ASHS 2024 Conference

Prohexadione Calcium Does Not Affect Thinning Efficacy of 1-aminocyclopropane-1-carboxylic Acid in ‘Golden Delicious’ - Annie Vogel
Carbohydrate Status of Apple Fruitlets following Chemical Thinner Application Informs Sink Strength and Fruit Set - Laura Hillmann
Performance of a reflectance spectroscopy model to predict apple fruitlet thinning efficacy - James Larson
Overexpression of the Coding Sequence of Ma1 Decreases Fruit Acidity in ‘Royal Gala’ Apple - Lailiang Cheng
Striking the Right Balance: Innovative PGR Strategies for Fruit Drop Mitigation and Color Enhancement in Apples - Sherif Sherif
Rapid Fruit Growth Rates of Honeycrisp Apples Cause Premature Dysfunction of Xylem, Reduced Peel Calcium, and Increased Susceptibility to Bitter Pit - Chayce Griffith
Carbohydrate And Nitrogen Storage Are Inversely Affected By Crop Load For 'Honeycrisp' And 'Gala' Apples - Thiago Campbell
Impacts of Rootstock and Crop Load Adjustment on Fruit Quality and Mineral Nutrients in ‘Honeycrisp’ Apple - Esmaeil Fallahi

Apple’s (Malus × domestica Borkh.) tendency towards biennial bearing necessitates management strategies such as fruit thinning and vigor control. Applications of plant growth regulators to manage crop load and vigor overlap in the spring. A precursor to ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC; Accede®) was recently registered as a chemical fruit thinner in the USA. Prohexadione-calcium (P-Ca) is a gibberellin biosynthesis inhibitor widely used to manage vigor. It is suspected that P-Ca may interfere with ACC precursors, decreasing thinning efficacy of ACC. We evaluated the effects and interactions of ACC and P-Ca on shoot growth, ethylene evolution, leaf area, and yield responses of mature ‘Golden Delicious’. The experiment was conducted in 2023, in Mills River, NC, USA. Treatments included ACC (400 mg∙L-1), P-Ca (250 mg∙L-1), ACC P-Ca, and an untreated control. Application of P-Ca occurred on three dates. ACC was applied when average fruit diameter was ~20 mm. Across all measured responses, there were no interactions between ACC and P-Ca. P-Ca had a negative main effect on shoot growth rate (48.7–75.4% reduction). ACC reduced leaf number of spurs 4 and 9 days after treatment (DAT). Ethylene evolution in fruit and spurs was increased by ACC 1, 4, and 9 DAT (spur: 1.1e4%, 5300%, and 515%, respectively; fruit: 9200%, 725%, and 222%, respectively). ACC had a negative effect on fruit number, yield, and crop density (60.1%, 56.5%, and 60.3% reduction, respectively). These results indicate that ACC and P-Ca can be used simultaneously to manage crop load and vigor, respectively

Crop load management of apple (Malus x domestica Borkh.) is one of the most important orchard management practices to ensure adequate fruit size and quality. Fruitlets are most sensitive to thinner applications early in the season, between 6mm and 20mm fruitlet diameter. During this time, abscission is associated with environmental and biological factors that influence fruitlet development, growth and sink strength. The carbohydrate economy of the fruitlet and its position within the cluster (king flower vs. lateral flowers) are primary factors contributing to the sink strength of individual fruitlets. We evaluated the relationship between the non-structural carbohydrate status of apple fruitlets in three different size classes (i.e., 90th, 50th, and 10th percentile of the population) and their respective likelihood to persist throughout the season. Persistence probabilities of these size classes were generated by an empirical fruit set prediction model based on the distribution of fruitlet mass and confirmed by actual measures of fruit set. Soluble carbohydrates and starch were quantified with an enzymatic assay procedure. Following chemical thinner application, the concentration of soluble sugars (glucose, fructose, sucrose, and sorbitol) was significantly reduced on a gram / gram fresh weight basis. Fruitlets in the 10th percentile generally had the lowest concentration of soluble sugars and starch and the slowest recovery rate following chemical thinner application. Fruitlets in the 90th percentile generally had the highest concentrations of soluble sugars and starch. Our data support that differences in the carbohydrate concentration of fruitlets contribute to their sink strength and abscission fate as predicted by a fruit set prediction model.

