ASHS 2025 Conference

Ongoing climate change has resulted in unusually high winter temperatures and earlier spring warming, which have caused major fruit trees to bloom earlier than in previous years. This shift is increasing the risk of spring frost damage, emphasizing the urgent need for eco-friendly, sustainable and cost-effective protective strategies. Considering these, this present study, cellulose nanofiber (CNF), a nanomaterial extracted from plant cell wall cellulose from wood and pulp via mechanical (RE) and chemical (TEMPO) processes, was combined with sodium alginate (AG), a natural substance extracted from seaweed. It was applied as a coating material to provide thermal insulation and assess its effectiveness in protecting pear cultivars ‘Niitaka’ and ‘Wonhwang’ and apple cultivars ‘Hongro’ and ‘Fuji’. As frost damage was forecasted to occur on March 30, 2025, cryoprotectants were applied to apples on March 28, 2025, and pears on March 29, 2025. In pears, treatments were applied to ‘Niitaka’ and ‘Wonhwang’ trees in an orchard in Jinju, Gyeongsangnam-do, South Korea. Five treatments (control, 1.0% RE-CNF, 1.1% TEMPO-CNF, RE:AG=8:2, and TEMPO:AG=8:2) were applied to five trees per cultivar. Spraying was conducted once at the early flower cluster visibility stage (Stage 4) for ‘Niitaka’ and at the half-inch green stage (Stage 3) for ‘Wonhwang’. For apples, treatments were applied to 15 trees each of ‘Hongro’ and ‘Fuji’ cultivars located in an orchard in Hamyang-gun, Gyeongsangnam-do, South Korea. The flower bud stage for both ‘Hongro’ and ‘Fuji’ was at the half-inch green (Stage 4) when a single spray was applied. The study established that in ‘Niitaka’ pears the TEMPO:AG=8:2 treatment achieved the lowest pistil and stamen damage rates at 64% and 83%, respectively, reducing damage by 17% and 11% compared to the control. In ‘Wonhwang’ pears, the pistil damage rate was lowest as 11% with RE-CNF, and the combined pistil and stamen damage rate was lowest as 56% with TEMPO-CNF, showing reductions of 14% and 9% compared to the control. In both ‘Hongro’ and ‘Fuji’ apples, the combined pistil and stamen damage rate was 18% and 7%, respectively, with the TEMPO:AG = 8:2 treatment, showing 12% and 21% reductions compared to the control. In conclusion, the CNF mixtures revealed effective frost protection by significantly reducing frost damage rates in pears and apples. Thus, it is considered the most suitable material for developing cryoprotectants to mitigate spring frost damage in these major fruit crops.

Apricot (Prunus armeniaca L.) production in Texas is limited by inconsistent and overall poor yields due to spring frost and loss of hardiness in buds associated with erratic temperature swings in late winter/early spring. Several plant growth regulators (PGRs) were evaluated for improving yields. PGRs were applied in the fall and spring to assess their potential for mitigating floral bud injury, improving bud hardiness, enhancing fruit set, and improving fruit retention rates. Two-year-old ‘Wenatchee Moorpark’ trees on ‘KRYMSK-1’ rootstock, spaced at 1.33 by 3.33 meters were used with a randomized complete block design with five single-plant replications. Fall applications were made at approximately 50% natural leaf fall of Ethephon at rates of 100, 200, and 300 mg/L-1, Accede (ACC) at rates of 500, 1000, and 1500 mg/L-1, and ProTone (S-ABA) at rates of 500 and 1000 mg/L-1. Following defoliation of the trees, white latex paint was also applied as a treatment to the entire canopy and trunk of dormant trees. Spring treatments aimed at improving fruit set were applied during full bloom and included Promalin (GA4+7, 6-BA) at rates of 1.17 and 2.34 L/ha-1, and ReTain (AVG) at rates of 889 and 1,778 mg/L-1. Additionally, evaluations were conducted on combination treatments of fall and spring applications. These treatments included Ethephon+Promalin+Latex; Ethephon+ReTain+Latex; Accede+Promalin+Latex, and Accede+ReTain+Latex, which were applied at the highest concentrations for each product evaluated individually in this study. Differential Thermal Analysis (DTA) was carried out on the 15th and 16th of February 2025 using 5 floral buds per tree as sub-samples. LT50 found Accede at 1500 mg/L-1 significantly improved bud hardiness by 4.67°C relative to the control. Additionally, treatments of Accede+Latex, Accede+Promalin+Latex, and all three combination treatments of Ethephon delayed floral bud development relative to control. However, Ethephon produced significant gummosis and visible injuries, whereas Accede produced negligible gummosis. Fruit set, as assessed by counting fruit on 50.8cm lengths of standard sample shoots, was improved using the highest concentration of ReTain (AVG). The mean fruit number increased from 1.2 for the control, to 5.0 for AVG, at P= 0.0002, occurring after exposure to temperatures below -4°C on March 19th. The results from this and future years of this trial are anticipated to assist in improving the feasibility of commercial apricot production within Texas and similar environments.

