Legume Rhizobium System

Legume Rhizobium System

Legume Rhizobium System -

The ability of legumes to enrich the soil has been known since Roman times. It was known that most crops decrease the fertility of the soil, but legumes increase it.

This is because of their ability to fix nitrogen from the air. In 1813 Sir Humphrey Davy proposed that legumes obtain their nitrogen requirements from the atmosphere. This was first demonstrated by the French chemist Boussingault in 1837. He observed that the nitrogen present in leguminous plants exceeded the nitrogen present in the seeds and the soil.

Hellriegel and Wilfarth (1888) later demonstrated that nitrogen fixation in legumes takes place by the active participation of microorganisms in root nodules.

Since neither the plant nor the microorganism can fix nitrogen independently, the process has been called symbiotic nitrogen fixation.

The root nodule bacteria were isolated by Beijerinck in 1888, and were grouped in the genus Rhizobium (Rhizo means root in Greek). These are gram negative motile, aerobic, non spore forming bacteria. They are mainly rod shaped, but a variety of morphological shapes are observed on isolation from nodules.

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