Influence of some growth retardants on growth, transpiration rate and CO 2 fixation of Caryopteris incana ‘Heavenly Blue’

Abstract

In an experiment between May and October 2011, the effect of growth retardants Alar 85 SP 0.4% and 1%, Bumper 25 EC 0.1% and 1%, Cultar 1% and 2%, Cycocel 0.3% and 1%, Mirage 45 EC 0.2% and 1% was tested on Caryopteris incana ‘Heavenly Blue’ young plants. The young plants were sprayed with the retardants three times during the summer. The influence of these retardants on the transpiration rate, stomatal conductance and net CO2 fixation of leaves was measured by LCi infrared gas analyzing instrument three times: first on the 1st day, second on the 24th day, and third on the 43rd day after the last spraying. The most effective growth retardant was Cultar used in 2% and 1% concentration (that gave the smallest plants), followed by Cycocel and Alar 85 SP; while the effect of Bumper 25 EC and Mirage 45 EC was minimal. The growth retardants affected not only the growth of the plants. They had also some (weak) effect on the transpiration rate, stomatal conductance and net CO2 fixation of leaves. In most cases Cultar 1% and/or 2% and in some cases Mirage 1% showed the lowest values in comparison with all the other treatments, but no statistical correlation was found between their dwarfing effect and the results from LCi measurements.