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one or more seed-associated phloem mobile phytohormones in regulation of floral initiation (i.e., the production of meristems of clearly recognizable flower primordia and includes all preceding reactions that are required if flowers are to be initiated

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Scanning electron microscopy was used to examine almond [Prunus dulcis (Mill.) D.A. Webb (syn. Prunus amygdalus Batsch, Amygdalus communis L.)] flower bud development for three cultivars (Nonpareil, Carmel, and Butte) from four California locations (which span the range of almond production in California) for 2 years, and for `Nonpareil' in a single location for a third year. The objectives were to document timing of floral developmental events and to better understand the extent of variation that exists within and among cultivars, locations, and years. Results indicated that the time of floral initiation relative to hull split varied among cultivars. Median time for floral initiation in `Nonpareil' was more than 3 weeks after the onset of hull split. For `Butte' and `Carmel', median time of floral initiation preceded the onset of hull split. Extensive variation in the timing of bud development events within a cultivar was apparent. Timing of developmental events varied among locations, but no patterns emerged consistent with the north to south range which spanned 4°15' latitude and 520 km. Among years, development occurred earliest in 1997, a relatively warm year, and was delayed in 1998 and 1999, relatively cool years. Results indicate an earlier onset of floral initiation than reported in the classical literature on the subject.

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Plants of Leucospermum cv. Red Sunset, a natural hybrid between L. cordifolium (Salisb. ex Knight) Fourcade and L. lineare R. Br., are in the induced state for flower initiation between April 25 and June 20 in South Africa. A gradual loss of the induced state occurs after June and by Oct. 22, plants have returned to the noninduced vegetative state. Heavy shading during summer prevented flower initiation. Defoliation reduced flower dry weight and style number. Shade and late removal of primary inflorescences adversely affected quality of secondary inflorescences.

Open Access

Floral initiation in coffee has been shown to be stimulated by short days in young plants, but the inductive stimulus for mature plants is still not clear. Experiments were conducted to determine whether floral initiation in immature and mature plants is promoted by short photoperiods, and delayed by long photoperiods. In a growth chamber study, 18-month-old coffee (Coffea arabica L. cv. Guatemalan) plants exposed to 8 hr photoperiods developed flower buds after 4 weeks, whereas no floral initiation was observed on the plants exposed to 16 hr photoperiods for ten weeks. Trees growing in the field were illuminated with incandescent light from midnight to 3:00 a.m. from July to December 1989. The control plants received no artificial light during the same time period. Night light interruption delayed flower initiation until the end of December on branches that were fully exposed to the light. On control trees, flower buds started to emerge at the beginning of November. These results indicate that in immature and mature coffee plants floral initiation is stimulated by short days, and delayed by long days.

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Scanning electron microscopy (SEM) and light microscopy (LM) were used to study the transition of meristems from vegetative to floral phase in erect primocane-fruiting (PF) blackberries [Rubus (Tourn.) L. subgenus Rubus] developed at the Univ. of Arkansas. Dormant root cuttings of A-1836 and APF-13 blackberries were dug from the field and planted on 28 Dec. 1996 and 1 Mar. 1997 to produce plants for use in a greenhouse study. In a field study, terminal buds of field-grown A-1836, APF-13, NC194, and summer-fruiting `Arapaho' were sampled on 21 Mar 1997 (before shoot emergence from soil), and then weekly from 14 to 28 May 1997. Flower bud primordia were first observed at five and six nodes of growth in greenhouse-grown A-1836 and APF-13 plants, respectively, 35 to 42 days after root cuttings were planted (DAP). Under field conditions, floral primordia were not observed until 21 May when A-1836 and APF-13 had at least 20 nodes of growth; NC194 did not differentiate floral structures until 10 July. The developmental patterns of the vegetative apical meristem in the PF selections, both field- and greenhouse-grown plants, were similar to those of `Arapaho'. Opening of the terminal flower of the inflorescence occurred 32 to 35 days after floral initiation in APF-13, and 8 to 10 days later on A-1836. Field-grown NC194 bloomed in late August. The first fruits of greenhouse-grown APF-13 were harvested 120 DAP. These findings demonstrate that PF blackberries form flower buds after a short period of vegetative growth.

