ASHS 2024 Conference

Mechanization Reduces Pruning and Harvest Labor Time in the Cider Apple Orchard - Carol Miles
Testing Agronomic Strategies to Reduce Biennial Bearing in Apples - Thiago Campbell
Identifying Local Apple Germplasm for Use of Hard Ciders in North Dakota - Wenhao Dai
The Fruitlet Size Distribution Model As A Thinning Decision Aid For Precision Crop Load Management Of Apple - Laura Hillmann
Deciphering the Proline-Mediated Flowering Delay Mechanism in Peach through Physiological and Metabolic Analyses - Hyunsuk Shin
Genetic Architecture of Important Traits for Prunus Crop Improvement - Michael Itam
Taste Acidity and Other Important Fruit Characteristics of New Peach Varieties Compared with Concurrent Varieties During 2022 and 2023 - Hemant Gohil
Role of Silicon in Peach Water Stress Tolerance - Noah Willsea

Biennial bearing in tree fruit can be problematic, and these patterns are not unique to tree fruit and occur in natural species. Masting, or the abundant production of seeds in some years, can also be observed in natural tree species. Despite extensive research, biennial bearing still affects commercial orchard production. Biennial bearing cycles are costly, with inconsistent yields and fruit quality occurring yearly. Crop load management is one commonly used management strategy to control biennial beating. However, trees can continue a biennial cycle the year following adequate crop thinning. We evaluated six different agronomic strategies to combat biennial bearing in apple trees; two for low-cropping trees (“off” year) and four for high-cropping trees (“on” year). In 2023, ‘Honeycrisp’ trees on B.9, G.41, G.890, and M.9-T337 rootstocks in their high-cropping year were root pruned, girdled, sprayed with ethephon, or fertilized with nitrogen (ammonium nitrate) in the fall, along with untreated control. Trees in their low-cropping year (2023) were defoliated and sprayed with gibberellic acid (GA 3 ) and untreated control. Due to the limited availability of low-cropping trees in 2023, only ‘Honeycrisp’ trees on B.9 and M.9-T337 rootstocks were used. All treatments were applied two to three weeks after full bloom except for nitrogen fertilization, which was applied in late August. Crop load, vegetative growth, and fruit quality were measured for treated trees and controls. Carryover effects of treatments were calculated to quantify the reduction/amelioration of biennial bearing incidence. In low-cropped trees, GA 3 had significantly higher return bloom from controls and defoliated trees. In high-cropped trees, no treatment had a significant effect on return bloom compared to controls. Vegetative growth was not affected by any treatment. Effective agronomic strategies for managing biennial bearing can be inconsistent and need to be further investigated for their impacts.

Hard cider is one of the fastest growing specialty beverages in the United States with an average annual retail sales of about $500 million in recent years. Cider apples refer to those that are specifically used for hard ciders (alcoholic) with unique traits, such as high acid, high tannin, and high total soluble solid that help ferment superior-quality hard ciders. In traditional hard cider production countries, hard ciders are made from cider-specific cultivars; however, hard ciders in the US are usually made from apples that were bred for fresh apple market because of inadequate fruit availability of cider-specific cultivars. In this study, apple germplasm grown at the NDSU Horticulture Research Farm near Amenia, ND (USDA hardiness zone 3-4a) was evaluated for the suitability of quality hard ciders. Specifically, four biochemical traits, total soluble solids (TSS), pH, titratable acidity (TA), and total phenolic compounds (TPC) that are the general attributes to the quality of hard ciders, were analyzed. Preliminary results showed that the average TSS was 15.75o Brix with the highest TSS reached 21.2o Brix. The fruit of some lines were very sour and tart indicating the high level of acidity and phenolics, which showed the great potential for quality hard cider production. The titratable acidity (malic acid) and total phenolic compounds in the apple juice of selected lines are being quantified. This research could identify local cider apple germplasm and provide apple growers and cider makers with the information on cultivar selections for quality hard cider production in ND and the surrounding region.

