Search Results
The objective was to develop a Thermal Units model to be used as a timing tool for two cultivars of Asiatic lilies: `Butter Pixie' and `Horizon'. Two-hundred-eighty-six plants of each cultivar were evaluated over a 2.5-year period. Environmental data were collected using thermocouples and data-loggers. Developmental events observed daily were: shoot visible out of the soil (VS), visible flower bud (VB), and open flower (OF). Rates of development (the inverse of the numbers of days to complete a given phenophase) increased with temperature up to a point. Thereafter, as temperature continued to increase, rate of development either slowed or declined. A piece-wise linear regression change point model was fitted to each data-set using S+ statistical package. This allowed the determination of the base temperature (Tb), optimal temperature (To), and the point of inflection (Ti). Tbs for the phenophase VS:OF of `Butter Pixie' and `Horizon' were – 0.4 °C and 3.0 °C, respectively. The resulting discontinuity of data prompted improvements in the thermal unit calculation formula. Using the new formula, thermal units were calculated. 1,102 °Cd and 833 °Cd had to be accumulated to complete the phenophase VS:OF for `Butter Pixie' and `Horizon', respectively. Predicted date of events were calculated and compared with the observed values. Subdividing the phenophase VS:OF into two (VS:VB and VB:OF) and using their respective Tbs and thermal units requirements reduced the error of prediction to 1.87 d from 2.13 d for `Butter Pixie' and to 1.86 d from 2.39 d for `Horizon'.
Bedding plants and many vegetable crop seeds are often sown in plug trays. Some crops, like marigold (Tagetes sp. L.), tend to stretch early after germination, especially if grown in low light environments. By the time growers apply plant growth regulators (PGRs), stretching of the hypocotyl has already occurred and seedling applications are ineffective. Seedling height may be controlled by applying the plant growth regulator directly to the seed. Seeds of `Bonanza Gold' marigold (Tagetes patula L.), `Cherry Orbit' geranium (Pelargonium {XtimesX} hortorum L.H. Bailey), and `Sun 6108' tomato (Lycopersicon esculentum Mill.) were soaked for 6, 16, or 24 hours in paclobutrazol solutions of 0, 500, or 1000 mg·L-1. After the soak treatment, seeds were dried for 24 hours prior to laboratory germination testing or sowing in plug trays. Percentage of emergence and seedling height were measured 16, 26, and 36 days after sowing. Laboratory germination of treated seeds was less than that of the control, which was attributed to the PGR being concentrated around the seed on the blotters. In contrast, seedling survival was unaffected in plugs. The higher concentration of PGR and longer times of soaking increased growth regulation, but also inhibited emergence of geraniums (71% vs. 99%). When seeds were imbibed 6, 16, or 24 hours, growth restriction was 31%, 31%, and 40%, respectively, for tomato, 61%, 37%, and 76%, respectively, for geranium and 30%, 38%, and 41%, respectively, for marigold. These results indicate that PGR application to geranium, marigold, and tomato seeds may be feasible using a 6- or 16-hour soak in 500 mg·L-1 paclobutrazol. Chemical name used: (±)-(R *,R *)-ß-[(4-chlorophenyl)methyl]-{XsalphaX}-(1,1-dimethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Some transplanted crops, like tomato and marigolds, tend to stretch very early after germination, especially if grown in low light environments. By the time growers apply growth regulators (PGRs), the stretching of the hypocotyl has already occurred and sprays are ineffective. Seeds of marigold `Bonanza Gold' and tomato `Sun 6108' were soaked for 6, 16, and 24 h in paclobutrazol solutions of 0, 500, and 1000 ppm. After imbibition, seeds were dried for 24 h before sowing in plugs. Sixteen, 26, and 36 days after sowing, seedling height and percent emergence were measured. Increasing concentrations of PGR and time of imbibition produced shorter seedlings. Tomato seedling heights measured 36 days after sowing were 1.9, 1.5, and 1.7 cm when imbibed in water for 6, 16, and 24 h, respectively. When PGR was used at 500 ppm, seedling heights were: 1.4, 1.2, and 1.2 cm, respectively. Similar reductions were observed for marigolds. It was hypothesized that some seeds have coats that are impermeable to PGRs. These impermeable coats might serve as PGR carriers, delivering the chemical into the growing medium of the plug cell. When the root emerges from the seed, it absorbs the growth regulator. These preliminary results indicate that this method of PGR application may be feasible and could benefit plug growers of marigold and other ornamental plant species prone to early stretching (e.g., cosmos).
Temperature effects the rate of development of Lilium (Asiatic hybrid). The long-term objective is to evaluate thermal units as a tool for crop timing. The objective of this work was to determine Lilium base temperature (Tb). One-hundred-ninety plants of two cultivars (`Butter Pixie' and `Horizon') were used. Phenological observations were made on plants during six plantings over a 2-year period. Developmental stages observed were: shoot visible out of the soil (SV), visible flower bud (BV), and open flower (OF). The two cultivars were grown in four different greenhouse compartments with settings at 13, 18, 24 and 27°C, respectively. During periods of extreme outdoor temperatures, actual temperature deviated from the settings. Actual temperatures were constantly monitored with copper-constantan thermocouples and stored in a datalogger. Rates of development were calculated as the inverse of the numbers of days to complete a given phenological phase. Tb values were obtained by calculating the x-interception of the linear regression describing rate of development as a function of mean air temperatures. Tb for `Butter Pixie' and `Horizon' for the entire growth cycle (SV through OF) were 0.4°C and 2.0°C respectively. The production cycle can be divided into two phases: SV–BV and BV–OF. For `Horizon', Tb for these phases were 1.4 and 1.9°C respectively. For `Butter Pixie', these Tb were 2.4 and –1.0, respectively. More observations of development at mean temperatures higher than 27°C and lower than 13°C are necessary in order to increase confidence on the obtained Tbs.