Post-bloom apple chemical thinning relies on the application of plant bioregulators to induce fruitlet abscission, reducing crop load to improve fruit quality and promote return bloom. Abscission rates following chemical thinner application are influenced by carbohydrate status of the tree and thus widely variable. Multiple applications are often needed for growers to reach a desired crop load. However, trees are only perceptive to chemical thinners for a 3 to 4 week period shortly after bloom. Rapid prediction of chemical thinner efficacy is critical to allow growers to make necessary applications in this narrow period of time without the risk of over-thinning. In 2021 and 2022 a predictive model using reflectance spectroscopy measured with a handheld spectrometer (Felix F-750; Felix Instruments; Camas, WA, USA) was developed to predict chemical thinner efficacy for ‘Honeycrisp’ in North Carolina, USA. This model was found to predict chemical thinner efficacy with greater than 85% accuracy as early 3 days following a chemical thinner application. In 2023 and 2024 validation of this model occurred on multiple cultivars: ‘Red Delicious’, ‘Granny Smith’, ‘Gala’, and ‘Fuji’; and in multiple growing regions: Michigan, New York, and North Carolina, USA. Performance of the developed model to predict chemical thinning efficacy in this wide range of situations will be discussed to determine commercial applicability of the model.

Vacuolar accumulation of malic acid, the predominant organic acid in apple (Malus domestica) and many other fleshy fruits, largely determines fruit acidity, a key trait for fruit taste and flavor. ALUMINUM-ACTIVATED MALATE TRANSPORTER 9 (ALMT9/Ma1) underlies a major genetic locus, Ma, for fruit acidity in apple. A natural mutation at base 1455 leads to a pre-mature stop codon that truncates the Ma1 protein by 84 amino acids to ma1, and this truncation significantly reduces Ma1’s malate transport activity by disrupting a conserved C-terminal domain, leading to low fruit acidity in recessive homozygous ma1ma1 genotypes. However, it remains unclear how Ma1 functions to transport malate across the tonoplast membrane. When the coding sequence of Ma1 was overexpressed in ‘Royal Gala’ apple (Ma1ma1) to determine its in planta function, to our surprise, the transgenic fruit had drastically reduced fruit acidity compared with the wild-type (WT). This led us to uncover that Ma1 undergoes alternative splicing. Two isoform proteins are generated by alternative splicing: Ma1beta being 68 amino acids shorter with much lower expression than the full-length protein Ma1alpha. Ma1beta does not transport malate itself, but interacts with the functional Ma1alpha, creating synergy with Ma1alpha for malate transport in a threshold manner when Ma1beta is equal to or exceeds 1/8 of Ma1alpha. In WT ‘Royal Gala’, Ma1 operates at this threshold. Overexpression of Ma1alpha triggers feedback inhibition on the native Ma1 expression via transcription factor MYB73, decreasing the Ma1beta level well below the threshold that leads to significant reductions in Ma1 function and malic acid accumulation in fruit. Overexpression of Ma1alpha and Ma1beta or genomic Ma1 increases both isoforms proportionally and enhances fruit malic acid accumulation. These findings reveal an essential role of alternative splicing in Ma1-mediated malate transport underpinning apple fruit acidity.

