ASHS 2025 Conference

Dormancy is an important strategy in perennial plants such as the tree fruit peach (Prunus persica), to protect them from damage during harsh environmental conditions such as winter weather. As day length and temperature decrease in the fall, floral and vegetative buds enter a state of endodormancy where they remain unresponsive to growth promoting environmental signals (Nilsson, 2022). Exposure to cold temperatures (typically ≤ 7° C) during the winter allows for chill accumulation and upon sufficient such chill accumulation, release from endodormancy occurs. This is followed by exposure to warmer temperatures in the spring leading to the end of eco- dormancy and bud break. In the field, low winter temperatures are often interspersed with periods of substantially warm weather thereby interrupting or negating the progression of chill accumulation and affecting bud break in the spring. Understanding responses of peach buds to intermittent warm temperature exposure is needed to mitigate crop loss due to temperature fluctuations. Experiments were conducted to determine the effects of such intermittent warm temperature exposure on chill accumulation in ‘Contender’ peach. Potted trees were maintained at ambient conditions in the field until around 50% of chill requirements (100 % = 1050 chill hours) were met. Following this, trees were subjected to one of three treatments: Control, Chill break I, and Chill break II, with 4 replicates per treatment. The Control group of peach trees were maintained under ambient conditions to reach their chill requirement. Chill break I and Chill break II were exposed to intermittent warm temperatures of continuous 14 °C in a growth chamber for 7 and 14 days, respectively. Following the treatment, trees were returned to ambient conditions. Peach buds were collected from each treatment at three stages and remaining buds were monitored to track floral bud break progression. Additionally, we determined the metabolite and phytohormone concentrations in ‘Contender’ peach buds that naturally accumulated their chilling requirements. Results indicate that as chilling progression increases, starch concentration increases. Concentration of the phytohormone ABA (abscisic) acid appeared to decrease upon completion of endodormancy. Together, these analyses are expected to help us gain a better understanding of dormancy progression in peach.

Peaches, nectarines, and plums are among the most popular and valuable stone fruits from the Rosaceae family. Their fruit are rich in bioactive compounds, including flavonoids, anthocyanins, carotenoids, phenolic compounds, vitamins, and antioxidants. In this study, the chemical attributes, bioactive compound content, and antioxidant activity of 18 peach cultivars (‘UFOne’, ‘UFGlo’, ‘UFBeauty’, ‘UFSun’, ‘Flordaprince’, ‘Gulfcrismon’, ‘UFBlaze’, ‘TropicSnow’, ‘TropicBeauty’, ‘UFGem’, ‘UFBest’, ‘Flordaglo’, ‘Flordabest’, ‘UFO’, ‘Flordaking’, ‘Flordacrest’, ‘UFSharp’, and ‘Flordabelle’), four nectarine cultivars(‘UFRoyal’, ‘Sunraycer’, ‘Sunmist’, and ‘Sunbest’), and four plum cultivars (‘Gulfrose’, ‘Gulfgold’, ‘Gulfblaze’, and ‘Scarlet Beauty’) were evaluated. Total soluble solids (TSS), titratable acidity (TA), TSS/TA ratio, and juice pH presented significant variations among cultivars. The highest TSS content was recorded in ‘Sunmist’ nectarine, while plum cultivars had the highest TA levels, particularly ‘Scarlet Beauty’. The TSS/TA ratio was highest in ‘UFSun’ peach. ‘Gulfrose’ plum showed the highest total anthocyanin concentration (TAC) level. Total phenolic content (TPC) varied significantly, with plum cultivars, particularly ‘Scarlet Beauty’, having the highest amount. Similarly, total antioxidant activity (TAA) was highest in ‘Scarlet Beauty’ and ‘Gulfrose’ plums, while ‘TropicSnow’ peach and ‘SunBest’ nectarine had the lowest TAA. Multivariate statistical analyses revealed clear separations among cultivars based on chemical and bioactive parameters. These findings provide valuable insights into the biochemical diversity of peach, nectarine, and plum cultivars, emphasizing the superior bioactive and antioxidant properties of plum cultivars.

