2,3-Dihydrofarnesoic acid, a unique terpene from trichomes ofLycopersicon hirsutum, repels spider mites

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Abstract
Lycopersicon hirsutum, a wild relative of the tomato, is highly resistant to arthropod herbivores. Both botanic forms ofL. hirsutum, L. hirsutum f.glabratum (C.H. Mull.) andL. hirsutum f.typicum (Humb. & Bonpl.), are resistant to two-spotted spider mites,Tetranychus urticae Koch. However, leaves and trichome secretions from f.typicum repel mites more so than those from f.glabratum. We have previously demonstrated that trichome secretions from LA 1363 and LA 1927, accessions of f.typicum, repelled mites. In this paper we report the identification of the primary component of trichome secretions responsible for repellency. Leaflet washes having compositions similar to trichome secretions were collected and separated into neutral and acid fractions; repellency was mainly associated with the acid fraction, which, when applied to nonrepellent leaflets of f.glabratum, rendered them repellent. Separation of leaflet washes by HPLC allowed purification and subsequent identification by gas chromatography-mass spectrometry and nuclear magnetic resonance of 2,3-dihydrofamesoic acid (3,7,11-trimethyl-6, 10-dodecadienoic acid) as the primary chemical component responsible for repellency. Application of this acid to leaflets ofL. esculentum rendered them repellent. Other volatile compounds present in minor amounts in the acid fractions were farnesoic acid and 16∶0, 16∶3, 18∶0, 18∶2, and 18∶3 fatty acids. This is the first report of the natural occurrence of 2,3-dihydrofarnesoic acid.