ASHS 2024 Conference

Strawberries (Fragaria × ananassa) are increasingly being grown in hydroponic systems, where effective nutrient management is critical for optimizing crop production and yield. Among essential mineral nutrients, potassium is a key nutrient that affect fruit quality in many fruiting crops. This study investigated how potassium to nitrogen (K:N) ratios regulate strawberry growth and development in a deep-water culture hydroponic system. We hypothesized that increasing the K:N ratios would enhance vegetative growth, fruit yield, and fruit quality. Bare-root plants of strawberry ‘Monterey’ and ‘San Andreas’ were grown indoor under a 23 °C air temperature and an 18-h photoperiod with an extended photosynthetic photon flux density of 350 µmol∙m–2∙s–1. The N level was kept constant at 77 ppm, while the study tested K:N ratios ranging from 1.5:1 to 4:5:1. Three weeks after nutrient treatments, strawberry plants showed similar crown number, crown diameter, leaf number, leaf area, and shoot dry mass regardless of K:N ratios in both cultivars. Increasing K:N from 1.5:1 to 4.5:1 linearly increased the root dry mass of Monterey’ but not in ‘San Andreas’. During the fruit production, K:N ratios did not affect the total number of fruits or total fresh mass of fruits. However, there was a linear decrease in the diameter, length, and fresh mass of individual fruits with increasing K:N ratio from 1.5:1 to 4.5:1 in both 'Monterey' and 'San Andreas'. Additionally, increasing K:N ratio from 1.5:1 to 4.5:1 slightly increased total soluble solids in ‘San Andreas’, but led to a greater increase in titratable acidity compared to the increase in total soluble solids in both ‘Monterey’ and ‘San Andreas’. These results suggest that increasing K:N ratios from 1.5:1 to 4.5:1 has little beneficial effect on overall plant growth, fruit yield and fruit quality for hydroponic strawberry production in deep-water culture systems.

In US open field nurseries, strawberry transplants for fruit production accumulate diurnal chilling hours (hours between -2 and 7°C) in the field prior to harvest and receive supplemental chilling as bare root plants in a cooler before being transplanted into a fruit production system. In nurseries in Northwestern Europe, tray plants are placed outside after rooting to accumulate diurnal chill hours and are moved into the cooler with leaves and substrate for supplemental chilling before being transplanted. The optimal amount of chilling varies among cultivars but is thought to contribute to a proper balance of vegetative vigor and floral development leading to best fruiting after transplanting into the production system. Climate change, labor cost and related issues cause problems in both nurseries and production. Therefore more and more growers and start-up companies venture into controlled environment production systems. Due to high cost, these systems require transplants that are optimally conditioned for early flowering. We evaluated the impact of diurnal chilling on vegetative and floral development of 250 cc strawberry tray plants in a controlled environment. 28 day old ‘Albion’, ‘Chandler’, ‘Monterey’, and ‘Sensation’ rooted daughter plants were moved into growth chambers where they received 0 (15°C 24 hours), 100 (4°C, 16°C), 250 (4°C, 19°C), or 450 (4°C, 24°C) chill hours over a six week period. Within each treatment, the same amount of chill hours were applied each day for the six week period. Among treatments, the non-chill temperature increased as the number of chill hours increased to ensure the same daily average temperature of 15°C. Chambers were fixed at 50% RH, 450 ppm CO2, 130-40 µmol m-2 s-1 for all treatments and a 12 hour photoperiod for ‘Chandler’ and ‘Sensation’ and a 16 hour photoperiod for ‘Albion’ and ‘Monterey’. After the treatment, all plants were dissected under the microscope to determine the number and development of floral meristems (flower mapping). Our results show that the plants in the 100 and 250 hour treatments produced more floral meristems and branch crowns than the 0 and 450 hour treatments across all cultivars. Additionally, in ‘Albion’ and ‘Monterey’, the plants of the 100 and 250 hour treatments had greater fresh mass and higher crown diameter than the plants in the 0 and 450 hour treatments. Finally, all cultivars except ‘Sensation’ had more flowers on plants in the 100 and 250 hour treatments than those of the 0 and 450 hour treatments.

