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Charlotte M. Guimond, Gregory A. Lang, and Preston K. Andrews

To examine the effect of timing and severity of summer pruning on flower bud initiation and vegetative growth, 4-year-old `Bing' cherry trees (Prunus avium L.) were pruned at 31, 34, 37, 38, or 45 days after full bloom (DAFB) with heading cuts 20 cm from the base of current-season lateral shoot growth, or at 38 DAFB by heading current-season lateral shoot growth at 15, 20, 25, or 30 cm from the base of the shoot. The influence of heading cut position between nodes also was examined by cutting at a point (≈20 cm from the shoot base) just above or below a node, or in the middle of an internode. Summer pruning influenced the number of both flower buds and lateral shoots subsequently formed on the shoots. All of the timings and pruning lengths significantly increased the number of both flower buds and lateral shoots, but differences between pruning times were not significant. There was significantly less regrowth when shoots were pruned just below a node or in the center of an internode, rather than just above a node, suggesting that the length of the remaining stub may inhibit regrowth somewhat. The coefficient of determination (r 2) between flower bud number and regrowth ranged from -0.34 to -0.45. In young high-density sweet cherry plantings, summer pruning may be useful for increasing flower bud formation on current-season shoots. The time of pruning, length of the shoots after pruning, and location of the pruning cut can influence subsequent flower bud formation and vegetative regrowth.

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Adam Dale, Angela Sample, and Elizabeth King

Experiments were conducted to determine the chilling temperature and length of time required to break dormancy in red raspberry (Rubus idaeus L.). Five weeks of 7 °C with no light was sufficient to break dormancy in `Autumn Britten', `Nova', `Polana', and `Tulameen', while at least 8 weeks were needed for `Titan'. Comparisons with various chilling unit models allowed a model to be developed that could account for the observed chilling variation. In this model, each chilling hour was weighted as follows: below 5.6 °C = 1; 5.7 to 8.0 °C = 0.5; 8.1 to 11 °C = 0; 11.1 to 13 °C = -0.5; and >13 °C = -1. Plants of `Nova' and `Tulameen' chilled before flower initiation occurred, broke dormancy, and the resulting lateral branches remained vegetative. When the plants were fruited in the greenhouse, we were able to produce a second crop on the fruiting canes when the lateral branches that had fruited were removed. These experiments show that raspberries can be manipulated so that plants chilled in mid-September in the Northern Hemisphere can be induced to fruit by the beginning of January.

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Hans C. Wien

the finding that for many sunflower cultivars, flower primordia are formed within 3 weeks after emergence ( Marc and Palmer, 1981 ; Yanez et al., 2012 ). If sunflower cultivars are sensitive to daylength before flower initiation, it allows a daylength

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Christine Yung-Ting Yen, Terri W. Starman, Yin-Tung Wang, and Genhua Niu

-type dendrobiums, several other dendrobiums also require low temperatures for flower induction. Flower initiation in D. phalaenopsis Fitzg. was induced by low temperature of 13 °C regardless of daylength ( Rotor, 1952 , 1959 ). In nature, the inflorescence of D

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Emily Hoover, S. McArtney, S. Tustin, M. White, and P. Hirst

Experiments were initiated to document the effect of cultivar, GA4+7, and number of fruit/spur on appendage number and flower bud initiation in apple. `Pacific Rose' is strongly biennial, `Braeburn' and `Fuji' are moderately biennial, and `Royal Gala' is not biennial. In the cultivar study, buds were sampled every 18 days starting at 50 days after full bloom and continuing through until leaf fall to determine the rate of appendage formation and appendage number in relation to doming. Because of the tendency for `Pacific Rose' to exhibit biennial bearing, the rate of appendage formation and the timing of doming were compared on nonfruiting trees, trees carrying a commercial crop, and trees sprayed with 300 PPM GA4+7 applied 14 days after full bloom. Number of appendages for the treatments were similar up to 100 days after full bloom. Presence of fruit on a spur has been demonstrated to inhibit flowering of apple. Spurs of `Pacific Rose', `Splendor', and `Royal Gala' were labeled with zero, one, two, and three fruit per spur and sampled three times during the season. As buds were harvested to count appendage number, the number of fruit per spur and the number of total seeds per spur were recorded. Correlation between number of seeds per spur and rate of appendage formation were done.

