The University of Arizona

College of Agriculture and Life Sciences

Enhance Economic Opportunities for Agricultural Producers
Optimizing Long Distance Transportation Conditions for High Quality Tomato Seedlings

Impact Nugget
UA researchers found that lowering the transport temperature for grafted tomato seedlings to 10-12 degrees C from the conventional 18 degrees C in refrigerated trucks significantly improved the flowering and development of the initial fruit; the largest grower of greenhouse tomatoes has adopted the practice, and saved an estimated $500,000 per year, or $3,100 per acre of greenhouse tomatoes annually. There is also a significant benefit found for transplant propagators who can now extend the transportable distance of their seedlings across two borders, from Canada to Mexico.

The production of high quality transplants is a critical technology that supports the success of the final crop. Healthy transplants mature predictably and yield well. In current industry practice, transplants are produced in an operation that is separate from final crop production. This recent trend is especially popular 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 are purchasing their transplants from specialized transplant producers. There is a growing nationwide interest in use of high quality grafted seedlings for greenhouse tomato production, but the source of grafted tomato seedlings is still limited in the United States. For example, greenhouse tomato growers in Arizona must purchase grafted seedlings from Canadian propagators, thus risking deterioration of transplants during transportation. Over the past several years, abnormal fruit development has been observed for the first truss (fruit set), attributed to the rigors of long distance transportation.

Further, Arizona greenhouse tomato growers have observed that transportation conditions, coupled with the status of flower development during transportation, and planting conditions after transportation, influence flower abortion and abnormal fruit development of the first truss. Significant yield delays and losses have resulted in part because the mechanisms that cause flower drop and abnormal fruit development during long distance transportation are not well understood.

What has been done?
Environmental conditions in temperature-controlled trailers full of grafted tomato seedlings were analyzed during a regularly scheduled two-day transportation from a Canadian propagator to Arizona growers. The goal was to understand how to optimize transportation conditions to minimize or eliminate the negative impact of transportation on the transplants and thereby on the early yield. UA researchers from the Controlled Environment Agriculture center collected information from the Canadian propagator and Arizona tomato growers on the current transportation situation and associated problems to define a hypothesis for preventing flower abortion and abnormal truss development. Simulation experiments were then conducted on campus to examine combinations of air temperature and light intensity during transportation. Research found that lowering temperature is effective to keep the seedling quality, which was quickly implemented to the seedling transportation conditions to Arizona and also to Mexico.

In 2005, the UA researchers found that treating seedlings with a 1-Methylcyclopropene (1-MCP), an inhibitor of ethylene-mediated reactions and widely used for postharvest management, had an effect similar to lowering temperature inside the trailers.  This finding is particularly important as application of 1-MCP may keep the seedling quality when lowering temperature is not an option.

The results show that lowering air temperature to 10-12C from the conventional 18C for transplants during transportation significantly improved the development of flower and fruits of the first truss. Based on the experimental results, the largest Arizona greenhouse tomato operation adopted transportation of the grafted tomato seedlings at lower air temperatures inside the trailers (10-12 degrees C.) Immediate analysis of transplant quality and early fruit development was conducted and normal truss development was confirmed by University of Arizona researchers.  Follow-up research results show that ethylene accumulation was the primary cause of the delayed fruit development causing yield reduction by long distance transportation at an inadequate temperature.  Application of 1-MCP during transportation was shown to improve the development of flower and fruits of the first truss, although lowering temperature was the most effective under the present experimental conditions.

Since this strategy has been adopted, the profit to the largest Arizona greenhouse operation by improving the transport conditions for transplants and thereby assuring normal first truss development without causing delay is roughly estimated at $500,000 per year or $3,100 per acre of greenhouse per year. There is also a significant benefit found for transplant propagators who can now extend the transportable distance of their seedlings across two borders, from Canada to Mexico.

Hatch Act
Controlled Environment Agriculture Program (CEAC), The University of Arizona

Chieri Kubota
Associate Professor Department of Plant Sciences
The University of Arizona
Tucson, AZ 85721-0036, USA
Tel: 520-626-7937
Fax: 520-621-7186

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