Symbiotic efficiency of Bradyrhizobium symbiovars on Chamaecytisus albidus plants grown under water stress and acidic pH

In this work, we analyzed the effect of water stress and acid pH on the growth of the endemic fodder legume Chamaecytisus albidus, inoculated with four strains of Bradyrhizobium, from three different symbiovars previously isolated from the plant grown in different eco-geographical areas of Morocco. We also assessed the competitiveness of the three symbiovars for plant nodulation under water stress and acidity. We analyzed the strain’s nodulation ability, rates of nodules occupancy, shoot, and root dry weights of plants grown at -100, -80, and − 60 MPa water potential, and 6.0 and 7.0 pH values. The strains CM64 and CJ2 belong to the symbiovar genistearum and strains CA20 and CB10 to the symbiovars retamae and lupini, respectively. The strains CB10 and CJ2 were the most infective regardless of the pH and water potential at which the plants were grown. The strain CB10 was also the most abundant in nodules from plants grown at any conditions examined. Reductions in the water potential altered the nodulation ability, the strains CB10 and CJ2 still being the more infective. These strains were also the most infective at pH 6.0 and 7.0. The highest values of shoot and root dry weights were recorded in plants inoculated with strain CA20 under all the irrigation regimes used. The reduction from 100% to 80 and 60% field capacity decreased the shoot dry weight of the plants by 31.23 and 67.06%, respectively. Moreover, there was a 37.95 and 61.74% decrease in plant root dry weight when grown at 80 and 60% of field capacity, respectively. Despite variations in the efficiency of each strain, overall, the pH did not affect either the SDW or the RDW of the plants. The inoculation of C. albidus with a mix of the four strains did not result in further improvement of nodulation or symbiotic efficiency. These results show that water deficiency drastically affects the growth of C. albidus and that the retamae symbiovar was the most effective under the conditions examined. This is the first report on the competitiveness of symbiovars for the nodulation of a legume under stress.