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Kenneth E. Cockshull and Anton M. Kofranek

Garden chrysanthemums [Dendranthemum ×grandiflorum (Ramat.) Kitamura] are characterized by early flowering in September and October when grown out-of-doors and by rapid flowering in short days (SD). However, as rooted cuttings of these cultivars frequently have flower buds present at the time of planting, their true response to daylength cannot readily be determined. Vegetative shoots were obtained by growing rooted cuttings in long days (LD), removing the terminal bud, and then pinching the emerging side shoots at a very early stage. On transfer to SD, the vegetative secondary side shoots quickly initiated flower buds that developed to anthesis more rapidly than those of `Bright Golden Anne' (BGA), a lo-week response group cultivar. `Bandit', `Buckeye', `Compatriot', `Freedom', `Jackpot', and `Sunburst Cushion' appeared to be in the 7-week response group, with `Baby Tears' in the 6-week and `Powder River' in the 8-week response groups. All cultivars rapidly initiated flower buds in LD and, although they produced significantly more leaves than in SD, flower initiation began within ≈13 LD from pinching. When pinched twice and grown using black cloth in summer, garden chrysanthemums can form attractive, uniformly flowering pot plants. Their rapid-flowering characteristic could also be of value in breeding programs for cut-flower chrysanthemums.

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Melissa Moher, Max Jones, and Youbin Zheng

., 2015 ), day/night temperatures ( Adams et al., 2009 ), and other environmental factors. The overall hypothesis of this study was that cannabis plants grown in vitro will respond to photoperiod by means of flower initiation. Specific objectives included

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Warner Orozco-Obando, Gwen N. Hirsch, and Hazel Y. Wetzstein

The general doctrine of flowering in Hydrangea macrophylla (Thunb.) Ser. is that floral induction occurs during the fall months with the flower appearing the following spring or summer. However, hydrangea cultivars differ widely in their relative abundance and duration of flower production. The objective of this study was to determine how developmental flowering patterns compared among different hydrangea genotypes. Flowering was characterized in 18 cultivars by assessing flower initiation in dormant buds of 1-year-old stems that received natural outdoor inductive conditions. Terminal and lateral buds were dissected and floral developmental stage categorized microscopically. In terminal buds, flower development was very consistent and occurred in 100% of buds for all cultivars except `Ayesha' (33%). In contrast, lateral buds showed a wide variation in flower induction among genotypes. `Ayesha', `Blushing Pink', `Freudenstein', and `Nigra' had 10% or fewer lateral buds with floral initials. `All Summer Beauty', `David Ramsey', `Masja', `Nightingale', and `Penny Mac' showed high levels of floral induction (>92%). Within a cultivar, flower development was more advanced in terminal than lateral buds. In several cultivars, a significant correlation between bud size (length) and floral stage was found. However, low r-square values indicated that flower stage was explained largely due to factors other than bud length. This study shows that floral induction patterns vary markedly among hydrangea cultivars and provides insight into why cultivars differ in the extent and reliability of seasonal blooming. Genotypes that possess floral primordia in lateral buds would be amenable to cultural practices that enhance lateral budbreak and recurrent blooming.

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Martin J. Bukovac, Paolo Sabbatini, and Philip G. Schwallier

The effect of ethephon on flowering and cropping of strongly alternate bearing spur-type `Delicious' apple (Malus domestica Borkh.) was evaluated in a 6-year study. Ethephon (200 mg·L–1), applied at 3, 3 + 6, and 3 + 6 + 9 weeks after full bloom in “on years,” increased flowering in “off years” by 33% and reduced flowering in “on years” by 17% compared with the control. The mean yield per tree for ethephon-treated trees over three “on years” and three “off years” was almost identical to that of the controls (82 vs. 80 kg/tree). However, the distribution of yield between “on” and “off” years was changed, 24% greater in “off years” and 10% less in “on years.” Ethephon reduced both the variation in yield, particularly in “off years,” and the magnitude of alternation. Ethephon had a direct effect on flower initiation because 1) it did not reduce shoot growth or yield in the “on years” (years of ethephon application) and 2) ethephon-treated trees initiated more flowers per kilogram of fruit produced than did the controls. The additional flowers initiated were functional because the amount of fruit produced per unit bloom density did not differ between control and ethephon-treated trees. Harvest maturity indices, namely internal ethylene concentration, firmness, starch index, soluble solids, and color, were not significantly affected, although internal ethylene concentration and starch index tended to be higher in fruit from treated trees.

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Willem J. Steyn, Samuel F. Ungerer, and Karen I. Theron

GA 3 in Israel ( Blumenfeld, 1981 ). In addition, there is concern that GA 3 application may reduce return bloom. A decrease in flower initiation in response to GAs has been reported for various fruit species ( Bangerth, 2006 ; Goldschmidt et al