Tree Fruit Research Laboratory

Dynamic controlled atmosphere (DCA) storage offers potential economic advantage for organic apple storage, but quantifying these benefits requires accounting for packout uncertainty, seasonal price dynamics, environmental, and location-specific heterogeneity. We developed an integrated empirical simulation that links multiyear storage trials with Monte Carlo revenue modeling to quantify DCA performance relative to controlled atmosphere and regular atmosphere storage. Storage experiments evaluated quality retention or packouts across storage durations and were represented by beta-distributions. A three-stage least squares model identified seasonal price patterns and key determinants of organic apple prices, producing monthly price predictions. Predicted prices were combined with simulated packouts to estimate by cultivar, storage length, and orchard the probability that DCA is revenue superior. Economic outcomes were cultivar, year, and site specific. For organic ‘Gala’ ( Malus domestica ), the probability that DCA dominates increased from 37.6% in Spring 2022 to 91.8% in Summer 2024, with median revenue advantages for DCA reaching $170,488 per storage room at peak. For ‘Honeycrisp’, orchard-level heterogeneity was pronounced. Orchard 1 achieved 100% DCA dominance in Spring 2024, whereas ‘Honeycrisp’ orchard 2 showed variable performance (high of 77.0% to 78.6% in Summer 2022 and Summer 2023). Weather-sensitivity analysis indicated location-specific responses. Elevated harvest temperatures slightly reduced DCA dominance for ‘Gala’ but sharply reduced it for ‘Honeycrisp’ (−26.1 percentage points on average). These findings indicate that DCA adoption should be tailored to cultivar, storage duration, and local environmental conditions. The framework provides probabilistic decision support for adoption and timing of DCA in organic apple supply chains by integrating storage performance, price seasonality, and packout uncertainty.

Vascular streak dieback (VSD) poses a significant threat to the sustainability of woody ornamentals in the United States, particularly Cercis spp. (redbud). This study aimed to develop reliable molecular diagnostic tools for detecting Ceratobasidium sp. D.P. Rogers (Csp), the fungus consistently detected from VSD-symptomatic redbuds and other woody ornamentals. Molecular markers can provide rapid and accurate detection for fastidious fungi such as Csp that are challenging to recover in culture media. However, current molecular tools for Csp detection lack sensitivity and specificity. To address this, specific PCR and quantitative PCR (qPCR) primers were developed, targeting the internal transcribed spacer (ITS) genetic region. The existing primers for the second-largest subunit of RNA polymerase II (RPB2), translation elongation factor 1-alpha (TEF1-α), and ATP synthase subunit 6 (ATP6) genetic regions of Rhizoctonia fungi were also redesigned to enhance the sensitivity and accuracy of detection for Csp. The CP-qP-Csp primer set, with a detection limit of 86.02 pg/μl, effectively detected Csp in VSD-symptomatic tissues, cultures, and soils and is recommended for molecular detection of Csp from woody ornamentals in the U.S. Cross-platform validation across seven laboratories confirmed the robustness of the assays. These findings provide nursery producers with critical early-detection capabilities, potentially preventing significant economic losses and contributing to the sustainability of woody ornamental production. Future research will focus on refining these assays for field applications and exploring the genetic characteristics of Csp across different hosts and pathogen interactions to better understand the epidemiology of VSD.

Abstract The expansion of the use of induced resistance (IR) has been, and remains, an attractive prospect for the management of woody plants, but little research has occurred assessing the ability of elicitors to induce the root defenses of woody plants. Eastern white pine (Pinus strobus) was used as a model plant to assess IR elicitation. Containerized plants were treated with phosphite (Phi), chitosan, curdlan (a β-1,3-glucan polymer), or silicon (Si) on 2022 June 7. The soluble phenolic levels, tissue levels of major resin acids (abietic and neoabietic), as well as the activities of peroxidase (POX), chitinase (CHI), and β-1,3-glucanase (βGLU) of fine roots were compared across elicitor treatments and nontreated controls on June 10, June 14, and June 27. There were no changes post-treatment to soluble phenolics or resin acids at any sampling point, but chitosan treatment resulted in an increase in POX and CHI activities, while curdlan increased CHI activity on June 10. On June 14, curdlan-treated plants had significantly higher POX and CHI activities, while Phi-treated plants had significantly higher POX activity. By June 27, curdlan- and Phi-treated trees had significantly higher CHI activities. Our data suggest that chitosan, curdlan, and phosphite stimulate biochemical responses and potentially prime root systems to respond to subsequent stresses, but there appears to be variation between these elicitors regarding rapid versus longer lasting IR effects.

