June 25, 2003

By Susan Thompson

This summer, Iowa gardeners are carefully tending their tomato plants, looking forward to enjoying their
own vine-ripened fruits. But for much of the year, Iowans must buy their tomatoes at grocery stores. The wholesalers who supply those tomatoes walk a fine line between having too many on hand, which leads to spoilage, and having too few, which leads to lost customers.

Richard Gladon has been on the Iowa State University horticulture faculty for 25 years. He researches
ways to make flowers last longer and to slow fruit and vegetable ripening.

Two years ago, an undergraduate student working with Gladon discovered he could delay tomato
ripening by applying 1-methylcyclopropene (1-MCP), a chemical commonly used to extend the life of
flower blossoms. This year, preliminary findings by a graduate student showed the ripening process can be restarted by treating the same tomatoes with the chemical that causes natural ripening - ethylene.

The U.S. Department of Agriculture identifies six stages of tomato development. Stage 1 is the green
stage, followed by "breaker" because the color is just "breaking" at the blossom end of the tomato. The next three stages are turning, pink and light red. The final stage is "red" and is the point at which the tomato is ready to be eaten.

Student Charles Rohwer found it's possible to delay ripening of tomatoes in the pink and light red
categories by treating them with 1-MCP. "These tomatoes are well along in the ripening process but aren't optimum for sale or consumption," Gladon says. He and Rohwer found that 1-MCP binds to the same receptors as ethylene, and depending on the dosage and stage of ripeness, would slow the ripening process from one to four days.

Applying 1-MCP to tomatoes in the earlier stages of "breaker" and "turning" didn't work as well. "The
tomatoes in these stages couldn't recover and would rot before they ripened," Gladon says.

Graduate student Abhijeet Patil repeated Rohwer's experiments and reached the same conclusions. Next, he and Gladon decided to apply ethylene to tomatoes in which the ripening process had been stalled by 1-MCP. "The data are completely preliminary," Gladon says. "But we've found that we can restart the ripening process in breaker and turning tomatoes by applying ethylene. It's like a switch that turns the process on. Red pigment formation and softening both are controlled by ethylene."
More research is needed, but Gladon is excited about the possibilities. "Wholesalers deal in huge amounts of material. If there is a glut of tomatoes, they don't have any choice but to flood the market or allow the fruit to spoil. If we can stop the ripening process, and then predictably restart it, we would be offering food handlers a very valuable product," he says.

(Susan Thompson is a communications specialist with the Iowa State University College of Agriculture.)