Using transgenic plants as greenhouse trap crops: prospects and lessons learned.

Transgenic modifications produced altered profiles of volatile organic compounds (VOCs) in the headspace of tomato Solanum lycopersicum cv. Micro-Tom. The Micro-Tom tomato plants were genetically modified to overexpress (OE) the carotenoid cleavage deoxygenase (CCD) gene (LeCCD1) that is involved in the carotenoid biosysnthesis pathway. Dual-choice trials with the transgenic and wild-type (WT) tomato determined a greater preference for transgenic tomato by the greenhouse whitefly Trialeurodes vaporariorum (Westwood) compared to the cabbage looper Trichoplusia ni (Hübner) as a site for oviposition. Gas chromatography-mass spectrometry (GC-MS) analyses indicated changes in the VOC profiles of WT and LeCCD1 plants, as certain compounds, α-copaene and 3-carene,were either present or absent in the two genotypes. However, there were no significant differences in the concentration of most compounds, such as β-phellandrene, caryophyllene and 1-R-α-pinene, and cabbage looper moths showed no preference in Y-tube olfactometer experiments for transgenic versus WT plants with both mated and un-mated females. Other work to increase the production of repellent apocarotenoid volatiles in Arabidopsis thaliana led to the successful production of OE AtCCD4 tomato plants overexpressing the Arabidopsis carotenoid gene. The AtCCD4 plants with the highest overexpression levels had reduced occurrence of whitefly oviposition relative to the WT plants. The increase in attractive and repellent volatiles in tomato has potential for application as a trap crop for whiteflies in greenhouse crops and as components in a “push-pull” strategy. As part of the strategy, the “pull” plants or “trap crops” will be “intercropped” with the tomato crop to reduce the pest pressure.