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ASHS 2024 Annual Conference

 

Fruit Characteristics of the Joy Peach Cultivars

Author:
Chunxian Chen US Department of Agriculture, Agricultural Research Service, Southeastern Fruit and Tree Nut Research Laboratory, 21 Dunbar Road, Byron, GA 31008, USA

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Abstract

A trio of peach cultivars, Crimson Joy, Liberty Joy, and Rich Joy, have been recently released by the US Department of Agriculture breeding program at Byron, GA. They ripen at Byron in early to mid-June, late June to early July, and mid-July, respectively. Additional data on their fruit development are needed to understand the ripening process and optimize harvest timing. This study was designed to measure and compare characteristics of ripening fruit harvested weekly from the three Joy cultivars in two trial orchards. Fruit characteristics were significantly different among the three cultivars, the trial locations, and the harvest weeks. Difference in the five size-related characteristics (fruit weight, flesh weight, pit weight, and equatorial and polar diameters) and soluble solid content (SSC) were statistically significant among the three cultivars. ‘Crimson Joy’ had the smallest averages in the size-related characteristics and ‘Rich Joy’ fruit had the largest. ‘Liberty Joy’ had the firmest fruit and least juice volume and blush rating value at maturation. Trees in the commercial block produced larger fruit than those in the Byron research block. Differences among the harvests were statistically significant for all the fruit characteristics, suggesting that the peach fruit experienced dramatic changes as ripening progressed. The weights and diameters, juice volumes, and SSC continued to increase in the harvests although with reduced firmness. Correlation coefficients varied greatly between these fruit characteristics along with R2 and P values. The highest positive correlations were observed among fruit weight, equatorial diameter, polar diameter, and flesh weight. Pit weight was positively correlated with them to a lesser extent. Firmness showed substantial negative correlations with several characteristics, including three weights, two diameters, juice volume, SSC, and blush rating value. SSC and titratable acidity were also negatively correlated. The data confirmed that peach fruit continued to size while ripening and should be useful to determine appropriate harvest timing, which could differ for commercial packing vs. roadside sales.

Peach (Prunus persica) are climacteric fruit and may ripen quickly with production of ethylene (Hayama et al. 2006) and changes of many fruit characteristics such as size, weight, color, firmness, soluble solid content (SSC), titratable acidity (TA), and volatiles (Fishman et al. 1993; Pinto et al. 2016; Xi et al. 2017). Many differences in the physicochemical properties were observed between melting and nonmelting peach fruit on tree and during storage, including size, weight percentage of cell walls, intrinsic viscosity, pectin content, and firmness (Fishman et al. 1993). The absorbance index of the skin of on-tree ripening peach fruit decreased linearly at a higher rate ∼2 weeks before harvest, changed dramatically and coincidentally with the “color break” of the skin, but SSC altered insignificantly (Pinto et al. 2016). Quantification of sugars, organic acids, and aroma volatiles suggested that sugars and acids provide the basic flavors, but aroma volatiles and flavor compounds determine unique flavors among different types of peaches (Xi et al. 2017). Assessing changes in ripening fruit characteristics is useful to understand ripening factors and processes, determine characteristics related to fruit eating quality and consumer preferences, and provide a guide on harvest timing and future breeding direction.

The peach breeding program at the US Department of Agriculture-Agricultural Research Service Southeastern Fruit and Tree Nut Research Laboratory (SEFTNRL) in Byron, GA, has served the medium to high chill production areas in the southeastern United States since 1937 (Chen 2021), and culminated in a recently released trio of Joy cultivars, Crimson Joy (Chen and Okie 2020a), Liberty Joy (Chen and Okie 2020b), and Rich Joy (Chen and Okie 2020c). They have different chilling requirements and ripening/harvesting seasons but share similar attractive high blush, yellow melting freestone flesh, normal acidity, and excellent firmness for handling, which have been the predominant fruit profile in the high-chill production area in the southeastern United States. ‘Crimson Joy’ fruit ripen in mid- to late June in Byron, GA, ‘Liberty Joy’ in late June to early July, and ‘Rich Joy’ in mid-July. In this study, characteristics of ripening fruit harvested weekly from the three Joy cultivars in two trial orchards were surveyed and compared, providing additional useful information on fruit ripening process of the three new peach cultivars and helping optimize harvest timing.

Materials and Methods

Peach cultivars.

