Parasitic plants may be able to communicate with other plants through chemicals, a team of Penn State entomology researchers has discovered.

"We discovered that parasitic plants can choose a stronger host over a weaker host by sensing the host plants' volatile chemicals," Justin Runyon (graduate-entomology) said.

The research team used Cuscuta pentagona, commonly known as the dodder plant, in the research experiment.

"The dodder plant is a parasitic plant that attaches to another plant and takes the resources from it," Consuelo De Moraes, assistant professor of entomology, said. "The dodder plant doesn't produce roots or leaves, and it doesn't photosynthesize"

During the first experiment, the team discovered 80 percent of the dodder plant's growth was toward the host, a tomato plant, Mark Mescher, assistant professor of entomology, said.

"We put the dodder seedlings in a vial of water in the center of a piece of circular filter paper next to a tomato plant," Mescher said. "The dodder plant grew in its normal circular pattern toward the tomato plant."

Runyon said the team assumed the plants used volatile chemical signals, but they wanted to rule out other cues like light that would cause the plant to grow toward a host.

The next experiment determined that it was the volatile chemical cues, and not light, which guides the parasite's choice, Mescher said.

The team constructed a device that excluded light and also gave the dodder plant a choice of two hosts, a pot of soil and a tomato plant, Runyon said. "The plant once again, grew toward the tomato, proving it is the volatiles that attract the parasite," he said.

The team tried different host plants, such as Impatiens and wheat, De Moraes said.

"We planted [dodder] seed between wheat and tomato, and they strongly preferred the tomato plant," Runyon said.

De Moraes, Runyon and Mescher isolated the individual volatiles of the wheat and tomato plant, then allowed the dodder plant to grow to each volatile in individual experiments.

"We found three volatiles that attracted the dodder plant; the rest of them had no obvious trend and none individually was as strong attraction as all of the volatiles together," Runyon said. "We showed they could find volatiles to find hosts."

Runyon added that the wheat has individual volatiles that repel the dodder plant, even though the wheat and dodder plant have a few identical volatiles.

"The dodder will grow to any plant as a general response, even if we give them just wheat, they will grow toward wheat," De Moraes said. "If you give them an option, they will make a choice by reading the volatiles and choose the stronger host."

Mescher said the difference in volatiles could affect other relationships, not just plant to plant.

"The larger issue relates to whether this kind of chemical signal that is important in plant to predator relationships," Mescher said. "Pollenaters use chemicals to find flowers and herbivores use chemicals to find food."

He also said a plant being eaten by a predator could send warning signals using chemicals to surrounding plants, causing them to release a propellant chemical and avoid being eaten.

De Moraes said they plan to investigate the volatile chemicals and discover the parasite's receptor mechanism and the host's possible defensive mechanism toward the parasite.