Abstract Background Extreme summer heat events in which temperatures exceed 40 °C are expected to increase in duration and intensity worldwide. Consequently, selecting heat-tolerant trees for future predicted climatic conditions will be one of the significant challenges for urban landscape managers. Method The effect of heat stress (44 °C for 4 hours) on chlorophyll variable:maximum fluorescence (Fv/Fm) ratios and Soil Plant Analysis Development (SPAD) values as measures of damage to the leaf photosynthetic system and leaf chlorophyll content was quantified in 8Acergenotypes (Acer pseudoplatanus‘Negenia’,A. pseudoplatanus‘Spaethii’,A. platanoides‘Royal Red’,A. platanoides‘Princeton Gold’,A. platanoides‘Emerald Queen’,A. platanoides‘Drummondii’,A. campestre,A. campestre‘Louisa Red Shine’). Results Fv/Fm ratios proved to be a sensitive indicator of heat damage and positively identified marked differences in tolerance to and recovery from heat damage between the 8Acergenotypes. Estimated leaf chlorophyll content (SPAD) was not sufficiently sensitive to distinguish differences in tolerance and recovery between genotypes. Conclusions Chlorophyll fluorescence Fv/Fm ratios, but not estimated leaf chlorophyll content (SPAD), offers a rapid screening technique for assessing the tolerance to and recovery from heat stress in leaf tissue of trees.

IGT/LAZY proteins play a central role in determining gravitropic set point angle and orientation of lateral organs across plant species. Recent work in model systems has demonstrated that interactions between IGT/LAZY proteins and BREVIS RADIX (BRX)-domain containing proteins, such as PH, RCC1, AND FYVE/RCC1-LIKE DOMAIN (PRAF/RLD), and BREVIS RADIX LIKE (BRXL) family members, are mechanistically important for setting gravitropic set point angle. Here, we identified peach PRAF/RLD proteins as interactors of the peach IGT/LAZY proteins PpeLAZY1 and DEEPER ROOTING 1 (PpeDRO1) from a yeast-two-hybrid screen. We also show that the BRX domains of these interacting proteins have high sequence similarity with PRAF/RLD and BRX family proteins from rice and Arabidopsis. Further, PpeLAZY1 and the peach PRAF/RLD interactors are all expressed at relatively high levels in leaf, meristem, and shoot tip tissues. Together, this evidence supports the importance and conservation of IGT/LAZY-BRX-domain interactions, which underlie setting gravitropic set point angle across angiosperms.

Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae) is the most expensive and challenging insect pest of commercial pear trees in the Pacific Northwest. Integrated pest management (IPM) programs are working toward relying more heavily on natural enemies to reduce insecticide use. Trechnites insidiosus (Crawford) (Hymenoptera: Encyrtidae) is the main parasitoid of C. pyricola, but little is known about its biology in the region. Developing sampling tools is important for the deployment of IPM programs, including monitoring of natural enemies. In this study, we examined 2 conventional monitoring methods: beat trays and yellow sticky cards, in addition to screened sticky cards and 3D-printed cylinder traps. Additionally, we tested an overwintering trap for the collection of parasitized C. pyricola. The trapping methods were tested in orchards in Oregon and Washington. Unscreened cards caught the most T. insidiosus and C. pyricola, followed by screened cards, cylinder traps, and then beat trays. Beat trays sometimes failed to catch any T. insidiosus, even when it was found in abundance via other methods. Screened cards and cylinder traps reduced bycatch and increased ease of identifying T. insidiosus. Specimens from the cylinder traps were also more suitable for use in molecular analysis. The overwintering traps were effective at capturing parasitized C. pyricola, but were highly variable year to year. The ideal trapping method will vary based on research needs (e.g., DNA preservation, reducing bycatch, catching higher numbers), but both screened sticky cards and cylinder traps were viable methods for monitoring T. insidiosus and its host.

