growth suppression and subsequent stunting of poinsettias as well as reduced bract size ( Faust et al., 2001 ; Lewis et al., 2004 ; Niu et al., 2002 ), whereas application of too little PGR may not sufficiently suppress stem elongation. Manipulating the
) applied as a foliar spray or a drench. PGRs are commonly used to prevent excessive poinsettia stem elongation ( Ecke et al. 2004 ). Currey and Lopez (2011) demonstrated that when applied early in the season, PGRs such as triazoles can be effective in
branch number ( Andersen and Andersen, 2000 ). Chemical suppression of stem elongation and increased branching is possible with the use of different types of PGRs. For example, applications of inhibitors of gibberellin synthesis or ethylene generators
often determines the physiological responses of the plant, including its impact on growth ( Galmes et al., 2007 ; Kim et al., 2012 ). Under mild drought stress, plants may acclimate to maintain metabolic functions. Reductions in stem elongation and
, 1976 ). Aside from breeding and controlling environmental factors to regulate stem elongation, PGRs are a common way of manipulating plant growth to achieve the desired shape and size. A major group of PGRs are the anti-gibberellin (GA) growth
postharvest handling ( Karlović et al., 2004 ; Niu et al., 2002 ). Optimal poinsettia height may vary depending on cultivar, intended use, and grower or consumer preference. To control poinsettia height, growers typically use PGRs to suppress stem elongation
Stem length of cut flower roses is one of the primary determinants of the sales price. Thus knowledge of the process of shoot elongation is useful in optimization of rose production. In this study shoot elongation was investigated by continuously logging `Cara Mia' rose shoot length using linear displacement position sensors (LDPS). Under natural conditions, elongation was found to occur mainly at night. The objective of this study was to investigate the role of environmental factors on rose stem elongation and to determine whether the process was related to an endogenous circadian rhythm or the absence of light. Measurements were made under various photoperiodic conditions (0, 8, 10, 12 and 24 hours night) and various temperature regimes. Under alternating light/dark regimes, regardless of photoperiod, shoot elongation rates follow a cyclical pattern with maximum values during dark periods and lower rates during periods of light. The elongation rate declined abruptly with the beginning of the light, suggesting that phytochrome activity might be responsible for this cessation of elongation. Under continuous light and constant temperature, the cyclical behavior was also observed, although the amplitude of the rhythm was smaller than under continuous light.
Abstract
Measurements of tomato (Lycopersicon esculentum Mill.) plant height after ozone fumigation showed that stem elongation was stimulated within the first 3 days after fumigation. The increased height is sustained for at least 10 days and occurs in both ozone-sensitive and ozone-tolerant cultivars and lines.
Wind, touching, and/or mechanical stress can restrict stem elongation. Removal of the registration of the growth retardant daminozide for use on edible crops increased interest in thigmotropic inhibition of stem elongation to control plant height in greenhouse crops, as well as a general desire by growers to decrease chemical inputs for floriculture crops. Since stem elongation varies diurnally, the question arises as to whether wind inhibition of stem elongation varies over a 24-hour period. Tomato (Lycopersicon esculentum) `MoneyMaker' and cosmos (Cosmos bipinnatus) `Imperial Pink' seedlings were placed under each of 10 wind perturbation treatments [applied for different durations and at different times during a 24-hour period; wind speed (perpendicular to the media) at seedling level was 30 km·h–1 (18.6 mph)] for 30 days. Data were collected on plant height and leaf number on days 1 and 30. The effect of wind on stem elongation differed with species; wind treatments restricted stem elongation more on cosmos than tomato (53% and 20%, respectively, across treatments). Tomato elongation was most restricted when seedlings received wind all day, all night, or all day and night. Within short-term treatments, internode length was least when tomato seedlings received a mid-day wind treatment. Cosmos elongation was most restricted when seedlings received a wind treatment all day or all night. Within short-term treatments, cosmos internode elongation was most restricted with early- and mid-day wind treatments. Data here suggest wind effects on elongation vary diurnally. In addition, the magnitude of wind effects on elongation varied with species and was greatest during the beginning of the day on cosmos, which mirrors when stem elongation is most sensitive to temperature fluctuations.
Seedling stem elongation increased as the difference (DIF) between day (DT) and night (NT) temperatures increased from 10 to 26C (DIF=DT-NT). Stem elongation was primarily dependent on DIF on all crops studied except spring bulb crops. Internode lengths decreased in tomato (68%), watermelon (80%), squash (32%), sweet corn (68%) and snap bean (26%) as the difference between day and night temperatures decreased 12 degrees (C). Cucumber internode length decreased by 84% as DIF decreased 16 degrees (C). The ratio of male to female cucumber flowers decreased from 14 to 1, as DIF decreased 12 degrees (C) from 23 DT/17 NT to 17 DT/26 NT. Stem elongation was very sensitive to cool temperatures during the first 3 hours of the morning. Stem elongation was almost the same if the seedlings were cooled for the first 3 hours of the day versus cooling the plants all day. The interactions between temperature on stem elongation and light quantity and quality, and photoperiod will be discussed. Application of DIF in both northern and southern greenhouses will also be discussed.