A seedling of a vine known as dodder is  attached to a tomato plant.

Dodder is a wiry, orange vine that steals water and nutrients from other plants. Scientists have now found that this vine chooses its victim by smell, growing its shoots in the direction of a plant's natural perfume.

A dodder tangle steals food and water from a glasswort plant.

The tendril of a young dodder plant stretches out to entwine a tomato seedling.

When a dodder seed sprouts, it doesn't grow roots to seek its own food. Instead, it grows a shoot that reaches out to other plants, tapping them for food. The baby vine needs to find a host within a week to survive. It then grows into a spaghetti tangle that can even ensnare(trap) more than one plant.

Also known as strangleweed and witches' shoelaces, dodders are listed among the 10 worst weeds in the United States. They can cost farmers millions of dollars by stunting their crops.

To figure out how a type of dodder vine known to prefer tomato plants finds a victim, scientists placed dodder sprouts near several possible targets. These targets included pots of moist soil, little jars of dyed water that created coloured lights, young tomato plants, and even a cup of perfume made from chemicals that tomato plants give off.

Seedlings grew toward the tomato plant. They also reached out toward the cup of tomato perfume. They tended not to grow toward the moist soil or coloured water. The scientists then used a different setup, hiding the targets in chambers connected to dodder sprouts only by curving pipes, so the vine could find them only by smell. Dodder sprouts still grew toward their favoured targets.

By placing dodder sprouts near different plants, the scientists found that the type of dodder that they were studying prefers tomatoes and a flower called impatiens. And when given a choice between tomato and wheat, vine seedlings grow toward tomato. The researchers then tested seven of the ingredients that make up tomato perfume separately.

Dodder sprouts were attracted to three of them. One of these ingredients turns up in wheat perfume, but the wheat perfume also contains a substance that repels dodder sprouts. This chemical could offer farmers one way to fight the vine and save their crops.

- Science News for Kids