The successful cultivation of blackberries in subtropical regions like Florida depends on selecting low-chill cultivars capable of withstanding high temperatures, disease pressure, and minimal chilling hours. This study evaluates the performance of 17 breeding lines alongside four commercial cultivars ('Freedom', 'Ponca', 'Horizon', and 'Osage') to determine their adaptability to Florida’s climate. The goal is to identify blackberry germplasm with the potential for high yields, good fruit quality, and post-harvest stability under these challenging conditions. Field trials were established in late June 2023 at the Citra Research Center, Central Florida, using three-month-old greenhouse-grown plants successfully transplanted into the field. Data collection focused on key production parameters, including total yield, single berry weight, and marketable fruit percentage. Fruit quality was assessed through pH, Brix, and organic acid composition (tartaric, citric, and malic acid). Subjective evaluations of firmness, flavor, and seed content were also conducted. Additionally, post-harvest performance was analyzed by monitoring decay, leakage, and red druplet reversion after seven days of cold storage at 5°C. Preliminary results indicate considerable variation among the evaluated cultivars. 'BLB', 'BLH', 'BLA', and 'Freedom' exhibited the highest yields, whereas 'BLG', 'BLP', and 'BLI' were among the lowest-yielding selections. Berry size ranged from 8.98 g in 'BLB' to 5.27 g in 'Osage'. Acidity levels varied significantly, with 'BLC' (pH 4.01) and 'BLJ' (pH 3.99) displaying the mildest flavor profiles, while 'BLP' (pH 3.60) and 'BLQ' (pH 3.62) exhibited higher acidity. Beyond fruit evaluations, plant vigor and structural characteristics were documented. Prior to last year’s harvest, primocane count and height were recorded, and this season, plants were rated based on vigor, overall health, and the proportion of green versus brown canes. Ongoing data analysis will further clarify cultivar performance in relation to plant growth and long-term productivity. This research provides valuable insights into selecting blackberry cultivars best suited for Florida’s subtropical environment. The findings will contribute to optimizing cultivar recommendations for growers looking to enhance yield, fruit quality, and marketability in sub-tropical climate production systems like Florida.

The current understanding of apple stem cold hardiness is very broad- there are certain cultivars generally accepted to be cold hardy or tender. There has been no comprehensive study of cold hardiness of apples at multiple timepoints over multiple years. In this study, cold hardiness was evaluated for 21 rootstock and 23 scion genotypes monthly throughout the dormant season over 4 years. Cold hardiness was measured using the electrolyte leakage method and the temperature at which 25% tissue damage occurs (LT25) was used as the cold hardiness phenotype. The four study winters varied drastically in intensity and had a significant effect on genotype cold hardiness. Contrasting phenotypic responses in cold versus mild winters demonstrated clear environmentally driven differences between inferior and superior genotypes. Another major finding from the study is the rapid deacclimation of rootstocks compared to scions in late winter/early spring- we observed that differences in mean hardiness between groups exceeded 6 °C in some years. Overall, this study represents the largest apple cold hardiness experiment to date in terms of cultivars used and timepoints examined, resulting in both novel implications for how grafted apples navigate cold hardiness during dormancy and which cultivars are best suited for unusual but increasingly common winter conditions.

Cold hardiness and dormancy are critical physiological adaptations enabling woody perennials to endure low temperatures in winter and initiate growth in spring. Hardiness in apple (Malus domestica) is genotype dependent, however maximum hardiness level gained by the buds is strongly regulated by environment. Understanding the relationship between dormancy progression and cold hardiness is essential for predicting plant responses to winter and spring freeze events, as well as optimizing breeding efforts for resilience and orchard decisions for frost management. Information on hardiness mechanism is becoming more crucial given the impact of global climate change in apple growing regions where earlier bloom dates have inherently greater risk of crop loss due to episodic spring frost events. The existing lethal temperature chart for apple floral buds is limited to the visible development stages and lacks critical temperature thresholds for the freeze resistance of floral buds during their transition out of ecodormancy. Further, there is no information distinguishing positional effects of individual florets of the apple cyme inflorescence with respect to their hardiness status. Because the ‘King’ floret is developmentally advanced compared to laterals and has the highest fruit growth and economic potential, the development of lethal temperature limits to inform its protection seems prudent. Thus, we evaluated the difference in LT50 between ‘King’ and ‘Lateral’ florets in ‘Gala’ on ‘Bud9’ rootstock during the transition phase from ecodormacy to growth resumption in 2022 and 2023. Our results demonstrated that cold hardiness is lost at early stages of, or transitions out of, ecodormancy; notably, this occurs prior to visible changes in bud phenology. Moreover, the ‘King’ florets are markedly less hardy than the ‘Laterals’ by approximately 6°C. The magnitude of difference in lethal temperatures between ‘King’ and ‘Lateral’ florets differed between years but remained significant. Increasing susceptibility to freeze mortality at higher temperatures was commensurate with an increase in the relative water content (RWC) of the buds and a marked decrease in sorbitol and sucrose concentration. In both years, an RWC of approximately 60% coincided with the visible green stage of bud burst. Our data indicate that decreasing sorbitol concentration can act as a potential biochemical marker for cold hardiness loss and inform protection measures of the ‘King’ fruit. Further study incorporating multiple commercially important apple cultivars will be beneficial in understanding the cold hardiness in apples.

