Modeling Chilling Requirement and Diurnal Temperature Differences on Flowering and Yield Performance in Strawberry Crown Production

In North America, over 800 million strawberry crowns are produced by nurseries each year for the strawberry fruit industry. A modeling approach is a quantifiable method to help nurseries predict optimal crown harvest date and potential fruit yield associated with the annual strawberry crown growing environment. Most available models that quantify growth conditions, e.g., chilling effects, use controlled environment chambers and target prediction of time of strawberry flowering, not fruit yield. This study used commercial field fruit yield data over a 6-year period and five geographically distinct locations to construct models to predict the effects of chilling, diurnal temperature difference, and their interaction with daylength on fruit yield and time to flower. Accumulative chilling unit (ACU) was estimated by using nonweighted (simple, M0) and weighted [Mu (Utah Model), M1, M2] accumulation of effective temperature units. The results showed that flowering time correlated with accumulative chilling hours using either a simple (M0) accumulation model or a weighted accumulation model (Mu, M1, M2). The best correlation of flowering time with ACU was a quadratic function (y = 82.27 − 0.049x + 1.74e −5 x 2 , where y = flowering time, x = ACU) and effective temperatures were from –2 to 15 °C. By contrast, fruit yield was only correlated with ACU using specific weighted accumulation models. The correlation was influenced by weighting factors and effective or inhibitive temperatures involved in the model. Therefore, temperatures have differential effects on fruit yield and on flowering time. When pooled across regions and years, fruit yield could be predicted only by the weighted accumulation Model 2 (M2), a quadratic function (y = –72.15 + 0.98x + 0.0022x 2 ) of the ACU accumulated from 45 d before crown harvest. Fruit yield response to ACU had an optimal level with yield reduction at other values. By contrast, fruit yield linearly increased with increasing difference in diurnal temperature across years and locations. However, the days to first flower were affected interactively by the diurnal temperature difference and daylength when geographically distinct locations are compared. The greater the difference in diurnal temperature at 2 to 3 months before crown harvest, the higher the subsequent fruit yield and the shorter the flowering time. An accumulative diurnal temperature unit of 180 degree-days resulted in 30% yield enhancement of Saskatchewan-grown crowns over California-sourced crowns. The greater diurnal temperature difference may be the major contributor to the Northern Vigour ® response of strawberry crowns produced in northern latitudes such as Saskatchewan.

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