|Keller, Markus -|
|Mills, Lynn -|
Submitted to: Australian Journal of Grape and Wine Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 2010
Publication Date: September 30, 2010
Citation: Keller, M., Tarara, J.M., Mills, L. 2010. Spring temperatures alter reproductive development in grapevines. Australian Journal of Grape and Wine Research. 16:445-454. Interpretive Summary: Variation in weather from year to year affects the production of grapes, the quality of the fruit, and its date of harvest. Highly variable temperatures in spring are becoming more common, and it appears that temperature early in the growing season can have a lasting effect on crop growth and fruit development. To test this hypothesis, we controlled the temperatures of buds on grapevines before budburst in spring until the first flowers that would form the grape cluster could be seen. Although higher temperatures in early spring caused faster shoot growth, the effects on the flowers and resulting fruit were mixed. The vines produced bigger flowers at higher temperatures, which in turn became bigger individual grapes. Higher temperatures early in spring also resulted in more individual grapes developing on each fruit cluster. Thus yield at harvest was positively related to temperature in spring. However, at harvest, the quality of the fruit was not related to early-season temperature: there were no differences in the sugar content, color, or acidity among our controlled-temperature treatments.
Technical Abstract: Climate variation contributes to fluctuations in reproductive output, and spring temperature is thought to influence flower production in grapevines. We studied the influence of temperature near budburst on reproductive development in field-grown Cabernet Sauvignon while minimizing the influence of other microclimatic variables. Dormant buds and emerging shoots were heated or cooled from before budswell until individual flowers were visible. Over three years, flower number per inflorescence was inversely related to pre-budburst temperature. Conversely, flower size, percent fruit set, and berry size increased with higher temperatures. Fruit set also increased as flower size and leaf area per flower increased; fruit set was erratic below 4 cm2 leaf area per flower. Berry mass and sugar content per berry increased with increasing flower size. Although yield per shoot varied three-fold among treatments, differences in fruit composition were minor. Variations in early-season temperatures may alter substantially grapevine yield formation. The temperature effect may be a combination of direct effects on floral development and indirect effects arising from differences in shoot growth. This study shows that variations in temperature near budburst may be an important cause of large variations in grapevine yield.