Root Pruning Effects on Growth and Yield of Red Raspberry

Abstract

Annual production systems for red raspberry (Rubus idaeus L.) have been proposed for off-season production or for increasing crop diversity in warm winter climates. However, yields in these annual systems are low compared with annual yields in perennial production systems. The yield reduction may be from the root pruning that occurs during removal and shipment of the canes from the nursery. This would result in significant root loss and may decrease the availability of root carbohydrates for reproductive development. To investigate this, ‘Cascade Delight’ red raspberry plants were root pruned during dormancy, and growth and fruiting of these plants were compared with non root-pruned controls the next season. Dry weights of all organs except floricane stems increased throughout the growing season; however, root pruning decreased root, floricane lateral, and total fruit dry weight compared with no root pruning. The yield decrease observed in root-pruned plants was because of a decrease in flower and fruit number per cane compared with the control. Total carbohydrate concentration in roots of root-pruned and non root-pruned plants decreased significantly between pruning and budbreak; however, root carbohydrate concentration and content were always lower in root-pruned compared with non root-pruned plants. The lower root carbohydrate availability in root-pruned compared with non root-pruned plants during budbreak apparently limited flower bud formation/differentiation, resulting in decreased yield. These results suggest that yields in annual red raspberry production systems are limited because of the loss of root carbohydrates during removal from the nursery. Management practices that increase yield per plant (e.g., by ameliorating root loss) or increase yields per hectare (e.g., by increasing planting density) are needed to render the annual production system economically viable.