Abstract: The leaf essential oils of lemongrass (Cymbopogon citratus) and Mexican sunflower (Tithonia diversifolia) were obtained with a yield of 1.02% (w/w) and 1.05% (w/w),respectively by hydro-distillation.The chemical components of the essential oils were investigated by GC-FID and GC-MS.Citral (49.76%),myrcene (8.54%) and nerol (5.92%) were the major compounds of the 20 identified components which accounted for 98.00% of the total lemongrass oil where 81.25% belonged to monoterpenoids and sesquiterpenoids. α-Terpineol (20.31%),1,8-cineole (14.67%),1,7,7-trimethylbicyclo［2.1.1］heptan-2-ol (14.32%),2,6,6trimethylbicyclo［3.1.1］hept-2-ene (13.51%) and 1,1,4,7-tetramethyldecahydro-1-H-cyclopropa［e］azulene-4-ol (7.39%) were the major compounds of the 20 identified components which accounted for 98.49% of the total Mexican sunflower oil where 95.85% belonged to monoterpenoids and sesquiterpenoids.Both essential oils had similar antinematodal activity with a broad spectrum.Among the four tested nematodes (Bursaphelenchus xylophilus; Meloidogyne incognita, Panagrellus redivivus and Caenorhabditis elegans),both oils showed the strongest inhibition on root knot nematode (M.incognita) with the IC₅₀ values of 1.068 μg/mL and 0.747 μg/mL respectively at 24 h and 48 h of treatment for the lemongrass oil,and 1.118 μg/mL and 1.039 μg/mL respectively at 24 h and 48 h of treatment for the Mexican sunflower oil.The results provided supporting data for activity-guided fractionation of the antinematodal components from these two oils as well as future development of the essential oils as the antinematodal agents.

Key words: Cymbopogon citratus, Tithonia diversifolia;essential oil;chemical composition;antinematodal activity;Bursaphelenchus xylophilus;Meloidogyne incognita