By Wendy Langhans
Fresh, ripe, jucy tomatoes. I’ll bet, if close your eyes right now, you can recall the smell. Maybe, your mouth is watering just a little bit too. But we’re not the only living things that are attracted to the scent of ripe tomatoes. Their smell also attracts certain plants. Plants? Yes - specifically - dodder plants.
According to University of California’s Integrated Pest Management Program , there are about 150 different species of dodder worldwide. It is estimated that each year, dodder costs California farmers $4 million in reduced tomato crops. Dodder is a parasitic plant - the green equivalent of Dracula. When dodder seeds sprout, they do not put down roots into the soil. Instead, their stems lengthen, twist and turn and seek out a nearby host plant. They attach their root-like haustoria to the host’s stem, penetrate it, and suck out water and nutrients.
But a dodder seedling has only a limited amount of time to find and attach itself to a plant. “A dodder seedling can survive several days without a host, but if it doesn’t come into contact with one within 5 to 10 days, the seedling will die.” So how does dodder find a tomato plant? By sniffing it out.
During photosynthesis, tomato plants release watery vapor through the process of transpiration . This vapor also contains volatile (perfume-like) chemicals, which are recognized by dodder (and hungry humans).
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Scientists at Penn State  discovered that dodder “has the ability not only to recognize its prey by scent but also to move toward it with a remarkable accuracy and efficiency.” As described in this NYT’s article , they “extracted volatile chemicals from the tomato plants and found that the dodder shoots would grow toward the chemicals even in the absence of a plant.” To watch a dodder seek out a tomato plant, check out this short video .
These researchers  also discovered that “another chemical compound from wheat actually repels the dodder seedlings”. Perhaps I should consider saving the water I use to boil pasta. Who knows, it might be useful for watering my tomato plants - the “Green Dracula” equivalent of garlic.
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