TRICHOME EXUDATES AND RESISTANCE TO BEET ARMYWORM (LEPIDOPTERA, NOCTUIDAE) IN LYCOPERSICON-HIRSUTUM F TYPICUM ACCESSIONS

Three accessions of Lycopersicon hirsutum f. typicum Humb. and Bonpl. were highly resistant to beet armyworm, Spodoptera exigua (Hubner), as indicated by reduced survival and growth on excised leaflets, compare d with leaflets of a susceptible tomato variety. Removal of trichome e xudates from LA 1777 and LA 2329 eliminated resistance affecting early instars; but this treatment had no effect on the resistance of PI 126 445. Primarily, lamellar factors must condition resistance in PI 12644 5 and contribute to resistance to later instars in LA 1777 and LA 2329 . Type-VI trichome exudates of all 3 accessions were topically toxic t o Ist-instar S. exigua, and this toxicity differed among the accession s (LA 1777 > LA 2329 > PI 126445). The lower toxicity of trichome exud ates on PI 126445 apparently accounts for their minimal role in resist ance in this accession. During feeding, Ist instars ruptured sufficien t numbers of type-VI trichome glands to account for the observed morta lity on both LA 1777 and LA 2329. Toxicities of trichome exudates from the accessions were not correlated with their sesquiterpene and total phenolic contents; the most toxic trichomes (LA 1777) had the lowest concentrations of volatiles detectable by gas chromatography, and tota l phenolic compounds. The important toxins remain unidentified. Identi fication of the lamellar factors from the accessions, and the toxins i n the trichome exudates of LA 1777 and LA 2329, will facilitate the us e of these accessions in breeding programs for resistance to S. exigua and possibly other pests of tomatoes.