Can Spectrophotometry Be Used to Quantify Zingiberene Sesquiterpenoids in Tomato Leaflet Extracts?

Tomato (Solanum lycopersicum), an important vegetable crop, is a host for numerous pests and pathogens. Consequently, tomato breeders are striving to improve pest resistance. Many accessions of the wild relative S. habrochaites display high resistance towards arthropod pests such as spider mites and whiteflies and the presence of the sesquiterpene hydrocarbon 7-epi-zingiberene on its trichomes has been associated with arthropod resistance. Consequently, tomato breeders are attempting to introgress 7-epi-zingiberene from wild to cultivated tomato. 7-epi-zingiberene has conjugated double bonds causing it to absorb UV light. In fact, absorbance at 270 nm of tomato leaflet washes has been used to aid introgression, but its use has not been critically evaluated. Consequently, we evaluated the relationships between UV absorbances in the 200-350 nm range and the concentration of 7-epi-zingiberene in plants from several interspecific hybrid generations of tomato. We also evaluated the absorbance spectra for isolated 7-epizingberene and it two oxidized forms. The wavelength of maximum absorbance of the isolated compounds was 264 nm. The strength of the relationship (R²) between absorbance measured at a single wavelength and quantity zingiberene ranged from 0.30 to 0.92 among generations evaluated. Additionally, the regressions of absorbance at a single wavelength on quantity always resulted in a non-zero intercept, indicating that single wavelength absorbance cannot be directly used for quantitation. Use of multiple wavelengths for quantitation was explored and their use can improve accuracy of quantitation. Measuring absorbance at multiple wavelengths or scanning in the UV range, backstopped by a method of quantitation such as gas chromatography could be a useful tool for aiding introgression.