The composition of the essential oil isolated from the rhizomes of Zingiber zerumbet Smith was determined using GC and GC–MS. Zerumbone (74.82%), humulene (6.02%), and β-copaen-4α-ol (4.32%) were identified as major compounds. E-Bisabol-11-ol (4.32%), E-bisabol-11-ol (0.92%), β-sinensal (0.57%), and α-himachalene oxide (0.19) were reported for the first time in its oil. Zerumbone was further isolated from the crude mixture of oil and identified by FTIR, NMR (¹H, ¹³C, DEPT, HXCO, and HMBC), and mass (EI-MS) spectral data. Zerumbone showed promising antifungal activity against three phytopathogenic fungi, namely Rhizoctonia solani (EC₅₀, 39.6 ppm), Sclerotium rolfsii (EC₅₀, 59.3 ppm), and Macrophomina phaseolina (EC₅₀, 147.4 ppm) compared with hexaconazole (EC₅₀, 18.3, 13.4, and 4.5 ppm, respectively). Zerumbone has also shown concentration-dependent affect on seedling growth of Phalaris minor Retz., compared with control and Triticum aestivum L. (wheat). Zerumbone strongly suppressed the root and shoot growth of P. minor seedling at 1000 ppm compared with control and wheat. It exhibited no or less effect on the germination of seeds of T. aestivum.

Essential oils fromSyzygium aromaticum, Cymbopogon flexuosus and Cymbopogon martinii were isolated by hydrodistillation method and analysed by GC-FID and GC-MS. Eugenol (87.1%) and citral (69.4%), respectively were identified as major compounds in clove and lemongrass oils while geraniol (81.6%) and geranyl acetate (12.4%) in palmarosa oil. Essential oils were evaluated for nematicidal activity against J2s of Meloidogyne graminicola. Results showed the mortality of J2s in clove and lemongrass oils ranged from 70.00-92.50% to 77.50-97.50% and 63.75-92.50% to 72.5-97.50% and that of palmarosa oil showed 70.00-95.00% to 73.75-98.75% mortality at 31.12 to 500 ppm after 24 and 96 hours. Geraniol, citral (sum of neral and geranial) and eugenol were also evaluated for their nematicidal activity. Results showed that geraniol (75.00-95.00% to 78.75-98.75%) possessed highest mortality followed by citral (67.5-93.75% to 72.50-97.50%) and eugenol (66.25-93.75% to 73.75-98.75%) at 31.12 to 500 ppm. Efficacy of the oils and compounds were comparable with carbofuran at 62.5ppm (76.0-87.67%) and 31.25ppm (70.67-83.33%) after 24-96 hours. Results showed that palmarosa oil possessed highest mortality followed by lemongrass and clove oils due to the presence of their major compounds.

Chemical composition of the essential oils of five Ocimum species namely Ocimum tenuiflorum syn Ocimum sanctum L. (green and purple), Ocimum kilimandscharicum Guerke, Ocimum viride Willd, Ocimum basilicum L. and Ocimum gratissimum L., obtained by a hydrodistillation was determined by GC and GC-MS. A total of one hundred three compounds were identified in the oils of five Ocimum species, of which fifteen compounds were found to be major (5.0–81.8 %) compounds. Analysis of Ocimum viride oil showed the highest amount of eugenol (81.8 %) among species besides germacrene D (7.0 %) and cis-ocimene (4.1 %). Ocimum tenuiflorum green and Ocimum tenuiflorum purple were found contain eugenol (75.5 and 33.8 %), β-elemene (9.9 and 15.7 %) and β-caryophyllene (9.6 and 21.3 %) as main compounds. Methyl eugenol (17.7 %) and β-caryophyllene (21.3 %) were also found to be an additional major compounds in Ocimum tenuiflorum purple oil. Camphor (28.8 %), β-selinene (11.4 %), α-selinene (9.6 %), maaliol (7.6 %), β-caryophyllene (6.4 %), β-gurgunene (5.2 %) were main compounds in Ocimum kalimanduscharicum oil. Similarly, Ocimum basilicum was found to contain methyl chavicol (46.0 %), trans-methyl cinnamaldehyde (20.0 %), linalool (16.7 %) while that of Ocimum gratissimum oil contain trans-methyl isoeugenol (51.9 %), cis-ocimene (18.7 %), germacrene-D (5.9 %), and β-caryophyllene (5.5 %) as major compounds. Results showed that Ocimum viride and Ocimum tenuiflorum green growing in the region rich source of oil (1.0 and 1.8 %) and eugenol (81.8 and 75.5 %) as compared to Ocimum tenuiflorum purple (33.8 %).