Biennial or alternate bearing is characterized by an abundance of blooming and fruiting in “on” years and a lack of blooming and fruiting in “off” years. Biennial bearing in fruit tree production has been extensively studied. However, it continues to be problematic in certain crops and cultivars. Fundamental physiological mechanisms controlling this behavior are still poorly understood. Along with carbohydrates in plant tissues, reserve nitrogen influences early-season growth in apples, with the percent contribution of reserve nitrogen being dependent on the current nitrogen supply. Because flowering and fruit set occur in spring alongside bud break, reserve nitrogen can significantly affect these processes too. We sought to understand the role carbohydrate and nitrogen storage in various plant tissues has on biennial bearing for ‘Honeycrisp’ apple. Apical buds, terminal shoots, and one-year-old spurs were collected in 2022

In apple orchards, addressing pre-harvest fruit drop in early-maturing, commercially valuable cultivars like ‘Honeycrisp’ and ‘Gala’ is crucial. This issue is largely linked to ethylene, a ripening hormone that, despite its role in enhancing fruit qualities, triggers premature fruit drop. From 2018 to 2021, extensive field trials were conducted across commercial and experimental orchards to refine the application of two ethylene-inhibiting products, ReTain (AVG-15%) and Harvista (1-MCP-1.3%), in mitigating this challenge in ‘Gala’ apples. Our findings confirmed AVG’s effectiveness in reducing fruit drop and stem-end splitting; however, AVG application consistently resulted in diminished fruit coloration. In the subsequent seasons of 2023 and 2024, our research pivoted towards identifying plant growth regulator (PGR) formulations that could balance the dual objectives of minimizing fruit drop and preserving color development in ‘Honeycrisp’ and ‘Gala’ apples. Key findings include: a) the multiple applications of Accede (ACC-10%) and Motivate (Ethephon-21.7%) starting from three weeks before harvest significantly enhanced red color formation in ‘Honeycrisp’ and ‘Gala’ apples, surpassing control and ReTain treatments, though Motivate increased the rate of fruit drop; b) ReTain, both alone and in combination with Accede, notably reduced fruit drop, with the ReTain-Accede mix also enhancing fruit coloration; c) combining ReTain and Motivate neither decreased fruit drop nor enhanced color; d) the positive impact of the ReTain-Accede mix on color was biochemically and molecularly validated; e) Accede's color-enhancing effect appears to be ethylene-independent. This research underscores the potential of specific PGR mixes in achieving a harmonious balance between reducing fruit drop and enhancing fruit coloration.

The influence of rootstock and time of crop load adjustment on ‘Honeycrisp’ apple fruit quality at harvest and after storage was studied over four seasons. Yield per trees varied from year to year because of biennial bearing. Trees on V.1 and G.30 were higher while those on G.969 often had lower yield per tree. Fruit from trees on M.26EMLA and G.30 were larger, while those on G.202 and G.969 were smaller than those on other rootstocks in two of three years. Fruit firmness at harvest and after storge was often inversely proportional to their size, so that fruits from trees on G. 202 often had higher but those on G.30 often had lower firmness at harvest and after storage. Percentages of fruit bitter pit among rootstocks at harvest was different than those after storage. However, fruit from trees on M.26EMLA, V.1, and G.30 generally had higher bitter pit than those on G.969 and G.202 rootstocks. Fruit fresh weight continually grew during growing season. However, the increase in percentage fruit dry weight reached a plateau on August 9, after which it leveled off. Trees receiving an “Early Heavy Thinning” and “Thinned Early to 1 Fruit/bunch” had lower yield but larger fruit with more bitter pit than Un-thinned-Control trees. Trees receiving a thinning on June 11 and June 25 had similar fruit size in the same season. However, bitter pit was increased, while fruit size decreased, as the hand thinning was delayed until July 8. Late hand thinning resulted in smaller fruit size with less bitter pit. Fruit potassium/ calcium (K/Ca) ratio did not change significantly between June 20 and August 8 within the same year. This research unveils importance of rootstock, time, and level of and thinning in the fruit quality of ‘Honeycrisp’ apple.

