Analyses and Optimization of Long Distance Transportation Conditions for High Quality Tomato Seedlings

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1 Analyses and Optimization of Long Distance Transportation Conditions for High Quality Tomato Seedlings Chieri Kubota and Mark Kroggel Controlled Environment Agriculture Program (CEAC), The University of Arizona, Tucson, AZ, USA Damian Solomon EuroFresh Farms Inc. Willcox, AZ, USA Leo Benne Bevo Farms Ltd. Milner, BC, Canada Keywords: controlled environment, flower abortion, grafted seedlings, illumination, photosynthesis, temperature, transplant production Abstract Increasing numbers of vegetable growers purchase their transplants from specialized transplant producers instead of using their own facilities to grow their own transplants. A drawback of purchasing transplants is the risk of deterioration to transplants during transportation from transplant producers to the growers. This limits the market size, as well as the potential sources of high quality transplants. To optimize the transportation conditions that can minimize/eliminate the negative impact of transportation on the transplants and thereby on the early yield, environmental conditions during a 2-day transportation in temperature-controlled trailers were analyzed to detect spatial variation and time course environmental changes inside trailers. The trailers were filled with 6 to 8 week old tomato grafted seedlings. Transplant quality and early fruit development were surveyed at the hydroponic tomato growers site for seedlings transported at different temperatures. Reducing air temperature inside the trailer to 12 o C from the conventional 18 o C significantly improved the development of flower and fruits of the first truss. Optimizing environmental conditions is critical for successful long distance transportation of quality seedlings for fresh vegetable production in greenhouse. INTRODUCTION Production of high quality transplants is a crucial technology to support the success of final crop production. Organizational separation of transplant production from the final crop production is the recent worldwide trend, especially for vegetable and floriculture crops that require special techniques, such as grafting or vegetative propagation, and facilities to produce desirable transplants. Increasing numbers of vegetable growers purchase their transplants from specialized transplant producers. There is a growing nationwide interest in use of high quality grafted seedlings for greenhouse tomato production, while the source of grafted tomato seedlings is still limited in U.S. Therefore, greenhouse tomato growers often purchase grafted seedlings from distant propagators, risking deterioration of transplants during transportation and successive delayed growth or fruit development. It has been observed that the transportation conditions, planting conditions after transportation and status of the flower development affected the resulting flower abortion and delayed fruit development of the first truss. However, mechanisms of flower abortion and delayed fruit development were left undefined and therefore significant yield loss and delay was often experienced. Transplant quality deteriorates quickly when placed under darkness at an ambient temperature for a prolonged period. An unfavorable dark storage environment

2 induces loss of chlorophyll (Conover, 1976), leaf abscission (Curtis and Rodney, 1952), and loss of carbohydrate reserves (Hansen et al., 1978; Davis and Potter, 1985). Combinations of low temperatures and dim light levels (1 to 5 mol m -2 s -1 PPF, depending on plant species and temperature) have been shown to extend storability of transplants of various floricultural and vegetable crops without inducing quality deterioration such as succulent elongation, leaf yellowing, or wilting (Heins et al., 1992; Kubota and Kozai, 1995; Kubota et al., 2003). Environmental conditions during transportation theoretically affect the quality of transplants and thereby the yield and quality of the final products originating from the transplants. Research has been conducted, toward containerized tomato seedling transportation for field growers. However, these plants are generally younger and smaller (5 to 6 weeks old, 10 to 16 cm height) (Leskovar and Cantliffe, 1991) than those that greenhouse hydroponic growers prefer (6 to 8 weeks old, 15 to 20 cm height). Furthermore, current North American market value of grafted seedlings is $1.00 to $1.50 per plant, being several times greater than bare root seedlings used for tomato production in the field. Nevertheless, as far as we know, no information is available on optimum transportation environmental conditions for such mature seedlings. Therefore, analysis of the current transportation conditions is crucial and is the first task in developing methods and techniques of transportation that will enhance further development of specialty crop industries. Our hypothesis is that temperature is the most critical environmental factor affecting the transplant quality and that by lowering temperature the problematic quality deterioration during transportation and associated negative impact on the early growth and yield may be prevented, thereby extending the effective duration (and therefore the distance) of transporting transplants. MATERIALS AND METHODS Tomato grafted seedlings were produced in the propagator s greenhouse operation (Bevo Farms, Milner, BC, Canada) using a conventional procedure. Six to eight weeks after seeding, grafted seedlings reached to the transportable size and were loaded into temperature controlled trailers. Each trailer accommodated 6 storied-racks each of which held 720 seedlings grown in 10-cm rockwool cubes (14,400 seedlings or 26 racks in total per trailer). Loading seedlings occurred during morning and the seedlings were transported to hydroponic tomato growers (FuroFresh Farms, Willcox, AZ, USA), approximately 3,000 km away from the seedling production site. Seedlings were unloaded from the trailers in early morning upon arrival to the hydroponic greenhouse operation and immediately inter-planted between rows of mature plants inside greenhouses, where plants were grown in a traditional continuous truss, high-wire tomato system. Trailer environment analysis Three transportation events were selected and environmental conditions inside the trailers were recorded using self-logging, battery operated small sensors (HOBO sensors series, Onset Computer Co., Pocasset, MA). Sensors were placed among seedlings upon loading in Canada and collected at the site of unloading in Arizona. Transportation temperature trial Based on the environment analysis inside the trailers and the separately conducted experiments, two levels of air temperature (12 o C or the conventional 18 o C)

