QUALITY ENHANCEMENT OF GREENHOUSE CROPS BY CONTROLLED ENVIRONMENT

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0229624
• Project Start Date: Oct 1, 2012
• Project End Date: Jun 30, 2017
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF ARIZONA
888 N EUCLID AVE
TUCSON,AZ 85719-4824

Performing Department
Plant Science

Non Technical Summary
Greenhouse crop production and controlled environment technology was traditionally developed to produce off-season crops as well as produce crops year-round. The technology can potentially enhance product quality (vigor and morphology for transplants; target phytochemicals; flavor and nutritional quality for food crops). Arizona is one of leading states in greenhouse controlled environment agriculture. With the higher solar radiation and lower relative humidity throughout the year and mild winter climate, commercial greenhouses in Arizona can conduct year round production of high quality vegetables. Under controlled environments, there are many factors we can optimize to improve the product quality. Such factors are light intensity, light quality, CO2 concentration, vapor pressure deficit, wind velocity, day length, air temperature, root zone temperature, nutrient solution formulation and concentrations, and irrigation frequency, etc. The goal of our research is to develop greenhouse controlled environment technology to enhance the product quality (and thereby value). During the project, model crop species will be used, including typical greenhouse food crops such as tomato, lettuce and bell pepper as well as specialty crop species that are currently not widely grown but have potential as future crops in US greenhouses such as strawberry and Asian leafy vegetables. We also use greenhouse vegetable seedlings of tomato and cucurbits for our study as greenhouse vegetable seedlings are high-value crops produced in nursery greenhouses. Our specific objectives in this 5-year project is 1) to quantify the seasonal changes and relationship between nutritional quality of selected food crops grown in greenhouse, 2) to evaluate salt/water stress as a factor affecting overall flavor and health promoting phytochemicals in greenhouse crops, 3) to evaluate light intensity and light quality affecting product quality of vegetable crops and seedlings, 4) to explore other aerial and root-zone environmental factors possibly applicable in greenhouse controlled environment, and 5) disseminate the information via growers short course, web-based greenhouse growers information resources, and scientific publications in collaborations with the University of Arizona Controlled Environment Agriculture Center (CEAC).

Animal Health Component

50%

Research Effort Categories

Basic

10%

Applied

50%

Developmental

40%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
205	1499	1020	40%
205	1499	2020	10%
205	2410	1020	40%
205	2410	2020	10%

Knowledge Area
205 - Plant Management Systems;

Subject Of Investigation
1499 - Vegetables, general/other; 2410 - Cross-commodity research--multiple crops;

Field Of Science
2020 - Engineering; 1020 - Physiology;

Keywords

cea

environmental control

greenhouse

hydroponics

protected cultivation

soilless culture

Goals / Objectives
Arizona is one of leading states in controlled environment agriculture. With relatively higher radiation and lower relative humidity throughout the year and mild winter climate, commercial greenhouses in Arizona can conduct year round production of high quality vegetables. As controlled environment agriculture was originally developed as a tool for extending production season in northern climate regions, there has been a need for research to optimize the technologies in semiarid climate. Understanding plant responses to aerial and root zone environments (light intensity, light quality, CO2 concentration, vapor pressure deficit, wind velocity, day length, air temperature, root zone temperature, nutrient solution formulation, EC, and irrigation frequency, etc.) is important to optimize the yield and quality of the harvested produce under southwestern U.S. semiarid climate conditions. In addition to the expected benefits to greenhouse growers, efforts to enhance the nutritional values of vegetables by controlled environments will contribute to improving American diet not only through enhancing consumption (quantity) but also through providing more nutritionally valuable options. The proposed study also gives fundamental information of plant stress response that can be utilized further to improve quality of greenhouse crops using molecular biology and genetics, which are currently recognized as a powerful tool but also an approach that sometimes encounters issues of public acceptance. The goal of our research is to develop controlled environment technology to enhance greenhouse product quality (and thereby value) while minimizing the loss of yields. During the project, model crop species will be used, including typical greenhouse food crops such as tomato, lettuce and bell pepper as well as specialty crop species that are currently not widely grown but have potential as future crops in US greenhouses such as strawberry and Asian leafy vegetables including mizuna and komatsuna. We also use greenhouse vegetable seedlings of tomato and cucumber for transplant quality enhancement study. Our specific objectives in this 5-year project is 1) to quantify the seasonal changes and relationship between nutritional quality of selected food crops grown in greenhouse and greenhouse environments, 2) to evaluate salt/water stress as a factor affecting overall flavor and health promoting nutritional phytochemicals in greenhouse crops, 3) to evaluate light intensity and light quality affecting product quality of vegetable crops and seedlings, 4) to explore other aerial and root-zone environmental factors possibly applicable in greenhouse controlled environment, and 5) disseminate the information via growers short course, web-based greenhouse growers information resources, and scientific publications in collaborations with the University of Arizona Controlled Environment Agriculture Center (CEAC).

