Abstract
Dormancy in fruit trees is a crucial process that involves many molecular and physiological mechanisms to protect plant organs from abiotic stresses throughout the winter months. This process has become an increasingly important focus of study in light of a changing and more volatile climate. Two plant hormones, abscisic acid (ABA) and ethylene, have been shown to play a role in the regulation of dormancy. Both ABA and ethylene-related compounds have been applied previously to fruit trees to alter the onset and duration of endodormancy, which is the phase of dormancy during which cold hardiness is greatest and buds are protected until a specific number of cold hours are met. We aimed to investigate pear (
Pyrus communis
cv. d’Anjou) endodormancy responses to the application of both compounds simultaneously using S-ABA and 1-aminocyclopropane-1-carboxylic acid (ACC), an ethylene precursor. Treatment initially resulted in earlier leaf abscission relative to untreated trees. Using freeze tests, we found that cold hardiness was generally higher for treated vegetative shoots in the weeks and months after application following an immediate temporary decrease in cold hardiness. Gene expression of an ABA catabolism gene related to
CYP707A
genes was significantly lowered in reproductive buds at two timepoints corresponding to higher cold tolerance of treated vegetative shoots. However, expression of other dormancy-related genes tested was not significantly different between buds of treated and untreated trees on these dates. Overall, this research indicates that pear dormancy and cold hardiness can be at least partially altered by hormone plant growth regulator application.