The Relationship between Different Fruit Load Treatments and Fruit Quality in Peaches

: The effects of different fruit load treatments during peach growth and development on the internal and external quality of peach fruit were studied. At 47 days after full bloom, the plant materials were divided into four treatments: about 100%, 75%, 50% and 25% of fruit were retained. The results showed that as the fruit load was reduced during fruit growth and development, the fruit weight, size, soluble solid contents (SSC), total sugar content, sugar/acid ratio and color quality increased, while the ﬂesh ﬁrmness, index of absorbance difference (IAD) and total acid content decreased. Compared with the control treatment in which the fruit were not thinned, the weight of individual mature fruit increased by 24.52%, 39.73% and 51.68% under three fruit thinning treatments (in which about 75%, 50% and 25% of the fruit were left on the tree). SSC increased by 30.78%, 37.63% and 49.69%; total sugar content increased by 13.58%, 22.33% and 31.42%; and the sugar-acid ratio increased by 13.25%, 13.59% and 19.47%, respectively, under the three conditions. In addition, the longitudinal, transverse and lateral diameters of fruit increased to varying degrees when the fruit load was reduced. Furthermore, the fruit ﬁrmness and IAD value of fruit skins decreased, and fruit ripening was advanced when the fruit load was reduced. The results showed that fruit quality and ﬂavor were improved signiﬁcantly by fruit thinning.


Introduction
Load regulation is an important horticultural measure to obtain high and stable yields in fruit tree production [1].High fruit loads affect a tree's nutritional status, weaken tree strength, age tree leaves [2,3], reduce fruit quality and delay the fruit ripening date, resulting in low generation rates of new shoots and poor-quality flower buds in the next year [4].Low fruit load treatments lead to lower yields and the over exuberance of trees, which seriously affect economic returns.Therefore, a reasonable load in fruit trees presents a means of ensuring fruit quality, yield and normal tree growth and development.
Fruit is the main sink organ of a plant, and fruit thinning can regulate the sink/source relationship between fruit and leaves, leading to changes in the light energy capture by leaves and the distribution of photosynthates, thus affecting fruit quality and yield [5].Studies have shown that the appropriate reduction in the fruit load can significantly improve both the external and internal quality of fruit, mainly reflected in the fruit size, single fruit weight, soluble solid contents (SSC), total sugar content, sugar/acid ratio and other indicators [6][7][8].Other studies have shown that beyond a certain point, the extent of fruit thinning has no effect on increases in SSC and vitamin C (VC) due to a decrease in the sink/source ratio, while titratable acid content increases significantly, and the fruit quality decreases [9].In addition, a reduction in the number of fruits enhances the fruit color [4,10] and growth and development, promoting maturation [11,12].
There are currently many studies on the effects of different fruit load treatments on fruit quality, but very little comprehensive research on fruit quality during growth and development.In this study, the 'Xiahui11' peach cultivar was chosen to investigate the differences in fruit quality under different fruit load treatments and explore the relationships between fruit quality indices and loading during fruit growth and development to provide a theoretical basis for the best loading treatment for peach trees.

