Biotic Stress Induced by Bacterocera cucurbitae (Melon Fly) Triggers Defense Related Phenylpropanoid Pathway (PPP) and ROS Detoxifying Enzymes in Cucurbits as Adaptation

The enzymes of phenylpropanoid (PP) pathway and antioxidant systems are among the plants broad spectrum of defense strategies and biochemical changes that respond to biotic stress. Melon fly (Bacterocera cucurbitae) is one of the detrimental pests damaging the cucurbitaceous family. Present study attempted to investigate the various enzymatic changes and antioxidant potential to post infection in cucumber (Cucumis sativus) and Chayote (Sechium edule). The enzymes phenylalanine lyase (PAL), tryrosine alanine lyase (TAL) and cinnamyl alcohol dehydrogenase (CAD) of PP pathway were constitutively expressed in the fruit tissues. These were low in healthy (8%), apparent healthy (13%) and remarkably high in infected tissues (25%). The enhanced PP enzymes upon Bacterocera cucurbitae infection were further confirmed by the increased total flavanoids (0.075%) and phenolic (12%) in the infected part. Antioxidant potential as evaluated measuring the ROS detoxifying enzyme activity revealed that antioxidant activity was increased in apparent healthy (50%) and infected tissue (60%) compared to the healthy tissue (37%). Both PP pathway and antioxidant enzymes were found significantly higher in infected chayote tissues as compared to cucumber and duration required for infection establishment in chayote (10 days) is also longer than cucumber (6 days). Considering these observations study indicates B. cucurbitae infestation in these fruits lead to up regulation and accumulation of PP pathway enzymes resulting in increased lignin synthesis which provide resistance for establishment of infection. The increased antioxidant potential combat and adapt to the infection induced biotic stress. The observed response in the chayote is markedly higher in upregulation of enzymes than in the cucumber which could be reason for its reported resistance against B. cucurbitae and susceptibility of cucumber. The melon fly is a damaged to many fruits and vegetable crops, especially 20 to 50% cucurbits fruits, fruits protect them self against melon fly damaged by used of various defense mechanism. Fruits inducible defense mechanism response with secondary metabolites and protein that act as directly and indirectly to insect caused avoid.

Author(s): Madhusudana Somegowda, V Vigneshwaran, Achur N Rajeshwar, Shivashankar S and Siddanakoppalu N Pramod

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