Effects of simulated and natural herbivory on tomato (Solanum lycopersicum var. esculentum) leaf trichomes

Plants respond to damage by herbivores with a variety of resistance characters including trichome production and the production of secondary compounds. These induced responses play important roles in species interactions, often protecting plants from herbivorous insects or pathogens, and there is growing interest in applying such information to solving pest problems in agriculture with the potential for using endogenous chemical elicitors instead of pesticides promising the development of more environmentally sustainable agricultural practices. The objective of this study is to investigate the extent to which trichomes are induced by the same stimuli shown to induce chemical responses in plants. Using the cultivated tomato (Solanum lycopersicum var. esculentum), the number of trichomes produced on leaves was compared after the application of the following treatments: simulated herbivory, natural herbivory, and jasmonic acid (JA) spray. Twenty-five plants were grown, and five randomly assigned to each treatment. Plants were grown in a greenhouse in a randomized block design to control for spatial effects. Treatments were applied after two true leaves had fully developed. Samples were collected from the terminal leaflet of the fifth true leaf, tissue examined using scanning electron microscopy, and the number of different types of trichomes on each sample was quantified. Our results showed significantly higher trichome production on the terminal leaflet of the fifth leaf of plants treated with herbivory and JA compared to control plants and plants treated with mechanical damage. Natural herbivory and JA induced nearly twice as many trichomes as compared to the control plants. There was also a trend showing an increase in glandular trichome Type VI in response to herbivory and JA, although the effect of treatment on trichome type was not statistically significant.