Responses of Heterodera glycines and Meloidogyne incognita Infective Juveniles to Root Tissues, Root Exudates, and Root Extracts from Three Plant Species.

The infective juvenile (J2) stage of endoparasitic plant nematodes uses plant chemical signals, released from roots, to localize and infect hosts. We examined the behaviors of soybean cyst nematode (Heterodera glycines) and root-knot nematode (Meloidogyne incognita) J2 in the presence of root signals from marigold (Tagetes patula), soybean (Glycine max), and pepper (Capsicum annuum). Signals were obtained from sources commonly used in phytoparasitic nematode chemotaxis studies: root tips, root exudates, and root extracts. Root tips from each plant species attracted M. incognita but H. glycines was attracted only to soybean. In contrast, root exudates prepared from marigold, pepper, or soybean seedlings were attractive to H. glycines but were repellent to M. incognita. Root extracts had the same effect as exudates. Fractionation of exudates by reversed-phase high-performance liquid chromatography (HPLC) (acetonitrile [CHCN] and 0.1% trifluoroacetic acid) revealed highly polar and less polar components affecting behaviors. Fractions eluting at 12% CHCN from all three plants attracted H. glycines and repelled M. incognita. None of the less polar HPLC fractions (>15% CHCN) affected H. glycines but those from G. max and T. patula repelled M. incognita. Differences among exudates and effects of fractionation on behavior are discussed.