## 1 Introduction  
Kiwifruit, known for its high nutritional value and delightful taste [1], is a significant fruit crop in many countries around the globe and for many consumers. The widely cultivated 'Hayward' cultivar, with its green flesh, dominates the global market, while yellow and red flesh cultivars have been recently introduced to the global market. Growers, the packing and storage industry, as well as consumer acceptance are influenced by quality characteristics such as fruit size, dry matter content, and sugar levels [2, 3], which all play a crucial role in determining the success of a kiwifruit cultivar and cultivation management. Additionally, these quality indexes have a great impact on the post-harvest behavior of the fruit [4]. Kiwifruit quality can be influenced by various factors, including extreme environmental conditions (e.g., high temperatures, radiation) and cultivation practices such as fertilization, irrigation, pruning, netting [5], or girdling [6]. Girdling, a traditional horticultural practice involving the partial removal of a ring of bark around the trunk or branch of a plant, is widely recognized for its impact on various agronomical traits, both quantitative and qualitative, and has been applied in several crops, including grapes [7], citrus [8], apples [9], peaches [10], and even in kiwifruit orchard management [6, 11]. At the physiological level, by selectively interrupting the basipetal flow, shoot girdling alters the source-sink relationships within the plant. This disruption redistributes the flow of assimilates, such as carbohydrates, and acropetally-produced compounds, such as auxins, towards the roots, leading to carbohydrate accumulation above the girdle zone [12] and provoking changes in mineral partitioning [12]. Furthermore, it can affect stomatal conductance [13], decrease leaf photosynthesis [14], and alter primary or secondary metabolism [13]. The impact of girdling on growth, fruit quality, and yield depends on the species, cultivar [9; 15], and timing of application [6; 11; 16]. However, despite its significance, the changes in fruit at the metabolic level caused by girdling are not extensively studied [16]. In avocados [17], kiwifruit [18], and mandarins [8], girdling increased fruit set or the number of fruits per tree and enhanced fruit maturity [18; 19]. Additionally, girdling has been found to reduce fruit drop in apple and Japanese persimmon [20; 21], increase fruit size and coloring [19], and raise the sugar content in grapes and citrus [4; 15; 22]. In plums, amino acids, organic acids, anthocyanins, and other phenols were accumulated in the fruit after girdling [16]. In apples, the soluble solids concentration and acidity increased, but the growth of the fruit was not affected, while firmness was improved [9]. Nonetheless, some species do not exhibit any significant changes in the studied fruit quality parameters [23]. Girdling of canes is a widely applicable practice in 'Hayward' kiwifruit vines. Wounded areas typically heal within 3-6 weeks after application, allowing the root system to retain its assimilate supply. Girdling of the main trunk produces even more fascinating results, increasing both the total soluble solids concentration and dry matter content of the fruits [6], which are two major quality parameters associated with fruit sweetness [24] and storage behavior [25]. In all cases, it has been reported that the timing of girdle application plays a crucial role in the extent of the plant's response [11]. The application of girdling after fruit set has been shown to increase fruit size and, consequently, yield without negatively affecting the plant's vigor [11]. When girdles were applied during the starch accumulation phase, they enhanced the dry-matter content of the fruit, consequently improving its quality [26]. Girdling in autumn, approximately 16-20 weeks after the midpoint of flowering, resulted in increased bud break and flower number in the following season [6; 11].