North, M. | bioRxiv Science

bioRxiv2022

Time to budbreak is not enough: cold hardiness evaluation is necessary in dormancy and spring phenology studies

Dormancy of buds is an important phase in the life cycle of perennial plants growing in environments where unsuitable growth conditions occur seasonally. In regions where low temperature defines these unsuitable conditions, the attainment of cold hardiness is also required to survive. The end of the dormant period culminates in budbreak and flower emergence, or spring phenology, one of the most appreciated and studied phenological events. Despite this, we have a limited physiological and molecular understanding of dormancy, which has negatively affected our ability to model budbreak. Here we highlight the importance of including cold hardiness in studies that typically only characterize time to budbreak. We show how different temperature treatments may lead to increases in cold hardiness, and by doing so also (inadvertently) increase time to budbreak. Therefore, erroneous interpretations of data may occur by not phenotyping cold hardiness. Changes in cold hardiness were very likely present in previous experiments to study dormancy, especially when those included below freezing temperature treatments. Separating the effects between chilling accumulation and cold acclimation in future studies will be essential for increasing our understanding of dormancy and spring phenology in plants.

plant biology↗

bioRxiv2022

Development of a new cold hardiness prediction model for grapevine using phased integration of acclimation and deacclimation responses

Cold injury limits distribution of perennial agricultural crops, though replacement of plants and other management practices may allow for some damage tolerance. However, winter damage to crops such as grapevines (Vitis spp.) can result in losses in yield the following year if buds are damaged, but over many years when vines must be replaced and reach maturity before fruiting. Despite risks, grapevines are cultivated at the edge of permissible climate and rely on cold hardiness monitoring programs to determine when cold damage mitigation and management practices are required. These monitoring programs represent a critical, but laborious process for tracking cold hardiness. To reduce the need for continuous monitoring, a model (WAUS.2) using cold hardiness data collected over many years from Washington state, USA, growers was published in 2014. Although the WAUS.2 model works well regionally, it underperforms in other regions. Therefore, the objective of this work was to develop a new model (NYUS.1) that incorporates recent knowledge of cold hardiness dynamics for better prediction outcomes. Cold hardiness data from V. labruscana Concord, and V. vinifera Cabernet Sauvignon and Riesling from Geneva, NY, USA were used. Data were separated in calibration (~2/3) and validation (~1/3) datasets. The proposed model uses three functions to describe acclimation, and two functions to describe deacclimation, with a total of nine optimized parameters. A shared chill response between acclimation and deacclimation provides a phased integration where acclimation responses decrease over the course of winter and are overcome by deacclimation. The NYUS.1 model outperforms the WAUS.2 model, reducing RMSE by up to 37% depending on cultivar. The NYUS.1 model also tends to be more conservative in its prediction, slightly underpredicting cold hardiness, as opposed to the overprediction from the WAUS.2 model. Some optimized parameters were shared between cultivars, suggesting conserved physiology was captured by the new model. Highlights- Multi-year cold hardiness data from three grapevine cultivars were used for modeling - Cold hardiness was modeled based on daily temperature and accumulated chill - Phased acclimation and deacclimation processes result in cold hardiness predictions - The new model was compared to the currently available model for grapevines - The model proposed here outperforms the currently available model

plant biology↗