Project Methods
[Plant growth] Selected plant species will be grown using methods widely used commercially by greenhouse growers. For tomato and bell pepper, a high-wire production system will be used with drip irrigation and aggregate substrates. An ebb-and-flood production system with substrate-filled trays will be used for leafy crops and vegetable seedlings. A raised gutter filled with soilless substrate with drip irrigation will be used for strawberry. Standard greenhouse environment conditions and fertilization/irrigation programs will be selected based on commercial greenhouse grower practices and/or from literature-based information. [Manipulation of selected environmental factors] In addition to the standard conditions (as the control), experimental treatments will be designed into the study to evaluate selected environmental factors affecting greenhouse crop growth and quality. Those factors are nutrient solution EC, nitrogen sources (ammonium to nitrate form ratio), air temperature, root-zone temperature, light intensity, light quality and vapor pressure deficit (VPD). Nutrient solution EC will be increased by adding sodium chloride. Root-zone temperature will be controlled by circulating water controlled at a selected temperature. Light quality will be manipulated using LEDs and photo-selective glazing. VPD will be controlled using a high-pressure fogging system. [Analysis of nutritional quality attributes] Harvested fruit will be pureed for the total soluble solids, pH, titratable acidity, and phytochemical analyses (carotenoids, ascorbic acid, total phenolics, chlorophyll, total anthocyanins, and ascorbic acid). Soluble solids, pH, titratable acidity, carotenoids and chlorophyll will be measured on fresh sample basis, and the rest will be measured after freeze-drying the samples. [Plant growth and morphology assessment] For seedlings, hypocotyl and internode length will be measured daily using a ruler. At the end of experiment, hypocotyl diameter, and aerial part fresh weight of the seedlings will be measured using a digital caliper and an electronic balance. After drying at 80oC for three days, stem dry weight and leaf dry weight will be also measured. Plastochron index (Erickson and Michelini, 1957) will be employed to quantify the plant developmental stage. Leaf area will be measured using a scanner for obtaining individual leaf images, whose area will be quantified using software developed for leaf area analysis (LIA32, Nagoya University, Japan). Other parameters used in growth and morphological analysis such as shoot-to-root ratio, relative growth rate, and specific growth rate will be obtained as needed. [Experimental design and data analysis] Experiment will be conducted using a randomized complete block design with a minimum of three blocks replicated in the same greenhouse. However, when this design is not feasible due to the limitation of facilities, we will employ the best experimental design selected through the necessary consultation with a statistician. Data will be analyzed with a statistical package JMP (SAS institute, Cary, NC).

