CARBON SUPPLY REDUCTION HAS A MINIMAL INFLUENCE ON CURRENT YEARS RED RASPBERRY (RUBUS-IDAEUS L) FRUIT PRODUCTION

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