Could new ethylene inhibitor work on fruit?

By Dr. Dana Faubion

Unlike most produce, apples and pears can be stored for long periods of time. In fact, many varieties of apples are stored for almost 12 months. The technology used to store fresh apples year round was developed in England shortly after World War I. Normal air is made up of many different gases, including 21% oxygen and around 0.03% carbon dioxide. The scientists found that by storing apples in low oxygen (2.0%) and elevated carbon dioxide (2.0 to 5.0%) at near freezing temperature, they could extend the storage life dramatically. They decided to call it gas storage. Anything with the word "gas" in it evoked memories of the WWI battlefields where mustard was not a condiment. The name was soon changed to controlled atmosphere (CA) storage.

Eastern Washington State hosts the highest concentration of controlled atmosphere storage facilities in the world. These facilities are used to maintain the eating and nutritional quality of both apples and pears, giving the world the enjoyment of Washington's fresh produce year round. It is hard to imagine what this industry would look like if we did not have controlled atmosphere storage.

The primary benefit of controlled atmosphere storage is that the low oxygen and elevated carbon dioxide inhibit the activity of the ripening hormone ethylene. Ethylene is a simple molecule, similar to acetylene. Most fruit produce it during ripening. Ethylene initiates and coordinates the changes as fruit progress from preripe to overripe. Reducing the fruit's temperature, lowering oxygen, and raising the carbon dioxide around the fruit are the only means we have to slow the ethylene-induced maturation process. By reducing the impact of ethylene, we can maintain fruit quality for up to 12 months.

Recently, a biochemist, Ed Sisler at North Carolina State University, discovered a compound that appears to act as an irreversible inhibitor of ethylene binding. In other words, with this compound present, the fruit cannot detect ethylene. This slows the following processes--respiration, the conversion of starch to sugar, and aspects of cell wall breakdown or fruit softening. The compound is called 1-methylcyclopropene (MCP). It appears to be safe and effective at very low concentrations (about three parts per billion). MCP is a gas, so it would be simple to blow into a storage room.

There are three years of research on MCP's effect on ethylene-sensitive flowers like roses and carnations. The cut-flower industry currently uses a silver solution in vase water to prevent ethylene biosynthesis and its acceleration of flower senescence (aging). Silver is not valued in wastewater, due to environmental concerns. MCP is currently being viewed as a strong potential alternative to silver, and registration is being pursued.

This season, researchers at Washington State University and U.S. Department of Agriculture have begun to evaluate MCP effects on apples. The ethylene-binding site on flowers is not different from the binding site in fruit. So, it will impact the effects of ethylene on fruit.

The chemical ReTain (aminoethoxyvinylglycine) inhibits ethylene production. MCP makes the fruit blind to ethylene. Direct comparisons between ReTain and MCP are not valid.

If MCP becomes available for use on fresh fruit, what will that mean to our industry? Will it mean that Gala apples can be stored for more than six months? Will we need controlled atmosphere storage? Will we be able to harvest fruit at a more mature stage and keep it longer? Ethylene can play a role in chilling injury symptom development--scald might be a form of chilling injury. Will it alleviate scald? Will it reduce the capital expense of fruit storage enough to give the competition a leg up? These are some of the many questions about this exciting compound. Depending on the answers from research, MCP may indirectly increase planting, consumption, and competition.

Dr. Dana Faubion is a Washington State University Tree Fruit Extension educator in Yakima, Washington.

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Could new ethylene inhibitor work on fruit?

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