WENATCHEE, Wash. – Delving into the secrets of the molds and fungi that can wreck a good apple or pear, Achour Amiri can be found working in packing rooms and warehouses throughout central Washington this time of year.
“Winter is when pathogens start to show up in storage,” said Amiri, assistant professor and researcher at the Washington State University Tree Fruit Research & Extension Center in Wenatchee. He specializes in diseases that spoil tree fruit.
“I visit packers to understand their problems,” he said. “Do they see unusual decay rates or decay that they’re not used to? I try to find out why and deliver solutions.”
Using geographic variability to maximize fungicide use
Apples and pears are stored for months, making them prime targets for molds and fungi. Packers protect them by spraying with fungicides before and right after harvest.
The challenge, Amiri said, is that packers have few options in their fungicide arsenal. In Washington, only three fungicides are permitted to be used postharvest. It can take years for new fungicides to come to market, especially for postharvest use, but when the same fungicides are used too often, pathogens have a better chance of outwitting them.
“It’s just like, in humans, when we take the same antibiotics over and over,” Amiri said. “The treatment doesn’t work anymore.”
His team is testing Washington fruit to find possible geographic variability in pathogens across the state. A clear picture of pathogen populations could help fruit packers make science-based decisions on what and when to spray.
“We are trying to develop best spray practices to slow down or delay development of resistance,” said Amiri. “Our target is to keep our few fungicides useful for the longest period possible.”
At the same time, he is investigating ways to amend pesticide use while efficiently controlling disease. A top priority is researching chemical and biological controls to manage postharvest disease in both the orchard and the packing shed for all tree fruit crops.
Fascinated by fruit, fungi
Apples, pears and cherries grew in Amiri’s childhood home, the foothills of the Atlas Mountains in Algeria.
“We grew fruit in our garden; that familiarity was something that drew me to plant research,” he said. “I chose biology over mathematics because I was attracted to investigating living microorganisms rather than abstractions.”
Attending universities in Algeria, Belgium and France, he worked to fight blue mold, a disease that devastates apple crops in Europe and the United States. He worked at South Carolina’s Clemson University on diseases of peaches and nectarines. At the University of Florida, he researched gray mold, the most devastating disease affecting the U.S. strawberry crop, before coming to WSU in 2015.
Solving problems of resistance, management
In Washington, his top targets include both blue and gray molds as well as bull’s-eye rot and other emerging diseases that strike tree fruit by rotting it from within.
Amiri is fascinated by molds and fungi, more than 80 of which thrive on tree fruit. Some harm the fruit but some are beneficial – they limit development of other pathogens.
Fungi can survive Washington’s freezing winters and hot summers and bypass many known resistance pathways, offering a tantalizing scientific puzzle.
“It’s important for us to understand how climate change and human practices can cause evolution in pathogens,” said Amiri, who is developing tools to predict, detect and measure important microbes. “That will give us better ideas to manage disease.”
• Learn more about WSU tree fruit research at treefruit.wsu.edu.