Three new peach cultivars, Crimson Joy, Liberty Joy, and Rich Joy, were used in this study. Trees were grafted on ‘Guardian’ rootstock and planted in 2013 randomly with dozens of other cultivars and advanced selections in two trial orchards, six trees of each cultivar together in each orchard to facilitate management and evaluation. One was a variety block in SEFTNRL, Byron, GA (designated as “Byron”) and the other in a commercial trial block in Fort Valley, GA (Designated as “Trial1”). Appropriate standard orchard management schemes and pesticide sprays on the two blocks were applied by the Byron and the commercial farm management teams, respectively, primarily managing pests and fungal diseases on fruit as well as controlling weeds.

Fruit sampling and characteristics measurement.

Fruit sampling and characteristics measurement were previously described (Chen et al. 2016). Nondestructive measurements were performed before destructive ones. Briefly, 15 ripening healthy fruits were randomly harvested weekly across the tree canopy of the three cultivars in 2016. The first harvest (W1) took place in the first week after yellow ground color appeared in the skin of the fruit and the next 2 or 3 weekly harvests (W2, W3, or plus W4) if ripening fruit remained firm and harvestable. Fruits were transported to the laboratory within 2 h, and measurements were started on the same day. The blush coverage was rated at the scale of 0 to 9 (0 = no blush to 9 = almost full blush). The measured and calculated fruit characteristics were fruit weight (g), flesh weight (g, calculated by fruit weight minus pit weight), pit weight (g), equatorial diameter (cm), suture-back polar diameter (cm), firmness (kg force), juice volume (mL), SSC (°Brix), TA (%, i.e., g/100 mL), SSC/TA ratio (SSC divided by TA), pH value, and blush rating value (0–9). Blush and ground color Hunter L, a and b values were also measured at the reddest and yellowest spots respectively using Chroma Meter CR-400 (Konica Minolta, Inc., Tokyo, Japan). The ratio of equatorial and polar diameters was also calculated to indicate the roundness of the fruit.

Data management and statistical analysis.

Data management, statistical analysis, and plotting were performed using Excel (Microsoft Corporation, Redmond, WA, USA) and SAS 9.4 (SAS Institute Inc., Cary, NC, USA), as previously described (Chen et al. 2016). The general linear model procedure in SAS was used with Tukey’s honestly significant difference test (α = 0.05) for the cultivars, harvest dates, trial locations, and some interactions. The CORREL, RSQ, and F.DIST functions in Excel were used to calculate correlation coefficients (r), R2, and P values between any two characteristics datasets.

Results and Discussion

Differences in peach fruit characteristics.

Fruit characteristics showed various differences and statistical significances among the three cultivars, the two trial locations, and the 4 harvest weeks, respectively (Table 1). Many differences were numerically small because fruit of the three cultivars were similar, but some differences were statistically significant. The difference in the means of the five size-related characteristics (fruit weight, flesh weight, pit weight, and equatorial and polar diameters) and SSC were statistically significant among ‘Crimson Joy’, ‘Liberty Joy’, and ‘Rich Joy’. The differences in the five size-related characteristics among the three cultivars appeared to be interpreted by their ripening seasons; generally later season peach fruit tended to be larger with more SSC and better taste, likely due to longer growth time. In addition, compared with the two other cultivars, ‘Rich Joy’ fruit were also largest in the juice volume, pH value, and blush rating value. ‘Liberty Joy’ had the firmest fruit and least juice volume and blush rating value.

Table 1.

Means, standard errors, and letters of statistical significance of peach fruit characteristics.i

Table 1.

Differences in the means of the three weights and blush rating values of all three cultivars between the two trial locations were not statistically significant, but other variables were, including two diameters, firmness, juice volume, SSC, TA, SSC/TA ratios, and pH values (Table 1). All the size-related characteristics indicated that trees in Trial1 (a commercial orchard) produced larger fruit than those in Byron (a research block). Such fruit size differences between commercial and research trials blocks had been observed anecdotally and demonstrated in this survey. The differences were presumably due to better management in some respects in the commercial setting than that for research; nonetheless, it was not part of this survey.

