Our objective was to systematically quantify the dose response from applications of several basic materials recommended for raising pH in acidic media. A peat (70%)/perlite (30%) medium was mixed with a pre-plant nutrient charge, a wetting agent, and 0, 0.3, 0.6, 0.9, 1.2, or 1.5 kg dolomitic hydrated lime/m3, resulting in a range in initial pH from 3.4 to 6.4. Five rates of flowable dolomitic limestone, five rates of potassium bicarbonate, two rates of potassium hydroxide, a supernatant of calcium hydroxide and a distilled water control were applied as single drenches. The medium was irrigated with distilled water when it dried to 50% container capacity as determined by weight. Media pH and EC of four replicates were tested at 1 day and 1, 2, 3, and 4 weeks after application as a saturated media extract. Flowable limestone and potassium bicarbonate both significantly raised medium pH by up to 2 units compared with the control, depending on concentration. As initial medium pH increased, the effect of the basic chemicals on medium pH decreased. For example, flowable lime applied at 0.5 L·100 L–1 of distilled water increased pH by 2 units at an initial medium pH of 3.4 and by 0.4 units at an initial pH of 6.4. Potassium hydroxide and calcium hydroxide drenches did not significantly raise pH. Potassium bicarbonate was easier to apply than the suspension of flowable limestone, however both chemicals provide practical methods for raising pH of soilless media.
A.J. Bishko and P.R. Fisher
Erin J. Yafuso and Paul R. Fisher
Oxygen supply to the root zone is essential for healthy plant growth, and one technology that can potentially supply additional oxygen is the injection of purified oxygen (oxygenation) into irrigation water. The objective was to evaluate whether oxygenation of irrigation water affected plant growth and substrate dissolved oxygen (DO) levels during mist propagation of unrooted cuttings and subsequent growth in containers. Dissolved oxygen measured at source tanks for ambient tap water (averaging 7.1 mg·L−1) or oxygenated tap water (31.1 mg·L−1) was pumped through fine (69 µm) mist nozzles for propagation of Calibrachoa ×hybrid ‘Aloha Kona Dark Red’ and Lobelia erinus ‘Bella Aqua’. There were no measured differences in root length or root dry mass for Calibrachoa and Lobelia propagated using oxygenated water compared with ambient water because DO of ambient or oxygenated water reached ≈100% oxygen saturation in water (8.7 mg·L−1) after passing through mist nozzles. To evaluate subsequent growth without the effect on DO of fine emitters, rooted cuttings of these two plant species and Pelargonium ×hortorum ‘Patriot Red’ were grown in 10.2-cm diameter pots. The plants were irrigated with either ambient (6.0 mg·L−1) or oxygenated (27.7 mg·L−1) nutrient solutions, delivered by top watering or subirrigation when the substrate dried to ≈45% of container capacity (CC), measured gravimetrically. Oxygenated water did not enhance root or shoot growth compared with ambient water for the three bedding plants. In addition, Pelargonium growth was not enhanced when irrigated at high moisture level (maintained at 80% CC) with oxygenated water compared with ambient water. In container substrate without plants, it was possible to increase DO of the substrate solution by 68% when a high volume of oxygenated water (200% container volume or 850 mL) was applied by top watering because existing substrate solution was displaced. In contrast, when containers were subirrigated at 45% CC, the smaller 180-mL volume of oxygenated water was absorbed by the substrate and did not increase DO compared with ambient water. Overall, irrigating with oxygenated water did not enhance root or plant growth of three bedding plants grown in porous, peat-based substrate. To increase oxygen supply to roots in container production, growers should focus on having adequate air porosity in substrate and avoiding overwatering.
