SURVIVAL OF RHIZOBIA/BRADYRHIZOBIA AND A ROCK-PHOSPHATE-SOLUBILIZING FUNGUS ASPERGILLUS NIGER ON VARIOUS CARRIERS FROM SOME AGRO-INDUSTRIAL WASTES AND THEIR EFFECTS ON NODULATION AND GROWTH OF FABA BEAN AND SOYBEAN

Abstract

Coculturing of eight rhizobial strains (Bradyrhizobium japonicum USDA 110, USDA 3447, RCR 3407, RCR 3442, Rhizobium meliloti TAL 1372, TAL 1373, R. leguminosarum biovar viceae RCR 1001, and RCR 1044) and five rock-phosphate-solubilizing fungi (Aspergillus egyptiacus, A. flavus, A. niger, A. ochraceus, and Penicillium citrinum) was tested on yeast extract-mannitol agar. B. japonicum strains USDA 110, USDA 3447, RCR 3442, R. leguminosarum biovar viceae RCR 1001, and RCR 1044 grew successfully in cocultures with the tested fungal species in yeast extract-mannitol agar without antagonism. Among these fungi, A. niger showed the highest potentialities to solubilize rock- phosphate at all incubation temperatures examined (15, 28, 38, and 42°C), and phosphate dissolution maximized at 28°C. Survival of Rhizobium/Bradyrhizobium strains and the best rock-phosphate-solubilizing fungus (A. niger) was evaluated monthly in four carrier materials (Peat, wheat bran, sugarcane baggase, and wheat straw) at 28 and 38°C. The number of colony-forming units recovered on agar plates for all cocultured microorganisms was the highest with peat as a carrier, followed by bran and sugarcane baggase. On the other hand, survival of cocultured microorganisms strongly reduced in wheat straw. Survival of all microorganisms was the best at 28°C. Cocultures of B. japonicum USDA 3447/A. niger and R. leguminosarum RCR 1044/A. niger were the more tolerant for storage conditions whereas the number of colony-forming units in cocultures of B. japonicum USDA 110/A. niger and R. leguminosarum RCR 1001/A. niger was strongly reduced. Peat or bran inoculants of R. leguminosarum RCR 1044/A. niger and B. japonicum USDA 3447/A. niger significantly increased dry matter yield, nitrogen (N) and phosphorus (P) contents of faba bean and soybean, respectively, when grown in alkaline soil amended with rock-phosphate.