The peach germplasm clonal repository at the Taiwan Agricultural Research Institute (TARI) is among the warmest locations worldwide for conserving peach [Prunus persica (L.) Batsch] cultivars (Wen and Sherman 2002). TARI maintains a diverse collection of ∼200 accessions of peach and nectarine germplasm specifically adapted to regions with mild winters. These mild winter temperatures provide an ideal environment for the collection and selection of low-chill peach cultivars, which are increasingly important due to the challenges posed by global warming and potential future climatic shifts (Huang et al. 2024).
The TARI peach breeding program has aimed to develop peach cultivars with low chilling requirements, preferably under 200 chilling units (CU). The program focuses on cultivars that thrive in humid, lowland subtropical conditions and produce attractive, juicy, sweet fruits with white flesh and minimal acidity. Since 2003, TARI has successfully released several peach cultivars with low chilling requirements, such as ‘SpringHoney’ (Ou and Wen 2003), ‘Xiami’ (Ou and Song 2006), and ‘Tainung No.7 HongLing’ (Huang et al. 2024).
As a continuation of these efforts, TARI has recently released a new fresh-market peach cultivar, Tainung No.9 HongJin. This cultivar has a chilling requirement of ∼74 h at temperatures below 14 °C, making it highly suitable for commercial production in subtropical, low-altitude regions. Notably, although most peach cultivars in Asia, including in Taiwan, are white-fleshed, Tainung No.9 HongJin is the first yellow-fleshed peach cultivar developed in Taiwan, offering greater diversity to both growers and consumers.
Origin and Development
Tainung No.9 HongJin is a fresh-market peach cultivar developed through a cross made in 2006 by Dr. Ien-Chie Wen at TARI. The cross involved two elite low-chill breeding lines, P87-04 and P93-28, selected by the TARI breeding program (Fig. 1). P87-04 originated from a cross between P5-9 and ‘TropicBeauty’, whereas P93-28 was derived from a cross of FL 90-35C and ‘Premier’. The seedling P5-9 resulted from crossing ‘TuTu’ with ‘FlordaGold’. The low-chill genes present in these lines, including those from ‘TropicBeauty’, ‘Premier’, ‘TuTu’, and cultivars released by the University of Florida, contribute to the adaptability of ‘Tainung No.9 HongJin’ to warm climates. Initially designated as P97-12Y, the seedling of ‘Tainung No.9 HongJin’ was first evaluated for its desirable traits in 2008. After its promising performance, TARI officially released the cultivar to growers in 2018. Since then, ‘Tainung No.9 HongJin’ has undergone annual performance evaluations at TARI.
Pedigree of ‘Tainung No. 9 HongJin’ peach.
Citation: HortScience 59, 11; 10.21273/HORTSCI18187-24
This report presents data from 2022 to 2024 for Tainung No.9 HongJin and the comparison cultivars, Tainung No.7 HongLing, TropicBeauty (Rouse and Sherman 1989), and UFSun (Sherman 2004). ‘Tainung No.9 HongJin’, ‘Tainung No.7 HongLing’, and ‘UFSun’ were established in 2017, and ‘TropicBeauty’ was planted in 2020. All cultivars were grafted onto Prunus persica (L.) ‘Kutao’ rootstock (Wen and Sherman 2002) and pruned to open-center form. The study has three replications, with each tree serving as a replication. The trees were spaced 4 m apart within rows and 5 m between rows at the Low Altitude Clonal Germplasm Repository at TARI in Wufeng, Taichung, Taiwan (lat. 24.03°N, long. 120.70°E, elevation 89 m).
Phenological data, including the Julian day for 50% leaf drop, 50% bloom, 50% leaf budbreak, and 50% harvest, were recorded. Fruit characteristics, such as fruit development period (FDP), fruit weight, size, firmness, soluble solids concentration (SSC), and titratable acidity, were determined from a sample of 10 fruits collected at peak harvest for each cultivar annually. FDP was measured from the date of 50% bloom to fruit physiological maturity. Fruit size was calculated as the average of the equatorial and sutural diameters. Fruit firmness, SSC, and titratable acidity (expressed as % malic acid) were measured using a digital texturometer (KG02-15; Caesar Instrument Co. Ltd., Taipei, Taiwan), a digital refractometer (PAL-1; ATAGO Co. Ltd., Tokyo, Japan), and a digital acidity meter (PAL-Easy ACID11, ATAGO Co. Ltd.), respectively.
The chilling requirement for ‘Tainung No.9 HongJin’ was estimated only during the 2023–24 season. Weekly samples of 20 single-node cuttings were collected from 15 Dec in 2023 to 30 Jan in 2024. These cuttings were incubated in a growth chamber set to 24 °C with a 16-h light/8-h dark cycle to simulate forcing conditions. Chilling hours in the orchard below 7.2 and 14 °C were recorded at each collection. The 14-°C threshold was applied based on the Taiwan low-chill model (Ou and Chen 2000) and a review by Erez (2024), which offers a more accurate estimation of chill accumulation in subtropical climates compared with traditional models developed for temperate regions (Huang et al. 2024). The chilling requirement for dormancy release was defined as the point when 50% of the cuttings exhibited flower budbreak.