Late spring frosts pose a recurrent threat to apple production, particularly under climate change scenarios that promote earlier bloom and heightened exposure to frost events. Recent evidence from our investigations on different apple-rootstock combinations suggested that rootstock genotype may influence scion resilience to frost, yet the underlying molecular mechanisms remain poorly understood. Field trials were conducted from 2021–2023 on 12-year-old ‘Gala’ and ‘Fuji’ trees grafted onto ten rootstocks, including ‘B.9’ and ‘M.26’, representing extremes of frost tolerance. Following three naturally occurring frost events, we have shown that ‘B.9’ rootstock consistently conferred lower bud mortality relative to ‘M.26’, independent of bloom timing. To dissect the molecular and biochemical mechanisms underlying the differential responses of these scion-rootstock combinations to frost, tissue-specific RNA-Seq analysis and untargeted metabolic profiling were conducted on floral buds, scion leaves, and rootstock sucker leaves from ‘Gala’-grafted trees. Samples were collected 12 h before and 6 h after the 2021 frost. Weighted gene co-expression network analysis (WGCNA) was employed to identify frost-responsive modules, and hub genes were validated via qRT-PCR in both ‘Gala’ and ‘Fuji’. Transcriptomic analyses revealed extensive gene regulation following frost exposure, including over 10,000 differentially expressed genes (DEGs). WGCNA identified three frost-correlated gene modules. Key hub genes were implicated in cold acclimation, ABA signaling, and cellular stress tolerance. GO and KEGG enrichment analyses highlighted significant representation of pathways associated with ABA response, cold response, and water deprivation stress. Metabolomic profiling of different tissues and genotypes further supported the transcriptomic findings and provided metabolic signatures associated with the identified gene networks. This work establishes a foundation for integrative omics approaches to dissect physiological cold tolerance mechanisms in apples and guides rootstock selection and germplasm improvement strategies.

Sonoma County, California is home to many small- to mid-scale apple orchards with diverse cultivars, management approaches and sales outlets. This poster will outline recent UC Cooperative Extension apple programming that responds to high-priority needs identified by apple growers, orchardists, and processors in this region. The new UCCE Specialty Crops Advisor based in Sonoma, Marin, and Napa Counties conducted a Needs Assessment that identified key issues and challenges for sustainable apple orchard system management. This poster will summarize key findings from the Needs Assessment. Stakeholders asked for educational programming on key topics to improve apple orchard health and yield. In response, outreach and Extension education activities focused on science-based sustainable apple orchard management strategies to accelerate practice implementation. This poster will outline these Extension efforts that responded to the Needs Assessment findings and will present evaluation survey results. For instance, stakeholders specifically asked for apple orchard management webinars, so the CE Advisor worked with local and UC partners to deliver a 5-part educational apple webinar series covering key aspects of sustainable apple orchard management. Findings showed that webinars increased attendees’ knowledge (100% of 35 respondents) and 97% reported they will use knowledge gained to manage apple orchards more sustainably. The CE Advisor worked closely with commercial apple growers to address tree health challenges in the orchard on a case-by-case basis. The most common pest issues in the region include codling moth, a suite of diseases, and rodents. Many apple orchards are managed as low-input systems, so tree water stress and nutrient deficiencies are common. The CE Advisor used science-based information and strategies to help growers address these issues. With grower permission, local apple orchard growers’ “Success Stories” are included in Extension educational presentations and materials to highlight examples of sustainable apple orchard management. This poster will include several of these “Success Stories” highlights. This poster will present findings outlining apple growers’ needs for Extension education and applied research in Sonoma County, California. It will outline UCCE activities implemented to increase growers’ practical knowledge and skills to guide sustainable decision making, increase orchard health and yield, and promote grower-to-grower knowledge sharing. Findings will help guide future work to enhance apple orchard sustainability and apple supply for the local food system.

