A 2-year study was conducted to investigate the influence of the light environment on source-sink relationships in `Titan' red raspberry. Treatments imposed included flower and cane removal in conjunction with partial or whole canopy shading. Raspberry plants were remarkably resistant to a reduction in carbon supply. Yields and primocane production were maintained even when canopies were shaded. Furthermore, if raspberry plants were prevented from producing a full crop in one year, yields the following year tended to be higher than normal. These data, and other studies demonstrating that raspberry roots are strong carbon sinks, suggest that raspberry plants may rely on stored carbohydrate to mature the current crop of fruits when current photosynthate is inadequate. This trait is characteristic of some perennial species adapted to progressively changing environments, but may not be optimal for horticultural situations where growing conditions are relatively constant from year to year. A large root storage capacity and excessive primocane production likely contribute to the relatively low yields that are typical of this species.
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