Fruit quality of apple is heavily influenced by crop load management practices. During the developmental window between bloom and 15mm fruitlet diameter, the general commercial practice is to apply chemical thinners to reduce the initial crop load based on the cultivar and market. However, thinning success varies from year to year, depending on bloom density, thinner selection and dose, climatic factors, tree health and cultivar. Precision crop load models such as the pollen tube growth model, the MaluSim model, and the fruit growth rate model have improved thinning success; however, labor-intensive measures has hindered broad adoption of the latter model which effectively predicts fruit set following thinner application. To improve grower adoption, we developed an alternative, time-efficient fruit set prediction model. The model has been tested on multiple cultivars over a three-year period at four distinct apple production regions throughout the United States. Abscission probabilities and fruit set predictions are based on the distribution of fruitlet mass and confirmed by actual measures of fruit set. The model starts at 6 mm fruitlet diameter and accounts for all thinners up to this time. A prediction is returned in ~8 days to inform repeat thinner applications while fruitlets are still highly sensitive to thinners. A user-guide, digital balance that automatically exports fruit mass to a laptop/tablet, and a macro-enabled Excel spreadsheet file have been developed and are available to growers to increase the precision around crop load management.

Freezing temperatures can harm peaches in late spring with advanced flowering due to climate change and consequently reduce their yield. Flowering delay is a prominent strategy employed to avoid such spring frost damage. Our previous study demonstrated that treatment with 5% sodium alginate 100 mM CaCl 2 (5AG) can delay the blooming, potentially avoiding frost damage. To elucidate the precise mechanism of flowering delay induced by 5AG in peaches, this study systematically and experimentally analyzed the changes of amino acid profiles in control and 5AG-treated peach plants at different day intervals (0, 1, 2, 11, 21, 25, and 28 DAT). Our findings revealed that the levels of arginine (Arg), glutamate (Glu), and proline (Pro) differed significantly between control and 5AG- treated peach shoots throughout the phenological development of flower buds. Furthermore, Arg and Glu amino acids, are involved in the Pro pathway. Computational metabolomics analyses identified the Pro metabolism related genes and their attributes, gene ontology, gene synteny and gene organizations, which represent diverse biological function of these genes, including flowering responses. In addition, qRT-PCR analysis results revealed that elevated expression of P5CS and P5CR genes, involved in Pro metabolism, led to increased Pro content in control plants. Conversely, 5AG treatment downregulated these genes, resulting in lower proline content. This result suggests that 5AG treatment may restrain gene expression related to Pro accumulation, thereby controlling Pro biosynthesis. In addition, our findings unveiled a direct connection between Pro content reduction and delayed flowering. Taken together, these results provide strong evidence that 5AG treatment significantly delays flowering by controlling Pro metabolisms in Prunus persica.

Numerous QTL and GWAS studies have been conducted on various species of Prunus, but there is limited knowledge on the overall genetic architecture regulating fruit quality traits among these species. As part of a 2022-funded SCRI- project to advance database resources for specialty crop research, efforts are directed towards collecting and curating all types of big data in the Genome Database for Rosaceae (www.rosaceae.org). We conducted an extensive literature review on over 120 QTL and GWAS studies on Prunus traits to extend the existing data in GDR. We aligned the traits to the peach genome to compare important traits in various Prunus species. The consensus map showing QTL hotspots will be accessible using various tools in GDR. Implications of the newly created resources and tools in GDR for breeding will be discussed.