Progress 10/01/12 to 06/30/17

Outputs
Target Audience:Greenhouse growers, vertical farms ventures, gardeners/hobbyists, open field producers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?In addition to offering academic training opportunities for undergraduate and graduate students, our project personnel have been active in training professionals in CEA. Specifically, we began offering an online non-credit course for CEA professionals who wish to better understand the technologies used for improving the product quality and productivities. We also offered more intensive hands-on trainings to individuals for learning basics of producing specific crops such as strawberry. How have the results been disseminated to communities of interest?The communication effort includes various invited talks at growers' conferences and scientific symposia. In addition, technological consultations were offered to stakeholders. Further, for reaching wider community, information website as well as social media were developed and effectively used for public communication. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Over the past five years (since 2012), this project contributed to creating a new industry sector in the US, especially in Arizona, practicing sustainable controlled environment technologies to produce high value quality products. My research on greenhouse vegetable seedling production for grafting and on the vegetable grafting process supported the founding of a new Arizona venture company of indoor high quality grafted seedling production, as well as supporting the introduction to the US of the first large, international nursery specializing in vegetable grafting. This new industry sector is expected to grow continuously as it has in other countries in Europe and Asia. The indoor nursery concept was developed through the McGuire Program for Entrepreneurship at the University of Arizona, where as PI of the project, I served as a domain expert advisor and two graduate students in Plant Science and Business were the founding members. This company is now in the process of expanding their facilities to produce millions of high quality grafted seedlings (the estimated gross revenue is over 1 million dollars). Another effort that generated significant impact was introducing strawberry as a greenhouse crop in Arizona and to other parts of the US, which are not traditionally considered strawberry producing regions. Arizona's strawberry industry virtually disappeared in 1960s, but has now begun to come back as a more sustainable industry to provide high quality berries using controlled environment technologies. Our effort led to a worldwide-recognized information site of greenhouse strawberry production and helped numerous companies to plan and initiate strawberry production. For research, we have contributed through conducting and reporting experimental results that are helping to develop the foundation of new technologies. For example, we showed that manipulating light quality using modern lighting technology such as LEDs is an effective way to enhance the plant growth and overall quality (visual quality and nutritional quality). In particular, the use of monochromatic blue light and monochromatic far-red light was shown to be valuable in applications to enhance plant growth through improving plant morphology. In greenhouse, supplemental lighting using LEDs is still new among growers, and we also assisted growers considering using LEDs by suggesting a simple decision support approach to evaluate the efficacy of supplemental lighting under their own growing conditions. We have also initiated a project to bridge controlled environmental agriculture and more traditional open-field crop production. For example, high quality lettuce transplants grown under fully controlled environment could establish uniform stands in the high temperature long-day condition outdoors, where traditional direct seeding would not. In strawberry, a unique physiological response associated with its sink-source balance was also recognized. These research efforts contributed to generating new research questions and technology ideas for future R&D in controlled environment agriculture.

Publications

• Type: Journal Articles Status: Published Year Published: 2017 Citation: Kubota, C., C. Meng, Y.J. Son, M. Lewis, H. Spalholz, and R. Tronstad. 2017. Horticultural, systems-engineering and economic evaluations of short-term plant storage techniques as a labor management tool for vegetable grafting nurseries. PLOS ONE http://dx.doi.org/10.1371/journal.pone.0170614
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Spalholz, H. and C. Kubota. 2017. Rootstock affected in- and post storage performance of grafted watermelon seedlings at low temperature. HortTechnology 27:93-98
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Hern�ndez, R., T. Eguchi, M. Deveci, and C. Kubota. 2016. Tomato seedling physiological responses under different percentages of blue and red photon flux ratios using LEDs and cool white fluorescent lamps. Scientia Horticulturae 213:270-280
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Eguchi, T., R. Hern�ndez, and C. Kubota. 2016. Far-red and blue light synergistically mitigate intumescence injury of tomato plants grown under UV-deficit light environment. HortScience. 51:712-719.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Hern�ndez, R. and C. Kubota. 2016. Physiological responses of cucumber seedlings under different blue and red photon flux ratios using LEDs. Environ. Exp. Bot. 121:66-74
• Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2017 Citation: Garcia, K. and C. Kubota. 2017. Physiology of strawberry plants under controlled environment: Diurnal change in leaf net photosynthetic rate. Acta Horticulturae (in press).
• Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2017 Citation: Garcia, K. and C. Kubota. 2017. Flowering responses of North American strawberry cultivars. Acta Horticulturae (in press).
• Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2017 Citation: Kroggel, M. and C. Kubota. 2017. Controlled environment strategies for tipburn management in greenhouse strawberry production. Acta Horticulturae (in press).

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:Greenhouse growers, master gardeners, open field producers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?One undergraduate student and one graduate student were trained in the project this year. How have the results been disseminated to communities of interest?A total of five invited talks were given at growers conferences (Plug & Cutting Conference in Orlando, FL; Greenhouse Crop Production and Design Short Course in Tucson, AZ; AmericanHort Greenhouse Solution in Pittsburg, PA). In addition, technological consultations as well as custom growers training programs were offered to stakeholders during this reporting period. What do you plan to do during the next reporting period to accomplish the goals?At the University of Arizona, we plan to continue research projects focusing on plant responses to environmental conditions. I am working with horticulture scientists of other land grant universities to develop a team to strengthen the research and extension capacities for various greenhouse crops.

