Determining Vegetative Maturity by Differential Thermal Analyses

Abstract

In the past, the laborious and time-consuming method of defoliation was used to determine vegetative maturity (VM) of various deciduous plants. Other methods such as water potential and electrotrical impedence have been explored without a positive response. A change of freezing events of water in plant tissue may be associated with VM. Differential thermal analysis (DTA) was tried to determine if the freezing events of water are related to VM. `Golden Delicious', `Gala', `Red Fuji' and `Antonovka' apple (Malus domestica Borkh.) trees were used to determine VM by defoliation. Different sets of 1-year-old trees grown in pots in the greenhouse were defoliated weekly from 1 Aug. until it was assured the trees had reached VM. Samples from the same trees were taken for DTA. The trees were observed for regrowth 2 weeks after they were defoliated, and the exothermic patterns from DTA were examined for the appearance of an exotherm at about –35 to –40°C. The comparison of regrowth from trees defoliated from a specific date were compared to the exothermic pattern of the same date. An exotherm appeared between –35 and –40°C ≈2 weeks before the apple trees ceased to show regrowth from the defoliation treatment. The exotherm appeared on 30 Aug. for Antonovka and `Golden Delicious' and regrowth of the trees ceased on 12 Sept. Regrowth ceased on 9 Oct. for `Gala' and `Fuji' preceded by the exotherm on 2 Oct. The conclusion was that the appearance of the exotherm at –35 to –40 °C could be used to determine VM.