Material
The experiments were conducted in 2022 in peach orchards in Experimental Park, Jiangsu Agricultural Science College, Nanjing city, Jiangsu Province (118.79772E, 32.04856 N; Altitude: 12 m).The experiments were performed on two main "Y"-shaped branches of Prunus persica (L.) Batsch.'Xiahui 11' peach cultivars with basically the same growth pattern.The trees were 7 years old, spaced in rows in a north-south direction, 2 m × 5 m apart, in a ridge cultivation, peach garden/grass management system.The soil type, fertilizer use, water management and pest control measures followed conventional practices.
The plant materials were divided into four treatments: T1 (all of the fruit were retained on the tree, forming the control); T2 (about 75% of the fruit were retained); T3 (about 50% of the fruit were retained); and T4 (about 25% of fruit were retained).The number of fruits was adjusted according to the tree stem cycle parameters and leaf-fruit ratios, and 10% of the fruit were retained in each treatment as an insurance factor.Fruit were thinned and set on 10 May (47 days after full bloom; 47 DAFB).Nine fruits of the same size from the middle and periphery of the tree crown were randomly collected from each treatment every 10 days or so (at 49 DAFB, 61 DAFB, 73 DAFB, 83 DAFB and at maturity), and immediately brought back to the laboratory.The fruit size, individual fruit weight, pericarp color difference, absorbance difference (IAD), firmness and SSC were determined sequentially.Three replicates were created, each comprising three fruits.Samples were quickly frozen using liquid nitrogen.
Fruit ripening stage samples for the different fruit load treatments, T1, T2, T3 and T4, were taken at 99 DAFB, 95 DAFB, 94 DAFB and 93 DAFB, respectively.Thirty fruits without disease, insect or mechanical damage were randomly collected from the middle and periphery of the tree crown of each treatment, to make three replicates of 10 fruits each [13].

Determination of Fruit Size
The longitudinal, transverse and lateral diameters of fruit were measured to a 0.01 mm accuracy using an electronic digital caliper (Guilin Guanglu Digital Measurement, Guilin, China), as shown in Figure 1.
fruit quality, but very little comprehensive research on fruit quality during growth and development.In this study, the 'Xiahui11' peach cultivar was chosen to investigate the differences in fruit quality under different fruit load treatments and explore the relationships between fruit quality indices and loading during fruit growth and development to provide a theoretical basis for the best loading treatment for peach trees.

Material
The experiments were conducted in 2022 in peach orchards in Experimental Park, Jiangsu Agricultural Science College, Nanjing city, Jiangsu Province (118.79772″E, 32.04856″ N; Altitude: 12 m).The experiments were performed on two main "Y"-shaped branches of Prunus persica (L.) Batsch.'Xiahui 11' peach cultivars with basically the same growth pattern.The trees were 7 years old, spaced in rows in a north-south direction, 2 m × 5 m apart, in a ridge cultivation, peach garden/grass management system.The soil type, fertilizer use, water management and pest control measures followed conventional practices.
The plant materials were divided into four treatments: T1 (all of the fruit were retained on the tree, forming the control); T2 (about 75% of the fruit were retained); T3 (about 50% of the fruit were retained); and T4 (about 25% of fruit were retained).The number of fruits was adjusted according to the tree stem cycle parameters and leaf-fruit ratios, and 10% of the fruit were retained in each treatment as an insurance factor.Fruit were thinned and set on 10 May (47 days after full bloom; 47 DAFB).Nine fruits of the same size from the middle and periphery of the tree crown were randomly collected from each treatment every 10 days or so (at 49 DAFB, 61 DAFB, 73 DAFB, 83 DAFB and at maturity), and immediately brought back to the laboratory.The fruit size, individual fruit weight, pericarp color difference, absorbance difference (IAD), firmness and SSC were determined sequentially.Three replicates were created, each comprising three fruits.Samples were quickly frozen using liquid nitrogen.
Fruit ripening stage samples for the different fruit load treatments, T1, T2, T3 and T4, were taken at 99 DAFB, 95 DAFB, 94 DAFB and 93 DAFB, respectively.Thirty fruits without disease, insect or mechanical damage were randomly collected from the middle and periphery of the tree crown of each treatment, to make three replicates of 10 fruits each [13].

Determination of Fruit Size
The longitudinal, transverse and lateral diameters of fruit were measured to a 0.01 mm accuracy using an electronic digital caliper (Guilin Guanglu Digital Measurement, Guilin, China), as shown in Figure 1.

Determination of Single Fruit Weight
The weight of each fruit was determined to an accuracy of 0.1 g using a JA5003 electronic balance (Shanghai Shunyu Hengping, Shanghai, China).

Determination of Firmness
The firmness of the fruit flesh was measured on both sides of the suture using a texture analyzer, model XT Plus probe (Stable Micro Systems, Godalming, UK).The probe diameter was 8 mm, the test depth was 5 mm and the penetration rate was 1 mm/s.

