Hand Pollinating Soybeans

The following Instructable will assist field workers in a soybean breeding program. Crossing (also called hybridizing) soybeans is very important to create varieties that provide farmers around the world with successful harvests year after year. Unfortunately, breeding between different individuals is not done in nature with soybeans; meaning insects or wind cannot do the job. This requires humans to do almost all of the work. Pollinating soybean flowers requires good eyesight and a steady hand to ensure success.  At first glance this process may appear to be complex---but as one works in the field the tasks quickly become second nature and the entire procedure can be done in as little as 2-3 minutes.

Several terms specific to plants are used in the subsequent text. Please refer to the following diagram in case a word is not clear. Soybean flowers are not incredibly different than other flowers you might see and it is relatively simple to pick out each part.

Photo Source: www.studyblue.com (diagram), http://extension.udel.edu (soybean plant)

Step 1: Materials Needed

1. Tweezers
2. Identification tag with twist tie
3. Pencil or marker
4. Small vial or petri dish
5. Male crossing parent
6. Female crossing parent
7. Kneepads (optional)
8. Magnifying glasses (optional)

Photo Source: http://www.nsrl.uiuc.edu

Step 2: Search for Bright Opened Flowers on Male Parent

Good pollen generally comes from flowers that open for the first time; petals’ colors will appear to be “cleaner” looking and healthier than others on the branches. Avoid browning or shriveled looking flowers as they tend to have lower quality pollen.

Photo Source: www.nsrl.uiuc.edu

Step 3: Gently Use Tweezers to Completely Remove Flower From Plant

In a pinching motion grab the end of the flower beneath where the green sepals are located. Avoid violent ripping of the bud that could damage the anthers and/or lose pollen.

Photo Source: http://www.nsrl.uiuc.edu

Step 4: Remove Petals One by One Until Anthers Are Seen

Use a peeling motion to carefully remove each colored petal. The anthers should be clearly seen, forming a ring around the female style and stigma.

Photo Source: Dr. Reed Palmer, USDA-ARS

Step 5: Test Pollen Amount Using a Fingernail

The anthers will contain a sufficient amount of pollen if yellow powder is left after gently tapping the flower once onto a fingernail.

Photo Source: Dr. Reed Palmer, USDA-ARS

Step 6: Place the Altered Flower Into a Vial or Petri Dish for Later Use

The male pollen located on these anthers will be used to fertilize the female crossing parent. Ensure the vial or coin bag is clearly labeled to avoid possible loss or confusion.

Photo Source: commons.wikipedia.org

Step 7: Locate Unopened Bud on Female Parent

Determine whether this bud’s female parts are mature by gently peeling off one sepal. If you can see the color of the petal the flower is ready to be crossed.

Photo Source: http://ipm.missouri.edu

Step 8: Remove Neighboring Buds or Open Flowers

This step is to help researchers later in the year identify which flower has been crossed and check to see if the process worked. Having multiple bean pods makes this aspect difficult.

Photo Source: Dr. Reed Palmer, USDA-ARS

Step 9: Tweeze Remaining Sepals on Selected Bud

Peel each sepal separately so that one can clearly see the petals beneath.

Step 10: Remove Petals One by One

Aim for having the tweezers grasp the tops of the petals. Grabbing below or on the middle has a high chance of damaging the important female parts. Additionally, using the tweezers as a wedge may assist you as you remove each petal. Refer to the picture to see how the flower should look like after the petals and sepals are removed.

Photo Source: http://ipm.missouri.edu

Step 11: Rub Male's Anthers Onto Female’s Stigma

Act as though the male’s anthers are paint brushes and “coat” the stigma with pollen.

Step 12: Record Parents on Tag

Female parent’s ID is left, followed by an “x” and then the male plant’s ID. Other numbers or subjects may be included. Please check with the supervising scientist for help regarding specifics.

Photo Source: Dr. Reed Palmer, USDA-ARS

Step 13: Tie Wire Tag One Branch Above the Recently Crossed Female Flower

Again, this will help future plant breeders recognize exactly where the cross was tried. However, this step may vary among breeding programs so ensure you are placing the tag correctly.

Photo Source: Dr. Reed Palmer, USDA-ARS

Step 14: Conclusion

If the hybridization was effective, in a few months you should see a bean pod with no sepals and a slight brown scar around its base. Later on, this seed will be used in further study and experiments, gradually removing bad varieties until a final high quality product is sent to the farmer for field planting.

Photo Source: Dr. Reed Palmer, USDA-ARS

Listed below are other sources where you can find more information regarding the biology/production of soybeans:

Iowa State Soybean Extension
USDA Profile for Soybean