Rhizobia Promote Rice (Oryza sativa L.) Growth: First Evidence in Cuba

There are few studies on rhizobia from rice plants. Thus, the objectives of this study were to characterize rhizobia from the rhizosphere of rice plants cv. INCA LP-5 and to assess the effect of their inoculation on rice growth under controlled conditions. Eleven rhizobia isolates were studied to determine if they were capable of producing polyhydroxybutyrate, indolic compounds, ammonium and phosphate solubilization. The effect of rhizobial inoculation on height, shoot dry weight, root dry weight root and shoot/root dry weight of rice plants was assessed too. Isolate Rf7 produced 9.6 mg L-1 of polyhydroxybutyrate. When tryptophan concentrations were increased in the culture medium, all isolates, except Rf1, showed increased production of indolic compounds up to 125 mu g ml(-1) with Rpd38 isolate. All isolates produced ammonium from amino acids and Rpd8 produced 8.4 mu g ml(-1) of ammonium. Rf7 and Rpr2 solubilized tricalcium phosphate. Isolates Rf7, Rpr1, Rpr2 and Rpr11 increased significantly the shoot plant growth at 50 days after inoculation. The results obtained provide the first evidence on the plant-growth promotion effect of rhizobia on rice in Cuba.