Growth of Sesbania rostrata (Brem) with stem nodules under controlled conditions

Abstract

ABSTRACTA series of experiments was carried out in an attempt to produce nodulated plants of Sesbania rostrata with qualities more closely resembling those in the wild than has been achieved to date. When groups of five plants were grown in a controlled climate chamber in pipes containing ∼12dm3 modified Jensen's medium with 6mol m−3 nitrate, the daily growth in height reached 5 cm and at 30 d the plants were ∼40cm high. At this time, the stems were inoculated with Azorhizobium caulinodans ORS 571 and the medium replaced with Jensen's medium without nitrate. In the subsequent 19‐d period ∼300 nodules (representing >50% of the potential infection sites) developed on each stem. The nodules increased linearly in size over this time to ∼15mg. Specific acetylene reduction activity, ARA ((μmol C2H4 mg−1 h−1) rose to 45 between days 5 and 10 after inoculation and plateaued; total ARA rose to ∼200 μmol C2H4 plant−1 h−1. Under the conditions described the plants grew vigorously, and reproducibly uniform yields of nodules with high ARA activities were obtained. As outlined, the procedure offers a standard system in which, within a 2‐week period after inoculation, individual strains of bacteria can be quantitatively compared in their ability to induce nodulation and N2‐fixation. Physiological and biochemical aspects of the nodulated system can be much more readily approached than with plants producing only root nodules. The inhibitory effects of stem nodules induced by wild type and two mutant strains of Azorhizobium on the development and activity of root nodules are described.