Deciphering eggplant's response to the eggplant shoot and fruit borer's frugivory

Abstract

Plant response to herbivory has been extensively studied using folivore as a model system. Plants exhibit various defense strategies in response to folivore attacks to protect and prevent themselves from further attacks. For example, chemical defense may accumulate in the leaves that can deter or kill the folivore. Apart from folivores, other herbivores such as frugivores, rhizovores and florivores are also commonly found. However, their interactions with the plant and its response against them remain understudied. This study used Eggplant, Solanum melongena L., and its major pest, ESFB, Lucinodes orbonalis, as a model system for studying frugivore-plant interaction. From our field observations, we hypothesized that Eggplant uses chemical defenses against ESFB by emitting volatile compounds from the leaf or accumulating defense metabolites in newly developed plant tissues after the attack. For this, experiments were designed where upon ESFB-infestation on fruit- volatile compounds of plant leaf were studied with GC-MS based study as well as newly developed fruits checked for defense metabolite accumulation post ESFB-frugivory employing UPLC-MS-based metabolomic studies. We found that the ESFB-infested fruit bearing plants experienced significantly low oviposition, and their second flush fruits were less infested. Metabolites significantly increased post-frugivory in the first flush fruits. Moreover, in the first flush-infested plants, metabolite levels in the second flush fruits significantly differed from the controls, suggesting that the metabolite induction by frugivory was not just local. Together, we discovered that the ESFB-frugivory leads to a systemic response in plant. Fruit, in spite of being a sink organ, sends a signal to the source, i.e., the leaf, which leads to the changes in the next flush fruits. In the future, the induced metabolites can be tested against the ESFB. Physical and surface chemical defenses can also be analyzed to find the basis of the lowered ESFB oviposition.