2,3-DIHYDROFARNESOIC ACID, A UNIQUE TERPENE FROM TRICHOMES OF LYCOPERSICON HIRSUTUM, REPELS SPIDER-MITES

Lycopersicon hirsutum, a wild relative of the tomato, is highly resist ant to arthropod herbivores. Both botanic forms of L. hirsutum, L. hir sutum f. glabratum (C.H. Mull.) and L. hirsutum f. typicum (Humb. & Bo npl.), are resistant to two-spotted spider mites, Tetranychus urticae Koch. However, leaves and trichome secretions from f. typicum repel mi tes more so than those from f. glabratum. We have previously demonstra ted 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 repell ency. Leaflet washes having compositions similar to trichome secretion s were collected and separated into neutral and acid fractions; repell ency was mainly associated with the acid fraction, which, when applied to nonrepellent leaflets of f. glabratum, rendered them repellent. Se paration of leaflet washes by HPLC allowed purification and subsequent identification by gas chromatography-mass spectrometry and nuclear ma gnetic resonance of 2,3-dihydrofarnesoic acid (3,7,11-trimethyl-6,10-d odecadienoic acid) as the primary chemical component responsible for r epellency. Application of this acid to leaflets of L. esculentum rende red 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 occurren ce of 2,3-dihydrofarnesoic acid.