Undesirable variants preferentially thrive — and cross with cultivated rice, transforming the crop into weeds
There has been a lot of research, recently, showing how global change — especially warming — can alter the habitat and preferred range of marine and terrestrial species. But rising levels of greenhouse gases can also, directly, do a number on agricultural ecosystems, a new study shows. At least for U.S.-grown rice, rising carbon dioxide levels give a preferential reproductive advantage to the weedy natural form — known colloquially as red rice (for the color of its seed coat).
Agriculture Department scientists raised rice in controlled lab environments. They grew some in
The result was a diminishing of the value and quality of the cultivated rice — essentially transforming it into a weed, explains Lewis Ziska of the USDA Agricultural Research Service in Beltsville, Md. “That’s sort of the science fiction aspect of this,” he says. Likening it to Invasion of the Body Snatchers, “Whatever [seed] the good plant produces is now going to be bad seed.”
In theory, this flow of genetic traits could go in the opposite direction as well — moving genes from crop plants to the weedy rice. But in the new trials that didn’t seem to happen. It was a one-way gene transfer from the weeds to the crop plants, Ziska and his colleagues report May 23 in PLoS ONE.
And because some half of cultivated rice grown in the United States has been bred to resist the effects of the most widely used weed killer, any hybrid offspring — the bad seed — can now carry this trait as well.
Ziska’s group grew conventional rice crops in: 300 parts per million
For instance, the weedy rice began flowering earlier. Now its pollen production was in sync with crop plants (where previously, most feral rice had flowered too late to pollinate cultivated rice). In addition, the red rice grew taller stems and more flowers — each conferring additional reproductive advantages, since pollen production increased and its release from unusually tall stems allowed it to travel beyond the plant that produced it (most rice tends to be self-pollinating).
The ability of the feral rice to successfully cross with the crop plants tripled between the lowest and highest
In addition, hybrids in the new tests retained the crop plant’s genetic immunity to a weed killer. Indeed, Ziska says, the latter feature may partially explain the diminishing value of herbicide treatments on rice in recent years.
Last year, Carol Mallory-Smith and Elena Sanchez Olguin of Oregon State University in Corvallis reported that resistance to the widely used weedy-rice-killing herbicide imidazolinone was being witnessed in commercial U.S. fields. Moreover, the Oregon State team noted, the lifetime of dormant red-rice seed in soil far exceeds that of cultivated rice, allowing the resistant hybrids to easily survive to infest the next season’s crop.
“But we’re going to try to make lemonade out of lemons,” Ziska vows. If the weedy red rice outperforms currently cultivated rice in high-
C.A. Mallory-Smith and E. Sanchez Olguin. Gene flow from herbicide-resistant crops: It’s not just for transgenes. Journal of Agricultural and Food Chemistry. Vol. 59, June 8, 2011. p. 5813. DOI: 10.1021/jf103389v.
L.H. Ziska, et al. Recent and projected increases in atmospheric CO2 concentration can enhance gene flow between wild and genetically altered rice (Oryza sativa). PLoS ONE, Vol. 7, published online May 23, 2012, p. e37522. doi: 10.1371/journal.pone.0037522.