ASHS 2025 Conference

Peach (Prunus persica) production in the southeastern United States, particularly in South Carolina, is challenged by high humidity, variable chill accumulation, and persistent disease pressure – especially from bacterial spot (Xanthomonas campestris pv. pruni) adn brown rot (Monilinia spp.). In response, Clemson University reestablished its peach breeding program in 2008 with the goal of developing fresh-market cultivars adapted to this region’s demanding conditions. After more than a decade of field evaluation and selection, three new cultivars have been released under the ‘CaroRes’ and ‘EveRes’ series: ‘CaroRes Wonder’ (USPP 36,072), ‘EveRes Ruby’ (USPP 36,112), and ‘CaroRes Delight’ (USPP approved). The ‘CaroRes’ name signifies both Clemson’s South Carolina origin and disease resistance, while ‘EveRes’ identifies cultivars that combine disease tolerance with a slow-softening phenotype, allowing fruit to remain firm on the tree longer than standard melting types. All three cultivars are vigorous, productive, and well-suited to southeastern U.S. orchard systems. The cultivars exhibit high fruit tolerance to bacterial spot. In replicated trials, they demonstrated reliable productivity and good pack-out percentages with minimal split pit incidence. The fruits are large, round, and clingstone, with light pubescence and a high percentage of red skin blush, ranging from 80% to 95%. All cultivars have yellow melting flesh, though ‘EveRes Ruby’ exhibits a firm, crisp texture at harvest that gradually softens over several days at room temperature, enhancing postharvest handling and shelf life. ‘CaroRes Wonder’ and ‘CaroRes Delight’ ripen in the early season, while ‘EveRes Ruby’ ripens in the early to midseason. Across all three cultivars, fruit quality evaluations consistently rated flavor, texture, and appearance highly. These releases provide new options for growers seeking disease-tolerant cultivars with excellent fruit quality, reliable performance, and adaptability to the environmental challenges of the Southeast. Their unique combination of field resilience, consumer appeal, and handling advantages makes them strong candidates for fresh-market production. Trees are available through licensed TN nurseries, including Cumberland Valley Nurseries and Vaughan Nursery.

The production of blackberry, a valuable fruit crop, is primarily limited to USDA Zones 5 and higher. However, wild species such as Rubus allegheniensis, R. alumnus, and R. rosa are widespread from Zones 5 through Zone 3a in Minnesota and Wisconsin. Native species are a valuable, untapped genetic resource, which could provide both hardiness for production in colder areas with short growing seasons and resilience to pests, diseases, and climate change for warmer areas. The use of native species for breeding has been limited as little research has been conducted to date. To access the utility of this germplasm, propagation protocols developed for them will need to be established. Because sexual and vegetative propagation requirements for the genus Rubus vary widely depending on taxa and genotype, this research aims to evaluate protocols specific to these species. Canes were collected from 24 northern locations to test rooting of softwood cuttings with either IBA and NAAm auxin treatments in early spring and again in summer. Additional canes were collected from one location to test the rooting of dormant cuttings using IBA and bottom heat to stimulate root growth. Results indicate that the suitability of softwood cuttings for propagation is dependent on the section of the genus, with samples over 30% of samples from section Procumbentes (dewberries) rooting, while sections Arguti, Canadenses, Rubus (highbush blackberries), Setosi (bristleberries), or Ideaobatus (raspberries) all had under 10% rooting rates. In addition, seeds were collected from 5 locations to test germination protocols. Seeds were divided between two stratification treatments(20°C control and a six-month at 4°C). Within those, seeds received either no scarification, physical scarification, 30 minute acid scarification, or 3 hour acid scarification treatments. The 30 minute acid scarified seeds were also divided between a control and aqueous smoke solution treatment. Results from germination tests indicated that long acidic scarification treatments do not result in increased germination at six months.