Impacts
What was accomplished under these goals? During the reporting period, the following studies were conducted to understand crop-specific physiological responses to greenhouse environmental conditions and its application to develop feasible greenhouse technologies to enhance the produce quality. As part of our continuous study to establish off season greenhouse strawberry production in AZ, we examined two cultivars 'Albion' and 'Nyoho' during 2014/2015 production season (harvesting from November to April) in our soilless production system. 'Albion' is a widely cultivated ever-bearing cultivar (UC Davis) and 'Nyoho' is a Japanese short-day cultivar. Planting was done on September 22, 2014 at 10 plants m-2 density using transplants with 4-5 true leaves. Before planting 'Nyoho' plants were conditioned to induce flower buds by placing them inside a chamber at 15C temperature during the night (16 hours) for 5 weeks. An early stage of flower primordia were confirmed under the microscope after 4 weeks. Styrofoam troughs with the substrate consisting of 1 peat: 1 coco coir: 2 perlite and irrigated and Yamazaki strawberry nutrient solution was used for fruit production. Flowers of 'Albion' were removed until October 20 and the first fruit harvest of 'Albion' and 'Nyoho' was recorded in the week of November 17. The crops were removed in the week of May 3 (the final harvest). The cumulative yield for 'Albion' and 'Nyoho' was (mean±SE) 8.1±0.7 and 6.3±0.02 kg m-2 respectively. Brix (TSS) was 8.9±0.21 and 10.6±0.09 % and total acidity (citric acid equivalent) was 10.1±0.19 and 10.4±0.10 g/L for 'Albion' and 'Nyoho' respectively. Other characteristics of these cultivars are; 1) similar to other short day cultivars, 'Nyoho' exhibited repeated flowering that allowed continuous fruit production throughout the crop, while 'Albion' exhibited a typical long gap (6-7 weeks) between the first and second peaks and another short gap (2-3 weeks) between the second and third peak of fruit production, 2) 'Nyoho' was more susceptible to powdery mildew and more attractive to aphids than 'Albion', 3) 'Nyoho' was more tolerant to tipburn than 'Albion', 4) 'Nyoho' developed more flowers per truss and making average fruit size smaller than 'Albion' (11.7±0.13 and 21.6±0.16 g, respectively). An empirical approach to conduct crop-specific cost and return analyses is presented in order to assist greenhouse growers to make better decisions in investing for appropriate supplemental lighting technology. Electricity cost of lighting was analyzed based on input power density and operation hours to obtain target mol of photosynthetic photon flux (integrated light) at varied lamp photon efficiency (micro-mol/J). Possible heating cost off-set by lighting was also considered in the analysis, assuming that all input electric energy for supplemental lighting eventually becomes heat, contributing to reducing heating demand. Crop specific efficacy of lighting was expressed as dollar return per mole of photosynthetically active radiation per square meter greenhouse, estimated from crop productivity (g/mol PAR) and typical wholesale value. The crop productivity was obtained from the linear regression of cumulative yield (kg/m2) of selected crops (lettuce, tomato and strawberry) over cumulative PAR (mol/m2) obtained in our previous studies conducted in Arizona as well as available data reported in the literature. The highest productivity (14 g/mol) was found for tomato (cluster type). Lettuce productivity varied widely (2.8-6.9 g/mol) but the efficacy of lighting (the return) was higher than those for tomato due to its higher wholesale price. The least productive crop was strawberry (1.5-2.1 g/mol) and even at a relatively high wholesale price of $10/kg, lighting cost exceeded the return estimated for most cases in our analysis. Tomato efficacy also varied depending on the growing conditions and type of tomatoes (low yield high value cultivars vs. high yield low value cultivars), suggesting the importance of technologies achieving higher efficiency and/or photon delivery methods such as intracanopy lighting (resulting in lower electricity costs). The approach presented here is easily adoptable by growers who have access to their historical data of yield, PAR and other conditions (environment and utility rate).

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Hern�ndez, R. and C. Kubota. 2015. Physiological, morphological, and energy-use efficiency comparisons of LED and HPS supplemental lighting for cucumber transplant production. HortScience. 50:351-357.
• Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2016 Citation: Kubota, C., M. Kroggel, A.J. Both, J.F. Burr, and M. Whalen. 2016. Does supplemental lighting make sense for my crop?  Empirical evaluations. Acta Horticulturae (in press)

