Influence of agricultural practices on the defense mechanisms of tomato plants against insect herbivores via trichomes and secondary metabolites

Abstract

In tomato production, yield reduction is often caused by both abiotic and biotic stresses, particularly the threat of herbivorous insects. However, tomato trichomes and secondary metabolites play a crucial role in the resistance of tomatoes against external threats. This study aimed to assess the effect of agricultural practices on the development of trichomes and their importance in the defense of tomato plants against insect herbivores, specifically the pest Zonocerus variegatus. A survey was conducted in two major tomato production areas in Southern Benin, presenting different agricultural practices that could influence the development of trichomes. Samples from 200 tomato plants were collected from various tomato fields and trichomes on leaf and stem samples were counted using an optical microscope. Additionally, to understand the responses of specific tomato varieties to attacks by insect herbivores, experiments were conducted on the varieties Akikon, Tounvi, and Thorgal cultivated in pots and then subjected to biotic stress by Z. variegatus, with both control and experimental batches. Three weeks later, leaf and stem samples were taken and the trichomes were observed and also counted. Subsequently, phytochemical screenings and quantification of secondary metabolites were performed on the experimental and control plants. Structural Equation Models analysis revealed a significant positive effect of cropping systems and fertilization methods on trichome density, but a significant negative effect of soil type and biopesticide use. The experiment results showed an increase in trichome density in response to pest attacks. Phytochemical screenings revealed considerable production of polyphenols and flavonoids in all three varieties. The rate of insect damage was highest in the Tounvi tomato variety, followed by the Akikon variety and finally the Thorgal variety which released more flavonoids and polyphenols. These findings underscore the vital function of trichomes in protecting tomato plants against herbivore insects. This study provides a theoretical and practical basis for advancing and integrating the roles of trichomes in controlling insect herbivores and improve tomato production.