Persian Walnut (Juglans regia L.) Bud Dormancy Dynamics in Northern Patagonia, Argentina

Abstract

Temperate deciduous fruit trees survive winter temperatures by entering a dormant phase in their aerial meristematic organs. Release from bud dormancy occurs after chill requirements (CR) have been satisfied, whereas bud burst/flowering follows heat requirement (HR) fulfillment. The physiological basis behind these metrics remains elusive. In this study, we are presenting the first multidisciplinary dormancy progression analysis in northern Patagonia, linking (1) forcing/field phenology, (2) bud anatomical development, and (3) soluble sugar (sucrose, glucose, and fructose) dynamics in Juglans regia L. CR and HR were determined for ‘Chandler’ and ‘Franquette,’ two walnut cultivars with markedly different CR, in artificial chill/forced heat trials (three seasons) and in-field chill/forced heat tests (five seasons) using excised twigs either with or without apical buds (non-decapitated and decapitated). The soluble sugar dynamics of ‘Chandler’ (high-performance liquid chromatography) and the anatomical changes of the buds (light microscopy) of the two cultivars were analyzed during endo-ecodormancy progression in one and two seasons, respectively. The CR defined by artificial chill tests proved to be an overestimation compared to the field determinations. Moreover, HR was the main driver in the phenology dynamics, as expected for a high-chill region. ‘Chandler’ showed an average of 10.3 field chill portions (CP) and 2,163 Growing Degree Hours (GDH°C) less than ‘Franquette’ for dormancy release and bud burst, respectively. These results were consistent with the transition of the shoot apex from the vegetative to the reproductive phase and the soluble sugar profile. The decrease in sucrose between 15 and 30 days after CR fulfillment could be a reliable biological marker for endodormancy release in walnut, while the increase in fructose and glucose is likely an osmolyte and cellulosic carbon source in pre-sprouting. In addition, we discuss the effect of paradormancy thanks to our apical bud experiment (with or without). Our results improve the current understanding of endo-ecodormancy progression in walnut and provide insightful results for walnut production (i.e., cultivation practices such as pruning) as well as for further application in dormancy modeling, to infer the ideotypes that should be bred for future climate conditions.

Climate change impacts on temperate fruit and nut production: a systematic review

“…Such temperatures are the main reason for the increase in heat and decrease in winter chill accumulation that have been observed in most places ( Campoy et al., 2011 ; Luedeling, 2012 ; Atkinson et al., 2013 ; Lippmann et al., 2019 ). For temperate fruit and nut trees, adequate winter chill and heat accumulation are critical requirements for satisfactory commercial production ( Gordo and Sanz, 2009 ; Cerutti et al., 2011 ; Luedeling et al., 2013 ; Darbyshire et al., 2016 ; Horikoshi et al., 2018 ; Fadon et al., 2020 ; Fernandez et al., 2020a ; del Barrio et al., 2022 ). Insufficient winter chill and increasing heat during key phenological stages can affect important physiological processes, leading to non-uniform flowering ( El Yaacoubi et al., 2014 ; Orlandi et al., 2014 ; Legave et al., 2015 ; Funes et al., 2016 ; Elloumi et al., 2024 ), delayed bud formation ( Bonhomme et al., 2005 ; El Yaacoubi et al., 2016 ; Yi et al., 2020 ; Barba-Espin et al., 2022 ), abnormal bud-break ( Bonhomme et al., 2005 ), fruit set reduction ( Hedhly et al., 2007 ; Ruiz and Egea, 2008 ; Benlloch-Gonzalez et al., 2018 ; Egea et al., 2022 ), and ultimately reduced yield potential ( Benmoussa et al., 2018 ; Moriondo et al., 2019 ; Mujahid et al., 2020 ; Fernandez et al., 2021 ).…”

“…Some other strategies, including the use of low-chill cultivars, dormancy avoidance, microclimate manipulation, and rest-breaking chemicals, have also been implemented to produce temperate fruit and nut crops in warm regions ( Rai et al., 2015 ; Fernandez et al., 2023 ; Meza et al., 2023 ). Because of changing weather patterns, several studies have evaluated the capacity of crops to perform in regions that are becoming suitable for agriculture ( del Barrio et al., 2021 , del Barrio et al., 2022 ; Meza et al., 2023 ). However, because of the climatic variability across the world, it is imperative that further research is conducted at the local level to ensure the selection of appropriate cultivars (refer to Luedeling, 2012 for a detailed explanation).…”

“…The main limitation to most of these studies, however, is that they are solely based on the configuration of bioclimatic conditions, without considering local agricultural land use distribution, competition between land uses, and the adaptive capacity of crops ( Houston et al., 2018 ; Sahu et al., 2020 ; del Barrio et al., 2021 ). A study in Argentinian Patagonia concluded that the increasing heat availability in the south of the southern hemisphere presents an opportunity for fruit and nut growers since new species and cultivars with temperate-climate requirements can be introduced into new regions outside their traditional ranges ( del Barrio et al., 2021 , del Barrio et al., 2022 ). Other studies evaluated the performance of olives in hot desertic areas to establish their yield potential and olive oil quality for future production ( Dag et al., 2014 ; Ben Rouina et al., 2020 ).…”