Modeling poinsettia stock plant canopies and their production of cuttings

Poinsettia (Euphorbia pulcherrima Willd. ex. Klotsch) shoots and cuttings growth and development were measured with three experimental factors to develop a model for the prediction of cutting yield. These factors were: shoot densities (SD) from 43 to 215 shoots m-2, daily light integrals (DLI) from 2.6 to 22.5 mol.m-2.d -1, and harvest intensities (HI) from 2 to 6 cuttings/plant .wk. Shoots on top of the canopy grew and developed at greater rates than shoots lower in the canopy, when SD decreased or DLI increased. However, additional DLI increases above 7.7 mol.m-2.d -1 had little effect on shoots. During the mature phase as DLI increased from 2.6 to 20.9 mol.m-2.d-l cutting yields increased from 2.3 to 5.8 cuttings/plant.wk, total shoots increased from 50 to 83 shoots/plant, and commercial size shoots (CSS), those shoots with 6.2 cm stem length and a leaf with a leaf area of ≥18.2 cm2, increased from 10.3 to 15.9 shoots/plant. CSS were always between 19 and 22% of total shoots, regardless of DLI, and always exceeded cutting yield 3 to 4 fold indicating that cutting yield was limited by incident solar radiation. Harvesting smaller cuttings resulted in more harvested cuttings/plant .wk. Shoot and leaf growth increased with increasing HI, whereas stem growth increased by increasing DLI. In the model shoot growth simulations were limited by available shoots during the scaffold phase and a carrying capacity, based on the cutting accumulation, during the mature phase. The model accumulated nodes on shoots, harvested cuttings, and accumulated cutting yield. This model is a useful tool for cutting producers to understand the effects of their management actions and environmental conditions on stock plant growth and development.