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A Pollination Moment
from Pollinator Paradise Farmer's Market E-mail reminders

9/14/2002
Deadly Nightshades

Would you eat a poisonous plant?  Of course not.  But you probably have eaten lots of relatives of poisonous plants.  The nightshade family contains some of the most poisonous plants known to man, but it also includes some of our favorites:  tomatoes, eggplants, peppers and potatoes!  The same family also includes plants that contain drugs such as nicotine, belladonna, atropine, and stramonium.   It even includes some favorite ornamental flowers:  Petunia and Nicotiana.

Whatever do all of these plants have in common?  Botanists organize plants into families based largely on the structure of their flowers and fruits.  So, one thing that many of the plants in the nightshade family have in common is a radially symmetrical flower with 5 lobes, often fused at the base to form a tube as in Datura and Nicotiana.  The flowers of tomato, eggplant, pepper and potato also have anthers fused into a central cone with a pore at the end where the pollen comes out.  Have a close look at the flowers of these crops next time you are in the garden.  They differ in color and size, but are similar in structure.

The best pollinators of tomato and eggplant are bees that "buzz" the flowers by rapidly vibrating their wing muscles.  Bumble bees and digger bees are able to use this buzz behavior, but honey bees can't.  The vibrations created by the buzz act like a tuning fork to shake pollen out of the anthers.  If you are in the garden when a buzz pollinator is present, you can hear her high-pitched sound, and you may see her sitting in the flower with her abdomen wrapped around the anthers to catch the pollen as it comes out the pores. 

Tomatoes are best pollinated by buzz pollinating bees, but many varieties will also self-pollinate if the wind shakes the flowers.  Thus pollination is not usually a problem for tomatoes grown outdoors.  In the greenhouse, however, growers used to have to pollinate tomato flowers by hand with a tuning fork, mimicking the buzz pollinators.  You can imagine how expensive that was!  Honeybees can be put in the greenhouse during the winter, but they don't like to visit tomato flowers because there is no nectar, just pollen.  Now, there are a few companies that use special technology to get bumble bee queens to continue laying eggs all year long, so bumble bee colonies can pollinate tomatoes in the greenhouse.  This makes tomatoes in the winter more affordable, but it also creates some knotty ecological problems.  Only one species of bumble bee is managed for pollination in the US, a species that is native to the eastern part of the country.  It is being introduced for greenhouse pollination in the west, but the risk of escape is great, and no one knows what effect this aggressive species may have on our native western bumble bee fauna.

So, enjoy your nightshade relatives now during the summer when they are plentiful and naturally ripe.  If you purchase them during the winter, consider the pollination issues that are involved in getting those red tomatoes to your winter table.

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September 14, 2002
Copyright 2002, Karen Strickler. All rights reserved.