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, percent seed by weight, and soluble solids content from six of KSU’s advanced selections (Hi 1-4, Hi 7-1, G4-25, G6-120, G9-109, and G9-111) were compared to the cultivars ‘KSU-Atwood’, ‘KSU-Chappell’, and ‘Ralph’s Whopper’. All advanced selections had average fruit weights over 120 grams with Hi 1-4 having the highest fruit weight (229.8 g). ‘KSU-Chappell’ had the lowest percent seed (4.7%), with Hi 1-4 having the second lowest (5.9%). Hi 1-4 had the highest soluble solids content at 25.9 Brix and all selections examined were above 21 Brix. Several selections including 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. According to the 2022 Census of Agriculture, there are over 90 commercial pawpaw growers in Kentucky. Pawpaw fruit has fresh market appeal for farmers' markets, community-supported agriculture, and organic markets, as well as processing potential for frozen pulp production. There are approximately 50 pawpaw cultivars commercially available. Kentucky State University has already released three pawpaw cultivars: KSU-Atwood™ in 2009, KSU-Benson™ in 2016, and KSU-Chappell™ in 2018. However, additional high-quality cultivars are needed. Pawpaw varieties with fruit weights over 120 g per fruit are considered to have a large enough fruit size 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’s research efforts are germplasm acquisition and evaluation. The selection Hawk238 was identified by a private grower as having a unique fruit type and promising characteristics as a potential new cultivar. In 2024, the fruit size and quality of the pawpaw cultivars Susquehanna and Shenandoah were compared to Hawk238. Fruit size was similar among ‘Susquehanna,’ ‘Shenandoah,’ and Hawk238, averaging 190 g, 155 g, and 154 g, respectively. The Brix of ripe fruit pulp was significantly lower in ‘Shenandoah’ (17.7 Brix) compared to ‘Susquehanna’ (25.4 Brix) and Hawk238 (24.3 Brix). The selection Hawk238 has a pleasing orange flesh with a mild banana-mango flavor and a large fruit size that would be excellent for processing. This selection, Hawk238, will be included in additional trials.

The North American pawpaw (Asimina triloba) is a tree fruit native to North America, and is being produced on a small scale commercially across the U.S. and internationally, with over 90 pawpaw growers in Kentucky alone. There are approximately 50 pawpaw cultivars available, but some of these varieties tend to be poor quality, low yielding, have small fruit size, or exhibit poor flavors. Kentucky State University’s pawpaw breeding program is striving to develop new improved pawpaw cultivars with good flavor and high yields. A pawpaw variety trial was established at the Kentucky State University Harold R. Benson Research and Demonstration Farm in Frankfort, KY, in 2017 consisting of two commercially available cultivars (‘KSU-Benson’ and ‘KSU-Chappell’) and two KSU advanced selections (Hi1-4 and Hi7-1). Data on number of fruit and clusters per tree and fruit weights were collected to compare advanced selections Hi1-4 and Hi7-1 to KSU-Benson and KSU-Chappell. The advanced selections Hi1-4 and Hi7-1 had large average fruit weights of 213 g (Hi1-4) and 167 g (Hi7-1). The cultivars KSU-Benson (179 g) and KSU-Chappell (234 g) also had large marketable fruit. Pawpaw fruit over 120 g are generally considered to be large enough for commercial sale and processing. Hi1-4 and Hi7-1 had an average yield of 12.8 kg and 12.0 kg per tree respectively in 2024, compared to KSU-Benson and KSU-Chappell with average yields of 16.9 kg and 27.2 kg respectively. Advanced selection Hi1-4 (1.7) and cultivar KSU-Benson (1.8) averaged under 2 fruit per cluster, while Hi7-1 (2.1) and KSU-Chappell (2.5) averaged slightly over 2 fruit per cluster. It is desirable for pawpaws to have fewer fruit per cluster and more single fruit, for ease of harvesting. Hi1-4 and Hi7-1 have large, flavorful fruit and high yields, and are planned to be released as new cultivars from the KYSU pawpaw breeding program in Fall 2025.