Determination of Soluble Solid Contents (SSC)
Fruit SSC on both sides of the fruit suture was measured using a digital Brix Refractometer, model PAL-1 (ATAGO, Tokyo, Japan), and the average value was taken as the SSC of the fruit [14].

Determination of the Index of Absorbance Difference (IAD) of the Pericarp
The IAD of the pericarp was measured using a vis/NIR portable spectrometer DA-Meter (TR Turoni SRL, Forlì, Italy), at the middle of the fruit on both sides of the fruit suture.The IAD can reflect the degree of fruit ripening by measuring the change of pigment (chlorophyll) content in fruit skins and calculating the difference in fruit skin absorbance between 670 nm and 720 nm, over an index ranging from 0 to 2.2.An IAD value of 2.2 represents an unripe fruit, and 0 represents full maturity [15,16].

Determination of Pericarp Color
The brightness value (L*), red saturation (a*) and yellow saturation (b*) of the fruit skin were measured using a ColorQuest XE colorimeter and the Hunter Lab color system, and the color saturation (C), hue angle (h) and a*/b* were calculated [17,18].

Determination of Soluble Sugar and Organic Acid Components
The soluble sugar components were determined using an Agilent 1260 high performance liquid chromatography (HPLC) system (Agilent Technology, Santa Clara, CA, USA) with a CARBOSep CHO-620 CA carbohydrate column (10 m particle size; 6 mm × 250 mm, Transgenomic Inc., Omaha, NE, USA) with a column temperature of 80 • C and a Refractive Index Detector (RID).The HPLC conditions were as follows: a mobile phase (ultrapure water), a flow rate of 0.5 mL/min and a sample extraction of 5 µL.Sucrose, glucose, fructose and sorbitol were identified and quantified by comparing retention times and peak areas with standard products [19].The total sugar content = sucrose content + glucose content + fructose content + sorbitol content.
The organic acids were determined using the same HPLC system equipped with a VWD UV detector and an Agilent Zorbax SB-Aq column (4.6 mm × 250 mm; 5 m ID).A chromatographic analysis was performed at a flow rate of 0.5 mL/min at 25 • C. The UV absorption of the eluent was measured at 214 nm.The mobile phase was a 0.02 mol/L KH2PO4 solution with pH 2.7 and 5 µL of an extract from each sample was analyzed using HPLC.Malic acid, quinic acid and citric acid were identified according to their retention times, and the organic acid content of the sample was calculated based on the standard curve and peak area [19].Total acid content = malic acid content + quinic acid content + citric acid content, and the sugar-acid ratio = total sugar content/total acid content.

Data Processing
SPSS 23.0 (SPSS Inc., Chicago, IL, USA) software was used for all data analyses.Significant differences between the average values obtained for fruit quality indices of different fruit load treatments were evaluated using analysis of variance techniques (ANOVA) and the Multiple Ranges Duncan's test was used to differentiate between the means (p < 0.05).Excel 2016 software was used for data mapping.

Comparison of Single Fruit Weights and Changes in Fruit Size
As shown in Figure 2, the single fruit weight under the four different fruit load treatments increased continuously, and ranked as T4 > T3 > T2 > T1 from the start of the experiment to fruit ripening.The single fruit weight at maturity in the three fruit thinning treatments, T4, T3 and T2, was greater by 24.52%, 39.73% and 51.68% compared with the control, respectively.From the middle stage of the experiment (about 73 DAFB) to fruit maturity, the longitudinal, transverse and lateral diameter of fruit in the different treatments ranked as T4 > T3 > T2 > T1 (p < 0.05).Following the middle stage of the experiment, the fruit growth rate accelerated significantly and entered a second expansion stage, indicating that the effect of different fruit load treatments on the fruit size acted mainly during the later stage of fruit growth and development.The fruit weight and size of T4 increased the fastest in the later growth stage, indicating that retaining 25% of the fruit provided a sufficient carbohydrate supply to each fruit, and was beneficial to fruit growth and development.

