Melon fly (Bactrocera cucurbitae) is the most common pest of cucurbits, and it directly causes damage to cucurbit fruits in the early developmental stage. The
infection of fruit tissues induces oxidative damage through increased generation of cellular
reactive oxygen species. The effects of melon fly infestation on the production of defensive
enzymes and
antioxidant capabilities in five cucurbit species, namely, bottle gourd, chayote, cucumber, snake gourd, and bitter gourd, were investigated in this study. The total phenolic and
flavonoid content was considerably higher in melon fly infestation tissues compared to healthy and apparently healthy tissues. The chayote and bottle gourd tissues expressed almost 1.5- to 2-fold higher phenolic and
flavonoid contents compared to the tissues of bitter gourd, snake gourd, and cucumber upon infestation. Defensive
enzymes, such as
peroxidase (POD),
superoxide dismutase (SOD),
polyphenol oxidase (PPO), and
catalase (CAT), were high in healthy and infected tissues of chayote and bottle gourd compared to bitter gourd, snake gourd, and cucumber. The activity of POD (60-80%), SOD (30-35%), PPO (70-75%), and CAT (40-50%) were high in infected chayote and bottle gourd tissue, representing resistance against infestation, while bitter gourd, snake gourd, and cucumber exhibited comparatively lower activity suggesting susceptibility to melon fly
infection. The
antioxidant properties were also high in the resistant cucurbits compared to the susceptible cucurbits. The current research has enlightened the importance of redox-regulatory pathways involving ROS neutralization through
infection-induced antioxidative
enzymes in host cucurbit resistance. The melon fly infestation depicts the possible induction of pathways that upregulate the production of defensive
enzymes and
antioxidants as a defensive strategy against melon fly infestation in resistant cucurbits.