Insufficient transport of calcium to and throughout the cortex of apple is a primary factor contributing to bitter pit, a disorder characterized by dark lesions on the fruit surface. Calcium transport, in-planta, occurs solely in the xylem. Progressive transport dysfunction of xylem limits calcium concentration in the peel and subtending tissue. Rapid fruit growth may accelerate xylem dysfunction due to the stretching, shearing, or compressing of xylem elements. The relative time course of these events and subsequent effect on calcium concentration of peel tissues is not well understood. Growth rate of fruit was manipulated by manually adjusting the crop load of 6th leaf ‘Honeycrisp' trees to either 4 (low), 8 (moderate), or 16 (high) fruit per cm2 of trunk cross-sectional area via bud extinction. Fruit mass, xylem functionality, and peel calcium content were assessed weekly throughout the season. Fruit tissues were frozen weekly to evaluate the expression of genes related to xylogenesis and calcium transport and for quantification of hormones. At maturity, 25 trees were harvested from each crop load treatment. Fruit were assessed for bitter pit, stored for three months in regular air (3⁰C), then reassessed. Crop load influenced both xylem functionality and bitter pit incidence of fruit. Low crop load fruit lost 80% of xylem functionality by 8 weeks after bloom, which was two weeks earlier than moderate crop. By seven and five weeks before harvest, total xylem dysfunction was observed in fruit of low and moderate crop load, respectively; xylem in high crop load fruit never became fully dysfunctional. Final fruit mass from low crop load trees was only 20 grams larger than fruit from moderate crop load trees, yet, these fruit had a roughly 100% increase in bitter pit incidence at harvest (27.3% vs. 12.6%). Only 4.1% of high crop load fruit were affected by bitter pit. Many previous studies have ascribed the positive relationship between fruit mass and bitter pit incidence to calcium dilution. Our data suggest, however, that the issue is one of transport limits that appear to begin very early in fruit development, exacerbated by the growth rate of fruit, resulting in less peel calcium and higher bitter pit incidence at harvest than fruit of relatively lower growth rates. Future analysis of endogenous hormone concentrations and expression of genes relating to xylogenesis and calcium allocation will facilitate a better understanding of the processes governing xylem dysfunction and its association to bitter pit disorder.

Effect of Gamma Irradiation on Survival, Fruit Characteristic, and Thorn Length in Different Varieties of Citrus - Dong-Hoon Lee
Consumer Preference and Willingness-to-Pay for Pawpaw Value-Added Products - Sheri Crabtree
Promising Advanced Selections from Kentucky State University’s Pawpaw (Asimina triloba) Breeding Program. - Jeremy Lowe
Assessment of Fruit Quality and Value-added Potential of 16 Pawpaw Cultivars and Advanced Selections - Kirk Pomper
Effects of Temperature and Light on Sunburn, and Preventing the Sunburn Damage by Chemical Suppressants in ‘Fuyu’ Sweet Persimmons - Yunji Shin
Crown Gall Associated with Higher Risk of New Butt Rot Pathogen in California Almond Orchards - Raymond Mireles
Assessment of Biomass and Carbon Storage of Satsuma Mandarin Trees in Jeju Island, Korea - Jee-Soo Park

