ASHS 2025 Conference

This session is being co-sponsored by Viticulture and Small Fruits (VSF) and American Pomological Society (APS)

As climate conditions continue to shift, heat stress poses a significant challenge to fruit production, affecting both yield and quality. This session will explore the physiological and biochemical responses of fruit crops to extreme temperatures, highlighting the key impacts on growth, composition, and overall marketability. Experts will discuss innovative mitigation strategies, including vineyard, berry, and orchard management techniques aimed at reducing heat stress impacts. Attendees will gain insights into practical, science-based approaches to safeguard fruit production in the face of increasing heat stress.

Speakers:

• Lee Kalcsits Associate Professor, Tree Fruit Physiology Endowed Chair of Tree Fruit Environmental Physiology and Management Programmatic Lead, Wenatchee Tree Fruit Research and Extension Center Washington State University, Department of Horticulture 
• Lisa Wasko DeVetter Associate Professor, Small Fruit Horticulture Department of Horticulture College of Agricultural, Human, and Natural Resource Sciences Washington State University NWREC
•  Everett P. Layton Ashmore, Ph.D. Postdoctoral Researcher Department of Viticulture and Enology College of Agricultural, Human, and Natural Resource Sciences Dave Bryla Research Horticulturist USDA-ARS Horticultural Crops Production and Genetic Improvement Research Unit, Corvallis, OR

Blueberries (Vaccinium sect. Cyanococcus) are prone to drought due to their shallow root system and limited ability to uptake water from the soil. Previous research has shown rabbiteye (Vaccinium virgatum) blueberries to be more tolerant than highbush varieties (Vaccinium corymbosum L.) to abiotic stresses. However, little is known about their response to drought and whether there are ecotype- or cultivar-specific responses. In order to breed for more drought-tolerant cultivars, this study aims to identify drought tolerant mechanisms within existing cultivars of both southern highbush (SHB) and rabbiteye (RE) blueberries. We evaluated seven cultivars of southern highbush and rabbiteye blueberry for physiological response and fruit quality characteristics under water deficit and recovery across two consecutive years. Overall, drought was found to decrease photosynthesis, stomatal conductance, electron transport rate, leaf relative water content, specific leaf area, chlorophyll content, maximum rate of Rubisco carboxylation (Vcmax) and maximum rate of RuBP regeneration (Jmax). Additionally, drought treatment was found to significantly decrease yield and average berry weight while increasing total soluble solids and berry firmness. Misty (SHB) was identified as the most drought tolerant cultivar due to maintenance of CO2 assimilation, stomatal conductance, and yield under drought conditions across both years, while Suziblue (SHB), Powderblue (RE), and Vernon (RE) were found to be more sensitive to water deficit. Star (SHB) was tolerant of drought in the short term but performed worse under repeated drought events.

Regional recommendations for blueberry irrigation exist, but few studies report the actual amount of water needed. The goal of this multiyear project was to determine the water requirements for growing northern highbush blueberry (Vaccinium corymbosum) in the U.S. Pacific Northwest. Weighing lysimeters were used to measure crop evapotranspiration (ETc) of three cultivars with various ripening seasons, including ‘Duke’ (early season), ‘Top Shelf’ (mid-season), and ‘Aurora’ (late season). Each lysimeter was constructed from steel and included a large soil tank (1.5-m wide × 0.9-m long × 1.0-m deep) positioned on four hermetically sealed, shear-beam load cells, housed inside an underground chamber. Plants were spaced 0.9 × 3.0 m apart in the lysimeters (one plant/lysimeter) and surrounding field (0.4 ha) and managed using standard industry practices, including raised planting beds mulched with Douglas fir (Pseudotsuga menziesii) sawdust, grass alleyways between the beds, irrigation with two lines of drip tubing per row, and fertigation with nitrogen and other nutrients as needed. During the first year after planting, ETc totaled 94–104 mm, depending on the cultivar, or 18–19% of total potential evapotranspiration (ETo) from initiation of the measurements on 1 June to when irrigation was turned off for the season on 23 September 2023. That year, crop coefficients (Kc), calculated by dividing ETc by ETo obtained from a nearby agricultural weather station, averaged 0.11, 0.15, 0.27, and 0.41 each month from June through September, respectively. The following year, the plants were lightly cropped (0.2–0.8 kg of marketable fruit per plant), and ETc totaled 175–343 mm, or 30–59% of total ETo. At that point, Kc averaged 0.31, 0.34, 0.45, 0.61, and 0.61 each month from 14 May to 30 September, which was the entire timeframe in which the plants were irrigated. This project is ongoing and will continue until the plants reach full production. Once the study is finished, a set of seasonal Kc curves will be developed for each cultivar and uploaded to regional websites called AgriMet and AgWeatherNet, where they will be used to automatically calculate irrigation water requirements using meteorological data from local weather stations.