Papaya ringspot virus (PRSV) is a devastating pathogen found throughout the tropics and subtropics. Understanding PRSV diversity and evolution is crucial for formulating timely management strategies and breeding resistant cultivars. The molecular epidemiology of PRSV-P was investigated by analyzing the nucleotide sequences of the coat protein gene of different PRSV isolates worldwide, including the sequence data generated by collecting infected samples from South Florida. PRSV samples were collected from different papaya growing regions in Homestead and the wild papaya plantations surrounding Lake Okeechobee. Distinct PRSV clades were identified, corresponding to the U.S. and South American region, Southeast Asia (excluding India), and specifically India. The sequences obtained in the present study showed a close correlation with the aligned with the sequences from Cuba, Mexico, Jamaica, Guatemala, Venezuela, and previous sequences of the Florida isolates. The estimates of PRSV diversity showed an increase in the viral diversity, as the majority of the papaya growing regions are forming a separate clade. However, the evolution is slow, which could be due to the implementation of control strategies and the cultivation of resistant transgenic papayas.

Lack of winter chill accumulation is a major limiting factor for blackberry production in regions with mild or absent winters. For blackberry buds to release endodormancy they must be exposed to a range of temperatures between 0-7°C for a period of time that is genotype-specific. Insufficient chill in blackberries results in incomplete bud development, irregular budbreak, extended flowering periods, nonsynchronous fruit set, and lower fruit yields. The University of Arkansas Division of Agriculture (UADA) Fruit Research Station, located in Clarksville, Arkansas, experiences 1000 hours of annual chill each year, inhibiting the identification of low chill germplasm in the Arkansas Fruit Breeding Program. This study compares two methodologies for determining chilling requirements in six blackberry cultivars (Von, Natchez, Navaho, Ouachita, Sweet-Ark® Ponca, and A-2491T). Long-cane blackberry plants were exposed to controlled artificial chilling in a cooler, with removal at six weekly intervals from 0 to 840 hours, followed by exposure to forcing conditions in a heated greenhouse. Concurrently, field-grown plants of the same cultivars were exposed to naturally occurring chill hours in the field with six stem cuttings per genotype collected biweekly and forced under a mist bed in a heated greenhouse. The number of buds broken, reproductive laterals, and open flowers were recorded on a weekly basis for both methods. Results indicated that both methods effectively differentiated chilling requirements across cultivars, with budbreak and flowering progressing more rapidly and synchronously once plants reached their cultivar-specific chilling requirement. This study aims to identify an effective, repeatable method of evaluating blackberry chilling requirement in Arkansas to inform breeding decisions and identify low chill material in UADA blackberry germplasm.

Blueberry is the second major fruit crop in Alabama, followed by peach. However, blueberry production in Alabama is marginal compared to neighboring states such as Florida, Georgia, and North Carolina. Alabama growers still rely on old rabbiteye cultivars due to a lack of access to southern highbush blueberries (SHB) that are adaptable to the region. SHBs are valued for their early maturation and fruit quality but have not been widely adopted in Alabama due to their susceptibility to spring frost and other possible biotic or abiotic stresses. This project aims to introduce frost-tolerant SHB cultivars in Alabama through multi-environment cultivar evaluation. A total of 12 cultivars and 25 advanced selections of SHB have been evaluated in two locations in Alabama: the E.V. Smith Research Center (EV) in Central Alabama and the Brewton Agricultural Research Unit (BW) in South Alabama. Plants have been evaluated for 50% bloom, average berry weight (g), yield per plant (g), Brix (%), titratable acidity (TA%), and firmness (g/mm). Data from 2024 revealed that San Joaquin (5,035 g) and NC5289 (3,798 g) had the highest average yield at EV. At BW site, TH-2976 (3,375 g) and NC5289 (2,984 g) showed the highest yield. Colossus and Patrecia produced the largest average berry weight for both locations. In the BW, Colossus had an average berry weight of 4.72 g and Patrecia 3.8 g. At the EV location, both Colossus and Patrecia had an average of 3.0 g berry weight. For Brix, FL12-213A (14.7) and NC5326 (14.2) had the highest values at EV, while NC5326 (14.2) and Sentinel (13.8) had the highest values at the BW location. Overall, late-blooming selections such as NC5314 and NC5289 were identified as more suitable for Alabama to mitigate spring frost damage. The frost-tolerant cultivars identified through this project will significantly benefit small to mid-sized growers in Alabama by ensuring stable fruit production.