3 were selected and tested for the two transportation events, occurring within one week in August, 2003, as shown in Table 1. The cultivar tested was Brilliant grafted to Maxifort root stock. All seedlings had visible first flower truss upon transportation (the largest flower buds were approximately 10 mm long). Seedlings transported at 12 and 18 o C were planted in two separate greenhouse compartments (1 ha floor area, Venlo-style glasshouse equipped with a pad-and-fan cooling system) adjacent to each other connected by a covered walkway. Status of flower development was surveyed for randomly selected 60 first trusses inside a greenhouse compartment after 3 and 4 weeks for 18 and 12 o C transported plants, respectively. Main effect of transportation temperature on number of normal and abnormal flowers was analyzed by t-test (JMP version 4.0, SAS Institute, NC, USA). RESULTS AND DISCUSSION Trailer environment analysis After loading seedlings, air temperature at the center of the load stabilized within 2-5 hours and remained in a range of o C until unloading approximately 40 hours after loading (Figs. 1a and 2). Relative humidity increased as air temperature decreased, and it was % during the transportation, due to the evapotranspiration from the seedlings and rockwool cubes containing nutrient solution. Trailer interiors were under complete darkness during the transportation (light sensor data not shown). Spatial variations of air temperature (Fig. 2) seemed to be affected by outside environmental conditions. In early March transportation, air temperature near the trailer floor surface had the lowest temperatures recorded during the transportation (Fig. 2), while such trend was not seen in mid September transportation (data not shown). Overall, difference in air temperature among trailers and the spatial difference inside trailer were o C. For tomato seedling storage, Hardenburg et al. (1986) recommended o C air temperature for less than 10 days, while other references stated that the optimum air temperature for storing tomato seedlings was 7.5 o C for 3 weeks (Heins et al., 1995; Gross et al., 2002). Although the transportation duration is only 2 days, transportation at 18 o C in dark moving trailers could reduce the carbohydrate reserves and deteriorate the seedlings during transportation. During past years, the hydroponic growers noticed the greater incidence of abnormal first truss development; 1) when seedlings were transplanted with well-developed first flower truss, 2) when seedlings were inter-planted into shady internal rows, and 3) when seedlings were transported in summer. In addition to carbohydrate loss during the transportation at the conventional 18 o C, accumulation of ethylene inside the trailers remained as a possible cause of flower abortion as ethylene generally affects flower thinning (Abeles et al., 1992). However, evidences of having a greater incidence when planted in shady internal rows suggested that it was more related to carbohydrate status during the transportation, associated with greenhouse environments before and after transportation. Young flowers generally have greater sink strength in roots and newly developing leaves than flowers (Ho, 1988). Under prolonged darkness and the successive shady environment of inside rows of inter-planting, the seedlings could not maintain enough carbohydrate supply for the flowers. Ethylene could potentially explain the seasonal differences since seedlings with more carbohydrate reserves grown in summer potentially have a greater metabolism and therefore ethylene production, which remained unclear. Effects of mechanical shock during transportation on plant growth after planting