Comparison of Single Fruit Weights and Changes in Fruit Size
As shown in Figure 2, the single fruit weight under the four different fruit load treatments increased continuously, and ranked as T4 > T3 > T2 > T1 from the start of the experiment to fruit ripening.The single fruit weight at maturity in the three fruit thinning treatments, T4, T3 and T2, was greater by 24.52%, 39.73% and 51.68% compared with the control, respectively.From the middle stage of the experiment (about 73 DAFB) to fruit maturity, the longitudinal, transverse and lateral diameter of fruit in the different treatments ranked as T4 > T3 > T2 > T1 (p < 0.05).Following the middle stage of the experiment, the fruit growth rate accelerated significantly and entered a second expansion stage, indicating that the effect of different fruit load treatments on the fruit size acted mainly during the later stage of fruit growth and development.The fruit weight and size of T4 increased the fastest in the later growth stage, indicating that retaining 25% of the fruit provided a sufficient carbohydrate supply to each fruit, and was beneficial to fruit growth and development.

Comparison of Fruit SSC
Figure 3 shows that SSC increased with increasing fruit growth and development The SSCs of fruit under the different fruit load treatments were significantly different in the different growth periods, especially from the middle period to maturity.At the later stage of fruit development, T4 showed the fastest rate of the increase in SSC, while T1 showed the slowest.The SSC of T4 was the highest and that of T1 was the lowest at maturity (p < 0.05).The SSCs at maturity of the three fruit thinning treatments, T2, T3 and T4 increased by 30.78%, 37.63% and 49.69% compared with the control, respectively.These

Comparison of Fruit SSC
Figure 3 shows that SSC increased with increasing fruit growth and development.The SSCs of fruit under the different fruit load treatments were significantly different in the different growth periods, especially from the middle period to maturity.At the later stage of fruit development, T4 showed the fastest rate of the increase in SSC, while T1 showed the slowest.The SSC of T4 was the highest and that of T1 was the lowest at maturity (p < 0.05).The SSCs at maturity of the three fruit thinning treatments, T2, T3 and T4, increased by 30.78%, 37.63% and 49.69% compared with the control, respectively.These results suggest that reducing the fruit load can significantly improve the carbohydrate metabolism ability of fruit.

Comparison of Pulp Firmness
Figure 4 shows that from the start of the experiment to fruit ripening, fruit firmnes without skin showed a trend of a continuous decline.The rate of the decrease in firmnes without skin of T1 and T2 fruit was low, and their firmness was the highest at maturity with no significant difference between them.The firmness of T3 and T4 decreased at relatively fast rate, and was the lowest at maturity, with no significant difference betwee them (p < 0.05).These results suggest that increasing the degree of fruit thinning leads t better fruit softening.

Comparison of IAD of Pericarp
As shown in Figure 5, the IAD value of the fruit pericarp decreased continuously dur ing the entire fruit growth and development period.The IAD of T4 decreased at the fastes rate and T1 decreased at the slowest rate.From the middle of the experiment to fruit rip ening, the IAD value of the pericarp in the different treatments ranked as T1 > T2 > T3 > T (p < 0.05).These results indicate that fruit thinning could weaken the green background color of the fruit pericarp and significantly improve fruit maturation at the same time.

Comparison of Pulp Firmness
Figure 4 shows that from the start of the experiment to fruit ripening, fruit firmness without skin showed a trend of a continuous decline.The rate of the decrease in firmness without skin of T1 and T2 fruit was low, and their firmness was the highest at maturity, with no significant difference between them.The firmness of T3 and T4 decreased at a relatively fast rate, and was the lowest at maturity, with no significant difference between them (p < 0.05).These results suggest that increasing the degree of fruit thinning leads to better fruit softening.
results suggest that reducing the fruit load can significantly improve the carbohydrat metabolism ability of fruit.

