Abstract
The experiments were conducted to determine the influence of fruit exposure to sun on fruit temperature, sorbitol content, and early watercore development in ‘Orin’ apples, using a simple measuring system of total integrated solar radiation. The system provided th correct measurement of solar radiation under high daytime temperature conditions above 30°C, the typical summer climate in Matsuyama. Positive correlations were found between the relative amount of fruit insolation measured from three directions (east, south and west) of the fruit equator and mean fruit temperature, although the correlation coefficients in experiments with R-type film were much higher than those with Y-type film. Analysis of 26 apples obtained from three experiments, two with R-type and one with Y-type film, also demonstrated positive correlations between the relative amount of fruit insolation and the mean and daily maximal fruit temperature, watercore rating, flesh firmness, fructose, glucose, sorbitol, and total sugars. Correlations between the degree of watercore and fruit temperatures (mean and maximum), flesh firmness, and sorbitol content were also significant. These results suggest that early watercore in ‘Orin’ apples is promoted by fruit exposure to sun mediated through increased fruit temperature and sorbitol accumulation.