Macadamia is a commercially valuable nut crop, but the global industry is predominantly based on self-infertile cultivars. Pollinator scarcity can result in reduced nut set and lower yields. The development of self-fertile cultivars provides an opportunity to produce consistent yield in the absence of pollinisers and pollinators and may enhance orchard profitability. While previous studies identified varying degrees of self-fertility in macadamia, a comprehensive understanding of genetic diversity within a broad range of germplasm and the mechanisms of this trait remain unexplored. This study involved 11 commercial cultivars to identify genetic variation and mechanisms associated with self-fertility. An outcross pollen exclusion method was employed to assess self fertility. The percentage ratio of self- to open-pollinated nuts were calculated as a measure of self-fertility. To investigate the mechanisms underlying self-fertility, spatial separation of male and female reproductive organs as well as site of pollen tube growth inhibition have been examined. Pistil length, stamen length and stigma-anther distance were measured over two flowering seasons. Fluorescence microscopy was used to observe the pollen tube growth after self-pollinations. The self-fertility ranged between 17%-65% for six cultivars (‘HAES 741’, ‘HAES 791’, ‘A38’, ‘UQM40’, ‘K’, ‘Q’), which were identified as self-fertile. Five cultivars (‘HAES 344’, ‘A16’. ‘Daddow’, ‘D4’, ‘A268’) were identified as self-infertile. Pistil length of self-fertile cultivars ranged from 12.5 to 14 mm. Except for ‘A268’, which had significantly shorter pistils (8.5 mm), the pistil length of the self-infertile cultivars ranged from 11.5 mm to 14.5 mm. Stigma-anther distance was not associated with self-fertility. It was found that all cultivars exhibited similar stigma-anther distance, ranging from of 6 to 8 mm. There was non significant difference between the self-fertile and self-infertile groups for morphological floral traits. Pollen tube was inhibited in the upper third of style in self-incompatible pollinations. This inhibition indicated gametophytic self-incompatibility in macadamia. Further study will use a diverse collection of macadamia germplasm, including commercial cultivars, breeding lines and wild accessions to estimate heritability of self-fertility. Additionally, differential expressed genes in the pistils of self-fertile and self-infertile cultivars will be examined to understand the molecular mechanism regulating the trait. This research will assist in breeding of high-yielding, self-fertile cultivars for future plantations, ultimately supporting the sustainability of macadamia industry.

Black raspberry (Rubus occidentalis) and purple raspberry (R. idaeus x occidentalis) are fruits known for their pleasant and distinctive flavors. However, unlike their more popular cousin red raspberry (R. idaeus), little is known about what defines the characteristic aromas of black and purple raspberry. Using SPME-GCMS, the chemical compounds in the headspace of pureed black raspberry (4 genotypes), purple raspberry (5 genotypes), and red raspberry (2 genotypes) were collected and identified through a combination of gas chromatography and mass spectrometry. Chemical concentrations were calculated by integrating the area under the chromatogram curve, and calibrated with an internal standard of 2-octanol. By utilizing a random forest model, chemicals that were the most important for distinguishing fruit types (red vs. black vs. purple) were determined. Of the top 30 chemicals, 12 chemicals were described on Flavornet as detectable by a human nose in gas chromatography-olfactometry (GC-O), and the typical aroma described. Those 12 chemicals were then evaluated individually for significant differences across types (red, black, and purple raspberry). Among the chemicals that differed significantly across species were D-Carvone (caraway aroma), 1,3,8-p-Menthatriene (turpentine aroma); β-Ionone (violet, flower, raspberry, and seaweed aromas); α-Ionone (violet aroma); 2-Hexenol (leaf, green, wine, and fruit aromas); and α-Terpineol (oil, anise, and mint aromas). These results have implications for breeding new black and purple cultivars with the expected characteristic flavor. This instrumental approach also allows for tracking these aromas in breeding populations when utilizing interspecific hybridization to broaden the black raspberry germplasm in breeding.

