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, 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 ??

Selection of legume crops Collection of nodules ISOLATION AND MAINTENANCE OF RHIZOBIUM Rhizobium isolation in media Preservation in slant Purified rhizobial cells Nodulation 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

Rhizobium Inoculation and Crop Response Inoculation Method Nitrogen Fixation Rhizobium culture Crop Response

Contribution of Rhizobium in biological N fixation Crop Rhizobium species Quantum of N fixed (kg N/ha/yr) Soybean R. japonicum Alfalfa R. meliloti Clover R. trifolii Groundnut R. sp Pea R. leguminosarum Cowpea R. sp Green/ Black gram R. leguminosarum Bengal gram Bradyrhizobium sp

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) kg b) kg d) 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) 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