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Hadi Susilo, Ying-Chun Peng, and Yao-Chien Alex Chang

for inflorescence development. Vegetatively propagated plants of the white, large-flowered Phalaenopsis Sogo Yukidian ‘V3’ in 10.5-cm pots with five or six leaves were used. The experiment was conducted over a period of 18 weeks. The 15 N

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James E. Faust and Royal D. Heins

The effects of temperature and irradiance on flower initiation and development were quantified to provide a basis for an inflorescence development model. The percentage of leaf axils forming an inflorescence increased as the daily integrated PPF increased from 1 to 4 mol m-2 d-1, while the rate of inflorescence development was a linear function of temperature from 18 to 26C. The appearance of a visible flower bud in the leaf axil was correlated with leaf blade length of the subtending leaf. Mathematical functions were used to describe leaf blade length at the time of visible flower bud as a function of temperature and irradiance, and also to describe the influence of temperature on the rate of leaf extension. The time of visible flower bud in the leaf axil was then predicted by measuring the current length of the subtending leaf blade and estimating the time required for the leaf blade to extend to the length required for visible flower bud appearance. A phasic development scale was used to describe the developmental status of an inflorescence from visible flower bud to anthesis. A model was then created which predicted time to anthesis based upon temperature and the current stage of inflorescence development.

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Hadi Susilo and Yao-Chien Alex Chang

( Susilo et al., 2014 ). We hypothesize that reducing fertilizer level during the forcing period would increase the contribution of previously stored N to inflorescence development. To our knowledge there is no conclusive evidence to support this hypothesis

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James E. Faust and Royal D. Heins

The effects of temperature and daily-integrated photosynthetic photon flux (PPFDI) on African violet (Saintpaulia ionantha Wendl.) flower initiation and development were quantified to provide the basis for an inflorescence development model. The percentage of leaf axils in which an inflorescence initiated and continued development increased as the PPFDI increased from 1 to 4 mol·m-2·day-1, while the rate of inflorescence development was a function of the average daily temperature (ADT). The appearance of a visible flower bud (VB) in a leaf axil was related to the growth of the subtending leaf blade. A polynomial model based on ADT and PPFDI was used to describe leaf blade length at visible bud (LBLVB). A nonlinear model was used to describe the influence of ADT on leaf expansion rate (LER). Inflorescence appearance in the leaf axil was predicted by measuring LBL and estimating the time for the leaf blade to develop to the length required for VB. A phasic-development scale was developed to quantify inflorescence development. Days required for an inflorescence to develop from VB to first open flower was described as a function of ADT and either inflorescence height or inflorescence development stage (IDS). Days from leaf emergence to first open flower for the inflorescence initiated in that leaf axil decreased from 86 to 55 as ADT increased from 18 to 26C.

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Mark Roh*

The effect of bulb storage and forcing temperatures on growth, flowering, and inflorescence development and the death of inflorescence (blast) of Lachenalia aloides Engl., `Pearsonii' was investigated. Following development of about 5 florets, bulbs were stored at 10, 12.5, 15, 20, and 25 °C for 15, 30, or 45 days and forced in greenhouses at 17/15 °C and 21/19 °C. Flowering was accelerated, and leaf length and floret number were reduced, when bulbs were stored at 10, 12.5, or 15 °C for 45 days compared to storing at 20 or 25 °C. Flowering was further accelerated by forcing at 17/15 °C compared to 21/19 °C. When bulbs were stored at 10, 15, 20, or 25 °C for 4 weeks and grown in greenhouses at 17/15 °C, 21/19 °C, 25/23 °C, and 29/27 °C, the incidence of inflorescence blast was increased when bulbs were stored at 10 and 15 °C and forced at 25/23 °C compared to low temperatures. Bulbs were forced in greenhouses maintained at 18/16 °C, 22/20 °C, or 26/24 °C for 12 weeks. During forcing, plants were subjected to constant or alternating forcing temperatures at 4-week intervals. Inflorescence blast occurred when the temperature was 26/24°C during the first 4 weeks after potting. Storing Lachenalia bulbs at 10&#176 to 15 °C before potting then forcing at 17/15 °C accelerated flowering and produced quality plants with short leaves and floral stems. Inflorescence development during bulb 10 °C treatment and inflorescence blast that occurred after only 3 days of 35 °C was demonstrated using scanning electron microscopy and magnetic resonance imaging techniques.

