Understanding chemical and molecular basis of eggplant- insect herbivore interaction

Abstract

Phenolics are a class of plant metabolites having role in both plant development and defence response, which are present in a wide range of plant families. Chlorogenic acid (CGA) is a secondary metabolite which is known for its deterrent nature against insect herbivores. Here we report the role of CGA in eggplant- S. litura interaction. In a randomized field of different eggplant varieties, a differential occurrence of S. litura larvae was observed on different eggplant varieties, and the S. litura occurrence negatively correlated with the abundance of CGA. Feeding S. litura on artificial diets spiked with CGA showed high neonate mortality, reduced larval mass gain, increased larval lifecycle etc., which shows the negative effect of CGA on larval performance and fitness. Larvae was shown to be metabolising CGA into caffeic acid and quinic acid, by an ester hydrolysis reaction. Two genes COE4 and COE15 were shown to be induced upon the ingestion of CGA in the larval midgut. Exogenous application of CGA and ds RNA of COE4 and COE15 were carried out, which opens a new horizon in the field of agricultural science to reduce crop loss

Steroidal alkaloids (SAs) are the secondary metabolites in Solanum melongena (Solanaceae) which are known to play an important role in plant defense mechanisms. Here I report the chemical basis of interaction between an agronomically important crop Solanum melongena and its generalist herbivore Spodoptera litura. A differential occurrence of S. litura was observed on different eggplant varieties in a randomized field. Upon metabolite profiling of eggplant leaves, a negative correlation between larval occurrence and concentration of SAs: solasodine (SD), solasonine (SN) and solamargine (SM) was observed. It was interesting to see that S. litura was unable to metabolize SAs and excreted them without any modification. Concentration-mortality relationship of SAs was studied on neonates and second instar larvae of S. litura. A reduced larval mass gain was observed upon feeding them with artificial diets spiked with SAs as compared to control diet. Larval mass gain showed a negative correlation with increase in the concentration of respective SAs.