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Q&A with USDA scientist Jim Mattheis

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Jim Mattheis arrived in Wenatchee as a Washington State University grad student in 1984, working at the WSU Tree Fruit Research and Extension Center on Western Avenue.

The U.S. Department of Agriculture - Agriculture Research Service office on the same campus hired him in 1988 as a research plant physiologist and he has been there since, currently serving as the researcher leader. He is joined by a handful of other researchers including Mark Mazzola, David Rudell, Yanmin Zhu and Loren Honaas and Rachel Leisso, along with a group of post-doctoral grads and technicians.

The group, housed in an office/laboratory built in 1978, is charged with expanding the knowledge of tree fruit production systems in the areas of plant disease and fruit quality. The work often includes collaboration with WSU researchers and grad students, all in an effort to boost the tree fruit industry, sometimes in ways the industry hasn’t yet realized needs a boost.

We are a scientific community doing research. We are here to do things that are risky, that ask the why questions,” he said. “The industry wants what works now. We’re looking at what we might need as time goes on.”

He sat down with the Wenatchee Valley Business World to share some of what that might mean.

Q: So, what do you guys do here?

A: We focus on two areas of research — plant disease management, primarily in the soil, and quality management, post-harvest storage and other things related to quality.

Much of the focus for soil management is around the loss of methyl bromide as a soil fumigant more than 20 years ago.

When orchards are replanted after they’ve been established for a long time, the same type of tree can have issues with the microbial community that’s developed in the soil. What used to happen, is a soil fumigant (like methyl bromide) would be used after the old trees were pulled out and before the new trees were planted.

The tree fruit industry wasn’t really using it, but Congress mandated ARS to develop a national program to look at replacements for methyl bromide. Part of our funding was redirected to that purpose even though it wasn’t directly applicable here.

Q: But the research results apply?

A: Yes. The program focuses on what’s living in the soil that causes the problem, looking at what methods can be used instead of fumigation to try and manage that community so it’s not pathogenic to the trees.

That’s Mark Mazzola’s program. His approach is to look at the biological-based solutions rather than chemicals. One of the methods he is working on is to use the seed meal that’s left when you press the oil out of canola seeds. You take what’s left and mix it in the dirt to suppress the pathogen community.

It has the additional benefit of working as a fertilizer.

He’s also looking at the effects of anaerobic soil disinfestation, where you take something as simple as the grass between the rows in the orchard, mow it into the tree row and cover it with black tarp. There’s been lot of work in that area with strawberries, but it has a universal application.

It’s a hot area for research worldwide for conventional and organic systems. When the chemicals you have are not as effective anymore, you need to look at other ways to do things.

The other side of the soil question is to focus on the rootstock, to see how it responds to pathogens in the soil. That’s the research being done by Yanmin Zhu.

The objective is to identify a pattern of gene expression that’s associated with the resistant or susceptible rootstocks, which can be used to develop new rootstocks.

Another component is tree response. Rachel Leisso looks at how the tree extrudes materials in the soil or makes chemicals to protect itself. Trees protect themselves, either directly or where other soil components favor the growth so the pathogens don’t do as well.

It’s a different way to think about disease management. It used to be, “Kill all the bad guys.” But sometimes it’s better just to have more good guys because the bad guys can’t compete as well.

Q: And research on the fruit quality side?

Mattheis: That’s where I come in. I work primarily in the post-harvest environment.

A lot of what happens with fruit quality is determined by what happened to it in the field. We do a little bit of work in that area, in collaboration with other people.

More of what we do is focused on manipulating the ripening with post-harvest technology, using temperature and atmosphere.

Apples and pears require a small amount of ethylene that they produce to ripen. Limiting that slows the ripening, which can be controlled with temperature.

We’ve learned different types of apples and pears behave differently after harvest.

Honeycrisp, it turns out, is sensitive to temperature in the low 30s that other fruits are fine with. You have to put it at 50 degrees for a week to get it used to being off the tree and then put it into a colder temperature.

It’s different than what the industry is used to doing for other varieties. That was a huge change.