The southeastern United States is a major producer of blueberries (Vaccinium corymbosum), however extreme weather events pose significant threats to blueberry production. On September 24, 2024, Hurricane Helene made landfall in Georgia, causing substantial damage to commercial blueberry fields, including uprooted or leaning plants, broken branches, and defoliation. Our project examines the effectiveness of staking leaning plants and humic acid application to enhance the recovery of blueberry plants after hurricane damage. Trials were conducted in five commercial sites with three different cultivars: ‘Farthing’, ‘Legacy’, and ‘Optimus’. Treatments included staking of leaning plants and the application of humic acid alone or in combination. Plant physiological responses were assessed using SPAD (chlorophyll content), leaf area index (LAI), chlorophyll fluorescence, and stomatal conductance (Gsw). Preliminary data indicate that staking leaning plants improved light interception, chlorophyll content, and photosynthetic efficiency in damaged blueberries. The application of humic acid did not result in enhanced plant recovery beyond staking alone. Root and canopy assessments are ongoing and will help determine whether the practice of staking damaged plants and the incorporation of humic acid contributes to long-term plant recovery. Our study will help blueberry producers implement evidence-based strategies to increase the resilience of blueberry fields following extreme weather events.

Substrate production in pots has emerged as a popular method for growing highbush blueberry (Vaccinium corymbosum). However, there is limited knowledge on the best strategies for irrigation in substrate. To address this issue, a multiyear study was conducted in a retractable-roof greenhouse using ‘Legacy’ blueberry to determine an optimal combination of drip emitters (two, four, or eight emitters per pot) and irrigation set point (-2 or -4 kPa) and frequency (a single continuous pulse of up to 45 minutes or short 3-minute pulses every 15 minutes to reach container capacity). The plants were grown in 25-L pots filled with a mix of peat, coir, and perlite. Tensiometers were installed horizontally into the center of the pots to monitor the matric potential and to determine when to trigger irrigation. Irrigation was triggered automatically using a data logger and applied until the pots reached container capacity determined by small weighing lysimeters. Yield was highest in plants with eight emitters in the second year (first year of fruit production), but this difference diminished in year 3. A similar relationship was observed for aboveground biomass. Root size was also highest with eight emitters. Leachate pH and EC were mostly similar among treatments, but EC was more uniform throughout the pot with eight emitters. In contrast, the lower set point and shorter irrigation frequency decreased the ability of the pots to reach container capacity, particularly when the plants were irrigated with only two emitters per pot. Overall, the plants grew best when irrigation was triggered at -2 kPa and applied in single continuous pulses with four or eight emitters per pot.

Discover how Driscoll’s, the global leader in fresh berries, attracts and hires top scientific talent to drive innovation in flavor, plant health, and sustainability. With R&D teams located across the U.S., Mexico, Europe, North Africa, and beyond, we employ a diverse range of scientists—from plant breeders and entomologists to molecular biologists and data scientists—who work collaboratively to deliver Only the Finest Berries™. This session offers an inside look at our hiring process, including what we look for in candidates, how to navigate our application and interview experience, and tips for standing out in a competitive field. Whether you're early in your career or a seasoned researcher, join us to learn how you can grow with Driscoll’s and be part of the science behind every berry.

Day length and temperature interactively influence flower bud initiation in blueberry (Vaccinium corymbosum interspecific hybrids) plants. When days are short and temperatures are low, blueberry plants initiate flower buds rather than vegetative buds. Night interruption and/or warmer temperatures limit flower bud initiation. Once differentiated, flower buds enter endodormancy, restricting reproductive development to specific times of the year. Some genotypes in the University of Florida Blueberry Breeding and Genomics program have been observed to bloom in the middle of the summer under long days and warm temperatures. To investigate this phenomenon, we conducted a controlled-environment experiment to assess flower bud initiation and dormancy responses in a summer-blooming genotype, ‘FL16-64’, compared to the standard southern highbush cultivar ‘Arcadia’. Plants were grown in growth chambers with factorial combinations of temperature and photoperiod treatments. Temperature regimes mimicked Florida field conditions: warm (28 °C day / 20 °C night) and cool (18 °C day / 10 °C night). Photoperiods included short (8 hours), neutral (12 hours), long (16 hours), and interrupted (8 hours 1 hour of night interruption) day lengths. There were 6 plants of each genotype per temperature-photoperiod combination. Results showed that warm temperatures promoted vegetative growth in both genotypes. ‘Arcadia’ developed flower buds primarily under short days and cool temperatures, and these buds entered endodormancy after differentiation. In contrast, ‘FL16-64’ initiated flower buds across all temperature and photoperiod treatments. Moreover, flower bud development was enhanced under warmer temperatures and neutral day lengths. Notably, these buds bypassed dormancy and progressed directly to bloom. These findings indicate that ‘FL16-64’ exhibits day-neutral flower bud initiation and some of its flower buds lack endodormancy, characteristics consistent with an everbearing growth habit. Everbearing blueberry genotypes could be used to produce blueberries during the domestic off season in Florida.