Effects of plant phenylpropanoid pathway products and selected terpenoids and alkaloids on the behaviour of the plant-parasitic nematodes Radopholus similis, Pratylenchus penetrans and Meloidogyne incognita
Plants produce a wide range of biologically active chemicals which have been extensively explored for nematode-antagonistic properties. Although phenylpropanoids are part of the chemical defence system of plants against pests and diseases, including parasitic nematodes, no comprehensive study exists which relates (levels of) phenylpropanoid compounds in roots to actual effects on nematode behaviour. Therefore, a broad spectrum evaluation was made of the effects of phenylpropanoids (simple phenolics and flavonoids) and selected monoterpenoids and alkaloids on the behaviour of the migratory endoparasites Radopholus similis and Pratylenchus penetrans and the sedentary endoparasite Meloidogyne incognita. In vitro bioassays assessed effects on chemotaxis, motility, viability and hatch. Compared with the other two nematode species, P. penetrans was remarkably insensitive to the test Compounds. Only phloretin was (limited) hatch inhibitive. This property was shared by other chalcone-related compounds for R. similis. Repellents and motility inhibitors for R. similis and M. incognita were found among the simple phenolic compounds. Flavonols stood out as repellent compounds for both these nematode species, while they were, in their degraded form, also motility inhibitors for M. incognita. Dopamine was an attractant for R. similis, while ferulic acid was strongly motility inhibitive and toxic (LC50 Of 120 mu g ml(-1)) for this nematode species. Salicylic acid was a strong attractant for M. incognita. The compound was also nematicidal (LC50 of 46 mu g ml(-1)) and an it-reversible inhibitor of hatch.