U.S – Scientists at Washington State University are set to launch new research to find safe, organic-friendly ways to defeat post-harvest diseases and foodborne illnesses in apples and pears, while extending their storability.

Increasingly popular with consumers, Washington-grown organic apples and pears thrive in the region’s dry, disease-discouraging climate. Off the tree, however, organic fruits are at the mercy of physiological disorders and fungi that can rot and destroy more than a third of the annual harvest before it gets to the table.

Achour Amiri, a Wenatchee-based plant pathologist, is partnering with a team of scientists and students, including food safety and postharvest systems specialists, to test promising technologies using heat and controlled atmosphere in storage. Funded by a four-year, US$1.5 million grant from the USDA National Institute of Food and Agriculture’s Organic Agriculture Research and Extension Initiative, the team is also exploring safer fruit coatings and timely sprays to limit infection and preserve organic fruit quality.

Growers currently utilize some organic treatments to keep fungi at bay in the orchard.

“Once the fruit is harvested, it’s a different story. Organic packers lack effective methods to stop post-harvest pathogens and physiological disorders. Rots are their number one challenge to packing and storing fruit. After five months, they can lose up to 50% of the crop just to rot.”

Achour Amiri, Plant Pathologist


One alternative that the researchers intend to explore is thermotherapy, or heat treatment. High temperatures shut down and kill microbes, including decay-causing fungi. Thermotherapy has also been shown to keep fruits and other produce fresh longer.

Amiri, who will work on the effect of heat on major fungal culprits, such as gray mold, bull’s eye rot, speck rot, and blue mold, commented that they are looking to find an optimal temperature to keep fruit quality and kill spores without damaging the fruit. Apple, pear, and stone fruit varieties may have varied susceptibility to heat, so the team will test different cultivars to learn how to use thermotherapy safely.

Another approach involves altering the controlled atmosphere in which apples and pears are stored. Traditionally, temperature, humidity, and levels of oxygen and carbon dioxide are steadily maintained to slow the ripening process and keep fruit fresh. Amiri’s team is testing a modified practice called dynamic controlled atmosphere storage, in which oxygen levels are progressively lowered.

“We’re hoping to show evidence that this can work in reducing decay and extending fruit quality.”

Achour Amiri, Plant Pathologist


Fruits give off gasses in storage. Scientists can analyze these exhalations to learn if the fruit is under stress, which affects freshness and firmness and can cause other disorders. Amiri seeks to find the limit before stress begins.

The team will also experiment with different spray materials made of biological agents, such as beneficial bacteria, and other safer ingredients that may combat rot-causing microbes.

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