Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2005
Publication Date: 7/31/2005
Citation: Antonious, G., Tejinder, K., Simmons, A.M. 2005. Natural products: seasonal variation in trichome counts and contents in lycopersicon hirsutum f. glabratum. Journal of Environmental Science and Health. 40:619-631. Interpretive Summary: To manage crop insect pests, there is a need for insecticides that are made with natural products. Wild relatives of tomato may offer natural sources of compounds for the development of biologically-based insecticides. The leaf hairs of wild relatives of tomato contain compounds that are toxic to some insects. Also, the leaf hairs can release sap containing these compounds. A study was conducted to determine the amount of the major chemical compounds from the leaves of a wild relative of tomato, and to determine how toxic the compounds are against two important global insect pests of vegetable crops. Five different types of Lycopersicum hirsutum f. glabratum, a wild relative of tomato, were studied. Two major chemical compounds (2-undecanone and 2-tridecanone) were removed from the leaves. The amount of these compounds varied by plant type and varied during different periods of the year. The higher the dosages, the more effective each compounds was against two insect pests. The 2-tridecanone was most effective against the B-biotype sweetpotato whitefly (adult stage). The 2-undecanone was most effective against the Colorado potato beetle (larval stage). Plant type PI 251304 produced the greatest quantity of the two compounds. Plant types of L. hirsutum f. glabratum may be valuable sources for natural product insecticides, and lead to less use of synthetic insecticides for crop production.
Technical Abstract: A study was conducted on potential sources for biopesticides for crop pests. Wild relatives of tomato have a pest-resistance mechanism within glandular trichomes of leaves as well as in the exudates of the trichomes. Type IV and VI glandular trichomes on the leaves of five accessions (PI 126449, PI 134417, PI 134418, PI 251304, and LA 407) of the wild species Lycopersicum hirsutum f. glabratum were counted after they were grown under greenhouse conditions. Major chemical compounds from glandular leaf trichomes of the accessions were extracted, purified, and quantified at different periods of the year by gas chromatography and mass spectrometry. The toxicity of two methylketones (2-undecanone and 2-tridecanone), the major constituents of the accessions, to adults of the sweetpotato whitefly, Bemisia tabaci (Gennadius) and 4th instar larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say) was determined using no-choice laboratory bioassays. The 2-undecanone resulted in 80% mortality of the 4th instar larvae of the beetles at the highest concentration tested (100 mg 2-undecanone mL-1 of acetone) while 2-tridecanone resulted in 72% mortality of whiteflies at 20 mg 2-tridecanone mL-1 of 65% ethanol. The concentrations of 2-undecanone and 2-tridecanone on the leaves of each of the five accessions of L. hirsutum f. glabratum and the mass spectra of these compounds were determined. Overall, the concentration of 2-undecanone on the leaves was significantly higher than 2-tridecanone. Concentrations of the two methylketones varied among accessions and during different periods of the year. The plants produced the highest concentrations during August. Each plant of accession PI 251304, on average, provided 354 g of fresh leaves (about 52,353 cm2 exposed leaf surface area) and produced 32.5 and 8.7 mg of 2-undecanone and 2-tridecanone, respectively. Among the accessions, this was high production of these compounds. Accessions of L. hirsutum f. glabratum may be a valuable source for natural product insecticides, which could minimize the reliance on synthetic insecticides for crop production.