With gibberellin reduced, other com- pounds in the plant shift according- ly. Research has shown increases in both phytol and the hormone abscis- ic acid following TGR appli- cation . Phytol contrib- utes to chlorophyll
production, which helps explain why treated trees often show im- proved color
and can recov- er from chronic chlorosis. Ele- vated abscisic acid helps trees close their stomata more rapidly during drought, reducing water loss and stress. It also stim- ulates protease inhibitors that en- hance resistance to some pathogens and leaf-feeding insects. And in some cases, paclobutrazol itself can inhibit the growth of fungal pathogens .
Mary Nell Holly: Example of growth control two years after treatment with paclobutrazol.
ment are typically smaller, with chloro- phyll more concentrated in their limited volume. These new leaves also tend to develop thicker waxy cuticles and in- creased trichome (leaf hair) density.
MORPHOLOGICAL CHANGES: WHAT ARBORISTS CAN EXPECT TGRs do more than change growth rates – they also influence leaf and root char- acteristics. Leaves produced after treat-
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