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Article

Effects of Elevated Temperature on the Phenology and Fruit Shape of the Early-Maturing Peach Cultivar ‘Mihong’

by
Seul Ki Lee
1,
Jae Hoon Jeong
1,*,
Taehwan Shin
1,
Sihyeong Jang
1,
Dongyong Lee
2 and
Dong Geun Choi
3
1
Fruit Research Division, National Institute of Horticultural & Herbal Science, Wanju 55365, Republic of Korea
2
Northern Horticulture Research Station, National Institute of Horticultural & Herbal Science, Cheorwon 24031, Republic of Korea
3
Department of Horticulture, Chonbuk National University, Jeonju 54896, Republic of Korea
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(10), 1222; https://doi.org/10.3390/horticulturae11101222
Submission received: 10 September 2025 / Revised: 26 September 2025 / Accepted: 2 October 2025 / Published: 10 October 2025
(This article belongs to the Section Biotic and Abiotic Stress)
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Abstract

This study investigated the effects of elevated temperature on the phenology and morphology of the early-maturing peach cultivar ‘Mihong’. The experiment was conducted from 2019 to 2024 in a temperature-gradient chamber at the National Institute of Horticultural and Herbal Science, Wanju, Korea, with four warming treatments (+2.2 °C to +5.0 °C above ambient). Higher temperatures delayed the onset of endodormancy and markedly shortened the period from endodormancy release to full bloom. Elevated temperatures also increased the LD ratio, with the proportion of fruits exceeding an LD ratio of 1.0 rising significantly with temperature. The LD ratio showed strong correlations with November mean temperature (MT11) and March maximum temperature (HT3) (r = 0.81) and was also associated with the average temperature (Temp3, r = 0.51) and duration (P3, r = −0.54) of the endodormancy release to full bloom phase. Stepwise and PLS regression identified temperatures in May, November, and March as key predictors of the LD ratio, while PCA revealed that temperature variables (Temp3, Temp5) and stage durations (P3, P4) were major contributors. These results confirm that climate warming alters the phenology and morphology of ‘Mihong’, reducing fruit quality and marketability, while providing a basis for predictive modeling and highlighting the importance of adaptive strategies such as shading or growth regulator application.

1. Introduction

The frequency and intensity of extreme high-temperature events have significantly increased due to climate change, posing a major concern for agricultural productivity. Globally, 2024 was confirmed as the warmest year on record, with the mean temperature 1.55 °C above the pre-industrial level (1850–1900) [1]. Similar warming trends have also been reported in Spain [2] and China [3], where recent decades have been identified as the warmest on record, highlighting the severe impacts of climate change on regional temperatures. According to the climate change scenario SSP8.5, the average annual temperature in South Korea is projected to rise by approximately 6.3 °C by the end of the 21st century [4]. This increase could cause various problems in fruit production, such as failure to meet the chilling requirements for fruit trees [5], changes in phenology [6], reduced fruit quality [7], and physiological disorders [8].
Peach (Prunus persica L. Batsch) is a widely consumed fruit in South Korea, with a nationwide cultivation area of approximately 20,127 hectares and an annual production of approximately 182,975 tons as of 2023 [9]. Peaches are primarily grown in open fields, although some early-maturing varieties are cultivated in greenhouses for earlier harvest. Greenhouse cultivation enables temperature control, earlier flowering, and regulation of harvest timing [10]. However, although early forcing may fulfill the minimum accumulated chill requirements as determined by standard chill models, it may not adequately address the physiological chill requirements necessary for normal dormancy release and floral development [11]. This mismatch could have a detrimental effect on fruit development, particularly in early-maturing cultivars. In addition, high temperatures during the early growth stages can excessively accelerate reproductive growth, shorten the fruit development period, alter fruit shape, and reduce quality [12].
Recently, the proportion of peaches with protruding tips and elongated fruit shapes has increased, adversely affecting both marketability and consumer preference [13,14]. Peaches with protruding tips are more frequently found in warmer regions [15], and the frequency of protruding tips varies among peach varieties and regions [16]. When chill requirements are not met, the fruit length-to-diameter ratio tends to increase [12]. Most related studies have focused on the effects of temperature changes after flower-bud differentiation. In contrast, few studies have examined how temperatures in late fall (before bud differentiation) and early spring (after bud differentiation) influence fruit shape.
Peach flowers form sequentially from June to November [17], and temperatures during this period affect style and ovary development, which may subsequently influence the final fruit shape [18]. Therefore, it is essential to investigate the mechanisms by which late-fall and early-spring temperatures influence fruit shape. The objective of this study was to elucidate the effect of elevated temperatures on the fruit shape of the early-maturing peach variety ‘Mihong’ and to determine the correlations between average temperature, the duration of each phenological phase, and the length-to-diameter ratio. We hypothesized that elevated temperatures would alter phenology and fruit shape, both of which could exert adverse effects on fruit quality and marketability.