Phenological and fruit characteristic data were analyzed using a completely randomized design (CRD) with analysis of variance in CoStat software (version 6.1; CoHort Software, Monterey, CA, USA). Mean separation was performed using Tukey’s honestly significant difference test at P < 0.05. Data on flower and leaf budbreak percentages were analyzed using a repeated measures design with a beta distribution (DIST = BETA) in the generalized linear mixed model procedure (PROC GLIMMIX) in SAS (version 9.4; SAS Institute Inc., Cary, NC, USA). The model included fixed effects for organ type (leaf and flower buds), date, and organ type × date interaction. Random effects included a random intercept for each replication (REP) and the effect of date (SUBJECT = organ type × REP), using the covariance structure that minimized the corrected Akaike Information Criterion (AICc). Data were rescaled to the original scale using the inverse link function (ILINK) in the LSMEANS statement. Mean separation was performed using the Tukey–Kramer test at P < 0.05.
Description
Tainung No.9 HongJin is a vigorous peach cultivar with an upright to spreading growth habit. The leaves feature reniform glands, and the flowers are self-fertile, with showy pink petals and bright yellow, abundant pollen. Blooming typically occurs in mid-February, with the fruit ripening period extending from early to mid-May in Wufeng, Taichung, Taiwan. The fruits are round with a slight taper toward the apex, and their skin displays an attractive red blush that covers a substantial portion of the yellow-orange ground color (Fig. 2). The Mandarin translation of a part of the name ‘HongJin’ reflects the fruit’s red skin (Hong) and golden flesh (Jin). ‘Tainung No.9 HongJin’ consistently exhibits melting flesh and clingstone characteristics.
Ripe fruits of ‘Tainung No.9 HongJin’ peach, initially labeled as 97-12Y, on the tree grown at Taiwan Agricultural Research Institute (A and B) and freshly harvested fruits (C).
Citation: HortScience 59, 11; 10.21273/HORTSCI18187-24
Performance
Phenology.
To evaluate phenological development from winter to spring, we compared ‘Tainung No.9 HongJin’ with our recent release ‘Tainung No.7 HongLing’ and two established low-chill peach, ‘TropicBeauty’ and ‘UFSun’ (Table 1). ‘Tainung No.9 HongJin’ showed an intermediate timing for 50% leaf drop, occurring later than ‘UFSun’ but earlier than ‘Tainung No.7 HongLing’, which had the latest leaf drop among the cultivars. In terms of 50% bloom, ‘Tainung No.9 HongJin’ reached this stage slightly earlier than ‘TropicBeauty’, which bloomed the latest, and later than ‘Tainung No.7 HongLing’, which was the earliest to bloom. For 50% leaf budbreak, ‘Tainung No.9 HongJin’ demonstrated a similar timing to ‘TropicBeauty’, both of which were slightly later than ‘Tainung No.7 HongLing’, which had the earliest budbreak. At the 50% harvest stage, ‘Tainung No.9 HongJin’ had a harvest time between that of ‘Tainung No.7 HongLing’, which was harvested the earliest, and ‘TropicBeauty’, which had the latest harvest.
Julian day of 50% leaf drop, bloom, leaf budbreak, and harvest for four peach cultivars, Tainung No.9 HongJin, Tainung No.7 HongLing, TropicBeauty, and UFSun, at the Low Altitude Clonal Germplasm Repository of the Taiwan Agriculture Research Institute (TARI) in Wufeng, Taichung, Taiwan, 2022–24.i
Chilling requirement.
The accumulated chilling hours below 14 °C steadily increased over the sampling period, reaching ∼313 h by late January (Fig. 3A). In contrast, the accumulation of chilling hours below 7.2 °C was minimal, remaining near zero throughout the period.
Chilling requirement estimation for ‘Tainung No.9 HongJin’ peach at the Taiwan Agricultural Research Institute (TARI), shown as accumulated chilling hours (A) and budbreak percentage in single-node stem cuttings (B). Weekly samples, each consisting of 20 single-node cuttings, were collected from the orchard and incubated in a controlled-environment growth chamber set to 24 °C with a 16-h light/8-h dark cycle. The chilling requirement for dormancy release was determined as the point where 50% of the cuttings exhibited flower budbreak (indicated by the long-dash line). Organ, Date, and Organ × Date refer to the effects of the type of buds, sampling timing, and their interaction, respectively. NS and *** denote nonsignificant or significant effects at P < 0.001, respectively. Data are presented as mean ± the SEM (n = 3). Different uppercase and lowercase letters denote significant differences among sampling timings within leaf buds and flower buds, respectively, according to the Tukey–Kramer test (P < 0.05).