Comparison of Pulp Firmness
Figure 4 shows that from the start of the experiment to fruit ripening, fruit firmnes without skin showed a trend of a continuous decline.The rate of the decrease in firmnes without skin of T1 and T2 fruit was low, and their firmness was the highest at maturity with no significant difference between them.The firmness of T3 and T4 decreased at relatively fast rate, and was the lowest at maturity, with no significant difference between them (p < 0.05).These results suggest that increasing the degree of fruit thinning leads t better fruit softening.

Comparison of IAD of Pericarp
As shown in Figure 5, the IAD value of the fruit pericarp decreased continuously dur ing the entire fruit growth and development period.The IAD of T4 decreased at the fastes rate and T1 decreased at the slowest rate.From the middle of the experiment to fruit rip ening, the IAD value of the pericarp in the different treatments ranked as T1 > T2 > T3 > T (p < 0.05).These results indicate that fruit thinning could weaken the green background color of the fruit pericarp and significantly improve fruit maturation at the same time.

Comparison of I AD of Pericarp
As shown in Figure 5, the I AD value of the fruit pericarp decreased continuously during the entire fruit growth and development period.The I AD of T4 decreased at the fastest rate and T1 decreased at the slowest rate.From the middle of the experiment to fruit ripening, the I AD value of the pericarp in the different treatments ranked as T1 > T2 > T3 > T4 (p < 0.05).These results indicate that fruit thinning could weaken the green background color of the fruit pericarp and significantly improve fruit maturation at the same time.

Comparison of Pericarp Color and Quality
As shown in Figure 6, the L*, b* and C values of the peach pericarp in the differen fruit load treatments showed a common trend of an initial increase followed by a decreas during the rest of the fruit growth and development period, with no significant difference among treatments.The surface color of the peach fruit became yellow and bright in th early stage of fruit development, and this yellow gradually became lighter and the fru surface brightness decreased from the secondary swelling stage (73 DAFB) to maturity The a* and a*/b* values of the four treatments showed no significant differences over th entire fruit development process.The a* and a*/b* values changed gradually during th early stage of the experiment, but rose sharply in the middle stage, and continued to ma ture, indicating an increase in the red color of the fruit pericarp and a gradual lightenin of the green color.Regarding the h value of the pericarp, there was little difference be tween the treatments.The h value changed gradually from the early stage to the middl and late stages of the experiment, then decreased sharply, and the red color of the pericar deepened, indicating that the color and quality of the fruit skins increased with the growt and development of the fruit.The degree of fruit skin thinning had little effect on the colo and quality of the skin.

Comparison of Pericarp Color and Quality
As shown in Figure 6, the L*, b* and C values of the peach pericarp in the different fruit load treatments showed a common trend of an initial increase followed by a decrease during the rest of the fruit growth and development period, with no significant differences among treatments.The surface color of the peach fruit became yellow and bright in the early stage of fruit development, and this yellow gradually became lighter and the fruit surface brightness decreased from the secondary swelling stage (73 DAFB) to maturity.The a* and a*/b* values of the four treatments showed no significant differences over the entire fruit development process.The a* and a*/b* values changed gradually during the early stage of the experiment, but rose sharply in the middle stage, and continued to mature, indicating an increase in the red color of the fruit pericarp and a gradual lightening of the green color.Regarding the h value of the pericarp, there was little difference between the treatments.The h value changed gradually from the early stage to the middle and late stages of the experiment, then decreased sharply, and the red color of the pericarp deepened, indicating that the color and quality of the fruit skins increased with the growth and development of the fruit.The degree of fruit skin thinning had little effect on the color and quality of the skin.