Presentation: Oral ASHS 2024 Keywords: CEA, greenhouse, Fragaria ×ananassa, temperature Utilizing Controlled Environment Agriculture to Enhance the Yield and Flavor of Strawberries Nicholas Cooley, Joshua Vanderweide, and Roberto Lopez In the U.S., strawberries (Fragaria ×ananassa) are the most popular berry fruit with a value of $2.8B. In 2022, strawberries experienced 12% growth in annual sales, with the majority of field production occurring in California and Florida. To meet consumer demand for flavorful, fresh, local, and year-round fresh strawberries, the industry is expanding controlled environment (CE) production of day-neutral (everbearing) cultivars in greenhouses and indoor farms. Within CEs, growers can potentially meet these demands through the manipulation of environmental parameters such as temperature, light, vapor pressure deficit, and carbon dioxide concentration. Despite the recent growth, CE growers are reporting low profitability. This imbalance of production and profitability stems from high energy costs, supra-optimal greenhouse temperatures during parts of the year, and low yield from the industry standard cultivar ‘Albion’. For producers to be considered profitable, they must reach an approximate annual yield of 15 kg∙m–2, which equates to a weekly yield of around 0.3 kg∙m–2. The objectives of our research are to 1) quantify the yield of other day-neutral cultivars in greenhouses; 2) determine how day and night temperature influence yield and fruit quality parameters; and 3) develop a model to predict the cardinal temperatures of each cultivar. Three cultivars, ‘Albion’, ‘Cabrillo’, and ‘Monterey’ were grown at day/ night temperatures (12 h/ 12 h) of 15/7, 18/10, 21/13, 24/16 or 27/19 °C, under a 16-h photoperiod, and a target DLI of 15 mol·m–2·d–1. Fruits were harvested three times weekly and at harvest, berry weight, diameter, color, shape, distortion, brix content, and flavor-related volatile organic concentrations were recorded. After 12 weeks of harvest, the highest average weekly yield was 0.17, 0.19, and 0.24 kg∙m–2 for ‘Albion’, ‘Cabrillo’ ‘Monterey’ at 18/10, 24/16, and 24/16 C, respectively. While the highest combined overall yield for all three cultivars was at 24/16 °C, the highest average berry weight differed. At day and night temperatures of 18/10, 18/10, and 15/7 °C, ‘Albion’, ‘Cabrillo’, and ‘Monterey had the highest average berry weights, respectively. Our results collectively indicate there are higher yielding day-neutral cultivars than the industry standard ‘Albion’.

Abstract: Strawberry nurseries face many challenges, and are considering controlled environment propagation as an alternative to conventional open-field propagation. Limiting factors to economic feasibility include stock plant yield (number of daughters produced per stock plant). From published research we know that increasing CO2 concentration and light intensity increases strawberry photosynthetic rate, however there has been no research on the effects of these treatments on the total stock plant yield of daughters. Our hypothesis is that higher light intensity and CO2 concentrations will improve plant growth and lead to greater total daughter plant production. The objective of this experiment is to increase stock plant yield by increasing CO2 concentration (500, 850, and 1200 μmol mol-1) and light intensity (DLI 14.4 and 28.8 mol m-2 d-1). Strawberry (Fragaria × ananassa Duch., ‘Monterey’) stock plants were transplanted into three controlled environment growth chambers, under combinations of CO2 and DLI treatments in a split plot design under 26°C, 65% relative humidity, and a 16-hour photoperiod. The stock plants were grown under treatment conditions for 70 days, and newly-formed daughters were logged every day. At the end of the experiment the stock plants and their daughter plants were harvested, and each daughter plant was evaluated based on its size (number of leaves, leaf area, and fresh/dry mass). Increasing CO2 concentration linearly increased stock plant yield, leading to 23.96% more daughter plants per mother plant from the 500 to the 1200 μmol mol-1 treatment. Plants under higher light intensity (500 μmol m-2 s-1) had 38% higher stock plant yield than those under 250 μmol m-2 s-1. These data support our hypothesis that increasing CO2 concentration and light intensity increase the total yield of daughter plants produced per stock plant. By optimizing CO2 concentration and light intensity, strawberry nurseries may be able to grow more daughter plants more efficiently in controlled environment nurseries than in the conventional open-field system.

The US strawberry industry needs healthy, high-quality transplants every year for fruit production. Following the challenges in open-field nurseries, research is focused on controlled-environment agriculture as a potential alternative to not only increase strawberry tip yield but also to produce healthier, virus-free transplants (rooted tips). Growing stock plants indoors where the runners grow vertically downward increases the yield and quality of tips, however, there is a lack of information on the general architecture of plants especially the spatial distribution of daughter plants and also the leaf area index (LAI) distribution of the daughter plants’ canopy in the growing space. This information is vital for future system design as it determines the distance between the shelves and the potential need for intracanopy lighting. Furthermore, besides temperature, photoperiod strongly affects the trade-off between runner Vs. flower production. Yet, there is also a lack of information on how photoperiod will change the yield, quality, and architecture of stock plants in CEA, specifically on long-day cultivars. Here, we examined 12, 16, and 20 h photoperiods with the same DLI of 26 mol m-2 d-1 on ‘Monterey’ as a long-day cultivar with two replications in time. The chamber environment was maintained at a high temperature of 26 °C, ambient CO2, and 65% relative humidity. The plant density was 9 plant m-2. Following 64 days of growth, parameters related to yield, architecture, and quality were recorded. Results showed that even under relatively high temperatures, with shortening the photoperiod, a linear increase in the number of tips was observed, increasing from ~36.3 to ~44.3 (18%) with the same DLI. Regardless of the photoperiod, the highest proportion of tips (30.8%) were harvested on the runners from 40 – 80 cm distance from the mother plant, though the highest LAI (53.2%) was recorded on the tips from 0 – 40 cm, causing a sudden drop (92.8%) in the light intensity after 40 cm where most of the tips are growing. This information shows the need for intracanopy lighting under 40 cm depth from the mother plants. Around 98% of the tips were harvested from 0 – 160 cm, showing the needed space for the growth of runners (i.e., the distance between the shelves). Several morphology and photosynthetic parameters were also recorded. The information from this study will be used as a base for a follow-up experiment comparing top versus intracanopy lighting.

