Gallic acid induces constitutive resistance against Bactrocera dorsalis infestation in mango fruit by its dual action

The Oriental fruit fly, Bactrocera dorsalis (Hendel) is a major insect pest of mango fruit worldwide resulting in huge loss of fruit quality and productivity. However, there exist a few mango varieties resistant to B. dorsalis infestation. The objective of the present study was, therefore to identify the major fruit component imparting resistance to B. dorsalis. Principal Component Analysis of phenolic acids in pulp and peel tissues of two resistant varieties, viz., Langra and EC 95862, revealed that among the phenolic acids present in the fruit, gallic acid was the most abundant component in both fruit peel and pulp while laboratory studies revealed that gallic acid was acutely toxic to B. dorsalis with its dual action as antioxidant in the host and a prooxidant in the insect. Field study with the preharvest application of gallic acid on young developing fruits of B. dorsalis susceptible Alphonso mango showed that it could protect the fruit against insect damage confirming that gallic acid is essentially responsible for providing constitutive resistance against B. dorsalis in Langra and EC 95862. Thus, preharvest application of gallic acid to developing fruits could be used as part of an Integrated Pest Management strategy to control infestation by B. dorsalis. Future work on breeding / development of transgenes of susceptible mango varieties with high levels of gallic acid in fruit peel is likely to provide the simplest means of inducing constitutive resistance against B. dorsalis infestation.