In this study, we investigated the variety-dependent survival of citrus seedlings and analyzed the pomological characteristics of fruits and thorn lengths following irradiation with gamma rays. Scions from the seedlings of the following citrus varieties, ‘Yuzu’, ‘Noeulhyang’, ‘Sarahyang’, ‘Namgam’ (nucellar), and ‘Meiwakumquat’ irradiated with gamma rays at 0, 60, 80, and 100 Gy were grafted onto trifoliate orange. At 6 months after grafting, the survival rates of ‘Yuzu’ and ‘Noeulhyang’ exposed to 100 Gy were 49.5% and 34.8%, and that of ‘Sarahyang’ and ‘Namgam’ (nucellar) exposed to 80 Gy were 51.6% and 46.8%, respectively. ‘Meiwakumquat’ exhibited the lowest survival among the varieties used in this study. Therefore, we classified ‘Meiwakumquat’ as highly susceptible to gamma radiation; ‘Noeulhyang’, ‘Sarahyang’, and ‘Namgam’ (nucellar) as intermediately susceptible; and ‘Yuzu’ as the least susceptible. We assessed the effects of gamma radiation on the pomological traits in irradiated ‘Tambit1ho’ and ‘Yuzu’. Among the 72 irradiated ‘Tambit1ho’ seedlings, the average seed number (number of seeds per fruit) varied between 0 and 18.6, whereas that in the unirradiated seedlings was between 8 and 18. Among the irradiated seedlings, the average seed number was less than 1.0 in eight seedlings. In addition, we observed variations in weight, rind and segment hardness, and sugar and acid contents. The thorn length of the flush in unirradiated ‘Yuzu’ was between 1.3 and 6.0 cm, whereas that of flush in gamma-irradiated seedlings was between 0.1 and 6.1 cm. Among the irradiated ‘Yuzu’ seedlings, the thorn length was less than 0.1 cm in two seedlings.(This work was carried out with the support of the Research Program for the National Institute of Horticultural

The North American pawpaw (Asimina triloba) is the largest edible tree fruit native to North America, with a flavor resembling a unique tropical-like blend of mango and banana. Commercial production and consumer interest in pawpaw is on the rise in the US and worldwide. Fresh pawpaw fruit has a short shelf life and does not store or ship well. Value-added products represent a great potential market to both diversify offerings of products containing pawpaw, and provide shelf-stable products that could be available year-round and circumvent the storage and shipping challenges of fresh fruit. Pawpaws can be utilized in many value-added products, including ice cream, yogurt, jam, custard, baked goods, hot sauces, wine, beer, and brandy. A pawpaw value-added product tasting was conducted in September 2023 at the Kentucky State University Research and Demonstration Farm as part of the annual Pawpaw Third Thursday Thing workshop. Participants tasted samples of slices of fresh pawpaw fruit of six varieties, pawpaw jam on crackers, and pawpaw ice cream. A survey was conducted evaluating preference and interest in purchasing pawpaw fruit, jam, and ice cream, and willingness to pay. The survey found that 93% of participants would be interested in purchasing pawpaw fruit at a farmers market, compared to 80% at a grocery store and 88% at an on-farm market or roadside stand. Ninety-five percent (95%) of participants would be interested in purchasing pawpaw jam if available in stores, and 95% of participants would also be interested in purchasing pawpaw ice cream if available in stores. Respondents would be willing to pay $2.20 per fruit, or $4.97 per pound for fresh pawpaw fruit. Respondents reported they would pay $7.22 for an 8 ounce jar of pawpaw jam, and $8.51 for a quart of pawpaw ice cream. Currently, pawpaw ice cream and jam are sold by very few retailers in specialty markets, so there is great opportunity for pawpaw producers to introduce high-value pawpaw products that are desired by consumers to their retail markets.

The North American Pawpaw (Asimina triloba) is a tree fruit native to the Eastern U.S. which is being produced in commercial orchards across the U.S. and internationally, with an increasing market and interest. There are approximately 50 pawpaw cultivars available, but many of these varieties have low yields with fruit sizes below the threshold of 120 grams needed for commercial sale and processing. New high yielding cultivars with excellent fruit quality would further assist in the development of the pawpaw industry. Kentucky State University serves as the National Clonal Germplasm Repository for Pawpaw. Two goals of the Repository research efforts are germplasm acquisition and evaluation. The repository contains over 2000 accessions from 16 different states; additionally, both open pollinated seedlings from superior genotypes and crosses of superior selections have been incorporated into the repository collection. Fruit weights from three of KSU’s advanced selections (Hi 1-4, Hi 7-1, and G6-120) were compared to the cultivars ‘KSU-Atwood’, ‘KSU-Benson’, ‘KSU-Chappell’, ‘Ralph’s Whopper’, and ‘Sunflower’. Fruit weights for Hi 1-4 (241.5 g) and Hi 7-1 (233.5 g) were significantly larger than ‘Sunflower’ (145.3 g). Hi 1-4 and Hi 7-1 show potential to be promising new releases and have been budded onto seedling rootstock for further evaluation.