4 were investigated for conifer species. Excessive mechanical stress during transportation reportedly suppressed the root growth of pine seedlings (Stjernberg, 1996). In the same study, Stjernberg (1996) compared various vehicle types and reported that transportation by trailers had 0.3 shocks per km with 2.6±1.8 g n average acceleration when traveled on paved road. In our preliminary test, a motion detecting sensor (HOBO H6 Motor On/Off Vibration Sensor, Onset Computer Co., Pocasset, MA) was placed inside the trailer and there was 127 shocks greater than 1 g n were recorded during transportation. Mechanical stress could also negatively impact seedling growth and development, since it could enhance ethylene production (Abeles et al., 1992; Beyl and Mitchell, 1983). Transportation on gravel road had reportedly 10 times more mechanical shocks (3.4 per km) with greater peak acceleration (12.2 g n ) than did on paved road (Stjernberg, 1996). More caution and improvement on racks may need to be considered to reduce mechanical shocks in transportation including unpaved gravel roads. In the present study, lowering air temperature is considered as one of potential strategies to effectively suppress carbohydrate consumption by lowering metabolic rates (dark respiration and ethylene production) during transportation. Illumination during transportation is also considered as effective for low temperature storage of seedlings (Heins et al., 1992; Kubota and Kozai, 1995). However, introducing light source inside the trailers may increase the costs significantly, while setting lower thermostat temperature will not increase costs in thermally well instated trailers. Transportation temperature trial Upon transplanting, no notable visible differences were observed between seedlings transported at 18 and 12 o C. After 4 weeks of transplanting, many seedlings transported at 18 o C showed either aborted or delayed fruit development in the first truss (Fig. 3). The incidence of either abortion or delayed fruit development was 95% and number of flower buds that exhibited abnormal development was 2.1 ± 0.31 per truss for 18 o C transportation, significantly greater than 12 o C transportation (33% incidence, 0.5 ± 0.39 abnormal fruits). Such abnormal development was typically seen in the peduncle closer to the stem, suggesting that these old flower buds, relatively large in size and visible at the time of transplanting, were negatively impacted by transportation. Among limited research, there are several reports focusing on optimum and economical means to transport seedlings for as long distance as possible. Risse and Moffit (1984) examined various types of containers for transporting and storing bare-rooted tomato seedlings. Handling and storage time (0 to 8 days) and temperature (5 and 15 o C) reportedly affected tomato seedlings morphology and yield (Leskovar and Cantliffe, 1991). Mena-Petite et al. (2003) investigated gas exchange and chlorophyll fluorescence responses of pine seedlings after storage and post-planting survival. Bare-rooted and soil plugged pine seedlings stored at 4 o C exhibited greater net photosynthesis, leaf water potential, chlorophyll a fluorescence parameters, survival percentage upon transplanting and root growth than did those stored at 10 o C. Clearly, lowering temperature during storage and transportation can suppress undesirable carbohydrate loss by respiration (Kubota and Kozai, 1995; Kubota et al., 1995), disruption of photosynthetic structure (Mena-Petite et al., 2003) and ethylene production (Kubota, unpublished data) during storage and transportation, and thereby contribute to maintain photosynthetic capacity and visual quality. In the present transportation tests, lowering temperature inside the trailers to 12 o C significantly reduced the incidence of abnormal first truss development.

5 Separately conducted experiments suggested that lowering temperature during transportation maintained photosynthetic and growth capacity of tomato seedlings and prevented delay in fruit development (Kubota and Kroggel, unpublished). The number of normal fruits per truss was not significantly different between 18 o C and 12 o C transported plants, although 18 o C plants were planted 5-day earlier than 12 o C plants. This indicates that transportation at 18 o C caused significant delay in first harvest and therefore loss of annual yield. Overall, the transportation at 18 o C created a significant reduction and delay of the first truss yield, and therefore it is predicted to decrease significantly the annual yield of tomato. Lowering temperature appeared effective at maintaining flower truss vitality allowing development of normal fruits, which is probably due to the suppression of respiratory carbohydrate loss and ethylene production at lower temperature. Lowering temperature further requires caution since chilling injury of tomato seedlings occurred at 5 o C or lower (Heins et al., 1995). Carefully conducted experiments testing various transportation conditions for tomato seedlings will reveal the mechanism of abnormal first truss development as affected by seedling developmental status and seasonal climate differences. Transplants are unique horticultural and agricultural products, since they are the final products of transplant producers as well as the valuable starting materials of final crop producers. By optimizing transportation conditions, transplant production will no longer be limited to the local market, but can step forward into the growing world-wide market demand. ACKNOWLEDGEMENTS CEAC Paper #P Financial support was provided by the Arizona Department of Agriculture, and the Controlled Environment Agriculture Center (CEAC), College of Agriculture and Life Sciences, The University of Arizona, Tucson, AZ. Authors would like to thank Merle Jensen, Tim Robinson, Ray Bleedveld, Martin Gruny, and Jack Benne for the assistance and support to conduct the analyses presented in this paper. Literature Cited Abeles, F.B., Morgan, P.W. and Saltveit Jr., M.E Ethylene in plant biology. Academic Press. Beyl, C.A. and Mitchell, C.A Alteration of growth, exudation rate, and endogenous hormone profiles in mechanically dwarfed sunflower. J. Amer. Soc. Hort. Sci. 108: Conover, C.A Postharvest handling of rooted and unrooted cuttings of tropical ornamentals. HortScience. 11: Curtis, O.F. and Rodney, D.R Ethylene injury to nursery trees in cold storage. Proc. Am. Soc. Hortic. Sci. 50: Davis, T.D. and Potter, J.R Carbohydrates, water potential, and subsequent rooting of stored Rhododendron cuttings. HortScience. 20: Gross, K.C., Wang, C.Y. and Saltveit, M The commercial storage of fruits, vegetables, florist and nursery crops. An Adobe Acrobat pdf of a draft version of the forthcoming revision to U.S. Department of Agriculture, Agriculture Handbook 66 on the website of the USDA, Agricultural Research Service, Beltsville Area (November 8, 2002).