As the demand for locally grown produce, particularly fresh fruits like blueberries and strawberries, continues to surge, the imperative for year-round production becomes increasingly evident. While these fruits are globally recognized for their extended-season production potential in controlled environments, the intricate environmental factors crucial for improved production and profitability remain partially understood, including the impact of soilless substrates. Amid growing concerns about the availability of internationally sourced substrates, such as coconut coir, this study explores an alternative approach to reduce reliance on such components, particularly in the cultivation of two small fruits rapidly integrated into controlled environments. Substrate stratification, involving the vertical layering of substrates within a single container, has shown promise in nursery and greenhouse settings, enhancing resource efficiency in terms of water and fertilizer inputs. However, no research has assessed the application of stratified substrates for fruit crops with the specific aim of reducing coir inputs in greenhouse production. Thus, the objective of this study was to investigate whether stratifying coir over low-cost, hammer-milled processed tree fiber could effectively decrease coir usage, dependency, and associated costs within the controlled environment fruit production industry. 'Albion' strawberries and 'Star' blueberries were cultivated in five substrate treatments, ranging from 100% coir to various stratified layers beneath coir, including 25%, 50%, and 75% coir compositions, as well as a 100% processed tree fiber treatment. Results suggest that employing substrate stratification enhanced plant growth for both fruit crops, indicating its potential utility in optimizing controlled environment fruit production while reducing reliance on costly substrate materials like coir. Further analysis will elucidate the full implications of this innovative approach on production efficiency and profitability.

Indoor propagation systems that use sole-source lighting in controlled environments can facilitate year-round production of disease-free, uniform strawberry liners. However, optimal conditions to propagate strawberry runner tips indoors are unknown. Runner tips of ‘Albion’ and ‘Fronteras’ strawberries were propagated indoors for 28 d under four photosynthetic photon flux density (PPFD) treatments: 75, 150, 225, or 300 ± 5 μmol·m–2·s–1 provided for 24 h·d–1 by white light-emitting diode fixtures. Runner tips were also propagated in a shaded greenhouse under mist. After propagation, plants were moved to a common greenhouse compartment and grown for 7 weeks to evaluate carryover effects on fruit yield (‘Albion’) or daughter-plant production (‘Fronteras’). Treatment responses were similar for both cultivars, except that shoot dry mass (DM) of ‘Fronteras’ followed a quadratic response with increasing PPFD, which peaked at 225 μmol·m–2·s–1. In contrast, shoot DM of ‘Albion’ linearly increased with increasing PPFD. Root DM of both cultivars also followed an increasing response with PPFD. However, there were no treatment differences in the number of shoots produced per plant or the length of the longest root. Interestingly, plants propagated under ≥150 μmol·m–2·s–1 had several dead shoots (up to 20%), likely attributed to plant stress. After the carryover phase, ‘Albion’ propagated under 225 or 300 μmol·m–2·s–1 were statistically different and produced the lowest fruit fresh mass compared to those grown in the greenhouse, whereas values were similar among plants propagated in the greenhouse or indoors under 75 or 150 μmol·m–2·s–1. No treatment differences were measured in the number of daughter plants produced by ‘Fronteras’. These findings suggest that although higher PPFD indoors promoted rooting and growth, plants propagated in the greenhouse were likely better adjusted to the dynamic greenhouse environment, which enabled them to reach the same growth and development of indoor-propagated plants at the end of the carryover phase.

As the interest in strawberry production in controlled environment agriculture is ascending, the demand for cultivars that yield premium-quality fruit is rising. To identify strawberry suitable for vertical farm production, 25 strawberry (Fragaria × ananassa) cultivars were selected for premium flavor from USDA National Clonal Germplasm Repository. Fruit productivity and quality traits, plant vegetative phenotypes, and photosynthetic rates were evaluated using strawberries grown in a walk-in growth chamber where photoperiod altered between short day and long day to promote flowering and fruit production. Our results show that strawberry ‘Mara des Bois’ produced the earliest harvest, and ‘Hood’ had the highest maximum productivity coefficient. The largest fruit was produced by ‘Chandler’, and the reddest fruit was produced by ‘Marshall’. Among the 25 cultivars, 11 exhibited fruit Brix levels above 0.9, and 3 had a fruit Brix:TA ratio of 1.0. Ongoing fruit flavor analysis aims to identify unique flavor compounds within these strawberries. Correlations linked time to first harvest and maximum productivity coefficient with canopy area, shoot height, and photosynthetic rate per plant, revealing the intricate sink-source dynamics in strawberry plants. Interestingly, no correlation was found between maximum productivity coefficient and any fruit quality trait, challenging the commonly held belief in the constant competition between crop productivity and quality. The information of strawberry growth and production in vertical farm environment provided in this study can assist indoor growers in cultivar selection and potentially contribute to future strawberry breeding programs.