Effects of gibberellic acid on the rheological properties of sweet cherry tissue

The application of gibberellic acid (GA3) has been well documented in the literature to enhance the size, firmness and soluble solid accumulation in sweet cherry, but there is little information regarding the effect of GA3 on the rheological properties associated with the impact and compression damage sensitivity of the tissue. GA3 application was evaluated on 'Bing' and 'Sweetheart' sweet cherry cultivars in two separate experiments. In 'Bing' the effect of a single application of 30 ppm of GA3 at either the straw-color or pit-hardening stages was compared with the effect of half of the concentration (15 ppm) being applied at both physiological stages. 'Sweetheart' was treated with 15 or 20 ppm of GA3 at the straw-color and pit-hardening stages, which was compared with a single application of 25 ppm of GA3 at the straw-color stage. In both experiments, untreated fruits were used as the controls. The soluble solid accumulation and fruit size distribution were determined at harvest. The rheological properties were characterized using the curve of strain vs. stress, obtained by a texturometer. Impact and compression damages were induced in the laboratory, and the incidence and severity of injured tissues were determined after 10 days at 0°C. The fruit size was improved and the fruit tissue was less sensitive to compression and impact damage following gibberellic acid treatment. 'Sweetheart' was more sensitive to impact and compression damage and had lower values of rheological parameters than 'Bing'. The timing of GA3 applications demonstrated that the application of 15 ppm of GA3 at both the pit-hardening and straw-color stages was more effective for improving the size and soluble solid accumulation and reducing the sensitivity of the tissue to injury than a single application of 30 ppm of GA3 at either the straw-color or pit-hardening stages in 'Bing' or of 25 ppm at the straw-color stage in 'Sweetheart'.