Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Dormancy in fruit trees is the process by which buds are set, hardened off, and protected during the cold winter months, then released to start growing again in the spring. This consists of multiple phases, including bud set, endodormancy, ecodormancy, and release from dormancy. Endodormancy involves a hardening off of the buds to become cold-hardy, and accumulation of enough chilling hours before they can grow again in the spring. Also during the fall, the leaves on the tree senesce, which includes turning brown and falling off. With the effects of climate change causing more unpredictable seasonal changes, better understanding and control over the onset of dormancy could be very useful for growers. Here we test whether the addition of two plant hormones involved in dormancy, ABA and ACC (a precursor to Ethylene), could induce the onset of endodormancy and improve cold hardiness sooner. We found that cold hardiness was increased in treated trees X weeks after spraying at the coldest temperatures. However, when we looked at gene expression of genes known to be markers of dormancy, we saw few changes between treated and untreated trees at this timepoint.

Technical Abstract: Dormancy in fruit trees is a crucial process involving 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, 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 onset and duration of endodormancy, the phase of dormancy in which cold-hardiness is greatest and buds are protected until a specific number of cold hours are met. We aimed to investigate pear (P. communis cv. 'D’Anjou') endodormancy responses to the application of both compounds simultaneously, using S-ABA and ACC, an ethylene precursor. Treatment initially resulted in earlier leaf senescence 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 CYP707A4 was significantly lowered in reproductive buds at two time points 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 (PGR) application.