Three new peach varieties and ‘Felicia’ ‘Evelynn’ and ‘Anna Rose’ were recently released from the Rutgers University tree fruit breeding program. These varieties are concurrent with some of the standard peach varieties. The comparison of taste acidity and other important fruit characteristics could help growers choose in case of planting these varieties or replacing the standard varieties during the same harvest window. Fruit characteristics such as flesh color, crop load, shape, skin color, fuzz, attractiveness, stone characteristics (free, semi-free, or cling), flesh color, bacterial spot, on fruits and leaves, taste acidity, juice total soluble solids (TSS) concentration (°Brix), and total titratable acidity (TTA) (%) were measured. Here we compare these varieties to highlight the differences and challenges amongst these varieties on their path to full consumer appreciation. Results indicate that average TSS and firmness were higher in ‘Felicia’ (12.9 brix; 12.4 lb) and ‘Evelynn’ (11.9 brix; 10.9 lbs.) compared to ‘Redhaven’ (11.1 brix; 8.14 lbs.). Also; average TSS and firmness were higher in ‘Anna Rose’ (14.4 brix; 13.68 lbs.) compared to ‘Klondike’ (12.0 brix; 11.3 lbs.) and ‘White Lady’ (10.9 brix; 9.64 lbs.). In summary, new yellow-fleshed peach varieties ‘Felicia’ and ‘Evelynn’ have great potential to replace the old standard variety, ‘Redhaven’. Similarly, the new white-fleshed peach variety ‘Anna Rose’ has great potential to replace old standard varieties ‘White Lady’ and ‘Klondike’.

Water stress in young fruit trees can reduce tree growth and impair future crop productivity. Silicon (Si) has shown a positive effect in mechanisms related to water relations, specifically water uptake and transport, as well as physiological and anatomical changes in leaves of annual plants. These findings suggest that Si could induce adaptive changes that could help trees cope with water deficit. The objective of this experiment was to evaluate the role of Si on water status, sap flow, and gas exchange of young peach trees under water deficit. Two-year-old ‘Julyprince’ peach trees grown under controlled conditions received either 100% (well-watered trees) or 50% (stressed trees) of their crop evapotranspiration needs three times a week. Once trees in the two treatments displayed a difference in water status, Si was applied weekly by foliar spray (0 or 20 mg L-1). The combination of these two factors resulted into a completely randomized factorial design with four treatments. Results showed an interaction between irrigation regime and Si application. Si increased sap flow in well-watered trees and reduced that of stressed trees, although this effect was more significant the day after irrigation. Furthermore, Si significantly improved the water status of trees under water deficit but did not influence that of well-watered trees. These results seem to indicate that the role of Si in improving tolerance to water deficit is temporary and dependent on the tree water status.

While fresh-eating, dessert apples dominate the apple market of Washington State, the over 30-fold national increase in volumetric cider production over the past 15 years indicates there is growing demand for specialty cider apples, or apple cultivars with positive cider-making attributes such as high polyphenol content. In a commercial cider orchard, the labor costs associated with thinning, pruning, and harvest comprise a majority of the annual variable production costs once the orchard is in full production; thus, reducing the labor time to perform these tasks has the potential to increase the appeal and profitability of growing cider apples. Further, when cider apples are pressed into juice soon after harvest, cosmetic damage and bruising of the fruit during harvest has minimal impact on juice quality, indicating a strong potential for harvest mechanization. This study separately examines mechanical hedging and mechanized over-the-row harvest (using a modified Oxbo-Korvan 930 harvester) in a multi-cultivar cider apple orchard. Mechanical hedging both sides of the orchard row occurred at a rate of 2.1-3.5 seconds per meter across 5 years. Across 16 cultivars and 3 years, mechanical harvest occurred at a rate of 2.7-3.1 seconds per meter, and the average capture efficiency was 82% with no significant differences between cultivars. Based on these results, a combination of mechanical pruning and harvest could significantly lower labor time, and thus the total production costs, associated with growing cider apples.

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.

Do Plant “Growth Regulators” Really Regulate Growth? Plant Development And Plant Growth Are Not Synonymous. - Ted DeJong
Using GDR to Enable Rosaceae Research - New Data, Functionality and Future Direction - Dorrie Main
Raspberry Cultivar Evaluation Trial in Mississippi - Apphia Santy
Evaluating Sufficiency Levels and Peach Leaf Analysis for Fertilizer Decision-Making - Juan Carlos Melgar
Common Mechanisms Controlling Fruit Shapes may be Mediated by Changes in Cell Wall Properties - Easther van der Knaap
Pomological Nomenclature: Recent Developments and Problems - David Karp