Comparison of Pericarp Color and Quality
As shown in Figure 6, the L*, b* and C values of the peach pericarp in the different fruit load treatments showed a common trend of an initial increase followed by a decrease during the rest of the fruit growth and development period, with no significant differences among treatments.The surface color of the peach fruit became yellow and bright in the early stage of fruit development, and this yellow gradually became lighter and the fruit surface brightness decreased from the secondary swelling stage (73 DAFB) to maturity.The a* and a*/b* values of the four treatments showed no significant differences over the entire fruit development process.The a* and a*/b* values changed gradually during the early stage of the experiment, but rose sharply in the middle stage, and continued to mature, indicating an increase in the red color of the fruit pericarp and a gradual lightening of the green color.Regarding the h value of the pericarp, there was little difference between the treatments.The h value changed gradually from the early stage to the middle and late stages of the experiment, then decreased sharply, and the red color of the pericarp deepened, indicating that the color and quality of the fruit skins increased with the growth and development of the fruit.The degree of fruit skin thinning had little effect on the color and quality of the skin.

Comparison of Fruit Internal Quality
As shown in Figure 7, as the fruit grew and developed, the total fruit sugar content rose, the total acid content fell and the sugar-acid ratio increased.The total sugar and total acid contents and the sugar-acid ratio of all treatments changed significantly from the middle stage of fruit development onwards.At fruit ripening, the total sugar content of different treatments ranked as T4 > T3 > T2 > T1 (p < 0.05), and the total sugar content of the three fruit thinning treatments, T2, T3 and T4, increased by 13.58%, 22.33% and 31.42%compared with the control, respectively.Regarding the total acid content, T1 and T2 were relatively low and T3 and T4 were relatively high, and there was no significant difference between T3 and T4 (p < 0.05).In terms of the sugar-acid ratio, T4 was the highest and had the best flavor.T2 and T3 had a relatively medium sugar-acid ratio, and T1 had the lowest sugar-acid ratio.Compared with the mature control, the sugar-acid ratio of the three fruit thinning treatments, T2, T3 and T4, increased by 13.25%, 13.59% and 19.47%, respectively.These results indicate that reducing loading can promote the accumulation of total sugars and organic acids in fruit, significantly improving the sugar-acid ratio, and the fruit flavor quality.

Comparison of Fruit Internal Quality
As shown in Figure 7, as the fruit grew and developed, the total fruit sugar content rose, the total acid content fell and the sugar-acid ratio increased.The total sugar and total acid contents and the sugar-acid ratio of all treatments changed significantly from the middle stage of fruit development onwards.At fruit ripening, the total sugar content of different treatments ranked as T4 > T3 > T2 > T1 (p < 0.05), and the total sugar content of the three fruit thinning treatments, T2, T3 and T4, increased by 13.58%, 22.33% and 31.42%compared with the control, respectively.Regarding the total acid content, T1 and T2 were relatively low and T3 and T4 were relatively high, and there was no significant difference between T3 and T4 (p < 0.05).In terms of the sugar-acid ratio, T4 was the highest and had the best flavor.T2 and T3 had a relatively medium sugar-acid ratio, and T1 had the lowest sugar-acid ratio.Compared with the mature control, the sugar-acid ratio of the three fruit thinning treatments, T2, T3 and T4, increased by 13.25%, 13.59% and 19.47%, respectively.These results indicate that reducing loading can promote the accumulation of total sugars and organic acids in fruit, significantly improving the sugar-acid ratio, and the fruit flavor quality.

Figure 7.
Comparison of the total sugar, total acid and sugar-acid ratio of peach fruit under different fruit load treatments.Note: Different lowercase letters above the columns indicate a significant difference at the 5% level between different treatments in different periods.

Correlation Analysis of Peach Fruit Quality Indices
As shown in Table 1, the fruit load was significantly negatively correlated with the single fruit weight and SSC, extremely significantly negatively correlated with total sugar content and extremely significantly positively correlated with the IAD value, but had no significant correlation with the firmness, L*, a*, b*, C, h, a*/b*, total acid or sugar-acid ratio.The results showed that the fruit quality indices of ripe peaches were negatively correlated with the fruit load, and that there was no significant relationship between the fruit load and skin color.

