The Interactive effects of temperature and light intensity on Vitis vinifera cv. Semillon Grapevines. I. Berry growth and development

Light and temperature are known to affect the development of grape berries and their ripening process but the interaction between temperature and light is less well understood. Accordingly, Vitis vinifera cv. 'Semillon' grapevines were grown in controlled environments from budbreak until harvest and exposed at three stages of berry development to nine short-term temperature and light treatments to assess the impact on berry development and the ripening process. Berry diameter and soluble solids were determined throughout the growing season and before and after the various treatments. In all cases for berry expansion, soluble solids concentration and sugar content, there were highly significant interactions between temperature, light intensity and growth stage. Results confirmed berries at the early stage of development (pea size) were mostly unaffected by the temperature and light combination whereas the mid (veraison) and late stages were highly susceptible to the treatments. Berry growth and sugar accumulation were not affected when treated at 25 °C at any stage of development but at 30 °C and especially 38 °C, these processes were increasingly affected; berries were reduced in size and sugar contents declined, indicative of reduced rates of ripening. However, these effects were exacerbated when the bunches were treated concurrently to high temperature and high light. These results suggest growers need to maintain the canopy to protect bunches from direct sun exposure to avoid the interactive impacts of high temperature and high light on berry ripening, especially late in the growing season.