Much scientific literature refers to plant development and growth as though they are synonymous. While plant physiology texts (E.g., Taiz et al. 2015) and horticulture texts (E.g., Sansavini et al. 2019) emphasize the roles of various plant hormones in coordinating plant development, they simultaneously refer to them as plant growth regulators. On the other hand, the same texts emphasize assimilation processes and the important role of carbohydrate and nutrient availability as well as water relations in enabling growth to occur. The terms growth and development are often used interchangeably and the literature rarely emphasizes the difference between plant development and plant growth. This causes confusion and a lack of clear thinking when attempting to develop explanations for plant growth responses in specific circumstances. Hormone physiologists often try to explain particular growth responses in terms of hormonal theory whereas environmental physiologists will likely explain the same responses in terms of environmental conditions and availability for the resources required for achieving growth. In this paper I will argue for a clearer differentiation between plant development and plant growth and suggest that plant hormones should not be thought of as plant growth regulators, but rather as plant development coordinators. Plant development coordinators (plant hormones) set up the conditions necessary for plant growth but availability of plant growth substances; carbohydrate and nutrient availability along with temperature and water relations, are often what actually regulate plant growth rates. Treating development and growth as separate but interdependent processes could clarify much understanding of the underlying processes involved in the regulation of plant growth. These concepts will be discussed in the context of understanding the mechanisms involved in several physiological phenomenon of fruit trees.

Initiated in 2003, the Genome Database for Rosaceae (GDR, www.rosaceae.org) is a comprehensive community database that provides access to curated and integrated genomics, genetics, and breeding data for the biologically and economically important Rosaceae family. It serves as steward of critical research and breeding data, and provides access to online query and analysis tools that enable researchers to readily interrogate this wealth of data, facilitating basic and applied research across Rosaceae. This presentation will highlight the impact of GDR on Rosaceae research, demonstrate new data and tools, and share plans for future development and sustainability options.

Many states in the US produce raspberries, however, most of the production is concentrated in three states: California, Oregon and Washington as most raspberry cultivars grow best in regions with cool summers and mild winters. However, newer raspberry cultivars have been developed exhibiting heat tolerance. Cultivars with heat tolerance provide an opportunity for the growers in the Southern states to include raspberries in their crop production. Local Mississippi growers are interested in incorporating raspberries into their productions. However, there lacks research-based recommendations on raspberry cultivars suitable for Mississippi's climate. The objective of this study was to evaluate raspberry cultivars in terms of plant growth, heat and cold tolerance, pest and disease resistance, berry yield, quality, and fruiting season to identify the best-suited cultivars for Mississippi. This experiment was conducted in a randomized complete block design with two types of fertilizer: conventional and organic. Data collection included measurements of plant growth and performance, berry yield and quality and fruiting season. The results showed that raspberry yield, single berry weight and fruit size were influenced by fertilizer treatment. The soluble solid contents, acidity, and fruit color were not influenced by fertilizer treatment. Raspberry yield was higher for “Polka”, “Encore”, “Heritage”, and “Latham” under conventional fertilizer. Cultivars “Himbo”, “Prelude”, ‘Bp1”, and “Encore” treated with conventional fertilizer had higher single berry weight. The average fruit size of cultivars “Prelude”, “Himbo”, “Encore”, “Bp1” treated with conventional fertilizer produced larger fruits in comparison to the other cultivars. The fruit's soluble solid content was highest in “Heritage”, indicating a sweeter taste. Cultivars “Polana” and “Anne” produced fruits with the highest acidity, indicating a tarter taste compared to other cultivars. Fruit color varied between cultivars, with differences in lightness, redness, and yellow coloration.

