ABSTRACT

Phytochemicals present in wild Lycopersicon taxa have been associated with pest resistance. Secondary compounds from the leaves of the wild tomato relatives L. hirsutum f. glabratum, L. hirsutum f. typicum, and L. pennellii (Solanaceae) have been identified as methylketones (2-tridecanone, 2-undecanone, 2-dodecanone, 2-pentadecanone), sesquiterpene hydrocarbons (zingiberene and curcumene), and glucolipids (sugar esters), respectively. The main constituents in crude extracts of tomato leaves were separated, purified, and screened for their insecticidal/acaricidal activity. Methylketones provided a strong insecticidal and acaricidal efficacy against the green peach aphid, tobacco hornworm, tobacco budworm, Colorado potato beetle, whitefly, and two-spotted spider mite. Two spider mite bioassays, one a measure of antibiosis and the other a measure of repellency, were used to determine the acaricidal performance of wild tomato leaf extracts. Wild tomato leaves possess pest-resistance mechanisms associated with their glandular trichomes and the exudates they produce. Type IV and type VI glandular trichomes on the leaves of six wild tomato accessions of L. hirsutum f. glabratum (PI 126449, PI 134417, PI 134418, PI 251304, PI 251305, and LA 407) were counted. Major chemical compounds from glandular leaf trichomes of the accessions tested were quantified using gas chromatography (GC) and mass spectrometry (GC/MS). The toxicity of two methylketones, 2-undecanone 270and 2-tridecanone—the major constituents of trichome secretions from the L. glabratum accessions tested—to adults of the sweet potato whitefly, Bemisia tabaci Gennadius, and fourth instar larvae of the Colorado potato beetle, Leptinotarsa decemlineata Say, was determined using no-choice bioassays. 2-undecanone caused 80% mortality of the fourth instar larvae of Colorado potato beetle at the highest concentration tested (100 mg 2-undecanone mL−1 of acetone), while 2-tridecanone caused 72% mortality of whiteflies at 20 mg 2-tridecanone mL−1 of ethanol. The concentration of 2-undecanone was greatest on the leaves of LA 407, and that of 2-tridecanone was greatest on PI 134417 compared to other accessions tested. Density of type VI trichomes varied among accessions and among sampling seasons. PI 134417 and LA 407 produced the highest number of type VI trichomes during the month of June. The two accessions of L. pennellii (PI 246502 and PI 414773) produced considerable concentrations of glucolipids. The two wild tomato accessions of L. hirsutum f. glabratum (PI 134417 and LA 407) are promising sources of 2-tridecanone and 2-undecanone that may be used for control of many insects and spider mites.