Differences in the means among the harvests W1 to W4 of all the three cultivars were statistically significant among all the fruit characteristics, suggesting that the peach fruit experienced dramatic changes during the weeks of the ripening process. The size-related weights and diameters, juice volumes, and SSC continued to increase in the harvests with reduced firmness. Compared with W1, the mean fruit weights of all the three cultivars had increased about 2.56%, 33.78%, and 59.26% in W2 to W4, and firmness reduced by 7.82%, 26.21%, and 22.79%, respectively. Descriptively, the first 2 weeks (W1–W2) might about correspond to the period of commercial harvest, which generally took place at the beginning of apparently full yellow background and red blush skin coloration, but fruit remain firm. The second 2 weeks (W3–W4) were the time of full biological ripening with gradually softening flesh and increasing aromatic flavor in the melting fruit. The results confirmed that peach fruit continued to size during the ripening process and harvest timing might substantially affect yield. In reality, fruit firmness at harvest and potential postharvest storage/shelf life are among the most important factors for fresh packing peach industries to determine when to harvest. However, fruit harvest at W3 and even W4 might be firm enough for roadside and express mail sales of the three Joy cultivars for these consumers to have larger, juicier and tastier peaches.

Changes of characteristics in weekly harvested peach fruit of the three Joy cultivars.

The weekly changes of ripening fruit characteristics showed more similarities than differences among the three Joy cultivars (Fig. 1A and B). ‘Crimson Joy’ was firm enough for only three weekly harvests, but ‘Liberty Joy’ and ‘Rich Joy’ were sufficiently firm for four, indicating fruit of the latter two cultivars appeared to be firmer or slower in softening/melting, resulting in a longer harvest window. Three weights (fruit, flesh, and pit) and two diameters (equatorial and polar) increased steadily during the weeks of harvests, suggesting fruit continued to size after fruit started the coloration of yellow background and red blush. Taking fruit weight as an example and compared with each previous weekly harvest, ‘Crimson Joy’ increased 19.52% from W1 to W2 and 18.90% from W2 to W3, respectively. ‘Liberty Joy’ increased 10.18%, 6.81%, and 12.95% from W1 to W2, W2 to W3, and W3 to W4, respectively. Likewise, ‘Rich Joy’ increased 13.15%, 38.83%, and 13.20%, respectively (Fig. 1A). As expected, however, fruit firmness decreased substantially, especially in ‘Crimson Joy’ harvested in W3 and ‘Rich Joy’ in W4. A further monitoring of the firmness change during the entire ripening process over multiple years could facilitate establishing a “ripe” firmness threshold to determine harvest timing related to commercial packing vs. roadside sales.

Fig. 1.
Fig. 1.

Changes of characteristics in weekly harvested ‘Joy’ peach fruit. (A) Includes FtWt = fruit weight (g), FlWt = flesh weight (g), PtWt = pit weight (g), EqDi = equatorial diameter (cm), PoDi = polar diameter (cm), Firm = firmness (kg), JuVo = juice volume (mL), SSC = soluble solid content (°Brix), TA = titrable acidity (% or g/100 mL), SSTA = SSC/TA Ratio, pH = pH value, and BlRa = blush rating value (0–9, 0 = no blush to 9 = almost full blush). (B) Includes BlHL, BlHa, BlHb, GrHL, GrHa, GrHb = blush and ground color Hunter L and a and b values, respectively, and BlRa. W1–W4 = harvest weeks 1 to 4. CJ = ‘Crimson Joy’; LJ = ‘Liberty Joy’; RJ = ‘Rich Joy’. BlRa was intentionally duplicated in the second chart as the secondary axis to keep it the same layout as the first chart.

Citation: HortScience 58, 4; 10.21273/HORTSCI17056-22

Although blush rating values generally tended to increase from earlier harvests to later ones, Hunter color L and a and b values changed irregularly among the three cultivars (Fig. 1B), probably because selection of measured spots was difficult and subjective on the fruit surface with different abundant red blush and scarce yellow background. More measurements with better spot selection criteria are needed to find the regularity of the color value changes and determine the utility of some of the measurements as indicators for fruit maturity or harvest timing (Fishman et al. 1993; Pinto et al. 2016). On the other hand, the colorimeter seemed like a useful tool because it gave clear values, but apparently it determined little other than when the green ground color changed to yellow. In this context, the blush coverage appeared to matter more as a ripening indicator than the shade of red or yellow.

It was worth noting that apparently the means of SSC and TA did not change as expected over W1 to W4 (Table 1, Fig. 1A), in which usually SSC and SSC/TA ratios were increasing whereas TA was decreasing. There was no reasonable explanation; the instruments used were among the first possible culprits.

Correlations between peach fruit characteristics.