2. Materials and Methods

2.1. Experimental Materials and Treatments

The experimental material was the early-maturing peach cultivar ‘Mihong’ (Prunus persica (L.) Batsch). In March 2019, peach trees were planted in temperature-gradient chambers (6 × 4 × 3 m and 25 × 4 × 3 m; L × W × H) at the National Institute of Horticultural and Herbal Science (Wanju, Jeollabuk-do, Korea; 35.830935° N, 127.033408° E). The trees were exposed to four different temperature treatments relative to ambient temperature (control), i.e., T1: +2.2 °C, T2: +3.2 °C, T3: +4.4 °C, and T4: +5.0 °C (Figure 1). These temperature treatments were applied from April 2019 to December 2024, with a maximum temperature increase of up to 6 °C above ambient. Each treatment included the following number of trees: control (2 trees), T1 (1 tree), T2 (2 trees), T3 (2 trees), and T4 (2 trees). Trees were planted in a single row at 3 m spacing. Standard orchard management practices, including pruning and pest control, were uniformly applied across all treatments. Replication was based on chamber sections, with each section considered as an experimental unit. Watering was regulated by four sections within the chamber, and soil moisture sensors (Teros21, METER Group, Pullman, WA, USA) were installed in each section. When the soil moisture reached −60 kPa, automatic irrigation was applied for 40–60 min, depending on the growth stage, to maintain consistent soil moisture levels.

2.2. Meteorological Data Collection

Temperature and humidity sensors were installed at the top of the control plot and three treatment plots (2, 12.5, and 23 m from the entrance) to collect environmental data at 1-min intervals. Based on the measured temperature data, the average temperature increase rate (°C/m) for each distance was calculated using linear interpolation, and the actual exposure temperature at each planting position was estimated.

2.3. Phenology Observations

The phenological phases (including endodormancy break and full bloom) and harvest dates were observed annually from October 2019 to 2024. The data collected over 5 years were analyzed using ANOVA. The onset of endodormancy was defined as the date when the accumulated chill units (CU), calculated using the Utah model [19], reached their minimum value and then immediately began to increase (Table 1). The date at which the cultivar reached 970 CU (the chilling requirement for ‘Mihong’) was used to estimate the endodormancy break [20]. Full bloom was defined as the date when 70–80% of the flowers had bloomed, and the date at which >50% of the fruit was harvested was recorded as the harvest date.

2.4. Fruit Shape Observations

Fruit shape was observed from 2021 to 2024. All mature fruits were harvested from every tree within each treatment plot. The length and cheek diameter of all harvested fruits were measured using vernier calipers, and the length-to-diameter (LD) ratio was calculated to define fruit shape. To compare the average LD ratio among treatments, 30 fruits of average size per treatment were selected for statistical analysis using ANOVA. To assess the distribution of fruits with LD ratios >1.0, data from all harvested fruits were used, and their LD ratios were categorized into the following classes: <0.8, 0.8–0.9, 0.9–1.0, 1.0–1.1, 1.1–1.2, and >1.2.

2.5. Statistical Analysis

Data were analyzed using R 4.5.1, and ANOVA was used to compare the means. Duncan’s test was applied to determine significant differences (p < 0.05). Average temperatures were calculated for the following periods to analyze the environmental factors affecting fruit shape: the time from harvest to dormancy onset (‘Temp1’), from endodormancy break to full bloom (‘Temp2’), from full bloom to harvest (‘Temp3’), 2 weeks after full bloom (‘Temp4’), 4 weeks after full bloom (‘Temp5’), and from full bloom to harvest (‘Temp6’). The duration of each phenological phase was also calculated: P1, from the previous year’s harvest to the onset of endodormancy; P2, endodormancy period; P3, from endodormancy release to full bloom; P4, from the onset of heat accumulation to full bloom; and P5, from full bloom to harvest. Pearson correlation analysis and linear regression were performed using the calculated average temperature and duration of each phase. Additionally, stepwise regression and PLS regression were performed using monthly temperature data. PCA was conducted using temperature and duration variables to examine their impact on the LD ratio.

