The impacts of simulated heatwaves on the induction and maintenance of bud cold tolerance in cultivated and wild-type Vitis species

Abstract

Low temperatures are required for the acquisition and maintenance of bud cold tolerance, which are necessary for grapevines to survive freezing temperatures in winter. Heatwaves during cold acclimation could undermine the induction and maintenance of bud cold tolerance, but this was untested. Over two studies, we explored how simulated heatwaves applied during grapevine cold acclimation impacted bud gene expression, metabolites, and cold tolerance during and after heat exposure in addition to phenology the following spring. In Study 1, we evaluated the impacts of heat on a cultivated grapevine, Vitis vinifera cv. Cabernet Franc, and in Study 2, between a cold-sensitive grapevine species (V. vinifera cv. Cabernet Franc) and a cold-tolerant wild grapevine species (V. riparia).

Each study was conducted at The Pennsylvania State University in Pennsylvania, USA, a cool-climate region, and was a 2×2 factorial design performed on young, potted grapevines. Four treatments were evaluated in Study 1: 1) “Early Heat,” a 10-day heatwave at approximately 5 °C above ambient temperatures in September, 2) “Late Heat,” a seven-day heatwave at approximately 10 °C above ambient temperatures in November-December, and 3) “Early + Late Heat” both September and November-December heatwaves, and 4) “Control,” vines grown under ambient vineyard conditions. In Study 2, responses were contrasted between V. vinifera or V. riparia when treated as a control (no heat exposure) or with a two-week simulated heatwave of 7 °C above ambient temperatures in October.

For both studies, heat application significantly impacted bud gene expression of pathways hypothesized to play a role in bud dormancy and cold tolerance (e.g., soluble sugar gene pathways) compared to buds from control vines; however, the impacts of heat on bud gene expression were transient for both heat applications (Study 1) and for both Vitis species (Study 2). Despite significant changes in the transcriptome during each heatwave, there were no significant impacts of heat on bud cold tolerance phenotypes for V. vinifera cv. Cabernet Franc when measured four times between November and January for Study 1 or for V. vinifera or V. riparia when measured once in December for Study 2. The “Early” heatwave, but not the “Late” heatwave, significantly delayed budbreak by four days in the following spring in Study 1, and there were no impacts of heat application in October on spring budbreak for either Vitis species in Study 2.