In Vitro Evaluation of Some Bacterial Isolates as Biofertilizers and Biocontrol Agents Against The Second Stage Juveniles of Meloidogyne incognita

REPRESENTATIVE soil samples were collected from the rhizosphere soils of different plant varieties grown in five Egyptian governorates. The soil samples were taken from areas where vegetable crops were moderately infected with nematodes causing galls on their root systems. The presence of plant parasitic nematodes (PPN) and free living nematodes (FLN) in the collected samples was estimated. In addition, one hundred and seventy six bacterial cultures which are well known as biofertilizers (some are able to fix nitrogen and the others solubilize either phosphate or potassium) were isolated. The isolated bacteria were screened based on their rate of growth. Thirty-five cultures of fast growing nitrogen fixing bacteria (NFB), phosphate solubilizing bacteria (PSB) and potassium solubilizing bacteria (KSB) and their cultural filtrates were tested in vitro as biocontrol agents against the second-stage juvenile (J2s) of the Meloidogyne incognita. In general, higher mortality percentages of nematodes were recorded by bacterial cultures than their comparative cultural filtrates. The highest mortality levels (100%) was recorded for cultures of NFB7, PSB2, and KSB2 at 10-1 dilution while it was 99.3, 99.0 and 97.8%, respectively, at a dilution of 10-2. NFB7 exhibited a high nitrogen fixation rate (4.2 µmole N2/ml/h), while PSB2 and KSB2 revealed effective phosphate and potassium solubilization efficiencies compared with the control treatments (1.94 fold of available phosphate and 2.0 fold of available potassium, respectively). NFB7, PSB2 and KSB2 isolates showed the highest protease, gelatinase and chitinase activities, which might be responsible for their nematicidal effect. The three bacterial isolates were identified as Paenibacillus polymyxa, Bacillus megaterium and Bacillus circulans, respectively.