3. Results

3.1. Average Temperature and Phenological Changes in Response to Treatment

In the temperature treatments, the temperatures were set at 2.2 °C, 3.2 °C, 4.4 °C, and +5.0 °C above ambient (the control) in T1–T4, respectively. Overall, the annual average temperature increased from 2020 to 2024, although a decrease was observed in 2022 (Figure 2).
The onset of endodormancy was delayed as temperature increased. The dormancy start date in the T4 treatment (Nov 19) was significantly delayed by up to 29 d relative to the control (Oct 22) (Table 2). The break from endodormancy was also delayed at higher temperatures, although not significantly. In contrast, full bloom was advanced with increasing temperature. In T4, it occurred approximately 17 d earlier (Mar 20) than in the control (Apr 6), and the T4 harvest was approximately 19 d earlier than in the control. The duration of growth stages tended to decrease with increasing temperature, although not significantly for endodormancy (Table 3). The time from endodormancy break to full bloom was significantly shorter (by 35 d) in T4 (41 d) than in the control (75 d). The maturation period from bloom to harvest was also shortened at higher temperatures; however, its duration (75–78 d) did not differ significantly among treatments. The onset and break of endodormancy were delayed with increasing temperatures, while full bloom and harvest occurred earlier.

3.2. Changes in Fruit Shape

Differences in fruit length, diameter, and LD ratio among the temperature treatments were analyzed from 2021 to 2024. Fruit length generally increased with temperature in all years (except in 2022), with T4 showing a 2.3–7.5 mm increase compared to the control (Table 4). In T4, fruit diameter decreased by 1.5–4.2 mm compared to the control (except in 2024). The LD ratio increased with temperature, reaching its highest value in T4 in 2022, at 0.97. Fruits with higher LD ratios displayed more protruding tips, rendering them non-marketable (Figure 3).
As temperature increased, the proportion of fruits with an LD ratio < 0.9 decreased, whereas that of fruits with an LD ratio > 0.9 increased (Figure 4). The proportion of fruits with high LD ratios was markedly higher in the T3 and T4 treatments. In 2023, a significantly higher proportion of fruits with an LD ratio > 1.0 was observed in the T2, T3, and T4 treatments (50.5%, 67.0%, and 58.5%, respectively).

3.3. Environmental Factors Affecting Fruit Shape

3.3.1. Correlations Between the LD Ratio and Monthly Average Temperatures

Correlation analysis was used to examine the relationship between monthly temperatures (monthly averages of daily mean, minimum, and maximum temperatures) and fruit shape (LD ratio). The LD ratio was highly correlated with temperatures in November, March, and May (Table 5). The strongest correlation was observed with the average temperature in November (r, 0.81), followed by the average maximum temperature in March (r, 0.81) and average minimum temperature in May (r, 0.74).
A regression analysis was conducted using the LD ratio as the dependent variable, with the average temperature in November, maximum temperature in March, and minimum temperature in May as predictors. The average temperature in November and the maximum temperature in March were identified as the most important predictors of the LD ratio (R2, 0.65; Figure 5).
To further identify key predictors of fruit shape, both stepwise multiple regression and partial least squares (PLS) regression analyses were performed. Stepwise regression selected nine temperature-related variables as predictors, with May mean temperature (MT5) and May minimum temperature (LT5) showing statistically significant effects on the LD ratio (p < 0.05). The model showed high explanatory power (adjusted R2 = 0.842), suggesting that late-spring temperatures play a pivotal role in influencing fruit morphology (Table 6).
To evaluate the relative importance of temperature variables in shaping the LD ratio while accounting for multicollinearity, a PLS regression was also performed. Variable importance in projection (VIP) scores identified HT5, HT11, HT3, LT11, and LT5 as key predictors, each with a VIP score exceeding the threshold of 1.0 (Figure 6). These results indicate that spring and late-fall temperatures, particularly extreme values, have a substantial effect on fruit shape. The PLS model achieved a comparable predictive performance (R2 = 0.86) while reducing the risk of overfitting.

