Abstract
Ovary temperatures of upward- and downward-facing flowers of ‘Junegold’ peach (
Prunus persica (L.) Batsch) were measured on five nights in March 1991 to determine whether differential survival of ovaries following frost was related to flower orientation. Flowering twigs were removed from mature trees and positioned horizontally approximately 1.5 m above ground level prior to occurrence of low temperatures (0–5°C). Thermocouples were inserted through the hypanthium to contact ovaries of upward- and downward-facing flowers, and temperature and meteorological data were logged every 5 min. Under clear, calm conditions, temperature of upward-facing flowers averaged 0.33°C lower than that of downward-facing flowers during the coldest period of the night, with maximal differences of 0.77°C. Under cloudy, calm conditions, temperature differences between upward- and downward-facing flowers were less frequently observed and lower in magnitude (0.08–0.15°C). Under windy conditions (> 2.5 m s
−1), no temperature difference between upward- and downward-facing flowers occurred despite strongly negative net radiation. Differences in radiant heat exchange when forced convection was minimized are proposed to have caused the differential temperatures between flowers of different orientation. Based on known values of ovary cold tolerance, it is concluded that differences in survival of up to 38% could occur due to flower orientation when air temperature reaches critical values.