A decision-support system for real-time management of Easter lily (Lilium longiflorum Thunb.) scheduling and height--I. System description
Abstract A decision-support system was developed for recommending night and day temperature settings to control the timing and height of Easter lily ( Lilium longiflorum Thunb.). Existing biological models and qualitative rules were combined into an overall model of the response of plant development rate to temperature. A process control algorithm was used to determine appropriate height control actions based on a graphical control chart of plant height over time. A knowledge-based system checked the feasibility of output from the development and height control models and generated a text report. This model was implemented on a personal computer in a program called “The Greenhouse CARE System” and has been linked directly with an environmental computer to control greenhouse temperatures. A companion article describes validation of this model.
Temperature effects on lily development rate and morphology from the visible bud stage until anthesis.
Day (DT) and night temperatures (NT) influenced Lilium longiflorum Thunb. 'Nellie White' stem elongation and development rate from the visible bud stage (VB) until anthesis. Plant height increase after VB was a function of the difference (DIF) between DT and NT (DT-NT). Plant height increased 90% as DIF increased from - 16 to 16C. A cubic model described bud development rate as a function of temperature from 14 to 30C. A linear model adequately described bud development rate as a function of average daily temperature from 14 to 21C. Based on the linear model, bud development rate increased 0.05 per day for each 1C increase in average daily temperature. The base temperature for bud development, i.e., the temperature at which bud development rate was 0, was calculated as 3.5C. Greenhouse forcing of vernalized Easter lilies is commonly divided into three phases: I) placement of vernalized bulbs in the greenhouse to flower initiation, II) flower initiation to VB, and III) VB to anthesis (De Hertogh and Wilkins, 1971). Plant morphological development differs during each of the forcing phases (De Hertogh and Wilkins, 1971). Growth during phase I is vegetative and consists of stem elongation and leaf expan- sion. Flower initiation, leaf expansion, and stem elongation oc- cur during phase II. Inflorescence expansion and stem elongation occur during phase III. Lily responses to temperature during phase III differed from those during phases I and II (Wang and Roberts, 1983). Lily development rate, quantified as days to unfold a leaf, is a de- creasing linear function of average daily temperature between 14 and 30C during phases I and II (Karlsson et al., 1988). Lily development rate during phase III is a nonlinear function of temperature (Healy and Wilkins, 1984). The effect of temper- ature on the rate of lily development decreases as DT and/or NT increase during phase III (Rob and Wilkins, 1973; Healy and Wilkins, 1984). Easter lily morphological development is thermomorpho- genie. For instance, internode length increases as the DIF be- tween DT and NT increases (Erwin et al., 1989). In addition, leaf orientation, leaf length, and flower length are also influ- enced by diurnal changes in temperature.
Inhibition of Root Growth and Polyamine Metabolism in Sunflower (Helianthus annuus) Seedlings Under Cadmium and Copper Stress
Although sunflower is usually regarded as a highly tolerant crop, impairment of root growth at initial stages of plant development may result in poor crop establishment and higher susceptibility to pathogen attack. In order to evaluate if Cd2+ and Cu2+ may impact on sunflower germination and initial root development, a pot experiment under controlled conditions was carried out. Possible involvement of polyamine metabolism in sunflower response to these stressors was also investigated. Although Cd2+ and Cu2+ treatments affect neither seed germination nor radicle emergence, sunflower seedlings grown in the presence of these heavy metals showed significant inhibition of root growth, being this inhibition greater for Cd2+. Both metals caused significant increases in proline contents at the highest concentrations tested (0.5 and 1 mM), and these increments were more pronounced for Cd2+ treatments, especially between days 3 and 10. Metals also increased putrescine (Put) contents at all concentrations assayed from the seventh day onward, causing no variations on this polyamine time-course pattern. Spermine and spermidine contents, however, were increased only by 1 mM Cd2+. Arginine decarboxylase seems to have been the enzyme responsible for Put increases under both metal treatments. This work demonstrates that initial root growth of sunflower seedlings may be significantly impaired in Cd2+ or Cu2+ contaminated soils. It also shows that polyamines are key biological compounds, which are probably involved in signaling pathways triggered under stress environmental conditions.