3.3.2. Correlation and PCA of Factors Influencing LD Ratio

To analyze the impact of temperature during each growth stage on fruit shape, correlation analysis was conducted between the average temperature during each growth phase and the LD ratio. The strongest correlation for the LD ratio was observed for the average temperature from endodormancy break to full bloom (Temp3) (r, 0.51). A moderate correlation was also observed with the average temperature from full bloom to harvest (Temp6) (r, 0.40; Figure 7).
Correlations between the LD ratio and growth stage duration were analyzed to examine the influence of growth stage duration on fruit shape. The duration from the previous year’s harvest to the start of dormancy (P1) showed the highest positive correlation with the LD ratio (r, 0.56). In contrast, the duration from endodormancy break to full bloom (P3) showed a high negative correlation with the LD ratio (r, −0.54), whereas the duration of the maturation period from full bloom to harvest (P5) showed a low correlation (r, 0.12) (Figure 8).
Based on these correlation results, a principal component analysis (PCA) was conducted to further explore the combined effects of temperature and growth stage duration on the LD ratio. PCA revealed that PC1 was primarily influenced by temperature variables, particularly Temp5 and Temp3, whereas PC2 was more influenced by the duration of growth stages, specifically P3 and P4. The variables with the largest vector lengths in the PCA biplot, such as Temp3 and P5, had the greatest impact on the LD ratio (Figure 9, Table 7).

4. Discussion

4.1. Changes in Phenology Due to Elevated Temperature

In winter, temperate fruit trees enter a period of endodormancy to avoid unfavorable environmental conditions, suppressing physiological activity [21]. Although it is difficult to clearly distinguish the onset of endodormancy from paradormancy, it is generally estimated to begin when accumulated chill units (CU), based on the Utah model, reaches a minimum and then start to increase [22]. In the present study, increasing temperatures delayed the onset of endodormancy, which in turn delayed leaf fall and the cessation of physiological activity in the trees [23]. Under climate change scenarios, elevated winter temperatures can hinder the timely fulfillment of chilling requirements (CR), thereby delaying endodormancy release and subsequently disrupting the timing and synchronization of flowering in apples [24]. In a model-based assessment conducted in Utsunomiya, Japan, a +5 °C increase in winter temperature was projected to postpone natural dormancy release in certain pear cultivars by up to one month, potentially disrupting subsequent phenological stages [25]. This delay in the onset of endodormancy could hinder the accumulation of stored nutrients, potentially limiting the energy available for early spring growth [26].
Beyond these physiological effects, molecular mechanisms also provide important insights into how elevated temperatures disrupt dormancy and flowering. At the molecular level, DORMANCY-ASSOCIATED MADS-box (DAM) genes are key regulators of dormancy release and floral bud enlargement [17]. Warmer winter conditions under climate change may sustain DAM expression, which can promote prolonged accumulation of abscisic acid (ABA) and suppression of gibberellins (GA), thereby causing delayed or uneven dormancy release and increasing the risk of floral organ malformation or abortion [27]. Moreover, sustained DAM expression may also inhibit floral organ growth even after dormancy release [17]. These molecular disruptions provide a mechanistic explanation that complements the observed physiological responses under elevated temperatures.
In spring, elevated temperatures can further affect the post-dormancy developmental stages of temperate fruit trees. If the accumulated growing degree hours over a 30-day period (GDH30) exceed the threshold of 6000 GDH, the overall growth period becomes compressed. Under such conditions, the tree may not be able to supply resources rapidly enough to sustain its maximum potential fruit growth rate, resulting in smaller fruit size [13]. In the present study, the interval between endodormancy break and full bloom was markedly shortened under elevated temperature conditions. This temperature-induced compression of developmental time may have restricted ovary maturation, thereby reducing pollination and fertilization efficiency and potentially leading to fruit asymmetry and morphological abnormalities. Overall, these physiological and molecular findings highlight that climate warming can profoundly alter both dormancy regulation and subsequent reproductive development, thereby threatening fruit yield and quality in temperate fruit trees. The early-maturing cultivar ‘Mihong’ used in this study has a high chilling requirement (CU 970), making it more sensitive to warming, which suggests that cultivars with lower chilling requirements may be less affected.

