Experimental study of fruit temperature dynamics within apple tree crowns

Inner and surface temperatures of several ‘Golden Delicious’ apples in orchard and air temperature were measured during more than 2 months. In addition to temperature measurements, the 3D canopy structure was measured to compute the light interception of each measured ‘Golden Delicious’ apple. From this we extracted quantitative information about fruit temperature dynamics and fruit temperature variability within a tree crown in relation to air temperature fluctuations and fruit sunniness. Especially, fruit temperature dynamics were analyzed at daily and monthly time scales and compared to the air temperature dynamics. Results showed that when an averaged fruit per tree and a daily time scale were considered, as it is commonly done in fruit or pest development models, fruit temperature was equal to air temperature. However, during daytime, large departure from air temperature and large inner temperature gradients which could have significant effect on fruit physiological processes were measured. Moreover, such departures were highly variable among fruits within a tree canopy. To explain such within tree variability, the light interception by fruits must be taken into account. From this experiment, useful relationships between fruit temperature, air temperature and fruit light interception for fruit physiological model were derived and explained from physical principles.