System development of glasshouse roses

Apart from the progress in control of environmental factors and optimization of the technical equipment with respect to an increase in productivity during the last decades, little attention has been paid to reveal the significance of plant structure and plant management on the growth and productivity of a rose crop. The aim of the present research was to enlarge the knowledge about the physiological background of rose crop production under controlled environmental conditions.

Plant architecture, as reflected in the number, diameter and cross sectional area (CSA) of basal shoots and laterals, can be highly controlled using plant related factors such as time of bending the primary shoot, removal of lateral or basal buds, height of pruning at harvest and disbudding of flowering shoots and by plant density. Treatments which invest in early stem development reduce flower production for the first 8 months but this financial loss amply pays itself in the next 2 cropping years. Plant architecture has a great influence on flower production. The number and diameter of second-order laterals as formed during the first 8 months, can explain more than 70% of the variation in number and weight of flowers harvested in the next 2 cropping years. Long-term flower production is hardly related to the number of basal shoots. New basal shoots compete with existing ones as indicated by the limited diameter increase, the higher mortality rate and the smaller flowering shoots for old basal shoots.

Disbudding of flowering shoots resulted in an increase in total non-structural carbohydrates in basal stem parts, mainly starch. Although used again for the subsequent flowering cycle, carbohydrate storage is much too low for playing an important role for new growth.

Rose crop growth primarily depends on the intercepted photosynthetically active radiation (PAR) which is closely related to plant architecture.. Under natural light and CO ₂ -conditions, a linear relationship between crop dry weight increase and intercepted PAR by the canopy was observed. Average light conversion efficiency (LCE) was 2.5 g/MJ PAR. A uniform leaf area index, i.e. light interception, is maintained by a continuous harvesting system controlled by the height of cutting at harvest and the bending or removal of blind shoots. Flush harvesting reduces the light interception i.e. crop growth. The percentage of dry matter distributed to harvested flowers was influenced by environmental conditions and method of harvesting. Although flower quality was highly influenced, the harvest index was neither affected by the applied treatments nor by plant density.

Actual levels of dry-matter production as achieved by the existing climate and crop conditions can be evaluated by comparing with the potential one, as simulated with the crop growth model ALSIM(1.0).