Abstract:

The experiments were conducted in an 8 years old grape orchard, ‘Red Globe’, to study the effect of sunlight, air temperature, wind speed and other factors on grape berry sunburn. The results showed that the higher temperature on fruit surface was the direct factor inducing grape sunburn. The threshold temperatures to induce sunburn ranged from 42.0℃ to 42.8℃(average temperature was 42.3℃) during fruit fast swell stage. It would reach to maximum after 12 minutes if the berries were suddenly exposed to the sunlight. The excessive sunlight increased both air temperature and fruit surface temperature. Therefore, excessive sunlight was the most important factor causing grape sunburn. The illumination per 10 000 lx could add about 1℃ on fruit surface at noon of a shiny and windless day in summer. The fruit surface temperature was significantly higher on the days without wind than when the wind speed was 1.5m﹒s^-1. When wind speed approached 3.0m/s, the fruit surface temperature decreased to a very low level within 6 minutes. The higher relative humidity increased grape sunburn under the same light and temperature conditions.

Key words: Grape, Sunburn, Threshold temperature, Temperature, Light, Wind speed, Relative humidity