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: Greenhouse growers Gardeners/hobbyists Master gardeners High school teachers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Two one-day workshops "Arizona Strawberry Day field day" were held in Tucson, AZ, reaching 60 attendees (from AZ, CA, NE, NM, OH, OR, WA and Mexico). How have the results been disseminated to communities of interest? • Three outreach presentations were made during various growers conferences. 1) Kubota, C. 2014. Hydroponic Strawberry Production. A lecture given at the Greenhouse Crop Production and Design Short Course held in March, 2014 (~80 participants; Tucson, AZ). 2) Kubota, C. 2013. Maximizing flavor and taste - the most exciting quality for urban food. A lecture given at the OFA Association of Horticulture Professional Short Course held in July 2013 (~60 participants; Columbus, OH). 3) Kroggel, M. 2014. Soilless strawberry production. A lecture given at the Cultivate'14 growers convention in July 2014 (~100 participants; Columbus, OH). What do you plan to do during the next reporting period to accomplish the goals? We plan to continue research projects focusing on plant responses to environmental conditions. I am working with horticulture scientists of other land grant universities to develop a team to strengthen the research and extension capacities for greenhouse berries.

Impacts
What was accomplished under these goals? During the reporting period, the following study was conducted to understand plant physiological responses to greenhouse environmental conditions and its application to develop feasible greenhouse technologies to enhance the produce quality. As part of our continuous study to establish greenhouse strawberry production in AZ, we examined planting systems and planting density. Two standard field production cultivars, 'Albion' and 'Portola' were planted at densities of 8 and 12 plants m-2 in 11-liter strawberry buckets and at 8 plants m-2 in continuous Styrofoam troughs in substrate consisting of 1 peat: 1 coco coir: 2 perlite and irrigated using standard Yamazaki nutrient solution with pH adjusted to result in a drainage pH of 5.5 - 6.5. Plants were planted, in a greenhouse covered with a single layer of F-Clean (ETFE) greenhouse glazing film with light diffusing characteristics and high UV transmission, in August 2013 and initial harvesting began in October. As of mid-February 2014 cumulative yield for 'Albion' at 8 plants m-2 in buckets, 12 plants m-2 in buckets and 8 plants m-2 in Styrofoam trough was (mean±SE) 5.0±0.4, 6.2±0.7 and 6.2±0.3 kg m-2 respectively. Cumulative yield for 'Portola' for the same period and planting systems/densities was 7.3±0.5, 9.1±0.3 and 8.7±0.4 kg m-2 respectively. Brix (TSS) was 8.6±0.15 and 6.0±0.08 and total acidity was 11.0±0.07 and 8.9±0.12 g/L citric acid equivalent for 'Albion' and 'Portola' respectively. While yields are acceptable, additional management techniques to improve fruit quality characteristics must be developed, and existing cultivars bred specifically to produce fruit with high flavor characteristics in greenhouse need to be introduced. As a project to develop horticultural lighting technology to enhance transplant quality, we worked on the LED lighting applications for vegetable seedlings. During the reporting period, we conducted side-by-side comparisons of growth and development of bell pepper seedlings under LED lighting with selected spectral qualities (100% blue or 100% red) and under the conventional HPS lighting (57 μmol m-2 s-1 PPF or 3.7 mol m-2 d-1 DLI) under relatively low DLIs (solar DLI: 5.2 mol m-2 d-1). In addition to evaluations of plant physiological and morphological responses to LED lighting, we evaluated electric energy use efficiency (plant dry mass obtained per input electric energy used for supplemental lighting) considering both experimental and theoretical values. We also grew tomato and cucumber seedlings under LEDs with various percentages of blue photon flux (0, 10, 30, 50, 75, and 100% over PPF) to better understand their growth and morphological responses to blue photon fluxes.

Publications

• Type: Journal Articles Status: Published Year Published: 2014 Citation: Hern�ndez, R. and C. Kubota. 2014. Growth and morphological response of cucumber seedlings to supplemental red and blue photon flux ratios under varied solar daily light integrals. Scientia Horticulturae 173:92-99

Progress 01/01/13 to 09/30/13

Outputs
Target Audience: Greenhouse growers Gardeners/hobbyists Master gardeners High school teachers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? One graduate student (MS in Plant Sciences) and one undergraduate student were trained in the project this year. How have the results been disseminated to communities of interest? We announced our strawberry project in a UA CEAC newsletter (June, 2013) (http://ag.arizona.edu/ceac/sites/ag.arizona.edu.ceac/files/Spring%202013%20Newsletter.pdf) which reached more than 2,000 subscribers. The PI (Kubota) gave a presentation entitled “Maximizing flavor and taste – the most exciting quality for urban food” in which the PIs introduced the project vision and missions at the OFA Association of Horticulture Professional Short Course (July 14th, 2013). The presentation at OFA reached about 60 people in the audience in the workshop focusing on greenhouse food production in urban settings. A new website was launched for hydroponic strawberry information (http://cals.arizona.edu/strawberry). What do you plan to do during the next reporting period to accomplish the goals? At the University of Arizona, we plan to continue research projects focusing on plant responses to environmental conditions. Hydroponic strawberry project will continue and we will add leafy crop focusing on their flavor profile as affected by environmental conditions.

