Root hair infection and nodulation in lucerne (Medicago sativa L.) as influenced by salinity and alkalinity

Experiments with lucerne (Medicago sativa L.) under bacteriologically controlled conditions on the effects of chloride, carbonate and bicarbonate of sodium, alkaline pH levels and saline/alkaline soil extracts demonstrated that increasing levels of salinity/alkalinity of the root medium resulted in a root system devoid of root hairs, mucilaginous layer and infection thread formation in spite of the optimum growth of Rhizobium under such conditions. The results point out the existence of 'alkali sensitive steps' in the early phases of nodulation which lead to an elimination of legume 'rhizosphere' as postulated by earlier workers.