With more than 20 million of trees planted in Washington State, ‘WA 38’ apple, commercialized as ‘Cosmic Crisp®’, is channeling the interest of the apple industry. Since the variety hit the market in 2019, consumers reported positive eating experiences and appreciation for its crispiness and juiciness. In suitable growing conditions, ‘WA 38’ can achieve high red coloration and satisfactory pack-out. One of the causes of loss is the ‘green spot’ (GS) disorder that impacts mainly the stem-hemisphere of the apple displaying skin discolored areas that might degenerate affecting the cortex. The onset of the GS occurs at the end of July, and the disorder incidence at harvest fluctuates year to year. Several mitigations approaches were investigated, but only bagging fruit at early stage of development provided positive results. Because the bagging practice is not economically sustainable on commercial scale, the application of a new foliar biostimulant (Plants for Plants 4-Vita) and Promalin (GA4 7 BA) were tested against untreated control. 4-Vita aims to protect the trees by abiotic stressors like drought and heat, stimulating water use efficiency and productivity. On the other hand, Promalin is known to improve fruit shape and size and reduce russeting by increasing epidermis cell elasticity. Our hypothesis focused on the potential positive effects of a biostimulant and a PGR in mitigating the GS in ‘WA 38’. The products were tested in season 2023 on a Granny Smith/M9-T337 orchard top-grafted in 2015 with ‘WA/38’ scions and trained to spindle, by applying them separately on distinct rows, bi-monthly, starting at 4 weeks AFB for 4 times. Productive parameters, pack out and GS incidence GS were assessed for each treatment. Results showed that Plants for Plants 4-Vita and Promalin did not improve yield and did not significantly mitigate the incidence of GS in comparison to untreated control.

RELEVANCE Sweet cherries (Prunus avium) have some historical production in the Four Corners area with renewed interest for fresh eating, baking, juicing and distilling. RESPONSE Six grafted cultivars were planted March 2014 as bare-root, 3-year old tree seedlings on a high mesa location at the NMSU Agricultural Science Center at Farmington at 5,640 feet above sea level (36°4’ N by 108° W). Cultivars ‘Bing’, ‘Skeena’, ‘Rainier’, ‘Benton’, ‘Santina’ and ‘Coral’ were grafted onto either Krymsk 5 or Krymsk 6 rootstock. Yield data was collected for 2019 and 2021 growing seasons. Trees were pruned during winter dormancy beginning in 2020 to control height. Lower yields in 2021 compared to 2019 are attributed to extensive pruning and to bird damage that was noticeably more impactful in 2021 compared to 2019. In all other years since planting, killing spring frosts reduced or eliminated flower production resulting in little to no fruit yield. When harvested, fruit sugar content (measured in °brix; the higher the °brix, the sweeter) ranged from 15.3° to 22.1° brix in 2019 and 13.3° to 24.6° in 2021. Sugar content is acceptable for any number of post-harvest fresh market to fermentation applications. IMPACT Cherry trees are among the first fruit trees to break dormancy on a high mesa site in Northwest, NM and have been prone to damaging spring frosts resulting in flower death and reduced fruit yields. When cherry have yielded, post-harvest metrics have favorable sugar content. Growers can expect to have non-bearing years related to spring frost risk and are advised to have cherry plantings as part of a diversified cropping system to lessen risk during non-fruitful years. PUBLIC VALUE STATEMENT The work is helping to support northwest New Mexico fruit growers.

