Changes in grapes composition during ripening of five Vitis vinifera L varieties as related to Tephritidae and Drosophilidae infestations

Vitis vinifera (L) is a great economically important crop. However, huge loss in fruits due to destructive pests hinders the improvement of its performance. The study of their biochemical profile, ripening dynamics, and defense mechanisms presents a great scientific interest. In this work, phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL) activities, proteins, sugar and malondialdehyde (MAD) were investigated during ripening of five grape varieties in Loudaya region (Marrakech, Morocco), three of them are allochthonous while two are autochthonous. The Dipterans infestations by Drosophila suzukii and Ceratitis capitata have been highlighted as a factor that stimulates the defense mechanism in ripeness stage of grapes. Sugars, proteins and MDA have shown a gradual increase in grapes maturation in all varieties. TAL activity decrease in the course of the maturation in contrast to the PAL activity increasing in the ripe grapes. High content of PAL, TAL, and MDA compounds were noted in the ripe infested grapes as compared to the healthy ones. A significant difference (P < 0.05) for all biochemical assays according to varieties, maturity and the condition (damaged/undamaged) were found. A PCA analysis highlighted different biochemical behaviours from the grapes concerning the flies' infestations (79.64% of total variation). The variables that have contributed to the discrimination of the grapes according to their stage of maturities were sugar, proteins and TAL. The higher concentrations of PAL (6.64 ± 0.57 EU), TAL (0.93 ± 0.05 EU) and MDA (58.32 ± 2.55 EU) especially in the injured grapes prove that flies infestation triggered a priming defense mechanism, directly activating defense reactions. The results obtained could be crucial in establishing a database of the Moroccan grapes biochemical defense which provides a foundation for new methodologies in the plants behavior against fruit flies stress.