Effect of Different Fruit Load Treatments on Overall Quality of Peach Fruit
As living standards improve, consumers have greater expectations of fruit quality.Numerous studies have shown that fruit thinning could significantly improve fruit quality [20] and fruit flavor.The results of this experiment showed that the single fruit weight, SSC, size, total sugar and sugar-acid ratio were significantly increased with progressive decreases in loading, which is consistent with the results of previous studies.In addition, fruit thinning improves the physiological status of fruit trees, which has been shown to significantly improve the color quality of apples [21].In this experiment, there were small differences in fruit color and quality among the different treatments, but no significant correlation between the color and quality indices of mature fruit and the fruit load, which

Correlation Analysis of Peach Fruit Quality Indices
As shown in Table 1, the fruit load was significantly negatively correlated with the single fruit weight and SSC, extremely significantly negatively correlated with total sugar content and extremely significantly positively correlated with the I AD value, but had no significant correlation with the firmness, L*, a*, b*, C, h, a*/b*, total acid or sugar-acid ratio.The results showed that the fruit quality indices of ripe peaches were negatively correlated with the fruit load, and that there was no significant relationship between the fruit load and skin color.

Effect of Different Fruit Load Treatments on Overall Quality of Peach Fruit
As living standards improve, consumers have greater expectations of fruit quality.Numerous studies have shown that fruit thinning could significantly improve fruit quality [20] and fruit flavor.The results of this experiment showed that the single fruit weight, SSC, size, total sugar and sugar-acid ratio were significantly increased with progressive decreases in loading, which is consistent with the results of previous studies.In addition, fruit thinning improves the physiological status of fruit trees, which has been shown to significantly improve the color quality of apples [21].In this experiment, there were small differences in fruit color and quality among the different treatments, but no significant correlation between the color and quality indices of mature fruit and the fruit load, which is inconsistent with previous research results.We speculate that this phenomenon might be caused by differences between tree species and cultivars.
Studies have shown that within a certain range, fruit quality improves with the reduction in the fruit load up to a certain point, but declines thereafter [9,22].In this study, all of the fruit quality indicators increased with progressive decreases in the fruit load, and the single fruit weight, SSC and total sugar content of mature fruit were significantly negatively correlated with the fruit load, which is not completely consistent with the previous research results quoted above.Previous experimental results showed that fruit quality of the late-ripening cultivar 'Xiahui 8' with about 50% fruit retention was significantly better than when 25% of the fruit were retained, except for the single fruit weight [23].This experiment studied 'Xiahui 11', an early maturing peach variety, and we speculate that this difference may be related to the nature of the fruit at maturity.Photosynthesis in the leaves produces assimilates for fruit growth and development, while some acids are also transported from the leaf to the fruit [24].The fruit growth and development cycle of early maturing cultivars is short, and less organic acids are transported to the fruit.Conversely, the fruit growth and development cycle of late maturing varieties is long, and relatively more organic acids are transported to the fruit, resulting in an increase in fruit quality with a decrease in the fruit load.

Effect of Different Fruit Load Treatments on Sugar and Acid Content of Peach Fruit
Soluble sugars and organic acids are not only important nutrients but also give flavor in fruit, and changes in the sugar and acid contents, and their relative proportions, directly affect fruit flavor quality [25].Some studies have shown that reducing the fruit load can promote the accumulation of sugar components and organic acids in fruit [6,26].In this experiment, as the fruit load decreased, the sugar and total acid contents increased to varying degrees during the growth and development of the peach fruit, which is consistent with the previously quoted research results.It may be that lower fruit load treatments, a reduced competition for carbohydrates between fruit and vegetative organs [27,28] and an increase in photosynthetic product entering individual fruit from leaves change fruit metabolism and the accumulation of soluble sugar components and organic acids, thus affecting the flavor quality of fruit [29,30].

