The rate of leaf unfolding as a function of temperature was determined for Begonia × hiemalis Fotsch under long-day (16 hours of light) conditions before flower initiation. Irradiance was maintained at 280 ± 20 μmol·m–2·s–1 (16.1 mol·m–2·day–l). The two cultivars Hilda and Ballet had similar rates of leaf unfolding in the range from 13 to 28C. The rate increased to a maximum of 0.116 leaves/day at 21C and then decreased at higher temperature. The following quadratic function (where T is the temperature in °C) was selected to describe initial long-day leaf unfolding rate in B. × hiemalis: leaves/day = -0.2083 + 0.03145 × T – 0.0007631 × T2, (r2 = 0.97). The leaf unfolding response to temperature varied for plants of `Hilda' and `Ballet' during short days (10 hours of light) following the initial long-day period. Plants of `Ballet' continued to unfold leaves at a similar rate as under initial long photoperiods, while the leaf unfolding rate for `Hilda' decreased to half the rate observed under long days.
Meriam G. Karlsson
Meriam Karlsson and Jeffrey Werner
The rate of leaf unfolding for Cyclamen persicum Mill. was determined at 8 to 24 °C. Temperature treatments started 9 weeks from seeding and after 8 weeks all plants were moved to 16 °C. The cultivars Miracle Salmon, Miracle Scarlet, and Miracle White produced leaves at a similar rate. The relationship of (leaves/d) = - 0.01727 - 0.02284 * °C + 0.005238 * (°C)2 - 0.000162 * (°C)3 (R 2 = 0.99) best described the leaf unfolding rate in response to temperature. The maximum leaf unfolding rate was estimated to 0.329 leaves/day at 19.1 °C. Flower buds (2 mm diameter) developed within 60 days from the start of temperature treatments except at 8 °C. Thirty-five additional days at 16 °C were required for cyclamen initially grown at 8 °C for 8 weeks to produce flower buds. Despite similar conditions during bud development, flowering was delayed 14 to 18 days for plants initially grown at 24 °C compared to those grown at 12 to 20 °C. Plants initially at 8 °C did not flower within 70 days at 16 °C. Leaf and flower numbers at first open flower increased as initial temperature increased from 12 to 24 °C while dry weight and height only increased to 20 °C. No correlation between leaf unfolding and rate of flowering or flower number was detected. Recommendations for 20 °C during early cyclamen growth can be expected to support rapid rates of leaf unfolding and development, and large flower numbers.
James E. Faust and Royal D. Heins
* Professor of Horticulture. Abbreviations: LUR, leaf unfolding rate; PPF, photosynthetic photon flux. 1 Graduate Research Assistant. We acknowledge the support of the Michigan Agricultural Experiment Station and Express Seed Co., Oberlin, Ohio
P.R. Fisher and R.D. Heins
A graphical control chart was developed to monitor leaf count of Easter lily (Lilium longiflorum Thunb.) and make temperature recommendations based on predictions of a leaf unfolding rate (LUR) model. The graph allows observed and target leaf count to be compared visually over time. Timing of the visible bud stage, when flower buds are visible externally on the plant, is important to time flowering for the Easter sales period. The optimum LUR and average daily temperature required to achieve a target visible bud date can be read directly from the chart. The approach provides an intuitive method for transferring quantitative models to growers.
John Erwin, Ken Altman, and Fran Esqueda
temperature on leaf unfolding over time. In general, leaf-unfolding rate per day (development rate) increases as average daily temperature increases within a limited temperature range ( Roberts and Summerfield, 1987 ; Vaid and Runkle, 2013 ). There is little
Joaquin A. Chong, Uttara C. Samarakoon, and James E. Faust
not the case during these experiments. Fig. 2. The effects of daily light integral (DLI) on leaf unfolding rate at different levels of the canopy (Level 1 to 5 being highest to lowest) of poinsettia 8 weeks after treatment application for ( A ) Level 1
Jens J. Brondum and Royal D. Heins
Dahlia “Royal Dahlietta Yellow” plants were grown in controlled temperature chambers under 25 different day and night temperature environments ranging from 10°C to 30°C. The day length was 12 hours with an average PPF level of 300 micromolm-2 s-1 at canopy level. Leaf unfolding rate, shoot elongation and flower development rate were determined and models developed. Leaf unfolding rate increased as temperature increased up to 25°C. Stem elongation increased as the difference between day and night temperature increased. Flower initiation was delayed at high (30°C) temperature and flower development rate increased as temperature increased from 10°C to 25°C. Plants are currently being grown under greenhouse conditions to provide data for validating the models.
P.R. Fisher and R.D. Heins
Timing of Easter lily (Lilium longiflorum Thunb.) for sales is complex because the date of Easter and the number of leaves formed on plants before flower bud initiation vary from year to year. A process control chart was developed that uses a leaf unfolding rate model of Easter lily to control development rate towards flowering. The technique allows observed and target leaf count to be tracked on a graph and compared visually over time. The optimum leaf unfolding rate and average temperature can be read directly from the chart without the need for mathematical calculation. The approach provides an intuitive method for transferring quantitative models to growers and can be applied to other management problem areas.
Yaping Si and Royal D. Heins
Sweet pepper (Capsicum annuum `Resistant Giant #4') seedlings were grown in 128-cell plug trays under 16 day/night temperature (DT/NT) regimes from 14 to 26C. In this temperature range, plant stem height, leaf unfolding rate, plant volume, internode length, stem diameter, leaf area, and shoot dry weight were primarily functions of average daily temperature (ADT). Internode length increased as ADT or the difference between day and night temperature (DIF) increased. The root-to-shoot ratio decreased linearly as DT increased and was not significantly affected by NT. Leaves were darker green under positive DIF than negative DIF temperature regimes. Increasing NT from 14 to 26C reduced the node at which the first flower appeared by an average of 1.2 nodes. Percent abortion of the first flower increased as DT increased. Plant quality, as defined by seedling index [(dry weight × stem diameter)/internode length], increased as DIF became more negative.
James E. Brown-Faust and Royal D. Heins
Saintpaulia ionantha `Utah' plants were grown in growth chambers at constant 15, 20, 25, and 30°C temperatures and daily photosynthetic irradiances of 1, 4, 7, and 10 mol1 m-2 day-1 delivered by 23, 92, 161, and 230 μmol m-2 s-1 for 12 hours. Models were developed describing leaf unfolding rate (LUR) and flower development rate (FDR) as a function of temperature and irradiance by recording the dates of leaf unfolding and flower opening over the course of the experiment and then calculating rates using regression. Both LUR and FDR increased as temperature increased from 15 to 25°C and then decreased. Both LUR and FDR increased as irradiance increased from 1 to 4 mol m-2 day-1. Increasing daily irradiance above 4 mol m-2 da y-1 did not significantly increase LUR or FDR. Model validation data are being collected from plants growing under 3 irradiance levels in greenhouses maintained at 15, 20, 25, and 30°C air temperatures.