4.2. Changes in Fruit Shape Due to Elevated Temperature

Peach development follows a double sigmoid growth pattern, characterized by active cell division during the initial stage (S1), endocarp hardening during the stone-hardening stage (S2), and prominent cell expansion during the final growth phase (S3) [28]. Exposure to elevated temperatures accelerates fruit growth during S1, thereby shortening the period of cell division, while simultaneously suppressing fruit growth during S3, resulting in overall inhibition of development [29]. High temperatures reduce photosynthetic efficiency and increase night-time respiration, ultimately limiting the accumulation of assimilates and inducing an imbalance in fruit development [30]. In apples, longitudinal growth dominates during the early developmental phase, whereas radial growth prevails later, leading to a progressive decline in the fruit shape index as development proceeds [31], although elevated temperatures have been reported to increase the index [32]. In peaches, fruit morphology is determined primarily by cell number rather than cell size [33]; consequently, high temperatures during early development (S1) may enhance cell division along the longitudinal axis, thereby increasing fruit length. In the present study, elevated temperatures in March led to increased fruit length and reduced fruit diameter, resulting in a higher LD ratio and fruits that were longer with more pronounced protruding tips. Peaches with a high LD ratio are prone to tip softening during postharvest handling and distribution, rendering them non-marketable and reducing their quality and commercial value [16].
Consumers tend to prefer round-shaped peaches with an LD ratio of approximately 0.8; for example, the representative mid-season cultivar ‘Cheonjungdobaekdo’ has an average LD ratio of 0.88 [34,35]. In the present study, the proportion of fruits with an LD ratio > 1.0 increased markedly with temperature, with >50% of the yield in the T3 and T4 treatments being unmarketable. Therefore, persistent high-temperature conditions will likely reduce fruit quality and marketability, ultimately impacting agricultural productivity and farmer income.

4.3. Impact of Growth Stage and Temperature on Fruit Shape

Various environmental factors influence fruit shape and flower bud development, with temperature being the most significant [36]. In Australia, higher maximum temperatures during the coldest period (July) have increased tip growth in some peach cultivars [37]. When chill accumulation is insufficient due to high temperatures the previous year, the growth of peach flower bud size and the development of reproductive organs is delayed [38]. High temperatures before flowering reduce both style length and ovary diameter, with a greater reduction observed in ovary diameter. Consequently, the ratio of style length to ovary diameter increases, which is associated with the final fruit shape [39].
In the present study, correlation analysis revealed that the LD ratio was most strongly associated with temperatures in the previous November (mean temperature, r = 0.81) and in March (maximum temperature, r = 0.81), followed by May minimum temperature (r = 0.74). These months coincide with critical phases in floral organ development and ovule preparation, indicating that temperature during these periods plays a key role in determining fruit morphology. In peaches, flower differentiation proceeds sequentially from the sepals to the petals, stamens, and pistils from June to November [17], followed by dormancy and the development and preparation of the ovules and ovary for fertilization [40]. These developmental stages align with the periods identified in our analysis, supporting the notion that temperatures during late fall and early spring can substantially influence fruit shape.
Both stepwise and PLS regression analyses consistently highlighted the critical role of late-fall and late-spring temperatures, particularly extreme values, in influencing peach fruit morphology. These findings suggest that fruit shape is not determined by a single temperature factor but results from sequential temperature influences across key phenological stages. Notably, temperatures in May were consistently identified as crucial, indicating that the conditions during the final stages of floral organ development and early fruit growth have a lasting effect on the quality of marketable fruit traits. These results are consistent with previous studies showing that elevated growth temperatures accelerate fruit development but reduce final size and quality of peaches [4,29].
The LD ratio is influenced by both external temperature and the duration of various biological phases. Peaches tend to produce protruding tips more frequently in warmer regions [16], and when chill accumulation is insufficient to break endodormancy, fruit shape becomes elongated [12]. In the present study, temperature during the period from endodormancy break to full bloom was strongly correlated with the LD ratio, with higher temperatures during this period leading to an increase in the LD ratio. These higher temperatures, therefore, likely resulted in elongated ovaries, ultimately impacting fruit shape at harvest. The LD ratio was more strongly influenced by the length of the period from dormancy break to full bloom (P3) than by the length of the maturation period (P5), suggesting that insufficient time for normal floral organ development after the break of endodormancy increases fruit-shape abnormalities [39]. The environmental conditions during the pre- and post-bloom periods critically influence fruit shape and quality, and elevated temperatures due to climate change may lead to shape abnormalities, ultimately reducing the yield of marketable fruit. Practical management options may help mitigate such impacts, with growth regulators such as hydrogen cyanamide partially compensating for insufficient chill, and shading practices alleviating heat stress to maintain fruit quality [41].

5. Conclusions

This study demonstrated that high temperatures significantly affected the phenology and morphology of the early-maturing peach cultivar ‘Mihong’. Warmer conditions delayed the onset and release of endodormancy while shortening the duration between dormancy release and full bloom. Elevated temperatures during this period likely hindered the normal development of floral organs, thereby affecting fruit morphology. These environmental changes also increased the LD ratio and the proportion of fruits with protruding tips, reducing fruit quality and marketability. These results indicate that ‘Mihong’, a high-chilling, early-maturing cultivar, is particularly vulnerable to warming, and that ongoing climate change may pose considerable challenges to maintaining fruit quality in its current production regions. Orchard management strategies such as shading or the application of growth regulators may help mitigate some of the negative impacts of warming. Furthermore, these findings provide a useful basis for improving predictive models of phenological and morphological responses under future climate scenarios.

