Observations of Ice Nucleation and Propagation in Flowers of Japanese Pear (Pyrus pyrifolia Nakai) using Infrared Video Thermography

Abstract

Ice formation and propagation in the flower and young fruit of Japanese pear 'Kosui' were investigated with infrared (IR) video thermography imaging system. The changes of thermal response (exotherm) in freezing events could be detected using the infrared thermography camera with exotherm rise of 2-5 °C accompanied by a marked color change in the tissues. With first bloom flowers, the temperature of peduncles decreased faster than that of the receptacle; the initial ice nucleation occurred primarily in petals, sepals and/or receptacle. Subsequently, ice was propagated along the peduncle. The temperature of receptacles was above that of peduncles during the freezing test at full bloom; the sepals and/or receptacle were initially frozen, then ice nucleation was extended to the petals along the peduncle. These results suggest that the sepals and/or receptacle where the initial nucleation occurred may be an intrinsic or extrinsic source of high ice nucleation activity in flowers of the Japanese pear 'Kosui'. In contrast with first bloom and full bloom stage, the exotherms during freezing could not be detected clearly in young fruits. However, cold injury appeared as a spotty stain on the skin of young fruits immediately upon being subjected to chilling.