Apples grown in high heat, high light, and low humidity environments are at risk for sun injury disorders like sunburn and associated crop losses. Understanding the physiological and molecular mechanisms underlying sunburn will support improvement of mitigation strategies and breeding for more resilient varieties. Numerous studies have highlighted key biochemical processes involved in sun injury, such as the phenylpropanoid and reactive oxygen species (ROS) pathways, demonstrating both enzyme activities and expression of related genes in response to sunburn conditions. Most previous studies have focused on at-harvest activity of a small number of genes in response to heat stress. Thus, it remains unclear how stress events earlier in the season affect physiology and gene expression. Here, we applied heat stress to mid-season apples in the field and collected tissue along a time course-24, 48, and 72 h following a heat stimulus-to investigate dynamic gene expression changes using a transcriptomic lens. We found a relatively small number of differentially expressed genes (DEGs) and enriched functional terms in response to heat treatments. Only a few of these belonged to pathways previously described to be involved in sunburn, such as the AsA-GSH pathway, while most DEGs had not yet been implicated in sunburn or heat stress in pome fruit.

カキ ‘刀根早生’ の米国輸出時にへた周辺の果底部に生じた汚損果の発生要因を検討した．シミュレーション実験では，脱渋・1-MCP処理果実の汚損果発生は30°C保持（7日間保持）で著しく，15°C以下ではほとんど見られなかった．PE折りたたみ包装は防湿段ボール梱包より25°Cおよび30°Cでの汚損果発生を増加させた．汚損果が多発した脱渋・1-MCP処理果実のPE密封包装は果実内酸素濃度を3％程度に低下，二酸化炭素濃度を5％程度に増加させ，エチレン生成を促進した．二酸化炭素吸収剤の同封は，袋内二酸化炭素濃度を下げ，汚損果の発生を軽減した．一方，CTSD脱渋と1-MCP処理はそれぞれ汚損果発生を助長した．以上の結果から，輸出時の汚損果発生の要因は，25°C以上の高温環境下において，脱渋および脱渋直後の包装資材への梱包による低酸素・高二酸化炭素状態でのストレスが汚損果を生じさせ，1-MCP処理によるエチレン作用の阻害が助長要因になると考えられた．‘刀根早生’ 果実の輸出には，脱渋処理と1-MCP処理は必須であることから，汚損果対策には梱包後の適切な温度管理が実現可能かつ効果的な方法である．

Abstract‘Honeycrisp’ is one of the most valuable apple cultivars grown in the United States and a popular breeding parent due to its superior fruit quality traits, high levels of cold hardiness, and disease resistance. However, it suffers from a number of physiological disorders and is susceptible to production and postharvest issues. Although several apple genomes have been sequenced in the last decade, there is still a substantial knowledge gap in understanding the genetic mechanisms underlying cultivar-specific traits. Here we present a fully phased, chromosome-level genome of ‘Honeycrisp’ apples, using PacBio HiFi, Omni-C, and Illumina sequencing platforms. Our genome assembly is by far the most contiguous among all the apple genomes. The sizes of the two assembled haplomes are 674 Mb and 660 Mb, with contig N50s of 32.8 Mb and 31.6 Mb, respectively. In total, 47,563 and 48,655 protein coding genes were annotated from each haplome, capturing 96.8-97.4% complete BUSCOs in the eudicot database, the most complete among all Malus annotations. A gene family analysis using seven Malus genomes shows that a vast majority of ‘Honeycrisp’ genes are assigned into orthogroups shared with other genomes, but it also reveals 121 ‘Honeycrisp’-specific orthogroups. We provide a valuable resource for understanding the genetic basis of horticulturally important traits in apples and other related tree fruit species, including at-harvest and postharvest fruit quality, abiotic stress tolerance, and disease resistance, all of which can enhance breeding efforts in Rosaceae.