Author Contributions

Conceptualization, S.K.L. and D.G.C.; methodology, J.H.J.; software, T.S.; validation, D.L.; formal analysis, S.K.L.; investigation, S.K.L.; resources, S.K.L.; data curation, S.J.; writing—original draft preparation, S.K.L.; writing—review and editing, S.K.L.; visualization, T.S.; supervision, D.G.C.; project administration, J.H.J.; funding acquisition, S.K.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Research Program for Agriculture Science and Technology Development [Project No. PJ017373], Rural Development Administration, the Republic of Korea.

Data Availability Statement

The original contributions presented in this study are included in the article material. Futher inquiries can be directed to the corresponding author.

Acknowledgments

The authors thank Su Hyun Yun at the National Institute of Horticultural and Herbal Science, Rural Development Administration for the critical reading of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Illustration depicting the various temperature treatments within the temperature-gradient chambers.
Figure 1. Illustration depicting the various temperature treatments within the temperature-gradient chambers.
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Figure 2. Mean annual air temperature recorded under the five temperature treatments (Control, T1–T4) from 2020 to 2024.
Figure 2. Mean annual air temperature recorded under the five temperature treatments (Control, T1–T4) from 2020 to 2024.
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Figure 3. Visual comparison of fruit shape in the early-maturing peach cultivar ‘Mihong’ under five temperature treatments (Control, T1–T4, 2021 season).
Figure 3. Visual comparison of fruit shape in the early-maturing peach cultivar ‘Mihong’ under five temperature treatments (Control, T1–T4, 2021 season).
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Figure 4. Proportion of fruits in each length-to-diameter (LD) ratio range in the early-maturing peach cultivar ‘Mihong’ under five temperature treatments (Control, T1–T4) during the 2021–2024 growing seasons.
Figure 4. Proportion of fruits in each length-to-diameter (LD) ratio range in the early-maturing peach cultivar ‘Mihong’ under five temperature treatments (Control, T1–T4) during the 2021–2024 growing seasons.
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Figure 5. Regression analysis evaluating the predictors of the length-to-diameter (LD) ratio among the mean daily temperature in November (A), maximum daily temperature in March (B), and minimum daily temperature in May (C). Asterisks indicate significance levels: *** p < 0.001.
Figure 5. Regression analysis evaluating the predictors of the length-to-diameter (LD) ratio among the mean daily temperature in November (A), maximum daily temperature in March (B), and minimum daily temperature in May (C). Asterisks indicate significance levels: *** p < 0.001.
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Figure 6. Variable importance in projection (VIP) scores for temperature-related predictors of the LD ratio from the partial least squares (PLS) regression model.
Figure 6. Variable importance in projection (VIP) scores for temperature-related predictors of the LD ratio from the partial least squares (PLS) regression model.
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Figure 7. Correlation coefficients between the length-to-diameter (LD) ratio and average temperatures during the six defined phenological stages: Temp1: from the previous year’s harvest to onset of endodormancy; Temp2: endodormancy period; Temp3: from endodormancy release to full bloom; Temp4: 2 weeks after full bloom; Temp5: 4 weeks after full bloom; Temp6: from full bloom to harvest. Asterisks indicate significance levels: * p < 0.05, ** p < 0.01, *** p < 0.001.
Figure 7. Correlation coefficients between the length-to-diameter (LD) ratio and average temperatures during the six defined phenological stages: Temp1: from the previous year’s harvest to onset of endodormancy; Temp2: endodormancy period; Temp3: from endodormancy release to full bloom; Temp4: 2 weeks after full bloom; Temp5: 4 weeks after full bloom; Temp6: from full bloom to harvest. Asterisks indicate significance levels: * p < 0.05, ** p < 0.01, *** p < 0.001.
