Index >> Rhizobium and Legume Root Nodulation >>Novel Approaches to Extend Root Nodulation

For instance, Rhizobium loti which can only infect species of Lotus was able to enter the root hairs of white clover and cause nodules under axenic experimental conditions. The success of this experiment depended on the critical levels and combinations of cellulase, pectinase and PEG. In fact, nodules on white clover roots induced by heterologous R. loti fixed nitrogen, were pink in colour and comparable to nodules normally induced by R. meliloti, a homologous Rhizobium.

Similarly, pre-treatment of seedlings of rice (Oryza sativa) and wheat (Triticum aestivum), both monocots, also resulted in root nodulation when inoculated with R. trifolii or R. loti or their mixture. The nodules were structurally sparsely infected and exhibited feeble nitrogenase activity.

What appears to be intriguing was the formation of nodules on the roots of rape seedlings even without enzyme and PEG treatment when inoculated with Rhizobium parasponium, a strain which produces nodules on roots of a non-leguminous tree genus, Parasponia. Unlike temperate legumes such as clovers which are normally infected by rhizobia through root hairs, infection in tropical Parasponia and other 'genera such as Aeschynomene, Sesbania and Stylosanthes is through wounds and points of lateral root emergence. While explaining these observations, due cognizance of different modes of entry of rhizobia have to be taken into consideration. Needless to say, as Cocking et al. of the Nottingham University, U.K. say, these researches "may have important consequences for both basic and applied aspects of nitrogen fixation."