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Floral initiation (FI) was studied both in greenhouse- and field-grown plants of primocane-fruiting (PF) blackberries recently developed by the Univ. of Arkansas. Root cuttings of A-1836 and APF-13 were dug from the field and planted in a greenhouse on 1 Mar. 1997. NC 194 was included only in the field study. Terminal apices were sampled weekly starting at 0 (just before emergence) nodes of growth on 21 Mar. Floral primordia were first seen at five and six nodes of growth in greenhouse-grown A-1836 and APF-13, respectively, 35-42 days after root cuttings were planted (DAP). Under field conditions, the same event was not observed until 21 May when A-1836 and APF-13 reached at least 20 nodes; NC 194 did not show evidence of floral parts until 10 July. Once FI occurred, floral differentiation proceeded uninterrupted until completion. Blooming occurred 32-35 and 40-45 days after FI in APF-13 and A-1836, respectively; NC 194 bloomed in late August. The first fruits of APF-13 were harvested 120 DAP. These findings demonstrate that PF blackberries form flower buds soon after a short period of vegetative growth. This information should be useful for implementing horticultural practices, such as programming of the harvest date.

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Time of flower bud initiation was determined for nine peach [Prunus persica (L.) Batsch.] cultivars, three in each of three chilling requirement groups (<500 hr, 500-750 hr, and 800-1050 hr below 7.2°C). Based on morphology of the apical dome, the first visible signs of flower bud initiation of all cultivars occurred between 15 July and 8 Aug. 1984, and between 1 and 20 July 1985. The earlier initiation period in 1985 may have been promoted by drought stress. Although significant differences occurred in time of flower bud initiation among chilling requirement groups in both years, they were not consistent from year to year, indicating that chilling requirement is not strongly associated with time of flower bud initiation. The rate of morphological development of flower primordia was not associated with earliness of flower bud initiation. ‘Diamante’, while early in flower bud initiation, showed a slow rate of subsequent flower development. No relationship was found between time of flower initiation and either time of bloom or time of fruit ripening of the cultivars.

Open Access

Abstract

Clerodendrum thomsoniae Balf. plants untreated and treated with a 0.3 mg drench of ancymidol (a-cyclopropyl-a-(4-methoxyphenyl)-5-pyrimidmemethanol) flowered under a 12 hr photoperiod and were mostly vegetative under a 15 hr photoperiod. Initiation of flower parts was 8 days earlier in ancymidol treated than untreated plants. Although ancymidol hastened the initiation of flower parts, untreated plants flowered at nearly the same time as treated ones. The shoot apex remained vegetative and axillary buds flowered in treated and some untreated plants. In untreated plants, flower induction in the axillaries was apparent at 12 days and only sepal and petal primorida were present at 16 days after the initiation of the experiment when the plants were 9 cm tall. In treated plants, induction was apparent 4 days after treatment; flower development was accelerated; and at 16 days all flower parts were differentiating.

Open Access
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Abstract

Recent interest in the production of Rhododendrons as potted plants has raised many questions concerning propagation, dormancy, flower initiation, and general patterns of growth and development. Cathey (1) has shown that general growth habit may be altered to give a more compact plant through the use of Phosphon or by B-nine. He found further that flower initiation could be stimulated after the production of 4-5 flushes of growth instead of the normal 8-9 flushes required under natural conditions, thus making this plant useful as a potted plant. Myhre (3) showed that large applications of phosphate fertilizer increased the number of terminal apices initiating flowers in ‘Cynthia’. In 1920, work in the Netherlands by Luyten and Versluys (2) indicated that leaf and flower initiation occurred early in the growth cycle, May 31 to June 8.

Open Access

Abstract

Histological examinations of forced buds of pecan [Carya illinoensis (Wang.) K. Koch] from mature trees revealed a state of physiological differentiation of pistillate flowers by early August of the year preceding their initiation, thus predisposing them to form pistillate floral primordia. Low temperature exposure was required for pistillate flower initiation. This vernalization requirement was facultative for floral cone development, but absolute for floret formation, and was evident before the onset of rest. Grafting and in vitro bud culture techniques demonstrated that events associated with floral induction are separate from changes in the bud apex induced by cold exposure.

Open Access