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Figure 8. Correlation coefficients between the length-to-diameter (LD) ratio and duration of five phenological periods (P1–P5). P1: from the previous year’s harvest to the onset of endodormancy; P2: endodormancy period; P3: from endodormancy release to full bloom; P4: from the onset of heat accumulation to full bloom; and P5: from full bloom to harvest. Asterisks indicate significance levels: * p < 0.05, ** p < 0.01, *** p < 0.001.
Figure 8. Correlation coefficients between the length-to-diameter (LD) ratio and duration of five phenological periods (P1–P5). P1: from the previous year’s harvest to the onset of endodormancy; P2: endodormancy period; P3: from endodormancy release to full bloom; P4: from the onset of heat accumulation to full bloom; and P5: from full bloom to harvest. Asterisks indicate significance levels: * p < 0.05, ** p < 0.01, *** p < 0.001.
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Figure 9. Principal component analysis of the length-to-diameter (LD) ratio, temperature (Temp1–6), and duration (P1–5) of different phenological periods.
Figure 9. Principal component analysis of the length-to-diameter (LD) ratio, temperature (Temp1–6), and duration (P1–5) of different phenological periods.
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Table 1. Chill unit (CU) accumulation based on the Utah model [15].
Table 1. Chill unit (CU) accumulation based on the Utah model [15].
Temperature (°)CUCU Calculation
T < 1.40∑CU
1.5 ≤ T ≤ 2.40.5
2.5 ≤ T ≤ 9.11
9.2 ≤ T ≤ 12.40.5
12.5 ≤ T ≤ 15.90
16.0 ≤ T ≤ 18.0−0.5
18.0 < T−1.0
Table 2. Mean dates of endodormancy onset, endodormancy release, full bloom, and harvest in the early-maturing peach cultivar ‘Mihong’ under five temperature treatments (Control, T1–T4), based on the average of five consecutive growing seasons (2019–2020 to 2023–2024).
Table 2. Mean dates of endodormancy onset, endodormancy release, full bloom, and harvest in the early-maturing peach cultivar ‘Mihong’ under five temperature treatments (Control, T1–T4), based on the average of five consecutive growing seasons (2019–2020 to 2023–2024).
TreatmentDate (Day/Month)
Onset of EndodormancyEndodormancy
Release		Full BloomHarvest
ControlOct 22 ± 10 cJan 23 ± 14 Apr 6 ± 4 aJun 22 ± 4 a
T1Oct 30 ± 10 bcJan 30 ± 11 Mar 27 ± 3 b Jun 13 ± 5 ab
T2Nov 9 ± 2 abFeb 1 ± 9 Mar 24 ± 3 bcJun 8 ± 5 bc
T3Nov 16 ± 4 aFeb 4 ± 7Mar 21 ± 3 bcJun 5 ± 5 bc
T4Nov 19 ± 5 aFeb 8 ± 7Mar 20 ± 4 cJun 3 ± 4 c
Lowercase letters after dates indicate significant differences (p < 0.05; Duncan’s multiple range test) within columns (i.e., between treatments).
Table 3. Mean durations of endodormancy, endodormancy release to full bloom, and full bloom to harvest in the early-maturing peach cultivar ‘Mihong’ under five temperature treatments (Control, T1–T4), based on the average of five consecutive growing seasons (2019–2020 to 2023–2024).
Table 3. Mean durations of endodormancy, endodormancy release to full bloom, and full bloom to harvest in the early-maturing peach cultivar ‘Mihong’ under five temperature treatments (Control, T1–T4), based on the average of five consecutive growing seasons (2019–2020 to 2023–2024).
TreatmentDuration (Days)
EndodormancyFrom Endodormancy Release
to Full Bloom		From Full Bloom
to Harvest
Control93 ± 1975 ± 15 a76 ± 5
T192 ± 1557 ± 11 ab78 ± 6
T285 ± 852 ± 11 b76 ± 5
T381 ± 846 ± 7 b76 ± 6
T482 ± 1141 ± 7 b75 ± 5
Lowercase letters after dates indicate significant differences (p < 0.05; Duncan’s multiple range test) within columns (i.e., between treatments).
Table 4. Fruit length, width, and LD ratio in the early-maturing peach cultivar ‘Mihong’ under five treatments (Control, T1–T4) during the 2021, 2022, 2023, and 2024 growing seasons.
Table 4. Fruit length, width, and LD ratio in the early-maturing peach cultivar ‘Mihong’ under five treatments (Control, T1–T4) during the 2021, 2022, 2023, and 2024 growing seasons.
