Biological sprout inhibitor could stop fungal growth
2017 saw European retailers and potato growers scramble to comply with rules requiring lower rates of the commonly used sprout inhibitor chlorpropham (CIPC). Since 2012, Europe has been drawing down its allowances for the chemical and has moved to require other measures, such as active recirculation in storages.
One reason for increased regulation of CIPC has been health concerns associated with a chemical byproduct, 3-chloroaniline, that has been tied to significant negative health effects at high enough levels, including possibly causing cancer.
Given increased global regulation, there has been a search for alternatives to CIPC. One such alternative sprout inhibitor is the biologically derived molecule 1,4-Dimethylnaphthalene (DMN), which is naturally found within potatoes.
The chemical has been used for several years and is the active ingredient of commercially available sprout inhibitors including those from Meridian, Idaho-based 1,4 Group.
Research on DMN is ongoing and its exact mode of action is still unknown. However, it is clear that what it does is distinct from how CIPC inhibits growth in tubers.
“We should always know what we’re putting in our food. We should have an idea of how it functions and what it does,” said Michael Campbell, biology professor at Penn State Behrend. “That is one reason why we’re very cautious about CIPC. We know how it functions and that has a lot of people nervous about how it functions.”
DMN effects on other organisms
Campbell has done work on both CIPC and DMN. Recently he led a team of undergraduates to look at what effects DMN would have on other organisms that might be present in a potato storage, namely fungus.
“It was serendipity,” he said. “I had a student in the lab who asked what does DMN do to other organisms and I said ‘I don’t know.’”
Starting with bread yeast, the students found that the molecule inhibited the growth of fungus. The release of the team’s full research is pending, in which they looked at how several fungal strains reacted to DMN, but Campbell related what happened when the team looked at one strain of fusarium.
The research showed that the molecule stopped the growth of the fusarium but didn’t kill it. Unlike CIPC, DMN’s effects on potatoes are temporary. That not only goes for DMN’s sprout inhibiting effect, but its effects on fungal pathogens as well. After application, it eventually will evaporate and once the chemical is not present, fungal organisms will begin to grow again.
Because of that, Campbell describes DMN’s effects as “fungistatic.” While the results are intriguing, the project is only a first step into finding out which fungal pathogens DMN affects and exactly how it affects them.
This research confirms what growers have told Addie Waxman for years. Waxman is the director of research at the 1,4 Group. Because of those reports, she began conducting her own experiments in her lab and saw the same effect.
“In fact, I saw it in research projects where I wasn’t even trying to look for a fungistatic effect,” she said.
Fungus can’t keep up
Waxman said the findings are both interesting scientifically and in in how growers use DMN.
While the fungistatic effect is temporary, she said it can be enough to solve fungal pathogen problems in some cases.
Waxman said this is due to the other microorganism living on potatoes in storage. While the DMN doesn’t allow the fungus to grow, the rest of the non-pathogenic organisms on the potatoes are still multiplying. When the fungus starts growing again, it can’t compete with the organisms that have been able keep growing and getting stronger in the meantime.
However, in some cases the initial load of fungal pathogens may be high due to wet weather and the potatoes might be more vulnerable due to damage, requiring more than DMN to address.
“That’s a lot to ask from any chemical,” she said.
In those cases follow-up chemical control might be necessary.
“In the United States, 1,4 DMN is often used with other conventional chemicals and that’s because the growers have seen that 1, 4 DMN helps with sprouting. They’ve seen a reduction in numbers with fungus and with other microorganisms,” she said.
Waxman also said there are other benefits of DMN that should be looked at. Similar to the initial reports she heard from growers on the fungistatic effect, she has been told that 1,4 DMN could also help prevent discoloration from bruise and possibly prevent weight loss.
The two chemicals have different characteristics, both chemically and agronomically. DMN is a liquid at room temperature unlike CIPC, which melted from its solid form before application. Also the way they inhibit sprouts is different, CIPC inhibits sprouting only where it physically touches the potato. On the other hand, Waxman said DMN induces a systemic genetic response.
Campbell said there are still plenty of questions to be answered when it comes to DMN and its effects on fungal organisms, including which species it affects, how exactly the fungistatic effect works and what is the dosage range of DMN.
“To me it’s been a thrill, because it’s always fun to be working with something that has utility to society but at the same time has great scientific questions with it,” Campbell said.