Defensive Mechanisms in Cucurbits against Melon Fly (Bactrocera cucurbitae) Infestation through Excessive Production of Defensive Enzymes and Antioxidants

Abstract

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.

Different responses of two maize cultivars to Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae infestation provide insights into their differences in resistance

“…Another significant enzyme in the phenylpropanoid cascade is CHS, and it catalyzes flavonoid biosynthesis (Dehghan et al, 2014). Phenylpropanoids have previously been shown to be induced to accumulate in the tissues of cucurbits in response to melon fly infestation, white cabbage exposed to cabbage butterflies, and flea beetles and cotton fed with Helicoverpa armigera and Spodoptera litura (Kovalikova et al, 2019;Dixit et al, 2020;Somegowda et al, 2021). In this study, on certain time points after S. frugiperda infestation, PAL4 and CHS6 were significantly upregulated, and the accumulation of total phenolics and total flavonoids was significantly increased.…”

“…Many research have already reported that the accumulation of phenolics and flavonoids in plants makes them resistant to a variety of abiotic and biotic stresses. Specifically, cucurbits with melon fly infestation tissues, compared with healthy and apparently healthy tissues, had significantly higher total phenolic and flavonoid levels (Somegowda et al, 2021). Phenolic acids and flavonoids, particularly quercetin, have also increased in white cabbage upon infestation by cabbage…”

“…In cowpea plants, the higher SOD and POD levels were observed in S. frugiperda injured leaves of the landrace Juti which showed higher resistance levels (Costa et al, 2020). In cucurbits, after melon fly infestation, in healthy and infected tissues of chayote and bottle gourd (resistant fruits) compared with bitter gourd, snake gourd, and cucumber (susceptible cucurbits fruits), higher activities of SOD, POD, polyphenol oxidase (PPO) and CAT were observed (Somegowda et al, 2021). After gall wasp Dryocosmus kuriphilus (GWDK) infestation, at all three stages of development, the activities of the POD and SOD enzymes were higher in the resistant chestnut variety leaves than they were in the susceptible chestnut variety leaves.…”