Contribution of Individual Bent Shoot Layers to Cut Flower Productivity in Shoot-bending ‘Asami·Red’ Roses

Abstract

We estimated the contribution of individual shoot layers in a multi-layered bent canopy to the cut flower productivity of roses (‘Asami·Red’). A two-layered bent shoot canopy was established and upper- or lower-layer bent shoots were replaced with artificial replicas of shoots. Replacing upper-layer shoots with replicas facilitated leaf abscission of lower-layer shoots, resulting in severe reduction in the total dry weight of cut flowers (TDWF) compared with plants having two intact bent shoots. When lower-layer shoots were replaced with replicas, the leaf area of upper-layer shoots increased and consequently the excision of lower-layer shoots had little influence on the TDWF. In another experiment, when a three-layered bent shoot canopy was established and light interception by lower-layer shoots was restricted completely by placing a shading film between two of the three layers, the leaf area of the uppermost shoots increased to compensate for the decreased leaf area due to leaf abscission of lower-layer shoots. The excision of lower-layer shoots resulted in more severe reduction of the TDWF than shading. These results suggest that in a multi-layered bent shoot canopy of roses, upper-layer shoots contribute to cut flower yield of plants, primarily through their current photosynthesis with high light interception. However, lower-layer shoots also contribute to cut flower yield by exporting assimilates retained previously, and hence these shoots should remain on plants until they die spontaneously.