The Vitis genus consists of two subgenera, Vitis and Muscadinia, which are both cultivated for wine, juice and fresh consumption. Fresh market breeding programs for grapes (V. vinifera) and muscadines (M. rotundifolia) aim to develop stenospermocarpic seedless and perfect-flowered cultivars. Despite chromosome differences and genetic divergence between the Vitis (2n=38) and Muscadinia (2=40) subgenera, stenospermocarpic seedlessness from V. vinifera was successfully introgressed into M. rotundifolia through conventional breeding. Currently, molecular markers for stenospermocarpy have not been developed or validated in Muscadinia and diverse Vitis accessions. Before the divergence of the Vitis and Muscadinia subgenera, two mutations occurred in perfect flowered ancestors, leading to male and female sterility and resulting dioecy in wild plants from both subgenera. Kompetitive Allele Specific PCR (KASP) markers have been recently developed targeting the known causal mutations resulting in male sterility (VviINP1) and stenospermocarpy (VviAGL11) in Vitis. The markers named, seedless_Arg197Leu_site56.fas and female_INP_indel_site56.fas, were evaluated for their diagnostic potential across Vitis and Muscadinia species through sequence alignments with published genomes. The predictive ability of these markers was assessed using a validation panel from the University of Arkansas Division of Agriculture Fruit Breeding program, which included 918 seedlings from Vitis x Muscadinia hybrid breeding populations. Additionally, a range of diverse Vitis and Muscadinia accessions with known phenotypes were included to enhance understanding of marker effectiveness, including cultivars, selections, and wild material from USDA germplasm repositories and public and private breeding programs. In total, 209 diverse accessions were assessed with the seedless marker, and 320 accessions were evaluated with the flower sex marker. The evaluation for seedlessness and flower sex took place over 2023 and 2024. Excluding incomplete phenotype and genotype data, the stenospermocarpic marker (seedless_Arg197Leu_site56.fas) accurately predicted seedlessness in 921 of 924 entries. Additionally, 148 out of 203 seedlings that did not produce fruit in both growing seasons were predicted to be stenospermocarpic. A t-test comparing vine caliper between seeded and seedless material (P =0.178) showed no difference in vigor between the seeded and seedless vine and suggested that the high number of seedless vines with no fruit may be caused by sterility factors linked to the introgressed Vitis stenospermocarpy locus. The flower sex marker (female_INP_indel_site56.fas) correctly predicted flower sex in 1,137 of 1,138 entries. Overall, the KASP markers showed outstanding predictive performance, achieving accuracy rates of 99.9% for flower sex and 99.7% for seedlessness across Vitis, Muscadinia, and hybrid germplasm.

'Ga. 6-1-269' is an hermaphroditic muscadine grape (Vitis rotundifolia) with bronze berries that was released by the University of Georgia (UGA) College of Agriculture and Environmental Sciences. Yields of ‘Ga. 6-1-269’ in Tifton, GA and Citra, FL trials were similar to other popular fresh-market muscadine cultivars. Berry size is very large (15-16 g) and similar to the cultivars 'Ga. 6-2-26' (Paulk®) and 'Supreme'. Fruit rot susceptibility of ‘Ga. 6-1-269’ was less than the bronze check cultivar 'Ga. 1-1-48' (Hall®) and similar to the black check cultivars 'Ga. 6-2-26' and 'Supreme'. Harvest time of ‘Ga. 6-1-269’ was about 5 days after 'Ga. 1-1-48' and about a week before 'Ga. 6-2-26' and 'Supreme'. ‘Ga. 6-1-269’ is recommended as an early-midseason fresh market bronze muscadine cultivar.