J.R. Fisher and S.T. Nameth
Ajuga reptans L. is an herbaceous ornamental mint grown in borders or as a groundcover, and is commonly propagated vegetatively and by seed. Three hundred and fifty-six A. reptans samples were obtained from growers in Washington, Michigan, Iowa, and Ohio, and screened for alfalfa mosaic virus (AMV), tobacco streak ilarvirus (TSV), cucumber mosaic cucumovirus (CMV), tomato aspermy cucumovirus (TAV), tomato spotted wilt tospovirus (TSWV), impatiens necrotic spot tospovirus (INSV), tobacco mosaic tobamovirus (TMV), potato virus × potexvirus (PVX), and 80 potyviruses, using direct antibody sandwich (DAS) and indirect enzyme-linked immunosorbent assay (ELISA). Viral-associated double-stranded ribonucleic acid (dsRNA) analysis was used to detect an apparent satellite (sat) RNA, and northern hybridization using a digoxigenin (DIG) labeled (S) CARNA-5 cDNA probe was used to confirm the identity of the apparent satRNA. No incidences of TAV, TMV, TSWV, INSV, PVX, or potyviruses were detected. CMV was detected in 11%, AMV in 22.2%, TSV in 3.7%, and mixed infections of CMV and AMV in 1.1% of the samples. SatRNA was detected in 36 A. reptans `Royalty', two `Rainbow', and two `Burgundy Glow' samples by dsRNA analysis, and confirmed by hybridization in 29 `Royalty' and one `Burgundy Glow' samples. Sixteen A. reptans `Royalty' seedlings grown from seed harvested from CMV-infected plants were tested by ELISA for CMV, AMV, and TSV. All were positive for CMV, and two were positive for a mixed infection of CMV and AMV. SatRNA was detected in all 16 seedlings by RT-PCR.
J.R. Fisher and S.G.P. Nameth
Cucumber mosaic virus (CMV) was isolated from the perennial ornamental mint, Ajuga reptans L. `Royalty', using melon aphids (Aphis gossypii Glover). The isolate and its associated satellite RNA (satRNA) were biologically and chemically characterized. The satRNA was cloned and sequenced and is 338 nucleotides long and does not induce lethal necrosis on `Rutgers' tomato (Lycopersicon esculentum Mill.) or severe chlorosis on tobacco (Nicotiana L. spp.). The virus is ≈28 to 30 nm in diameter and reacts to CMV serological subgroup I antibodies. The virus is able to infect `Black Beauty' squash (Cucurbita pepo L.), cucumber (Cucumis sativus L.), and `Howden' pumpkin (Cucurbita pepo) but is not able to infect green bean (Phaseolus vulgaris L.) or cowpea [Vigna unguiculata (L.) Walp. ssp. unguiculata]. The virus is able to efficiently replicate its satRNA in tobacco and `Black Beauty' squash but replication is less efficient in cucumber, based on accumulation of double-stranded satRNA.
J.H. Lieth, P.R. Fisher, and R.D. Heins
A growth function was developed for describing the progression of shoot elongation over time. While existing functions, such as the logistic function or Richards function, can be fitted to most sigmoid data, we observed situations where distinct lag, linear, and saturation phases were observed but not well represented by these traditional functions. A function was developed that explicitly models three phases of growth as a curvilinear (exponential) phase, followed by a linear phase, and terminating in a saturation phase. This function was found to be as flexible as the Richards function and can be used for virtually any sigmoid data. The model behavior was an improvement over the Richards function in cases where distinct transitions between the three growth phases are evident. The model also lends itself well to simulation of growth using the differential equation approximation for the function.
P.R. Fisher, J.H. Lieth, and R.D. Heins
Stem elongation of commercially produced flowering poinsettia (Euphorbia pulcherrima L.) is often sigmoid. However, sigmoid mathematical functions traditionally used for representing plant growth fail to adequately describe poinsettia stem elongation when a shoot has a long vegetative growth period. A model was developed that explicitly described three phases of poinsettia stem elongation: 1) the initial lag phase, where stem length increases approximately exponentially; 2) a period when elongation is linear; and 3) a plateau phase, where elongation rate declines to zero and stem length reaches an asymptotic maximum length. The timing of the plateau phase was linked to flower initiation date. Fit of the resulting model to data from single stem `Freedom' poinsettia grown with different periods between transplant and flower initiation had an R2 of 0.99. Model parameters had clear biological meaning, and the poinsettia model has horticultural application for simulation and graphical tracking of crop height.
