Unlike many human brothers and sisters, plant siblings appear to do their best to get along, sharing resources and avoiding competition.

In a study of more than 3,000 mustard seedlings, scientists discovered that the young plants recognize their siblings — other plants grown from the seeds of the same momma plant — using chemical cues given off during root growth. And it turns out mustard plants won't compete with their brethren the way they will with strangers: Instead of rapidly growing roots to suck up as much water and minerals as possible, plants who sensed nearby siblings developed a shallower root system and more intertwined leaves.

"It's possible that when kin are grown together, they may balance their nutrient uptake and not be greedy," plant biologist Harsh Bais of the University of Delaware said in a press release. The work will be published in an upcoming issue of Communicative and Integrative Biology.

Two years ago, co-author Susan Dudley of McMaster University in Canada observed a similar pattern in the sea rocket, a common seashore plant that also appears to favor its siblings. But the initial studies of kin recognition have been criticized for failing to control for complicating factors, such as resource depletion caused by competition between the unrelated plants. And until now, the researchers didn't know how plants managed to identify their kin.

As seedlings grow, their developing root system gives off a variety of chemical signals, and the researchers guessed that these secretions might play a role in sibling recognition. To test their theory, the scientists grew wild Arabidopsis thaliana in a sterile liquid containing root extracts from sibling plants, unrelated plants or their own roots. Because each plant was grown in a highly controlled setup, the researchers could be sure any changes in growth were due to differences in the root extracts.

As shown in the time-lapse videos below, the seedlings exposed to root secretions from unrelated plants grew significantly longer and more elaborate root systems than those grown in secretions from their siblings. The top video shows unrelated plants, while the bottom one shows siblings.

However, when the scientists blocked root secretions using a chemical called sodium orthovanadate, the differences disappeared, suggesting that the sibling identification system indeed depends on chemicals released by growing roots.

The researchers say their results may have significant implications for farming and agriculture. Although no one knows for sure how sibling recognition would affect crops grown in large monocultures, some researchers think that decreased competition among plants from identical seeds may make monocultures more susceptible to insects and disease.

However, Bais says that the effect of growing a plant with its siblings is likely to be species-dependent, as initial studies have been contradictory. "There is a possibility that the explanation of the trade-offs is not that simple," he wrote in an e-mail. "We have found that plants could resist pathogens better when grown with siblings compared to strangers, so I would take this with caution and not stretch it to all the plant species."

Regardless of how sibling recognition affects agriculture, it may be an important consideration for the home gardener.

"Often we'll put plants in the ground next to each other and when they don't do well, we blame the local garden center where we bought them or we attribute their failure to a pathogen," Bais said in the press release. "But maybe there's more to it than that."

Photo: An Arabidopsis plant.

BlueRidgeKitties/Flickr

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