Natural bacterial cell-free extracts with powerful nematicidal activity on root-knot nematode

Chemical analysis of hexane and ethyl acetate soluble fractions obtained from the rhizobacteria Pseudomonas jessenii strain R62 and Pseudomonas synxantha strain R81 was carried out using gas chromatography-mass spectrometry and their nematicidal activity was evaluated against root-knot nematode, Meloidogyne incognita second stage juveniles (J2). Results showed that the hexane extract of both strains, together with mixed ethyl acetate extract, were found to have better nematicidal activity than their individual ethyl acetate fractions above 100 ppm. Some of the chemical compounds of these bioactive fractions were identified using gas chromatography-mass spectroscopy (GC-MS) analysis. A total of sixteen and six similar compounds were detected in hexane and ethyl acetate fractions, respectively from both bacteria. The major compounds, namely hexadecenoic acid and hexadecanoic acid may be responsible for the nematicidal activity.