Root system development in perennial crops is critical for the long-term survival of trees. Long lived coarse roots form the rigid structure that supports the dynamics of the absorptive fine root system. The woody root scaffold developed early in a tree’s life can shape lasting aspects of mature root system structure and function, including the extent of soil exploration. Research on early root scaffold development under different propagation and field management conditions has untapped potential for orchard system improvement. Rootstock propagation method significantly influences root system architecture (RSA). Seed propagation in Prunus species produces a vertically oriented taproot at germination, with lateral roots developing along this main axis. In contrast, clonally propagated rootstocks (e.g., cuttings, tissue culture) develop adventitious roots from a wound site or callus, often resulting in shallower, clustered root systems emerging from a concentrated point of origin. While clonal propagation exhibits trait uniformity and a high rate of initial root production, excessive root crowding and limited vertical distribution could lead to structural deformities, increased susceptibility to soil-borne disease, and reduced soil exploration for water and nutrients as trees mature. Studies have shown that a greater number of roots increases initial transplanting success, but a profusion of scaffold roots may result in competition for space, leading to permanent changes in RSA detrimental to long-term tree health. This study examines RSA traits (the spatial configuration of roots, including distribution, morphology, and topology) for coarse roots in commercial almond rootstock cultivars that were either seed or clonally propagated and subjected to full or deficit irrigation regimes. We evaluate how propagation method influences root angle (deep water access), scion growth (survival and vigor), root crowding (potential disease risk), and root distribution (soil exploration) in this 3-year common garden experiment. We found that rootstock significantly influenced traits like mean root diameter and convex hull (p < 0.05), suggesting genotypic differences in root vigor and extension into the soil profile. Propagation method did not significantly affect root angle after the first season, but prolonged exposure to deficit irrigation conditions in succeeding years will be important to understanding the adaptive capacity of these traits over time. As climate variability intensifies, understanding how rootstock propagation impacts RSA traits–particularly those relevant for accessing water stores, such as deeper root systems, elevated root vigor, and greater root length density at depth–will be essential for improving almond production in drought conditions, suboptimal soils, and other marginal environments.

Apple (Malus X domestica Borkh.) cultivars require a pollinizer for cross-pollination to ensure fruit set when planted in contiguous blocks found in modern apple orchards. The overlap of bloom time between pollinizing crabapples (Malus spp.) and commercial cultivars is a critical component for adequate fruit set to occur. Bloom time and duration is correlated with temperature, suggesting this relationship could be influenced by climate change. Understanding the influence temperature has on bloom phenology of these pollinizing crabapples is important to ensure proper cultivar and pollinizer combinations are made by growers. 4 commercially available pollinizing crabapple cultivars (‘Indian Summer’, ‘Mt. Blanc™’, ‘Mt. Evereste™’, ‘Snow Drift’) were replicated 5 times in completely randomized design. In spring of 2024 and 2025, pollinizers were analyzed 1-2 times per week for developmental stages from silver tip to petal fall. These two years represented one of the warmest and then coldest springs on record in Kentucky, respectively. Commercial apple cultivars were also analyzed for comparison. The stage progression data for each pollinizer cultivar was modeled using growing degrees days (GDD) base 6.6°C. In both observed years, the first crabapple to bloom was ‘Indian Summer’ and the final crabapple to bloom was ‘Mt. Blanc™’. In the first year, ‘Indian Summer’ bloomed on Julian Day (JD) 88 at 166.4 GGD and in the second year bloomed on JD 92 at 179.8 GDD. 'Mt. Blanc™’ bloomed on JD 104 at 250.1 GDD and 244.9 GDD in years one and two, respectively. In year one, ‘Gold Rush’ began bloom on JD 97 at 199.4 GDD, which overlapped with ‘Mt. Evereste™’ and ‘Snow Drift’, whereas in the second year ‘Gold Rush’ began bloom on JD 93 at 179.4 GDD and stopped blooming on JD 108 at 279.8 GDD, which overlapped with ‘Mt. Evereste™’, ‘Snow Drift’, and ‘Mt. Blanc™’. There was little bloom overlap in 2024, with the earliest crabapples blooming earlier and more rapidly than the cultivars. In 2025, bloom overlap improved but little overlap occurred with more than two pollinizers at a time. These results show bloom overlap can be influenced by different temperature patterns during winter and spring, and pollinizer selection needs to be carefully considered. It can be concluded that using growing degree-days can help predict bloom time for pollinizers. In Kentucky, limited bloom overlap of apples and pollinizers could indicate a concern for northern apple growing regions as spring temperatures become more variable with climate change.