S06 - Session O1 - Optimizing photosynthetic activity of high-wire cucumber production systems using a functional-structural plant modelling approach.

Authors: Gerhard Buck-Sorlin *, Pierre-Emmanuel Bournet, Landry Rossdeutsch, Vincent Truffault

High-wire cucumber production systems are increasingly being employed in French commercial greenhouses at the expense of classical V-shape systems. This technique offers the advantage of optimizing the architecture of plants for photosynthesis while allowing high plant densities. Nevertheless, the functioning of high-wire systems is still not well-known, in particular with respect to photosynthetic activity. In this prospect, an experimental study was conducted over a full year with two 5-month crops inside a 312 m 2 heated glasshouse compartment. Fruits were harvested five times a week. Performance indicators were established from the collected data. The photosynthetic contribution of each leaf stage was quantified using a measurement chamber, and the leaf with the most important photosynthetic potential (defined as reference leaf) was identified. Second, pairs of values both for the light intensity and CO 2 concentration were applied to the reference leaf, making it possible to assess the setpoints to be considered for optimizing biomass generation. In order to integrate experimental data and expert knowledge, a functional-structural plant model (FSPM) was implemented. The model is able to simulate the dynamics of 3D plant architecture development, light penetration into the canopy, photosynthetic activity at leaf level, as well as fruit production. It was first used to estimate the plant response to a range of light intensities and CO 2 concentrations in terms of photosynthetic activity and compared with experimental data. In a next step, the model was extended to calculate the central carbon pool dynamics and fruit dry weight evolution over a production season. The average fresh fruit weight could also be estimated and compared with measured values. High-wire production appears to be a promising production mode compared with classical V-shape systems. The harvest is enhanced and the fruit quality is increased. FSPM can be a suitable approach to improve the management of such a system.