Activity against Meloidogyne incognita of volatile compounds produced during amendment of soil with castor bean cake.

Summary: Incorporation of castor bean cake into the soil results in the emission of four main compounds: skatole, γ -decalactone, 4-methylphenol and phenol. The toxic effects of these compounds on the life cycle of Meloidogyne incognita were studied here. Only phenol did not reduce hatching of M. incognita second-stage juveniles (J2) at any of the concentrations tested. The other compounds reduced J2 hatching by 42.1 to 59.3% at the highest concentrations. When J2 were immersed in Tween 80® solutions of each compound, at their respective LC50 values and inoculated into soil with tomato plants, reductions in the numbers of galls (48.5-69.3%) and eggs (42.8-62.5%) were observed in comparison with the control; this result was similar to that of carbofuran. The highest reductions in the numbers of galls (21.8-88.5%) and eggs (49.6-98.9%) occurred with all compounds when the highest concentration (500 mg l−1) was applied to the substrate at the moment of J2 inoculation. Volatile compounds of γ -decalactone and skatole failed to cause J2 immobility or mortality. However, phenol caused 95.8% and 4-methylphenol caused 100% mortality. With fumigation, the highest concentration (1000 mg (l substrate)−1) of any tested compound reduced gall numbers at a similar rate to the nematicide dazomet (98.7-100%) and reduced egg numbers (87.1-99.7%). The volatile compounds skatole, γ -decalactone, 4-methylphenol and phenol have a nematicidal effect on the life cycle of M. incognita and alter its pathogenic behaviour on the plant. [ABSTRACT FROM AUTHOR]