Keywords: Seedling emergence, air temperature, absolute and relative growth rate., β-carotene, lycopene, metabolic activity.
In order to grow ornamental plants in non-controlled environments, the effect of temperature on seedling emergence and growth must be known in order to optimize plant production. The aim of this research was to compare the growth of statice and viola seedlings, dur¬ing the winter in the Valley of Mexico, under three production conditions: a polyethylene-covered tunnel, shade netting that cuts light transmission by 50 %, and in the open. We measured air temperature (0C), emergence percentage (E%), leaf area (LA) per plant and dry weight biomass (DWB) per plant at 10, 18, 24, 31 and 35 days after planting (dap) in statice seedlings, and at 21, 28, 35, 43 and 52 dap in viola seedlings. In addition, the absolute growth rate (AGR), the relative growth rate (RGR) and the net assimilation rate (NAR) were calculated. Compared to the outdoor treatment (control), The polyethylene tunnel and shade netting produced higher E% values: 95 and 93 % for statice and 97 and 95 % for viola, respectively. Two different sigmoid curves of dry matter accumulation were observed in both species. The polythene tunnel produced higher DWB than the other conditions (P≤0.05) with an average temperature of 19.5 0C and high thermal oscillation, but without frost. In the polyethylene tunnel, maximum DWB, LA and AGR (88 mg∙seedling 1, 15.1 cm2∙seedling 1, and 7.4 mg∙d-1, respectively) were observed at 35 dap in statice and 52 dap in viola (43.6 mg∙seedling 1, 7.6 cm2∙seedling 1 and 2.4 mg∙d-1, respectively) before transplanting. The polythene cover prevented temperatures below 0 0C, which explains the greater seedling growth in this environment.