Correlation coefficients and R2 values varied greatly between these fruit characteristics (Table 2), so did P values and statistical significance (Supplemental Table 1). The highest positive correlations (highlighted in green in Table 2) were observed among fruit weight, equatorial diameter, polar diameter, and flesh weight. Pit weight was also positively correlated with them to a weaker extent. These correlations were statistically significant according to their P values (Supplemental Table 1). The next high-correlation group was between any of the four fruit size characteristics with pit weight and juice volume, respectively. Firmness showed substantial negative correlations with several characteristics, including the five size-related characteristics (weights and diameters), juice volume, SSC, and blush rating value. SSC and TA were also negatively correlated (r = –0.76, R2 = 0.57, P = 0.28).

Table 2.

Correlation coefficients and R2 values of any two fruit characteristics.i

Table 2.

The distribution and trendlines of some positively and negatively correlated fruit characteristics were displayed to visualize their correlations, respectively (Fig. 2A and B). It showed fruit weight or either diameter could be used as an indicator of fruit sizes (Fig. 2A). In addition, the average ratios of equatorial and polar diameters of ‘Crimson Joy’, ‘Liberty Joy’, and ‘Rich Joy’ fruit were over 0.98, 0.98, and 0.99, respectively, corroborating their round shapes. Firmness had weak negative correlations with the equatorial diameter, SSC, blush rating value, and juice volume, which were consistent with the trend that peach fruit on trees continued to become bigger, sweeter, redder, and juicier while softening in the ripening process. In this context, the data might be useful to determine appropriate harvest timings for the three cultivars, which should differ between harvests for packing and roadside sales.

Fig. 2.
Fig. 2.

Distributions and trendlines of some fruit characteristics correlated positively and negatively. (A) The positively correlated examples are fruit weight, pit weight, flesh weight, equatorial diameter (EqDi), and polar diameter (PoDi), with equations and R2 values displayed. (B) The negatively correlated examples are firmness, EqDi, soluble solid content (SSC), blush rating value, and juice volume, without equations and R2 values displayed.

Citation: HortScience 58, 4; 10.21273/HORTSCI17056-22

References Cited

  • Chen, C. 2021 Peach cultivar releases and fruit trait distribution in the USDA-ARS Byron program Acta Hortic. 1304 1 29 36 https://doi.org/10.17660/ActaHortic.2021.1304.4

    • Search Google Scholar
    • Export Citation
  • Chen, C, Bai, JH, Okie, WR & Plotto, A. 2016 Comparison of fruit characters and volatile components in peach-to-nectarine mutants Euphytica. 209 2 409 418 https://doi.org/10.1007/s10681-016-1648-8

    • Search Google Scholar
    • Export Citation
  • Chen, C & Okie, WR. 2020a ‘Crimson Joy’ peach HortScience. 55 6 972 973 https://doi.org/10.21273/Hortsci14983-20

  • Chen, C & Okie, WR. 2020b ‘Liberty Joy’ peach HortScience. 55 6 951 952 https://doi.org/10.21273/Hortsci14907-20

  • Chen, C & Okie, WR. 2020c ‘Rich Joy’ peach HortScience. 55 4 591 592 https://doi.org/10.21273/Hortsci14720-19

  • Fishman, ML, Levaj, B, Gillespie, D & Scorza, R. 1993 Changes in the physicochemical properties of peach fruit pectin during on-tree ripening and storage J Am Soc Hortic Sci. 118 3 343 349 https://doi.org/10.21273/JASHS.118.3.343

    • Search Google Scholar
    • Export Citation
  • Hayama, H, Shimada, T, Fujii, H, Ito, A & Kashimura, Y. 2006 Ethylene-regulation of fruit softening and softening-related genes in peach J Expt Bot. 57 15 4071 4077 https://doi.org/10.1093/jxb/erl178

    • Search Google Scholar
    • Export Citation
  • Pinto, C, Reginato, G, Mesa, K, Shinya, P, Diaz, M & Infante, R. 2016 Monitoring the flesh softening and the ripening of peach during the last phase of growth on-tree HortScience. 51 8 995 1000 https://doi.org/10.21273/HORTSCI.51.8.995

    • Search Google Scholar
    • Export Citation
  • Xi, WP, Zheng, Q, Lu, JF & Quan, JP. 2017 Comparative analysis of three types of peaches: Identification of the key individual characteristic flavor compounds by integrating consumers’ acceptability with flavor quality Hortic Plant J. 3 1 1 12 https://doi.org/10.1016/j.hpj.2017.01.012

    • Search Google Scholar
    • Export Citation

Supplemental Table 1.

P values and significance (α = 0.05) for correlation coefficients of any two fruit characteristics.

Supplemental Table 1.
  • Fig. 1.

