Relationships between trichome types and spider mite (Tetranychus evansi) repellence in tomatoes with respect to foliar zingiberene contents

Zingiberene, a sesquiterpene present in glandular trichomes of Lycopersicon hirsutum Dunal var. hirsutum 'PI-127826', is responsible for the high leve l of arthropod resistance in this taxon. The current paper has the followin g objectives: (a) to quantify zingiberene content in tomato plants obtained from the interspecific cross L. esculentum Mill. x L. hirsutum var hirsutu m; (b) to identify, classify and quantify glandular and non-glandular trich ome types present in those plants; (c) to assess the level of resistance of those genotypes to spider mites (Tetranychus evansi); (d) to estimate corr elations between glandular trichomes, zingiberene contents and mite repelle nce. Zingiberene content were quantified by a colorimetric method (Freitas, 1999); trichomes were counted from foliar paradermic slide preparations; m ite resistance was assessed by a repellence test (Weston & Snyder, 1990). T he results indicate that indirect selection for zingiberene content led to correlated increases both in the number of glandular trichomes (particulary type IV) and in the levels of mite repellence. These results were found bo th in BPX-368 [=F2 ( L. esculentum 'TOM-556' x L hirsutum var. hirsutum 'PI -127826')] and in the subsequent generation BPX-368B (which represents one additional backcross to L. esculentum). Zingiberene appears therefore to be the main factor involved in mite repellence. Density of glandular trichome s in tomato leaflets markedly influences total zingiberene content. Type IV trichome density was the highest, and it was highly correlated to zingiber ene content.