Citation: HortScience 59, 11; 10.21273/HORTSCI18187-24
Leaf buds required fewer chilling hours to achieve a 50% budbreak compared with flower buds (Fig. 3B). The budbreak percentage of leaf buds increased rapidly after mid-December, suggesting that leaf buds of ‘Tainung No.9 HongJin’ have a relatively low chilling requirement for dormancy release or may not fully enter into endodormancy. By late December, leaf budbreak reached ∼80% to 90%, indicating a high responsiveness to the accumulated chilling hours or release from endodormancy.
Conversely, flower buds exhibited a slower budbreak response, gradually increasing from about 30% in mid-December to more than 80% by late January. The percentage of budbreak for flower buds remained consistently lower than that for leaf buds throughout the sampling period; these two types of buds had different response curves, highlighting that flower buds had a weaker endodormancy response than vegetative buds, which might not have entered endodormancy during the 2023–24 season.
These findings suggest that it is capable of blooming and resuming vegetative growth under 0-chill-hour (<7.2 °C) conditions. The estimated chilling requirement for breaking flower bud dormancy in ‘Tainung No.9 HongJin’ is ∼74 h of temperatures below 14 °C.
Fruit characteristics.
The FDP, defined as the number of days from 50% bloom to physiological fruit maturity, varied among the cultivars. ‘TropicBeauty’ exhibited the longest FDP at 83.8 d, followed by ‘Tainung No.9 HongJin’ at 82.1 d. ‘Tainung No.7 HongLing’ and ‘UFSun’ had shorter FDPs of 78.9 d and 75.7 d, respectively (Table 2).
The fruit development period and fruit characteristics of ‘Tainung No.9 HongJin’ peach compared with three other peach cultivars Tainung No.7 HongLing, TropicBeauty, and UFSun, at the Low Altitude Clonal Germplasm Repository of the Taiwan Agriculture Research Institute (TARI) in Wufeng, Taichung, Taiwan, 2022–24.i
‘Tainung No.9 HongJin’ had a fruit weight of 143.8 g, positioning it between the heavier ‘Tainung No.7 HongLing’ (169.1 g) and the lighter ‘TropicBeauty’ (129.9 g) and ‘UFSun’ (106.0 g). In terms of fruit size, measured as the average of the equatorial and sutural diameters, ‘Tainung No.9 HongJin’ produced fruits with a size of 62.5 mm. This was statistically similar to ‘TropicBeauty’ (62.3 mm) and ‘Tainung No.7 HongLing’ (68.3 mm). UFSun had significantly smaller fruits, with a size of 31.3 mm, distinguishing it from the other cultivars.
‘UFSun’ had the highest firmness at 2.66 kg·mm−2, significantly higher than the other cultivars. In comparison, ‘Tainung No.9 HongJin’ had a firmness of 0.79 kg·mm−2, similar to ‘Tainung No.7 HongLing’ (0.99 kg·mm−2) and ‘TropicBeauty’ (0.92 kg·mm−2). This indicates that ‘Tainung No.9 HongJin’ has moderate firmness, making it suitable for handling and storage. The notably higher firmness of ‘UFSun’, a non-melting-flesh cultivar, contrasts with the melting flesh characteristic of ‘Tainung No.9 HongJin’, ‘Tainung No.7 HongLing’, and ‘TropicBeauty’.
‘Tainung No.7 HongLing’ had the highest SSC at 13.0°Brix, followed closely by ‘Tainung No.9 HongJin’ at 12.5°Brix. ‘UFSun’ and ‘TropicBeauty’ had comparable SSC of 11.8 and 11.4°Brix, respectively.
‘TropicBeauty’ showed the highest acidity at 0.68%, significantly higher than the other cultivars. ‘Tainung No.9 HongJin’ had an acidity level of 0.38%, which was similar to ‘Tainung No.7 HongLing’ (0.28%) and ‘UFSun’ (0.41%).
Overall, Tainung No.9 HongJin offers a desirable balance of fruit development period, size, firmness, sugar content, and acidity, making it a strong candidate for growers seeking a high-quality, low-chill peach cultivar. As the first yellow-fleshed peach cultivar developed in Taiwan, ‘Tainung No.9 HongJin’ provides a unique addition to the fresh market, offering greater diversity to both growers and consumers. Its performance is comparable to established local white-fleshed fresh-market peach such as ‘Tainung No.7 HongLing’, ‘SpringHoney’, and ‘Xiami’. This makes Tainung No.9 HongJin a valuable cultivar for enhancing peach production in subtropical low-altitude regions.
Availability
The ‘Tainung No.9 HongJin’ peach has secured the Taiwan Plant Breeder’s Rights (Certificate No. A02354) issued by the Ministry of Agriculture, Taiwan. For research purposes, a restricted amount of nonindexed bud wood can be accessed upon submission of a formal request to the Crop Genetic Resources and Biotechnology Division of TARI.
References Cited
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