Impacts
What was accomplished under these goals? During the reporting period, the following study was conducted to understand plant physiological responses to greenhouse environmental conditions and its application to develop feasible greenhouse technologies to enhance the produce quality. Two cultivars of strawberry (Fragaria ×ananassa) ‘Albion’ and ‘San Andreas’ were grown hydroponically in a Styrofoam raised trough system filled with a mix of substrates (coco coir 25%, peat 25% and perlite 50%) in our greenhouse. The tipburn controlling method that was reported in previous year was continuously evaluated with a minor modification of the system to cover and create high vapor pressure deficit at night. While ‘San Andreas’ yielded at 8.4 kg/m2, exceeding the benchmark yield of 7 kg/m2, for winter production and ‘Albion’ yielded at 5.5 kg/m2, the fruit quality (Brix) was significantly lower in San Andreas than Albion. This year we have also established a pruning method to induce flowering when plants become too vegetative.

Publications

• Type: Journal Articles Status: Published Year Published: 2012 Citation: Kubota, C., M. Kroggel, M. Torabi, K.A. Dietrich, H.-J. Kim, and C.A. Thomson. 2012. Changes in selected quality attributes of greenhouse tomato fruit as affected by pre- and postharvest environmental conditions in year-round production. HortScience 47:16981704.

Progress 01/01/12 to 12/31/12

Outputs
OUTPUTS: During the reporting period, the following study was conducted to understand plant physiological responses to greenhouse environmental conditions and its application to develop feasible greenhouse technologies to enhance the produce quality. Two cultivars of strawberry (Fragaria x ananassa) Albion and Camino Real were grown in a Styrofoam raised trough system filled with a mix of substrates in our greenhouse. One of the issues growing strawberry in semiarid greenhouse environments is preventing tip/calyx burn. Tip/calyx burn is associated with the relatively high VPD (or low humidity) in the greenhouse, causing excessive transpiration and lower turgor to limit calcium supply to the growing meristematic tissues. Earlier study showed that guttation is a plant health indicator for strawberry suggesting a turgor sufficient to supply calcium and can be observed under low night time VPD (< 0.1 kPa; Bradfield and Guttridge, 1979). For this reason, we examined a night time application of floating cover on top of strawberry canopy to maintain high humidity (low VPD) inside the cover. A clear polyethylene film was used for the cover and treatment was applied from sunset to shortly after sunrise every day for 40 days. PARTICIPANTS: Chieri Kubota, Professor, School of Plant Sciences, joint appointment with Department of Agricultural and Biosystems Engineering; Bio5, The University of Arizona; Mark Kroggel, Research Specialist, School of Plant Sciences, The University of Arizona; Diana Vercillo, undergraduate student, The University of Arizona; Alex Dragotakes, undergraduate student, The University of Arizona TARGET AUDIENCES: Our target audiences include US greenhouse growers, scientists, engineers and other professionals working in the various areas of controlled environment agriculture. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Guttation was observed for plants of both cultivars under floating cover almost every morning while no guttation was observed for untreated plants. The night time high humidity treatment exhibited significantly lower percent calyx burn (16.7%) and tip burn (9.0%) than non-treated control (48.6% and 47.2%, respectively) throughout the experiment. When uncovered, Cultivar Camino Real had more tip/calyx burn (58.9%) than Albion (37.0%). The nighttime average VPD was 0.09 kPa under the floating cover and 0.88 kPa in air inside the greenhouse. No particular difference was observed for disease, as foliage was completely dry during the day (average VPD: 1.6 kPa) For a larger scale operation, automated curtain may be a possibility as a low cost solution of tip/calyx burns for strawberry grown in semiarid greenhouses.

Publications

• Kubota, C. and M. Kroggel. 2012. Nighttime Greenhouse VPD Control for Soilless Strawberry Production in Arizona. HortScience 47(9):S251. (Abstr.)