Heat before flowering reduces fruit size in day-neutral strawberries

The optimum temperature for fruit and achenes of day-neutral strawberries to develop was characterized in two field trials in Florida and Ontario and in controlled environments. In the field, fruit became smaller mainly because weather before flowering became hotter. Ovule number was influenced by the mean temperature during the week before and the week after the point corresponding to 462 degree-days before flowering. Also, 12 °C appeared to be the optimum temperature for ovule initiation. Fruit volume per ovule, cell number, and cell size were determined by the mean temperature 176 degree-days before flowering, and was greater below 15 °C. Since cell divisions did not vary after flowering, cell volume played a relatively minor role on fruit volume. When there was a smaller proportion of developed achenes, the achenes were larger and had a similar contribution to fruit development as when there was a larger proportion of them. Also, they were larger and had a higher germination rate when temperatures were higher. The results indicate that with 12 °C as the optimum temperature for fruit development a daily range of 6–18 °C would give consistently large fruit.