Hormic dose of ultraviolet light (3.7 kJ•m-2) induced disease resistance in tomato fruit. The biochemical nature of induced resistance by UV light was investigated by histochemical techniques. Ultraviolet light induced plasmolysis of the epicarp and few mesocarp cell layers, and collapse of these cell layers led to the formation of cell wall stacking zone (CWSZ). The treatment also stimulated the biosynthesis of phenolic compounds (Prussian blue reaction) in the epicarp and mesocarp cells. Biochemical reinforcement of the cell wall through lignification (Maule test) and suberization (berberine fluorescence) was also induced. These responses originating from the activation of phenylpropanoid path were principally localized in the CWSZ and were induced before inoculation by B. cinerea. The intensity of these responses was significantly increased in UV-treated tissue in response to infection. These responses were also induced in the inoculated control tissue but were either less substantial (phenolics, lignification, and suberization) or delayed.
Eighteen strawberry genotypes were evaluated for their phenolic content and antioxidant capacity using several methods. High antioxidant capacity was found for `Harmonie', `Saint-Jean d'Orléans', and `Saint-Laurent d'Orléans', which were reported to have better shelf life than `Kent'. `Harmonie', `Saint-Jean d'Orléans', `Orléans', and some advanced selections had higher hydroxycinnamic acids, benzoic acids, and flavonols than `Kent'. The significant variation in antioxidant capacity and total phenolic compounds clearly shows the potential value of certain new cultivars and advanced lines as parents in a breeding program. The future plan is to examine individual antioxidant and their role in disease resistance and extension of shelf life and to use selected genotypes as parents to developed new lines.