The North American pawpaw [Asimina triloba (L.) Dunal] is a native tree-fruit that is in the early stages of commercial production in the United States. Pawpaw fruit have fresh market appeal for farmers markets, community supported agriculture, and organic markets, as well as processing potential for frozen pulp production. For the processing market, fruit with a large size of over 120 grams and less than 6 percent seed by weight, are desirable for processing for pulp recovery for value-added products such as hot sauce. Kentucky State University has already released three pawpaw cultivars, KSU-AtwoodTM in 2009, KSU-BensonTM in 2016, and KSU-ChappellTM in 2018. However, new high yielding cultivars with excellent fruit quality would further assist in the development of the pawpaw industry. The objective of this study was to determine the fruit quality of 16 pawpaw cultivars and advanced selections. Fruit weight, percent seed, and brix were determined for the cultivars and advanced selections grown at the Kentucky State University Research and Demonstration Farm in Frankfort, Kentucky. The cultivars and advanced selections evaluated were A3-1, A6-1, KSU-AtwoodTM, KSU-BensonTM, KSU-ChappellTM, G4-25, G6-120, G9-109, Hi 1-4, Hi 7-1, Hy3-120, NRVT 3-10, NRVT 3-4, Sunflower, Susquehanna, and Tallahatchie. Average fruit weight ranged from Tallahatchie at 138g to A-6-1 at 277g per fruit. A number of advanced selections had large fruit size and these included A6-1 (277g), Hy3-120 (258g), A3-1 (216g), Hi1-4 (214g), NRVT3-4 (208g), Hi7-1 (202g) and G9-109 (201g). Average percent seed for fruit ranged from G6-120 at 8.2 percent seed to the cultivar KSU-ChappellTM at 4.5 percent seed. A number of advanced selections had low percent seed and these included A6-1 (4.7%) and G4-25 (5.8%). Average percent Brix for fruit ranged from NRVT 3-10 at 19.8 Brix to the cultivar KSU-ChappellTM at 28.2 Brix. Many of these advanced selections show promise as potential new cultivars. Examples of hot sauce made from pawpaw pulp extracted from cultivars will be discussed.

As global warming progresses, sunburn damage in fruit production is becoming increasingly prevalent. However, there has not been much research on the patterns of sunburn occurrence and effective prevention measures for ‘Fuyu’ sweet persimmons. This pilot study explored the impact of strong light and high temperatures on sunburn occurrence in ‘Fuyu’ sweet persimmons, characterized the temporal pattern of sunburn development, and evaluated the efficacy of chemical suppressants in reducing damage. ‘Fuyu’ persimmons were harvested from an orchard in Jinju-si, Gyeongsangnam-do, South Korea, at 60 days (weak light intensity (WLI) conditions), 72 days (strong light intensity I (SLI-I) conditions), and 79 days (strong light intensity II (SLI-II) conditions) after full bloom. The harvested fruits were divided into five treatment groups: control (Distilled water), 2% Cellulose Nano Crystals (CNCs), 2% Sodium Alginate 300mM CaCl2 (AG), 6% Kaolin 0.1% Tween20 (K), and 2% Vapor Gard® (VG, transpiration inhibitor). Thermocouples were attached to each fruit to measure fruit surface temperature (FST) under the following conditions: WLI (using a chamber set to 200 µmol/m²/s light intensity) and SLI-I, -II (direct sunlight and temperature) conditions. When exposed to WLI conditions, the increase in fruit surface temperatures (FST) compared to air temperatures (AT) was minimal, and no sunburn was observed. Conversely, non-acclimated fruits exposed to SLI-I displayed extensive sunburn damage within a day. However, acclimated fruits under SLI-II revealed differences in sunburn. The kaolin treatment, which exhibited the lowest browning, also showed a significant reduction in FST. However, the carotenoid content was lower in the kaolin treatment compared to the control. To confirm the findings from controlled experiments, field trials were conducted for two years to evaluate the effectiveness of sunburn suppressants. In the first year, kaolin treatment reduced the severity of sunburn by half compared to other chemical suppressants. In the second year, 6% kaolin and a mixture of kaolin and carnauba wax were applied. Both kaolin and a kaolin-carnauba wax mixture effectively reduced sunburn to 30% of the control. These effective treatments decreased FST by up to 3.5℃, maintained high chlorophyll content, and augmented antioxidant enzyme activities. In conclusion, the kaolin treatment combined with carnauba wax was identified as the most promising material for preventing sunburn damage in ‘Fuyu’ persimmons under these environmental circumstances.