They weren’t excited about running cold rooms at 50 degrees. If you did that with Delicious or Gala, it would be problematic. For Honeycrisp, it doesn’t make much difference in firmness or texture. It will create other problems though, so we started looking at if we’re stuck with a week of 50 degrees, what else can we do? One of the things we tried is turning on the CA for that week to see if low oxygen level is a problem in the warmer temperature.

Q: How do you test it?

Mattheis: We have a lab here, 140 fruit box-sized CA rooms for experiments, so we can do a lot of variations.

Every new variety presents a challenge because they all behave differently.

During the first few years, orchardists just put it into a box and sell it. The price is high, demand is high. There’s not a big volume, so no need for long-term storage. As the volume increases, the industry has to figure out how to store it. We have some time to figure it out. That’s been a big advantage from a research standpoint.

We also look at the disorders, like superficial scald (where brown or black patches appear on the skin during or after storage). We’re trying to design a test to see if we can identify which fruit are most or least likely to get the disorder.

That can help with the decision-making process about what fruit to sell when. It’s especially useful for organic fruit.

If there’s a test that can help make decisions about which fruit will last longer and you’re trying to have organic fruit to sell in the summer, it would be helpful.

That program, led by Dave Rudell, a research expert in metabolomics, is pretty far down the line, with some commercial people using the analysis.

Another potential way to predict which fruit will store longer is to look at the molecular biology, the gene expression, as opposed to a chemical test.

Loren Honaas, a research molecular biologist, is looking at that aspect, the diagnostic genomics.

Q: Do people also come and ask for help?

A: Yes. Diagnostics is the other thing we do. People bring in fruit and say, “Can you help us understand what might have happened?”

If someone goes to the doctor with a broken leg, it’s pretty easy to diagnose. Browning disorders with apples are a little more difficult. It can be a function of a lot of different things. We haven’t been as successful, but we haven’t spent as much time on it. If we have four scientists here, they might get four different answers.

Part of our challenge is to improve the system so we can collect more information, so if something fails we can figure it out and be able to say, if you do this, nothing bad will happen.

With Honeycrisp, at first we didn’t think they would lend themselves to long-term storage and CA. When they came out of storage, they tasted bad. Really bad. By doing more work, we realized maturity played a role.

Honeycrisp doesn’t soften, so you can’t tell when it’s mature by the usual methods. One of the components of maturity, which we had noticed before, was how much acid the apples had, the tart component. Fruit from an orchard with a high amount of acid at harvest stored better in long-term storage. But warehouses saw no value in doing the test before because they had other methods to measure maturity.

Now many warehouses test the acidity at harvest on all varieties. In a single year, you can see a huge variation in acidity from orchard to orchard when you see little difference in other forms of maturity. It’s important. The acid is the fuel that gives them the ability to respire and continue to live. The more they have, the longer the legs.

It’s not as easy as some of the other tests. But as soon as you have a reason, you do it.

Q: How do you decide what to research?

A: The warehouses and growers set research priorities, which drives some of it. And we see what problems are being experienced by people who come to us.

A third one comes from us. We are a scientific community doing research. We are here to do things that are risky, that ask the why questions. The industry wants what works. We want to know what might happen if we push it further, like how low can the oxygen go without the fruit starting to ferment. We try to find other things to measure. The industry wants it to work now. We’re looking at what we might need as time goes on.

Q: Will you work yourself out of job?

A: There’s always something new. One of the interesting things about apples is it responds to the local environment.

A Fuji grown in Brazil is not the same as it is in Wenatchee. The post-harvest treatment also varies. That makes it necessary for people in a lot of different places to do what appears to be the same things. If Stemilt adopts the Brazilian Fuji storage protocol, it won’t work.

Exporting is a whole different issue.

Here export is big, but the domestic market is strong, with its own set of challenges. If you’re shipping fruit from Washington to Florida, you have to build in something to account for the period when the warehouse doesn’t have control over the product. We are moving into that research because of the whole organic expansion. The trucks are not the best environment to store fruit.