    Changes of characteristics in weekly harvested ‘Joy’ peach fruit. (A) Includes FtWt = fruit weight (g), FlWt = flesh weight (g), PtWt = pit weight (g), EqDi = equatorial diameter (cm), PoDi = polar diameter (cm), Firm = firmness (kg), JuVo = juice volume (mL), SSC = soluble solid content (°Brix), TA = titrable acidity (% or g/100 mL), SSTA = SSC/TA Ratio, pH = pH value, and BlRa = blush rating value (0–9, 0 = no blush to 9 = almost full blush). (B) Includes BlHL, BlHa, BlHb, GrHL, GrHa, GrHb = blush and ground color Hunter L and a and b values, respectively, and BlRa. W1–W4 = harvest weeks 1 to 4. CJ = ‘Crimson Joy’; LJ = ‘Liberty Joy’; RJ = ‘Rich Joy’. BlRa was intentionally duplicated in the second chart as the secondary axis to keep it the same layout as the first chart.

  • Fig. 2.

    Distributions and trendlines of some fruit characteristics correlated positively and negatively. (A) The positively correlated examples are fruit weight, pit weight, flesh weight, equatorial diameter (EqDi), and polar diameter (PoDi), with equations and R2 values displayed. (B) The negatively correlated examples are firmness, EqDi, soluble solid content (SSC), blush rating value, and juice volume, without equations and R2 values displayed.

  • Chen, C. 2021 Peach cultivar releases and fruit trait distribution in the USDA-ARS Byron program Acta Hortic. 1304 1 29 36 https://doi.org/10.17660/ActaHortic.2021.1304.4

    • Search Google Scholar
    • Export Citation
  • Chen, C, Bai, JH, Okie, WR & Plotto, A. 2016 Comparison of fruit characters and volatile components in peach-to-nectarine mutants Euphytica. 209 2 409 418 https://doi.org/10.1007/s10681-016-1648-8

    • Search Google Scholar
    • Export Citation
  • Chen, C & Okie, WR. 2020a ‘Crimson Joy’ peach HortScience. 55 6 972 973 https://doi.org/10.21273/Hortsci14983-20

  • Chen, C & Okie, WR. 2020b ‘Liberty Joy’ peach HortScience. 55 6 951 952 https://doi.org/10.21273/Hortsci14907-20

  • Chen, C & Okie, WR. 2020c ‘Rich Joy’ peach HortScience. 55 4 591 592 https://doi.org/10.21273/Hortsci14720-19

  • Fishman, ML, Levaj, B, Gillespie, D & Scorza, R. 1993 Changes in the physicochemical properties of peach fruit pectin during on-tree ripening and storage J Am Soc Hortic Sci. 118 3 343 349 https://doi.org/10.21273/JASHS.118.3.343

    • Search Google Scholar
    • Export Citation
  • Hayama, H, Shimada, T, Fujii, H, Ito, A & Kashimura, Y. 2006 Ethylene-regulation of fruit softening and softening-related genes in peach J Expt Bot. 57 15 4071 4077 https://doi.org/10.1093/jxb/erl178

    • Search Google Scholar
    • Export Citation
  • Pinto, C, Reginato, G, Mesa, K, Shinya, P, Diaz, M & Infante, R. 2016 Monitoring the flesh softening and the ripening of peach during the last phase of growth on-tree HortScience. 51 8 995 1000 https://doi.org/10.21273/HORTSCI.51.8.995

    • Search Google Scholar
    • Export Citation
  • Xi, WP, Zheng, Q, Lu, JF & Quan, JP. 2017 Comparative analysis of three types of peaches: Identification of the key individual characteristic flavor compounds by integrating consumers’ acceptability with flavor quality Hortic Plant J. 3 1 1 12 https://doi.org/10.1016/j.hpj.2017.01.012

    • Search Google Scholar
    • Export Citation
Chunxian Chen US Department of Agriculture, Agricultural Research Service, Southeastern Fruit and Tree Nut Research Laboratory, 21 Dunbar Road, Byron, GA 31008, USA

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Contributor Notes

I thank Luke Quick for help in managing peach blocks in the US Department of Agriculture (USDA) Byron Station, Bryan Blackburn for harvesting and measuring peach fruit used in this work, and Dr William Okie for reviewing the manuscript. The research was partly supported by the USDA National Programs of Plant Genetic Resources, Genomics and Genetic Improvement (project no. 6042-21000-005-000D). This article reports the results of research only. Mention of a trademark or proprietary product is solely for the purpose of providing specific information and does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that may also be suitable.

C.C. is the corresponding author. E-mail: chunxian.chen@usda.gov.

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