Late spring frost is a major challenge to stone and pome fruit production in northern New Mexico. In this study, three cultivars of peach (Prunus persica)—Challenger, China Pearl, and Contender on Nemaguard rootstocks were planted at 4x10ft planting density with three replications in a 30x72ft high tunnel in April 2017, but severe leaf chlorosis appeared later in the season. We kept the better west row and removed the central and east row. In 2018, tissue-cultured GF677 and Rootpac® R were planted in May and budded in August 2018. Trees were trained to open vase system. Thermostat-controlled propane heaters and fans were employed for frost protection. In 2021, we began securing the sidewalls and the doors of the high tunnel and setting up heaters. In 2022 and 2023, the high tunnel system plus heating system was sufficient to protect blooms and fruitlets from late frosts, and yields averaged 15.8 kg/tree in 2022 and 12.3 kg/tree in 2023, respectively. There was no significant difference among cultivars in either year. However, there were significant differences between rootstocks in 2022, with trees on Nemaguard averaging 24.3 kg/tree across cultivars, while trees on GF677 and Rootpac® R averaging 11.2 and 11.8 kg/tree, respectively. The nearly two years older in age for trees on Nemaguard could contribute to this difference in 2022. There was also a reasonable crop in 2024. By the end of 2024, Trees on Nemaguard with 1-2ft new growth were smaller than plants on GF677 and Rootpac® R, with 1.5-4 ft new growth. There were limited replications in this high tunnel study but GF677 and Rootpac® R were more suitable than Nemaguard rootstock for the high pH soil conditions in New Mexico. Cherry had limited fruit set during this study. In 2022 and 2023, we observed deformed flowers without petals and some flowers with blackened pistils. Only handfuls of cherries were harvested in both 2022 and 2023. The high temperatures inside the high tunnel in summer could affect the floral bud initiation/ development. More studies are needed to clarify the deformed flowers. Growers should be cautious with sweet cherry production in high tunnels in northern New Mexico.

Previous studies in the southeastern United States have reported benefits of irrigated vs non irrigated orchards, including no major effects of soil-applied fertilizers on fruit yield and quality. However, the benefits of irrigation systems and foliar fertilization effects on yield, and fruit nutrient profiles and quality are limited. This study was conducted in a nine-year-old peach orchard using a split-plot randomized complete block design with two irrigation systems, drip vs micro-sprinkler as whole-plots, and foliar treatments as split plots. Preharvest foliar applications included water (control), nanocellulose crystals (CNC 3%), Calcium (Ca 6%), Potassium Silicate (K2SiO3), plus the combination of CNC with Ca and K2SiO3. Trees received no soil-applied fertilization, and irrigation was managed using the Peach Smart Irrigation App recommendations (https://smartirrigationapps.org/peach-app/). Even though no significant differences were observed in irrigation systems or foliar treatments for fruit weight or perimeter, all foliar treatments resulted in higher total yield compared to the control under drip irrigation. Under micro-sprinkler irrigation, only K2SiO3 and CNC increased total yield relative to the control. Regarding texture, control fruit showed decreased firmness after two weeks of storage at 2 °C and 90% relative humidity. There were main effects of irrigation in total soluble solids (TSS), where micro-sprinkler (10.27%) had higher TSS than drip irrigation (9.67%). Overall, these findings suggest that drip irrigation and foliar applications, particularly with CNC and K2SiO3, may enhance yield in peaches.

Understanding fruit growth and developmental patterns is crucial, as they directly influence fruit size, morphology, and ultimately, yield. While conventional models describe fruit growth and development based on parameters for the whole fruit, how tissue growth in different fruit regions is coordinated to drive overall fruit growth and development remains unclear. Here, we investigated the relationship between the spatial variation of growth rates and fruit morphology in persimmon (Diospyros kaki), a fruit tree species with highly diverse fruit morphology. Starting two weeks after blooming, fruits from four cultivars were marked with dotted lines routinely. Those fruits were sampled and used for the reconstruction of 3D fruit models. The relative positions and distances between points marked were used as parameters for the local growth. All cultivars exhibited more active growth near the calyx than near the apex, particularly during the early stages of fruit development. However, the extent of these spatial differences varied among cultivars. In flattened fruits, growth was highly concentrated near the calyx, with remaining minimal in other portions. In contrast, elongated fruits exhibited a gradual growth gradient from the calyx toward the apex, with high growth even near the apex. These findings provide a foundation for fruit shape regulation and elucidation of physiological disorders in persimmon.

A forum for discussion of potential collaborations with regards to fruit, vegetable, and edible crops – i.e. citrus, breeding, production systems, postharvest, pomology, crop management, viticulture, etc.