Potatoes produce a molecule that is converted by microbes and causes potato parasites to hatch. The Kobe University discovery of this three-way relationship not only adds a new perspective to how plants interact with their environment, it also opens an avenue for developing countermeasures against the parasite.

The potato cyst nematode is a root parasite in plants like potatoes and tomatoes that can cause large-scale yield loss if left untreated. Their eggs can survive in the soil for up to 20 years and hatch when they detect certain molecules, called “hatching factors,” secreted by the roots of their target species.

Kobe University phytochemistry scientist Mizutani Masaharu says, “If we apply hatching factors to agricultural soils before planting the plants and so induce the parasites to hatch prematurely, this so-called ‘suicide hatching’ might be effective parasite control. However, this class of chemicals is difficult to identify because they are secreted in very small amounts.”

The Kobe University researcher and his team previously discovered that among the two known hatching factors, plants only secrete one, called “solanoeclepin B” (SEB), while soil microorganisms convert this into the other known form, called “solanoeclepin A” (SEA).

He explains, “When we measured the process’s reaction rate, we noticed that the amount of SEB in the soil initially increased when we applied tomato root secretions to soils. This led us to hypothesize that there must be another, hitherto unknown molecule that the plants had produced and secreted. In the soils, we conjectured, soil microbes converted it into SEB and then further into SEA.”

As experts on the interactions of plants with their soil environment, the team set out to identify the mystery component and its environmental relevance with chemical detective work and genetic analysis.

In the journal New Phytologist, the Kobe University team published the nature of the chemical, which they termed “solanoeclepin C” (SEC), together with the realization that this compound is secreted by the plants 20 times as much as the previously identified SEB.

“Importantly, we could show that the newly identified SEC does not cause the parasites to hatch. However, it is converted in the soil to SEB as a decay process that is dramatically sped up by microbial action. This indicates that maybe it is the secretion of SEC that is of physiological relevance to the plants, but through the chemical’s conversion to SEB and further to SEA, the parasites are then activated. This is the first time that this kind of three-way relationship has been found for this class of chemicals,” Mizutani says.

Plants often secrete chemicals to attract soil microorganisms to help them obtain water or nutrients, in exchange for carbon-rich compounds. A similar interaction might be the plant’s intention in this case, too.

Mizutani explains, “Trying different environmental conditions for the plants, we found that they secreted SEC, and to a much lower extent SEB, especially when they are starved of nitrogen or phosphorus, which are essential nutrients.”

This is a typical pattern for plants calling for microbial help, and it may well be that a chemical side effect of this emergency call system got hijacked by the parasites. However, the real physiological purpose of the secretion remains to be clarified in future studies.

“At first glance, a hatching factor seems to be a component that has only unfavorable activity for a plant and it’s curious why they would produce it. But we are looking forward to future work clarifying the beneficial effects this class of chemicals has for the plants,” says Mizutani.

On the topic of using these molecules agriculturally to induce suicide hatching, the phytochemist says, “This class of chemicals is structurally complex and thus difficult to make. But if we keep looking, we might find an equivalent that has similar effects and is easier to produce.”