The increasing demand for tree fruit production necessitates optimizing nutrient balance in intensified orchard systems to maximize profits efficiently. While peach growers are advised to follow Extension and recommended guidelines for fertilization, such recommendations may not align with orchard-specific variables and environmental conditions. As a consequence, crop sufficiency ranges may require updating to reflect modern growing practices and environmental factors. Although leaf nutrient analysis is the most reliable method for diagnosing tree nutritional status, the prevalence of annual fertilizer application, driven by the low cost of fertilizers relative to crop value, often leads to excessive fertilization in peach orchards. Consequently, our objective was to evaluate established sufficiency levels and leaf analysis as tools for determining the need for annual fertilizer applications. To achieve this, we implemented a two-year study involving two fertilization programs in an orchard with three rows of 17 peach trees: two rows adhered to grower standard, annual fertilization, while the remaining row followed a rational fertilization program. The latter implied applying fertilizer only when leaf analyses indicated nutrient concentrations below established sufficiency thresholds for peaches. Leaf analyses were conducted annually in July, and if nutrient concentrations were within or exceeded sufficiency thresholds, no fertilizer was applied postharvest or the following spring. If nutrient concentrations fell below sufficiency thresholds associated with a significant difference in yield and fruit quality between the two programs, fertilization occurred in late summer and during bloom time the following spring. We assessed tree quality and productivity by measuring yield (total weight of all the fruit per tree) and fruit quality (size and brix) annually. The results of the first year showed that despite deficient leaf nitrogen and phosphorus concentrations and other nutrients such as potassium, calcium, and magnesium remaining within or above their sufficiency ranges, we observed no significant differences in yield or fruit quality between trees subjected to rational and standard fertilization practices. Consequently, fertilization for the upcoming year was deemed unnecessary in trees following the rational program. The outcomes of this study are expected to guide peach growers in making informed decisions based on updated data, reducing the environmental impact of overfertilization, which is inefficient for fruit production and uneconomical, and enhancing farm profitability.

Fruit shape variation is abundantly present in horticultural crops. This variation is critical to highlight the market class as well as the culinary purpose of the produce. Many of the underlying genes have been cloned in tomato, offering insights into the molecular mechanisms of morphological diversity. Specifically, members of the OFP, TRM and SUN family regulate produce shape variation in tomato and other crops, thereby highlighting the importance of these three families in regulating phenotypic diversity. Despite the knowledge of the genes, mechanistic insights into the function of members of these three gene families are lacking. Our research on the tomato genes OVATE and OFP20 has shown that changes in produce shapes are noticeable early in the development of the flower. Cell counts in ovaries at anthesis implied that changes in cell division patterning may underlie morphological diversity. However, gene expression studies showed that morphological changes were associated with cell wall processes and not with changes in cell division patterning.

In addition to botanical names, at least a dozen distinct categories of nomenclature are applied to plant cultivars, including various forms of cultivar denominations, breeders references, and trade names. Two sets of rules, the International Code of Nomenclature for Cultivated Plants (9th ed., 2016), and the Explanatory Notes on Variety Denominations Under the UPOV Convention (2022) provide current guidelines for plant cultivar nomenclature. In some instances UPOV and ICNCP rules differ, and stakeholders may wish to consider whether it would be feasible to seek harmonization, and the mechanisms by which that might be achieved. This session will trace a brief history of cultivar denomination rules for U.S. plant patents. The United States Patent and Trademark Office, which issues plant patents, does not provide detailed nomenclatural guidelines. In the past two decades a new model for plant nomenclature has prevailed, in which an alphanumeric code serves as the official cultivar denomination, and this is paired with a trademark, either registered or unregistered. The relationship between cultivar denominations and trade names can be complex and fluid. As co-editor of the Register of New Fruit and Nut Cultivars, the presenter professionally researches all new pomological cultivar denominations and trade names, to avoid publishing names that conflict with previous names or nomenclatural standards. The establishment of an official cultivar denomination has important practical consequences that are sometimes ignored by breeders and rights owners. When a cultivar has been granted a plant patent or plant breeders’ rights, the cultivar denomination recorded by the statutory plant registration authority that issues the grant becomes officially established (a “statutory epithet”), and cannot be casually changed or replaced by the rights owner. When such informal synonyms are used, they are best regarded as trade names, often as unregistered trademarks. Common mistakes and pitfalls in nomenclature are described.