumRhizobium species species Quantum of N Quantum of N

fixed fixed (kg N/ha/yr)(kg N/ha/yr)

SoybeanSoybean R. japonicumR. japonicum 60-8060-80

AlfalfaAlfalfa R. melilotiR. meliloti 100-200100-200

CloverClover R. trifoliiR. trifolii 100-200100-200

GroundnutGroundnut R. sp.R. sp. 50-6050-60

PeaPea R. leguminosarumR. leguminosarum 52-7752-77

CowpeaCowpea R. sp. R. sp. 80-8580-85

Green/ Black gramGreen/ Black gram R. leguminosarumR. leguminosarum 50-5550-55

Bengal gramBengal gram Bradyrhizobium sp.Bradyrhizobium sp. 85-11085-110

LET US SUM UP

Rhizobium fix atmospheric nitrogen in symbiotic

association with host legumes.

It was estimated that a total of 175 million metric

tonnes of N is fixed per year through legume-

Rhizobium symbiosis.

Rhizobium lives symbiotically inside the nodules

and fix nitrogen which is converted to plant

accessible forms.

Contd…..

Rhizobia invade the roots of legume plants through

root hairs and form effective pink colored nodules

in the tap or lateral roots.

Most Rhizobia are host specific and nodulate

specific legumes.

Contd…..

Q. Choose the correct answer :

i) From which crop do you expect to isolate Rhizobium?

a) Cereal crops c) Legumes

b)Oilseeds d) Grasses

ii) How much Nitrogen does Rhizobium contribute?

a)10-50 kg c) 200-250 kg

b)50-200 kg d) 400-500 kg

Contd…

ASSESSMENT

Contd…

iii) How much rhizobial culture required inoculate 30 M

ha legume crop?

a) 5,000 tonnes c) 15,000 tonnes

b) 20,000 tonnes d) 10,000 tonnes

iv) What type of nodules generally selected for isolation

of effective rhizobia?

a) White-coloured c) Pink-coloured

b) Green-coloured d) Blue-coloured

ASSESSMENT

Model Answers :

i) Legumes

ii) 50-200 kg Nitrogen

iii) 15,000 tonnes

iv) Pink-coloured nodules

REFERENCES

i) Soil Microbiology – N. S.Subba Rao

ii) Advances in Microbiology – N. S.Subba Rao

iii) Bio-fertilizer and Organic Farming – NIIR Board

iv) Nitrogen fixing organisms

(Pure and applied aspects) – J. I. Sprent and

P. Sprent