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Grete Waaseth, Roar Moe, Royal D. Heins, and Svein O. Grimstad

Varying photothermal ratios (PTR) were supplied to Salvia ×superba Stapf `Blaukönigin' during pre-inductive vegetative development with the exception of a short germination period under uniform conditions. In addition, both unvernalized plants and plants receiving a saturating vernalization treatment of 6 weeks at 5 °C were given two photosynthetic photon flux (PPF) levels (50 or 200 μmol·m-2·s-1) during subsequent inductive 16-hour long days. There were no effects of PTR treatments during vegetative development on subsequent flowering. However, the higher PPF level during inductive long days significantly accelerated floral evocation in unvernalized plants, lowering the leaf number at flowering. The effect was practically negligent after the vernalization requirement was saturated. In a second experiment, varying periods (4, 7, 10, and 14 days or until anthesis) at a PPF of 200 μmol·m-2·s-1 during 20-hour days were given at the beginning of a long-day treatment, either with or without preceding vernalization treatment. Flowering percentage increased considerably as the period at 200 μmol·m-2·s-1 was extended compared with plants grown at a lower PPF of 50 μmol·m-2·s-1. However, the leaf number on flowering plants was not affected, except in unvernalized plants receiving the highest PPF continuously until anthesis, where leaf number was reduced by almost 50%. We propose that the PPF-dependent flowering is facilitated either by the rate of ongoing assimilation or rapid mobilization of stored carbohydrates at the time of evocation. Abortion of floral primordia under the lower PPF (50 μmol·m-2·s-1) irrespective of vernalization treatment indicates that the assimilate requirement for flower bud development is independent of the mechanism for floral evocation.

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Gilles Galopin, Laurent Crespel, Jean C. Mauget, and Philippe Morel

). The floral transformation sequence consists of three successive phases: 1) floral induction with the formation of the bud composed of eight vegetative preformed primordia (B 1 ); 2) floral evocation with an increase in the size of the meristem and an

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Kitren G. Weis, Stephen M. Southwick, and George C. Martin

Gibberellic acid reduces return bloom in many fruit tree species. Reducing bloom may cut costs of hand thinning apricot, peach and plum fruit. Sprays of 250 ppm GA, during floral bud evocation (June 1993) resulted in bud death and abscission as determined by light microscopy sections in `Patterson' apricot (Prunus armeniaca L). GA treatment in May did not cause observable effects. August treatments, immediately prior to floral initiation, did not impede differentiation. Treatment of `Elegant Lady' peach (Prunus persica [L.] Batsch.) buds with 75-250 ppm GA, in late June, 1993 (evocation phase) did not have any discernable effects in that season with respect to abscission or differentiation. Treated peach buds differentiated simultaneously with untreated buds in early August. The patterns of response to GA treatment imply `windows of opportunity' with respect to effectiveness of GA treatments. The specific response suggests that apricot buds possess differing levels of sensitivity to GA treatment and probably reflect distinct phases in transition to flowering. In August buds were already `determined' and were in a potentially floral state that was irreversible.

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Raymond Kessler and Stan P. Myers

Early development of lateral buds is demonstrated as one of the evocation events in Kalanchoes (Kalanchoe blossfeldiana Poelln.). Lateral buds of `Cactus Candy', `Gelbe Melody', and `Jupiter' that were ≈5 mm long or less showed no signs of a change to the reproductive state after 21 short days. However, larger lateral buds for `Jupiter' did show floral initiation while those of `Cactus Candy' and `Gelbe Melody' did not. Studies of the vascular arrangement indicate the presence of four dorsal and four ventral bundles connecting leaves to the stem. Vascular connections to lateral buds arise from vascular cambium but do not appear to connect to any of the bundles that supply leaves.

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Li-Yun Chen, Chien-Young Chu, and Min-Chang Huang

Experiments were conducted on 6-month-old chinese ixora (Ixora chinensis Lam.) from February 1999 to April 2000. Floral development was studied with scanning electron microscopy (SEM) to determine the flowering sequences. Morphological characters were used to clarify the stages of flowering processes. The time of organogenesis and flowering arrangement was established through field observations. Floral evocation occurred in early September, floral initiation occurred in the middle of September and floral differentiation began in late September. A distinctly convex apex with bracts around the shoulder indicated the beginning of reproductive development. Subsequently, primary inflorescence axes were observed and differentiated into secondary, tertiary, and quaternary inflorescence axes consecutively in about one and a half months. Once the terminal apex reached the inflorescence bud stage, it would flower without abortion, and this may be assessed as no return. The sepals, petals, stamens, and pistil were well developed thereafter and anthesis was achieved in January through March in the following year. The observation of floral differentiation sequences and investigation of floret arrangement made it certain that chinese ixora had cymose inflorescence (cyme), but not corymb. A quadratic equation was established to predict floret number from the differentiation level (a quantitative description of differentiation stage) of a developed inflorescence.

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Richard L. Harkess and Robert E. Lyons

Histological and histochemical examination of floral initiation was conducted to determine the pattern of flowering in Rudbeckia hirta, a long-day (LD) plant. Plants were grown under 8-hour short days (SDs) until they had 14 to 16 expanded leaves. Half of the group of plants was moved to LD conditions consisting of natural daylength plus a 4-hour night interruption. Rudbeckia hirta had a pattern of differentiation in flowering similar to that reported in species requiring one inductive day for initiation. Rudbeckia hirta required 8 LDs for evocation and 18 LDs for completion of initiation. Involucral bracts initiated after 18 LDs, after which the receptacle enlarged and was capped by a meristematic mantle of cells signaling the start of development. Floret primordia did not initiate, even after 20 LDs. Increases in pyronin staining were observed in actively dividing cells of the procambium, leaf primordium, and corpus of the vegetative meristems. After 8 LDs, the pith rib meristem stained darkly, a result indicating the arrival of the floral stimulus. An increase in pyronin staining was also observed in the meristematic mantle covering the receptacle after 18 LDs, a result indicating increased RNA levels.

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Bruce W. Wood

ethylene modulates this balance. Conclusions Findings here support the theory that the autonomous floral pathway dominates floral initiation process acting between floral induction (i.e., processes required for evocation) and vernalization (inductive

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Bruce W. Wood

., 2004 ; Worley 1979a , 1979b ). For example, sugars appear to be major regulators of floral genes involved in certain vernalization and subsequent floral initiation and evocation processes ( Wetzstein and Sparks, 1983 ; Wood, 1989 , 1995 ). This

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Yi-Lu Jiang, Yuan-Yin Liao, Tzong-Shyan Lin, Ching-Lung Lee, Chung-Ruey Yen, and Wen-Ju Yang

related to floral initiation, including sodium naphthalene acetic acid, ethephon (Ethrel TM ), ethephon with urea, a commercial mixture of gibberellins (GA 4 and GA 7 ) with benzyl adenine known as Perlan TM , paclobutrazol, hydrogen cyanamide, 2-ethylene

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Charles L. Rohwer and Royal D. Heins

initiation, evocation, or development under LD ( Tables 1 , 2 , and 4 ). Plants given 6 weeks of 10-h prevernalization SD flowered 4 d faster than plants given 11-h SD ( Table 2 ). These data show that subsequent forcing time may be reduced by extended