Isolation, identification and bioactivity of air-borne organic volatile emiochemicals for chilo partellus from zea mays and sorghum bicolor seedlings.

Abstract

Volatiles released from maize (in-bred A) and sorghum (serena' cultivar) seedlings which Chilo partellus attack were trapped on three solid adsorbents: reverse phase, Porapak Q and charcoal. The trapped organic volatiles were then eluted into vials using dichloromethane as the solvent. The eluted aliquots were concentrated by blowing a stream of nitrogen gas and analyzed on GC and GC-MS, packed with methyl silicone column and FID detector. The compounds identified from Zea mays were: toluene 4.4(%, octanal 0.7<%, nonanal 2.9%, (3 E)-hexenyl acetate 3.7%, cis-dihydro carveol, 1.4%, (3E)-4,8-dimethyl1,3,7-nonatriene, 21.4%,decanal, 3.2%, 3-eicosene 1.0%, copaene 41.8%, zingiberene, 6.8%, a-bergamotene, 3.7%, 8-Cedrene, trace, cis-caryophyllene, 26.4%, B-caryophyllene 4.1%, (a+B)-humulene 2.5%, a-amorphene 0.8%, patchoulene 2.3%, l-chloro hexadecane, 5.1(Yo, lidol 2.7%, cadinene 6.9%, y-cadinene, 0.9%, a-Farnesene trace, B-springene 8.8%, ( caryopbyllene oxide 1.0%, , l-pentacontanal 2.1%, and 12 compounds identified from Sorghum bicolor seedlings were: octanal 0.9%, decanal 9.3%, octadecanal 1SYO, transcaryophyllene 31.5%, B-farnesene 1.9%, B-humulene 0.9%, tridecanal 1.6%, l-pentacontanol 1.7%, cedroI2.4%, 2-hexyldecanol, 2.3%, 3,7,II-trimethyl-2,6,10-dodecatrienol 1.5 %, and bis-(2-methoxyethyl)phthalate 29.4%. Active compounds for each sample were determined usmg Gas chromatography coupled with electro-antennal detector (GC-EAD) technique, Sorghum bicolor sample showed one weak active peak corresponding to bis (2-methoxyethyl) phthalate 29.4%, while Zea may's sample showed 5 active peaks corresponding to (3E)-4,8-dimethyl-l,3, 7-nonatriene 21.4 %, cis-caryophyllene 26.4%, l-chloro hexadecane 5.1 %,a-farnesene trace, B-springene 8.8%. Among the identified compounds, (3E)-4,8-dimethyl-l ,3,7-nonatriene, caryophyllene andcc-famesene have been found to be attractive to the insect pests. Thus odours emanating from these crops may playa role in the orientation of its insect pests towards the plants and in ultimate recognition of the host plant for feeding and oviposition. To contribute towards this vital knowledge the composition of Zea mays and Sorghum bicolor volatiles were determined in the most natural state of the plant as possible. This meant that artifacts due to root or leaf damage were to be avoided as much as possible by using whole plant (no root or leaf cutting was done). It was also necessary to trap volatiles released at night in order to ascertain why Chilos attack these plants at night.