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Norberto Maciel and Richard Criley

The colorful and pendulous inflorescence of Heliconia rostrata Ruiz & Pavon terminates an erect and herbaceous-musoid axis of a sympodial rhizome system. Each hapoxanthic axis bears a variable number of leaves (5 to 10) subtending the inflorescence. The number depends on the time between shoot emergence and flowering stimulus. Inflorescence initiation and development occurs without external evidence of this process until the inflorescence emerges from the pseudostem. The morphological changes occurring at the terminal shoot apex of the H. rostrata as it changes from vegetative to the flowering stage are described and illustrated by photomicrographs in this paper. The anatomical sections reveal that the apex on vegetative phase is domed, and a maximum of four furled leaves including one leaf primordium can be observed surrounding it. The growth of the leaf primordium is highly synchronized with growth of the most recently formed leaves. With the transition to inflorescence development, more primordia are observed on the apex, which ultimately give rise to the bracts. Except for the first sterile bract, a cincinnus primordium (flower cluster) is detectable in the axil when the next bract begins to develop. Flower differentiation on the cincinnus begins when many bracts are well-developed. The increase of longitudinal height on the internodes is among the first detectable morphological changes in the apex. Under inductive conditions, the transition to the reproductive stage is achieved early in plants with three or more unfurled leaves. The reproductive plant status is easier to detect under the microscope when the inflorescence has at least three bracts.

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Zehuang Zhang, Qihua Lin, and Qiuzhen Zhong

expressions of ‘Fugong-1’ at three different phases of inflorescence development, the smallest of which was WT1 vs. WT2 at 689 and WT2 vs. WT3 at 715 ( Table 1 ). The MT1 vs. MT2 was 707, which was similar to the number of different expressions at the

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Samuel Salazar-García, Elizabeth M. Lord, and Carol J. Lovatt

The developmental stage at which the shoot primary axis meristem (PAM) of the `Hass' avocado (Persea americana Mill.) is committed to flowering was determined. Three-year-old trees were subjected to low-temperature (LT) treatments at 10/7 °C day/night with a 10-h photoperiod for 1 to 4 weeks followed by 25/20 °C day/night at the same photoperiod. Before LT treatment, apical buds of mature vegetative shoots consisted of a convex PAM with two lateral secondary axis inflorescence meristems lacking apical bracts each associated with an inflorescence bract. Apical buds did not change anatomically during LT treatment. However, the 3- and 4-week LT treatments resulted in inflorescences at 17% and 83% of apical buds, respectively. Trees receiving 2 weeks or less LT, including controls maintained at 25/20 °C, produced only vegetative shoots. Apical buds of 2-year-old trees receiving 3 weeks at 10/7 °C plus 1 week at 20/15 °C produced 100% inflorescences. GA3(100 mg·L-1) applied to buds 2 or 4 weeks after initiation of this LT treatment did not reduce the number of inflorescences that developed. `Hass' avocado apical buds were fully committed to flowering after 4 weeks of LT, but were not distinguishable anatomically from those that were not committed to flowering.

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Thomas Bjorkman and Karen Pearson

Production of broccoli in areas where summer temperatures exceed 30C is difficult because the head may not form properly. The high temperature causes an unevenness in the head due to widely differing sizes of buds. The sensitive stage of development was determined for the early maturing variety `Galaxy' by exposing it to 1-week at 36C at varying developmental stages, and subsequently analyzing the head structure. The injury is a cessation of bud enlargement during the high-temperature exposure. There is no corresponding cessation of bud initiation at the apex. The patter of injury is consistent with susceptibility over a relatively small range of bud development: even with a 1-week exposure, only about 1/3 of the buds will be affected. The plant's most developmental stage at this sensitive period still appears vegetative, but the youngest leaves are just beginning to reorient as a consequence of the reduced stem elongation rate. The meristem is less than 1 mm wide, and scanning electron micrographs show floral primordia just forming, still subtended by leaf primordia. The injury is fully expressed when the head is first exposed (≈10 mm wide), though it becomes more apparent as the head matures. The buds that were delayed in development by the high temperature developed into fertile flowers, albeit about a week late.

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Samuel Salazar-García, Elizabeth M. Lord, and Carol J. Lovatt

Inflorescence and flower development of the `Hass' avocado (Persea americana Mill.) were investigated at the macro- and microscopic level with three objectives: 1) to determine the time of transition from vegetative to reproductive growth; 2) to develop a visual scale correlating external inflorescence and flower development with the time and pattern of organogenesis; and 3) to quantify the effect of high (“on”) and low (“off”) yields on the flowering process. Apical buds (or expanding inflorescences) borne on summer shoots were collected weekly from July to August during an “on” and “off” crop year. Collected samples were externally described and microscopically analyzed. The transition from vegetative to reproductive condition probably occurred from the end of July through August (end of shoot expansion). During this transition the primary axis meristem changed shape from convex to flat to convex. These events were followed by the initiation of additional bracts and their associated secondary axis inflorescence meristems. A period of dormancy was not a prerequisite for inflorescence development. Continued production of secondary axis inflorescence meristems was observed from August to October, followed by anthesis seven months later. In all, eleven visual stages of bud development were distinguished and correlated with organogenesis to create a scale that can be used to predict specific stages of inflorescence and flower development. Inflorescence development was correlated with minimum temperature ≤15 °C, whereas yield had little effect on the timing of developmental events of individual inflorescence buds. However, the high yield of the “on” year reduced inflorescence number and increased the number of vegetative shoots. No determinate inflorescences were produced during the “on” year. For the “off” year, 3% and 42% of shoots produced determinate and indeterminate inflorescences, respectively.