Characterization of phosphate and potassium solubilization, and antifungal activity of bacteria isolated from rhizosphere of Allium ascalonicum (L.) grown in Ninh Hai district, Ninh Thuan province, Vietnam

Bacteria in the rhizosphere of red onion plants grown in Ninh Hai district, Ninh Thuan province were isolated, tested for P, K solubility and antifungal ability. Bacteria were isolated and cross-cultured on two media, NBRIP containing apatite and modified Aleksandrov containing mica. Dissolved P was measured molybdate colorimetric method and dissolved K was determined based on turbidity through present of sodium tetraphenylborate. Antifungal performance was limited to selected lines and was performed by co-culture. Bacterial identification was based on two-way sequencing for 16S rDNA sequences. The five best strains out of a total of 33 isolates were TH8, TH9, TH10, VH3 and VH5, which were able to dissolve phosphate in the range of 29.4 – 54.4 mg/L P2O5, and dissolved in potassium in the range of 13.0 – 26.4 mg/L K2O, and were resistant to A. niger with inhibition efficiency from 57% – 62.6% after 7 days of co-culture. Two strains VH5 and TH8 were also capable of antagonizing F. oxysporum with the inhibition efficiency of 60.2% and 70.7%, respectively. The identification results showed that TH9, TH10 and VH5 were homologous to Enterobacter sp., TH8 was homologous to E. soli, and VH3 was homologous to Novosphingobium sp. Enterobacter and Novosphingobium had been reported to promote plant growth in addition to salt tolerance and resistance to heavy metal pollution, so these bacterial strains could be applied to the cultivation of red onions in Ninh Thuan.