Some Observations on Infection ofArachis hypogaeaL. byRhizobium

Abstract

The infection process in Arachis hypogaea by rhizobia differs from that normally found in Trifolium spp. in that no infection threads are formed. The root hairs, which are long (up to 4 mm), septate, and often with large basal cells, occur only at the sites of emerging lateral roots. Infection occurs only where the root hairs have large basal cells. Rhizobia cause curling and deformation of the root hairs (as in Trifolium spp.) but enter the root at the junction of the root hair and the epidermal and cortical cells. The bacteria are distributed intercellularly via the middle lamellae and enter the cortical cells through the structurally altered cell wall, often close to the host cell nucleus. The root hairs and large basal cells become infected in the same way. Within the cortical cells of the emerging lateral root the rhizobia multiply rapidly and the invaded cells divide repeatedly to form the nodule tissue. Bacteriod formation occurs only when the host cell ceases to divide.