Temperature affects the rate of rose shoot development. In this study heat units were used to quantify “physiological age”. The objective was to determine whether rose shoots require the same number of heat units to reach various stages regardless of climatic conditions. The dates of occurrence of “bud break” (BB), unfolding of each leaf, “visible flower bud” (VFB), and harvest (H) were observed for 126 shoots of 'Cara Mia' roses growing under 5 different temperature and light regimes. Average air temperature (T) and photosynthetic photon flux density (PPFD) levels were recorded hourly. Heat units, defined as the sum of the difference T-Tb (units: °C hr-1) where Tb is the base temperature, were found to be a suitable for tracking most phases of rose crop development. The duration of the phase from H to BB showed considerable variation and thus could not be predicted this way. The duration from BB to VFB or H could be predicted reasonably well to occur at 5900 ± 670 and 12300 ± 1000 °C hr-1 (Mean ± Std. dev.), respectively, assuming Tb =6 °C. The occurrence of unfolding of each leaf can be predicted similarly. PPFD integrals had no significant effect on any development rates.
The main objective of this project was to develop a crop simulation model for greenhouse cut flower roses. An intermediate step towards the completion of that objective is the building of a model for the growth and development of a collection of shoots of various ages throughout the canopy. The canopy is represented as ten 20 cm thick layers. The shoot and leaves (age and location) are tracked as they grow into and through these layers using a model developed previously. Leaf area (LA) and leaf area index (LAI) for each layer is computed. A light distribution submodel, based on cumulative LAI, estimates the amount of radiation intercepted by each leaf. It is assumed that multiple shoots originating the same day from the same layer are identical. The model also simulates the effect of harvest of the shoots in the canopy. Currently, work is proceeding on data collection for prediction of carbohydrate partitioning within the canopy. Future work will focus on model validation.
`Butter Pixie' and `Horizon' Asiatic lilies (Lilium spp.), were grown at several temperatures. The phenological events of visible shoot (VS), visible flower bud (VB), and open flower (OF) were recorded daily. Based on these events, phenophases from VS to VB (VS:VB), from VB to OF (VB:OF), and from VS to OF (VS:OF) were defined. Daily rates of development to complete a phenophase increased with temperature. Nonlinearity was obvious for all phenophases around 25 °C for `Horizon' and 27 °C for `Butter Pixie'. A piece-wise linear regression change point model was fitted to each dataset. The base temperature (Tb), the temperature at which the nonlinearity occurred (Ti), and the temperature for fastest development (To) could then be determined. Tb for the phenophase VS: OF was -0.4 °C for `Butter Pixie' and 3.0 °C for `Horizon'. Ti for `Butter Pixie' was 25.7 °C for VB:OF and 26.1 °C for the phenophase VS:OF. However, Ti for `Horizon' was found only for the phenophase VS:OF. To complete the phenophase VS:OF, 1102.2 degree days (°Cd) were predicted necessary for `Butter Pixie' and 833.2 °Cd for `Horizon'. Predicted time of events was compared with observed values. Subdividing VS:OF into VS:VB and VB:OF and using their respective Tb and TU reduced the average prediction error from 2.13 to 1.87 d for `Butter Pixie' and from 2.39 to 1.86 days for `Horizon'.
Temperature effects on the rate of flowering rose shoot development were previously modeled using a thermal units (heat units) approach. The current objective was to validate this model for three rose cultivars and to determine its suitability for use in rose production. Flowering shoots of `Cara Mia', `Royalty', and `Sonia' plants, grown in greenhouses at three temperature settings, were observed daily to determine when each of the following developmental events occurred: “harvest”, “bud break”, “unfolding of each leaf”, “visible flower bud”, and “shoot ready for harvest”. Each stage was defined to facilitate accurate, repeatable observations. Average hourly air temperatures were used in computing the accumulated thermal units (TU) required for shoots to develop from from one stage to the next. The base temperature (used in the TU computation) did not differ significantly among the cultivars; the value of 5.2C was used. Using these to predict the days on which the shoot was ready for harvest resulted in ±2 day accuracy for most shoots of `Royalty' and `Sonia' and ±2.5 days accuracy for most `Cara Mia' shoots. This indicates that this method is suitable for timing of rose crops and deciding on temperature set-points.
Cut-flower production of three snapdragon (Antirrhinum majus L.) cultivars (`Potomac Pink', `Winter White', and `Potomac Light Pink') in growing trays vs. ground beds was evaluated in five different plantings over a period of a year and a half. The experiments evaluated the quality of cut flowers from plants in ground beds or in small vs. large trays either raised or placed directly on the ground bed. The quality of flowering shoots was lower when plants were grown in raised trays rather than in on-ground trays or in ground beds, but other treatments did not affect quality consistently. Flowering shoot grade (a subjective quality indicator) correlated well (r = 0.8) with the ratio of shoot dryweight to shoot length (an objective quality indicator). Our results confirm that the flower quality of snapdragons grown on ground trays can equal that of those grown in ground beds.
Abstract
‘Cara Mia’ rose (Rosa hybrida L.) leaf net photosynthesis rates were measured at four leaf temperatures over a range of irradiance levels. With the four leaf ages measured, a non-rectangular hyperbola with physiologically meaningful parameters was found to adequately represent the photosynthetically active radiation (PAR) responses. Maximal net photosynthetic rates exhibited a convex pattern with temperature with an optimum between 30 and 37C. The PAR compensation and saturation points both increased with temperature.