Relationship between fruit cracking and changes of fruit diameter associated with solute flow to fruit in cherry tomatoes

Abstract

The course of cracking in cherry tomato (Lycopersicon esculentum Mill.) grown in water culture in a glasshouse in relation to the diurnal changes in fruit size and the rate of solute uptake was investigated. 1. When cracking in 250 fully ripe 'Sun Cherry' was checked hourly during 10 days in July, about 83% of the cracking occurred between 4 : 00 and 10 : 00. 2. Diurnal changes in diameters of fully ripe fruits measured by a laser beam sensor system starting at 0 : 00 and during summer and autumn revealed that in summer, 'Sun Cherry Extra' diameters increased from 3 : 00 to 6 : 00, then decreased from 8 : 00 to 14 : 00, after which it again increased gradually during the daytime but sharply after sunset. A similar trend was observed in the autumun with 'Sun Cherry' but to a lesser extent. A rapid increase in fruit diameter coincided with the time of fruit cracking. 3. The diurnal change in solute flow rates through plants of 'Sun Cherry Extra' was investigated using a sap flow system, the flow in the stem and petioles was always directed distally during the day and night cycle; the flow rates in both tissues were much faster during the day than at night. In contrast, the solute in the peduncles flowed proximally during the late morning to evening and distally during the dark period, indicating that solute flow to fruits occurs during the evening and early morning hours. The results suggest that the rapid expansion of fruit was induced by solute inflow into the fruit during the night to early morning; fruit skin cannot endure the internal pressure, leading to the cracking of the fruit.