Roots of Colophospermum mopane. Are they infected by rhizobia?

Abstract

Roots of Colophospermum mopane are infected with bacteria that resemble rhizobia but also show similarities with Frankia spp. The infection causes continuous degeneration of infected roots and stimulates the development of new lateral roots. This results in the formation of coralloid-like outgrowths that resemble cluster roots or proteoid roots. High densities of bacterial colonies, embedded in slime sheaths, occur on the root surfaces Infection takes place during early root development and bacteria were observed in young, undifferentiated cells behind the apical meristem. In response to the infection, the infected host root cells deposit cell wall material so that the bacteria are contained in thick-walled cells. We propose that the root clusters be regarded as primitive root nodules