The wood decay fungus, Ganoderma adspersum, with no prior record in North America has emerged as a pathogen of almond in the San Joaquin Valley within the past decade. Incidence of the disease appears highest in orchards on ‘Nemaguard’ rootstock with high levels of crown gall, a bacterial disease caused by Agrobacterium tumefaciens. The putative association of G. adspersum with crown gall has been hypothesized, but not formally evaluated in the field. In February 2024, over 6,000 trees were surveyed across two orchards and rated for incidence of each disease. Both orchards were on ‘Nemaguard’ rootstock and included ‘Nonpareil,’ ‘Monterey,’ and ‘Fritz’ varieties. Results of Chi-square test for binomial ratings of two categorical variables indicate a significant association between G. adspersum and crown gall infection on all varieties in both orchards. Furthermore, when the variables were fitted using the generalized linear mixed model, infection with G. adspersum (independent variable) was found to have a significant effect on the association (response variable) for ‘Nonpareil’ variety at one site. For each unit increase in the incidence of crown gall, the probability of infection with G. adspersum increased by more than 1×109 fold on ‘Fritz’ and ‘Monterey’ at both sites, and ‘Nonpareil’ at one site, and by more than 87-fold on ‘Nonpareil’ at the second site. The results support the hypothesis that crown gall predisposes almonds to infection by G. adspersum. Further studies are needed to address the mechanism by which crown gall infection predisposes almond to G. adspersum with the long-term goal of improving the economic lifespan of California almond orchards.

In October 2020, the Republic of Korea set a landmark goal to achieve net zero emissions by 2050. However, the national greenhouse gas emission statistics did not account for carbon absorption by agricultural lands, including orchards, due to the absence of adequate calculation systems and data. Recognizing the significant role of photosynthesis in fruit trees like Citrus in carbon sequestration and climate change mitigation, this study aims to address this gap. We focused on developing allometric equations for estimating biomass and carbon stocks of citrus trees, particularly in orchards across Korea, with a case study on Jeju Island, a principal citrus cultivation area. Measurements of height, crown width, and the diameter of rootstock and trunks were conducted, observing an increase with tree age, though trunk diameter showed considerable variability. The study encompassed trees aged 5–45 years of the Satsuma Mandarin (Citrus unshiu Marc. cv. Miyagawa), a major citrus cultivar cultivated in Korea. Components including leaves, branches, trunks, and roots were harvested, dissected, fresh weighed, and oven-dried to develop dry to fresh weight ratios for dry biomass calculation. Allometric equations with trunk diameter as the sole independent variable were formulated for the Satsuma Mandarin tree. Furthermore, the total carbon content for trees aged 5–45 years was assessed through direct and destructive harvesting, revealing a carbon content range of 44.13 to 46.85% across different tree organs, with root carbon content increasing with age. This comprehensive study provides crucial insights into the biomass and potential carbon fixation capabilities of citrus trees, contributing significantly towards the accuracy of national carbon stock estimations. This work was carried out with the support of the Research Program for the National Institute of Horticultural