The Science Behind Shatter

Image by Pamela Smith

Shattering is an all-too descriptive name for what happens when soybeans pop from their pods prior to harvest. Just as the seeds plummet prematurely from their pods, so fall shattered hopes of yields and profits.

Unfortunately, the excessive moisture and delayed harvest led to plenty of instances of this problem in 2018. A tough seam holds the soybean pod together. Scientists call it the pod “suture.” The pod suture can withstand some normal wetting and drying in the fall. A soybean’s moisture can vacillate between 8 and 13% within a day, as the air temperature and humidity rise and fall.

But, the longer mature soybeans sit in the field, the more wetting and drying cycles they go through, and the weaker the pod and the pod suture can become, says Jessie Alt, a research scientist and plant breeder with Pioneer, now Corteva Agriscience. Anything that causes a bean to stand beyond its ideal harvest time will heighten the risk of shattering.

Soybean breeders have been battling to free soybeans from their tendency to shatter, but it is an inclination born from the plant’s fierce drive to reproduce successfully. Wild soybean plants actually evolved to self-seed by throwing soybeans as far from the plant as they could.

Breeding this out is a slow process, Alt notes. Unlike diseases or insects, shattering is difficult to induce in the field, and no single gene or group of genes controls it. Untangling this characteristic from the soybean’s germplasm is not a straightforward task.

“I’ve been doing this for over 20 years now, and shattering is something we work on every year,” she explains. “Shattering is a lot more like breeding for yield--you need lots of locations, different environments and replications to study it, and we continue to make nice, slow, steady progress.”

During the 2012 drought year, extreme heat and dryness led to abnormal shattering, Alt adds. But, in those cases, the pod is more brittle and more likely to launch seeds when it pops open. This year, pods opened slowly and many seeds hung for a period of time before dropping. Disease can also heighten the risk of shattering by compromising the plant’s health.


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