Treatment2021202220232024
Length
(mm)		Width
(mm)		LD
Ratio		Length
(mm)		Width
(mm)		LD
Ratio		Length
(mm)		Width
(mm)		LD
Ratio		Length
(mm)		Width
(mm)		LD
Ratio
Control75.2 c86.3 a0.87 b73.2 b82.7 a0.89 bc73.7 c82.8 a0.89 b73.4 c79.9 d0.92 a
T177.4 bc87.7 a0.88 b71.0 c82.6 a0.86 c74.0 bc82.7 a0.90 b74.5 c84.5 bc0.88 b
T279.2 ab87.8 a0.90 b70.7 c76.5 b0.93 b72.7 c76.2 c0.96 a77.3 b86.5 ab0.89 b
T379.3 ab87.6 a0.91 b75.7 a78.6 b0.97 a75.7 ab78.9 b0.96 a77.4 b84.3 c0.92 a
T480.8 a84.8 a0.95 a76.2 a78.5 b0.97 a76.0 a79.0 b0.96 a80.9 a88.0 a0.92 a
Lowercase letters after dates indicate significant differences (p < 0.05; Duncan’s multiple range test) within columns (i.e., between treatments).
Table 5. Pearson correlations between length-to-diameter (LD) ratio and the monthly mean of daily mean, maximum, and minimum temperatures.
Table 5. Pearson correlations between length-to-diameter (LD) ratio and the monthly mean of daily mean, maximum, and minimum temperatures.
Average Daily TemperatureJunJulAugSepOctNovDecJanFebMarAprMay
Mean0.64 ***0.54 **0.36 *0.45 **0.43 *0.81 ***0.020.330.180.76 ***0.330.68 ***
Maximum0.50 **0.47 **0.210.55 **0.270.79 ***0.040.53 **0.330.81 ***0.35 *0.57 ***
Minimum0.70 ***0.56 **0.42 *0.320.47 **0.79 ***00.180.080.61 ***0.240.74 ***
* p < 0.05, ** p < 0.01, *** p < 0.001.
Table 6. Results of the stepwise multiple regression analysis showing the effects of monthly temperature variables on the LD ratio. Only variables selected by the model are presented. MT5: mean temperature in May; LT5: minimum temperature in May.
Table 6. Results of the stepwise multiple regression analysis showing the effects of monthly temperature variables on the LD ratio. Only variables selected by the model are presented. MT5: mean temperature in May; LT5: minimum temperature in May.
VariableParameter EstimateStd. Errort Valuep-Value
(Intercept)1.2310.2365.213<0.001
MT5−0.1930.092−2.0970.047
LT50.1130.0472.4120.024
Model R20.885
Adjusted R20.842
Table 7. Principal component loadings for each variable across the first five principal components (PC1–PC5). The table presents the importance (weight) of each variable in explaining the variance of the data in each principal component.
Table 7. Principal component loadings for each variable across the first five principal components (PC1–PC5). The table presents the importance (weight) of each variable in explaining the variance of the data in each principal component.
VariablePC1PC2PC3PC4PC5
Temp10.3650.1880.1350.318−0.319
Temp20.2760.3750.2340.336−0.263
Temp30.348−0.3080.069−0.0490.076
Temp40.289−0.0020.153−0.812−0.197
Temp50.3800.1920.015−0.209−0.011
Temp60.3880.044−0.1740.110−0.218
P10.345−0.097−0.4270.0610.192
P2−0.122−0.1400.7550.012−0.119
P3−0.2690.475−0.088−0.055−0.040
P4−0.2060.492−0.197−0.246−0.266
P5−0.207−0.440−0.2650.029−0.783
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Lee, S.K.; Jeong, J.H.; Shin, T.; Jang, S.; Lee, D.; Choi, D.G. Effects of Elevated Temperature on the Phenology and Fruit Shape of the Early-Maturing Peach Cultivar ‘Mihong’. Horticulturae 2025, 11, 1222. https://doi.org/10.3390/horticulturae11101222

AMA Style

Lee SK, Jeong JH, Shin T, Jang S, Lee D, Choi DG. Effects of Elevated Temperature on the Phenology and Fruit Shape of the Early-Maturing Peach Cultivar ‘Mihong’. Horticulturae. 2025; 11(10):1222. https://doi.org/10.3390/horticulturae11101222

Chicago/Turabian Style

Lee, Seul Ki, Jae Hoon Jeong, Taehwan Shin, Sihyeong Jang, Dongyong Lee, and Dong Geun Choi. 2025. "Effects of Elevated Temperature on the Phenology and Fruit Shape of the Early-Maturing Peach Cultivar ‘Mihong’" Horticulturae 11, no. 10: 1222. https://doi.org/10.3390/horticulturae11101222

APA Style

Lee, S. K., Jeong, J. H., Shin, T., Jang, S., Lee, D., & Choi, D. G. (2025). Effects of Elevated Temperature on the Phenology and Fruit Shape of the Early-Maturing Peach Cultivar ‘Mihong’. Horticulturae, 11(10), 1222. https://doi.org/10.3390/horticulturae11101222

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