Effects of Different Fruit Load Treatments on Peach Fruit Growth and Development
In this experiment, the effect of fruit thinning on fruit development occurred mainly during the middle and late stages of the experiment, possibly because the early stage of fruit development occurred during a period of slow growth, when the assimilates produced by leaves were sufficient for fruit development, and "source-sink" conflicts were not pronounced.As the fruit grow and develop further, especially in the middle and late stages of the experiment (the second fruit expansion stage), rapid growth and "sourcesink" issues become increasingly prominent, increasing the effect of fruit thinning [31].In addition, the I AD value of ripe fruit was positively correlated with the fruit load.The low fruit load treatment might result in early fruit ripening due to the low number of fruits, which could reduce competition for carbohydrates among fruit and between the fruit and the vegetative organs [27], thus increasing the carbohydrate supply for each fruit, which is conducive to fruit growth and development and early fruit maturity.This phenomenon has also been observed in both litchi [32] and grapes [11,33].
For the early peach 'xiahui 11' used in this experiment, the lower the load, the better the fruit quality, but the improved quality cannot outweigh the loss in the economic benefit resulting from the lower yield.Previous experiments have shown that the quality and yield of medium-ripening peaches 'Xiahui 6' [34] and late-ripening peaches 'Xiahui 8' [23] were higher when the fruit load was maintained at 50%, with both a relatively high fruit quality and yield providing the maximum economic benefit.Therefore, in actual production and cultivation, technicians should manage the peach tree fruit load according to the local situation to ensure the double benefits of optimal fruit quality and yield.

Conclusions
The yields per 100 m 2 of the four experimental treatments retaining 100%, 75%, 50% and 25% of the tree fruit load were calculated as 367.17, 292.20, 267.62 and 194.60 kg, respectively.The external and internal qualities of fruit were both high when 25% of the fruit was retained, and their flavor quality was significantly improved.There was little difference in the fruit flavor quality between the treatments retaining about 50% and 25% of the fruit, and the yield of the treatment with 50% fruit retention was higher than that with 25% fruit retention.In actual production, fruit farmers can leave or remove fruit according to market conditions, and achieve a balance between fruit quality and yield to maximize their economic return.

Figure 2 .
Figure 2. Comparison of single fruit weight and size changes in peach fruit under different fruit load treatments.

Figure 2 .
Figure 2. Comparison of single fruit weight and size changes in peach fruit under different fruit load treatments.
Horticulturae 2023, 9, x FOR PEER REVIEW 5 of 1 results suggest that reducing the fruit load can significantly improve the carbohydrat metabolism ability of fruit.

Figure 3 .
Figure 3.Comparison of soluble solid contents of peach fruit under different fruit load treatments

Figure 4 .
Figure 4. Comparison of pulp firmness of peach fruit under different fruit load treatments.

Figure 3 .
Figure 3.Comparison of soluble solid contents of peach fruit under different fruit load treatments.

Figure 3 .
Figure 3.Comparison of soluble solid contents of peach fruit under different fruit load treatments

Figure 4 .
Figure 4. Comparison of pulp firmness of peach fruit under different fruit load treatments.

Figure 4 .
Figure 4. Comparison of pulp firmness of peach fruit under different fruit load treatments.

Figure 5 .
Figure 5.Comparison of peach fruit pericarp IAD values under different fruit load treatments.

Figure 5 .
Figure 5.Comparison of peach fruit pericarp I AD values under different fruit load treatments.

Figure 6 .
Figure 6.Comparison of color and quality of peach pericarp under different fruit load treatments.Note: Different lowercase letters above the columns indicate a significant difference at the 5% level between different treatments in different periods.

Figure 6 .
Figure 6.Comparison of color and quality of peach pericarp under different fruit load treatments.Note: Different lowercase letters above the columns indicate a significant difference at the 5% level between different treatments in different periods.

Figure 7 .
Figure 7.Comparison of the total sugar, total acid and sugar-acid ratio of peach fruit under different fruit load treatments.Note: Different lowercase letters above the columns indicate a significant difference at the 5% level between different treatments in different periods.

Table 1 .
Correlation analysis between fruit load and quality indicators of Xiahui 11 ripe peaches.

Table 1 .
Correlation analysis between fruit load and quality indicators of Xiahui 11 ripe peaches.