Arboriculture & Urban Forestry 42(1): January 2016 specialize in commercial production usually apply concentrations from 50 mg·L-1 to 5000 mg·L-1 , once or twice at one to two week intervals (Carey 2008). THE FUTURE OF CYTOKININS IN ARBORICULTURE AND HORTI- CULTURE Potential uses for cytokinin phytohormones in- clude: to decelerate senescence and to promote growth and bud formation, to improve graſt- ing results, to be used as branching agents, and to improve branching angles (Mok 1994). Regulating Reproductive Phase Change, Senescence, and Dormancy The phytohormone gibberellic acid (GA) is as- sociated with phase change to reproductive competency, and ethylene is associated with various forms of plant tissue senescence. Cytoki- nins mixed with anti-GAs may have synergistic effects on branching (Werbrouk et al. 1996), and cytokinin combined with anti-ethylene prod- ucts may have synergistic effects on preventing senescence and promoting continued growth. Not only are the degradation processes that accompany senescence delayed by exogenous application of cytokinin, but in some instances there is a genuine reversal in phase change that marks rejuvenation (Moore 1998). Several researchers have successively used exogenous cytokinins to induce rejuvenation in plants with success in pines (Zhang et al. 2003; Carey 2008) and spruce (Day and Greenwood 2011). Cytokinins in conjunction with a reduc- tion in nutrient levels may control height, as cytokinins can help prevent leaf yellowing or senescence that occur with nutrient deficiency (Funnell and Heins 1998; Banko and Stefani 2008). Cytokinin applications may be useful for high-chill crops grown in low-chill areas. Cytokinins applied during the early stages of winter dormancy or in the late stages of dor- mancy can induce plants to be released from dormancy earlier (Cline et al. 2006). This is currently done for fruit crops, such as apple, plum, and peach (Alvarado-Raya et al. 2000). The influence of cytokinins on bud num- ber and activation offers promise as a means of regulating flowering. BA increases the number 9 of buds that form, and when managed properly with subsequent application of the flowering pro- moting phytohormone gibberellic acid, growers may increase the number of flower buds. BA + GA mixes have also been used to thin the flowers on apples to avoid uneven fruit yield. In the lat- ter case, the phytohormone mixture is sprayed on flowering trees in heavy flower years to cause flow- ers to drop off (Western Plant Growth Regulator Society 2000). The effect of cytokinins on flower- ing have been studied in numerous other plants; however, the results are inconsistent (Carey 2008). Improving Grafting Results Since cytokinins are involved in cellular differen- tiation and xylem formation, graſts treated with cytokinins potentially survive at a higher percent- age or close more quickly (Valdés and Fernández 2004). Exogenous cytokinins induce phloem re- generation and callus formation in coleus wounds, cause graſts to close faster, and cause root stocks to move more nutrients to scions (Valdé and Fernán- dez 2004). Cytokinins have also improved graſt success in spruce (Picea spp.), improved scion bud sprouting in some citrus, and improved graſt suc- cess in in vitro graſt experiments (Meier et al. 2012). However, Hartmann et al. (2001) and Werner et al. (2003) caution that cytokinins do not provide uni- form results in promoting successful graſts because phytohormone levels vary for each plant species as well as the type of cytokinins used and their timing. For example, rose graſts tended to sucker below the graſt union more when treated with cytokinins. In plant propagation, the best-known and most far-reaching use of cytokinins at the moment is as a component of these techniques are not directly associated with regulating crown development, tissue culture media. While this applica- tion has widespread implications for tree breed- ing and production programs (Moore 1998). Branching Agent Plants that normally produce few branches during production can be encouraged to branch with cy- tokinins. Many plants have to be manually pinched, pruned, sheared, or disbudded during production in order to stimulate branching. This is a time- consuming and therefore expensive procedure. In woody plants, cytokinins have been studied as a ©2016 International Society of Arboriculture
January 2016
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
