Influence of arbuscular mycorrhizal fungi on the nematicidal properties of leaf extracts of Thymus vulgaris L.

The effect of arbuscolar mycorrhizal fungi (AMF) on the nematicidal activity of Thymus vulgaris against the rootknot nematodes Meloidogyne incognita and M. javanica was investigated in two in vitro experiments. In the first experiment egg masses of M. incognita and M. javanica were immersed for 3 weeks in aqueous leaf extracts of thyme plants non-inoculated or previously inoculated with Glomus mosseae or mixed AMF strains (Sclerocystis sinuosa, Glomus claroideum-1, G. claroideum-2 and G. claroideum-3). Thereafter the hatching test continued in distilled water for five more weeks. In the second experiment egg masses of both Meloidogyne species were exposed to the different thyme extracts for 4, 8 and 16 hours and then incubated in distilled water for 8 weeks. Distilled water and 5 mg/ml aqueous solution of fenamiphos nematicide were used as controls. Numbers of second stage juveniles emerging weekly were expressed as cumulative percentages of the total egg content of the egg masses. In the first experiment juvenile emergence from eggs of both Meloidogyne species immersed in thyme extracts for three weeks was completely suppressed since the first week. Hatching of eggs of M. incognita in all the extracts was significantly lower than that in water control, although emergence in the extract from uninoculated thyme plants was significantly higher than the others and no statistical different from that of aqueous fenamiphos solution. Emergence of M. javanica juveniles was significantly lower after immersion in all the extracts than in distilled water control and aqueous fenamiphos solution. In the second experiment a 4-hour exposure to the extract from thyme inoculated with G. mosseae and mixed AMF population significantly reduced the final hatch of M. incognita in comparison to distilled water. A 16-hour exposure to the extract from mixed AMF inoculated plants resulted in a significantly lower egg hatch than the shorter exposure times, whereas no statistical difference was found between 4 and 8 hour exposure to both extracts. Emergence of M. javanica juveniles was statistically lower than in water only after 16 hours exposure to the extracts from mixed AMF strains inoculated plants, but no difference was found among the different exposure times. Growth of T. vulgaris was significantly increased only by the infections of mixed AMF strains.