**Dodder (Cuscuta spp)**

Most projects in my laboratory involve plants in the genus Cuscuta. My students and I have been investigating dodder's host-searching behavior as well as its nutritional requirements.


Dodder on Salicornia	Dodder on Arabidopsis	Dodder on tomato

Natural history of dodders
This genus is composed of approximately 150 species, all of which are obligately parasitic (i.e., they are fully dependent upon a plant host for food, water, nutrients, and physical support). Mature vines are typically yellow or bright orange and superficially resemble cooked spaghetti with a light coating of orange tomato sauce. Despite their almost complete lack of chlorophyll and leaves, dodders are true flowering plants, and are closely related to morning glory. Because there there is no reliable way to kill dodder short of using a flame-thrower or acid sprays, it is a feared weed in farm settings. Many of the common names for Cuscuta reflect this agricultural importance: angel's hair, devilguts, devil's hair, devil's ringlet, dodder, goldthread, hailplant, hairweed , hell bind, love vine, pull down, stranglevine, strangleweed, tangle gut, witches' shoelaces. It's a bad plant, but good for experimenting on the mechanisms of host selection.

Upon emergence, the yellow, leafless seedlings begin counterclockwise circumnutation (twining) and sometimes (if they are lucky) make immediate contact with a host. When the host is far away, dodders have an eerie ability to grow toward a host, utilizing a variety of sensory cues. Emergence, circumnutation, and subsequent attachment to a host can be extremely rapid (view 200 MB time-lapse), at least for a plant. Dodder seedlings that fail to find a host die within approximately 10 days, although the exact time depends on humidity, temperature, and probably original seed size.

Dodder tendrils eventually puncture through host stems with modified roots called haustoria that begin as swellings (prehaustoria) on the concave surface of a coiling tendril (below). These haustoria are powerful enough to puncture tinfoil, and also have the ability to enzymatically degrade host stem tissue.

Once the stem surface has been breached, haustorial invaginations make connections with host phloem tissue (and sometimes also with host xylem), and then proceed to extract water, carbohydrates, and other solutes. Shown below is a stained cross section showing dodder (yellow tissue) parasitizing pigweed. The host is rarely killed, but always inconvenienced.