P.R. Fisher, J.H. Lieth, and R.D. Heins
The objective was to predict the distribution (mean and variance) of flower opening for an Easter lily (Lilium longiflorum Thunb.) population based on the variability in an earlier phenological stage and the expected average temperature from that state until flowering. The thermal time from the visible bud stage until anthesis was calculated using published data. `Nellie White' grade 8/9 Easter lilies were grown in five research and commercial greenhouse locations during 1995, 1996, and 1997 under a variety of temperature and bulb-cooling regimes. Distributions of visible bud and anthesis were normally distributed for a population growing in a greenhouse with spatially homogenous temperatures. The variance at anthesis was positively correlated with variance at visible bud. The mean and variance at visible bud could therefore be used to predict the distribution of the occurrence of anthesis in the crop. The relationship between bud elongation, harvest, and temperature was also incorporated into the model. After visible bud, flower bud length measurements from a random sample of plants could be used to predict the harvest distribution. A computer decision-support system was developed to package the model for grower use.
P.R. Fisher, J.H. Lieth, and R.D. Heins
A model was developed to quantify the response of Easter lily (`Nellie White') flower bud elongation to average air temperature. Plants were grown in greenhouses set at 15, 18, 21, 24, or 27C after they had reached the visible bud stage. An exponential model fit the data with an R 2 of 0.996. The number of days until open flowering could be predicted using the model because buds consistently opened when they were 16 cm long. The model was validated against data sets of plants grown under constant and varying greenhouse temperatures at three locations, and it was more accurate and mathematically simpler than a previous bud elongation model. Bud length can be used by lily growers to predict the average temperature required to achieve a target flowering date, or the flowering date at a given average temperature. The model can be implemented in a computer decision-support system or in a tool termed a bud development meter.
P.R. Fisher, R.D. Heins, and J.H. Lieth
Stem elongation response to a single foliar application of the growth retardant chlormequat chloride [(2-chloroethyl) trimethylammonium chloride] for poinsettia (Euphorbia pulcherrima Klotz.) was quantified. Growth retardant applications did not affect final leaf count or timing of visible bud, first bract color, or anthesis. There was a statistically significant effect of growth retardant concentration on stem elongation, with a range from 289 ± 15 mm (mean 95% confidence intervals) for the control plants to 236 ± 17 mm at 4000 ppm. The growth-retarding effect during the first day after the application was not significantly different between 500 and 4000 ppm, and concentration primarily affected the duration of growth-retarding activity. A dose response function was incorporated into a three-phase mathematical function of stem elongation of single-stem poinsettia to predict elongation of treated and untreated plants. The model was calibrated using a data set from plants receiving 0, 500, 1000, 1500, 2000, 3000, and 4000 ppm, with a resulting R 2 of 0.99. Validation of the dose response model against an independent data set resulted in an r 2 of 0.99, and predicted final stem length was within 12 mm of observed final length.
Paul R. Fisher, Royal D. Heins, and J. Heinrich Lieth
Stem elongation of poinsettia (Euphorbia pulcherrima Klotz.) was quantified using an approach that explicitly modelled the three phases of a sigmoidal growth curve: 1) an initial lag phase characterized by an exponentially increasing stem length, 2) a phase in which elongation is nearly linear, and 3) a plateau phase in which elongation rate declines as stem length reaches an asymptotic maximum. For each growth phase, suitable mathematical functions were selected for smooth height and slope transitions between phases. The three growth phases were linked to developmental events, particularly flower initiation and the first observation of a visible flower bud. The model was fit to a data set of single-stemmed poinsettia grown with vegetative periods of 13, 26, or 54 days, resulting in excellent conformance (R 2 = 0.99). The model was validated against two independent data sets, and the elongation pattern was similar to that predicted by the model, particularly during the linear and plateau phases. The model was formulated to allow dynamic simulation or adaptation in a graphical control chart. Model parameters in the three-phase function have clear biological meaning. The function is particularly suited to situations in which identification of growth phases in relation to developmental and horticultural variables is an important objective. Further validation under a range of conditions is required before the model can be applied to horticultural situations.