6 Hansen, J., Stromquist, L.H. and Ericsson, A Influence of the irradiance on carbohydrate content and rooting of cuttings of pine seedlings (Pinus sylvestris L.). Plant Physiol. 61: Heins, R.D., Lange, N. and Wallace Jr., T.F Low-temperature storage of bedding-plant plugs. p In: K. Kurata and T. Kozai (eds.), Transplant Production Systems, Kluwer Academic, Dordrecht, The Netherlands. Heins, R.D., Kaczperski, M.P., Wallace Jr., T.F., Lange, N.E., Carlson, W.H. and Flore, J.A Low temperature storage of bedding plant plugs. Acta Hort. 396: Kubota, C Environmental control for growth suppression and quality preservation of transplants. Environ. Control in Biol. 41: Kubota, C. and Kozai, T Low-temperature storage of transplants at the light compensation point: air temperature and light intensity for growth suppression and quality preservation. Sci. Hort. 61: Kubota, C., Niu, G. and Kozai, T Low temperature storage for production management of in-vitro plants: effects of air temperature and light intensity on preservation of plantlet dry weight and quality during storage. Acta Hort. 393: Leskovar, D.I. and Cantliffe, D.J Tomato transplant morphology affected by handling and storage. HortScience 26: Mena-Petite, A., Robredo, A., Alcalde, S., Dunabeitia, M.K., Gonzalez-Moro, M.B., Lacuesta, M. And Munoz-Rueda, A Trees. 17: Risse, L.A. and Moffitt, T Shipping tomato transplants in returnable shipping containers. Transactions of the ASAE. 27: Stjernberg, E.I Mechanical shock during transportation: effects on seedling performance. New Forests. 13: Table 1. Number of flowers normally and abnormally developed on first truss of tomato seedlings as affected by air temperature during 2 day transportation from British Columbia, Canada to Arizona, USA. Temp. Loading date Unloading/ Planting date No. of normal fruits per truss No. of aborted or delayed per truss 18 o C July 30, 2003 August 1, ± ± o C August 4, 2003 August 6, ± ± 0.39 t-test NS **

7 20.0 [a] 19.5 Air Temperature ( o C) Truck 1 Truck 2 Truck 3 [b] 100 Relative Humidity (%) Truck 1 Truck 2 Truck Time From Loading (hours) Fig. 1. Air temperature (a) and relative humidity (b) inside the trailers full of transplants during 2-day transportation from British Columbia, Canada to Arizona, USA. The data was obtained through September 7-9, 2002.

8 20 19 Air Temperature ( o C) Time From Loading (hours) Front Center roof Center rack Mid-line Center floor Rear Fig. 2. Environmental conditions among trailers full of transplants during 2-day transportation from British Columbia, Canada to Arizona, USA. The data was obtained thorough March 18-20, Six sensors were located in the front most edge on the shelf at the middle height (Front), in the central top most shelf (Center roof), in the center of the load among the plants (Center rack), in the center of the load near the gaps between two rows of racks (Mid-line), in the central bottom shelf (Center floor), and in the rear most edge on the shelf at the middle height (Rear) inside the trailer. Fig. 3 First fruit truss developing of a tomato plant transported at 18 o C. The two flowers closer near to the stem either aborted or experienced delay in fruit development, followed by three normal fruit development.