THE USE OF CHLOROPHYLL FLUORESCENCE TO DETERMINE THE EFFECTS OF DIFFERENT ACCLIMATION TEMPERATURES ON STRAWBERRY LEAVES EXPOSED TO MILD FROST DAMAGE

This research was conducted to understand the effects of different acclimation temperatures on strawberry (Fragaria × ananassa) leaves exposed to mild frost damage. Measurement of chlorophyll fluorescence (F_v/F_m) is a quick method for determining cold damage to the plant photosynthetic apparatus. Potted strawberry plants of the cultivars ‘Honeoye’ and ‘Chandler’ were grown in a temperature controlled (24-26°C day, 18°C night) greenhouse in East Lansing, MI, USA until the plants had five fully expanded leaves. Plants were then exposed to either 4°C, 8°C or 12°C in three temperature controlled rooms for two days before being exposed to a simulated mild frost at -2°C for six hours. A completely randomized plot design was used for this experiment with twenty plants in each treatment plot. Control plants were untreated. Plants exposed to -2°C were brought back to the greenhouse where chlorophyll fluorescence was measured for five consecutive days. Leaves exposed to -2°C were not affected by frost until the third day of measurements, at which time chlorophyll fluorescence values (F_v/F_m) were significantly lower than those of control plants. Different acclimation temperatures did not affect the F_v/F_m values. On the third day ‘Chandler’ plants exposed to -2°C had lower F_v/F_m values than those of ‘Honeoye’. Complete recovery was observed on the fourth day of measurements. In conclusion, we observed delayed, transitory damage to the photosynthetic process in strawberry leaves subjected to temperatures of -2°C for 6 hours, but complete recovery occurred within 4 days.