March 22, 2023

Two genetic pathways that result in ‘weedy rice’ recognized by researchers

Weedy rice, generally known as pink rice, is a expensive downside that impacts producers in Arkansas every rising season. Weeds scale back grain high quality and affect yield which might result in tens of millions of {dollars} of misplaced income every rising season.

Scientists might have now made headway in figuring out why some kinds of rice are extra herbicide-resistant than others which results in extra weeds. Researchers in Arkansas and Missouri have confirmed two genetic pathways that result in herbicide resistance in weedy rice.

Most herbicide-resistant weedy rice in Arkansas inherited the trait by way of gene movement from herbicide-tolerant cultivated rice varieties, stated Nilda Burgos, professor of weed physiology and molecular biology for the Arkansas Agricultural Experiment Station. However some weedy rice developed the resistance independently because of steady use of particular herbicides.

The Agricultural Experiment Station is the analysis arm of the College of Arkansas System Division of Agriculture.

Weedy rice is a significant downside in Arkansas, which produces almost half the rice grown within the U.S. In 2020, rice contributed greater than $1.1 billion to the state’s agricultural financial system, in keeping with the 2022 Agricultural Profile revealed by the Division of Agriculture.

Arkansas produces about half the nation’s rice. However this yr’s crop is projected to be down from current years because of enter price hikes and different components. Planted acreage this rising season topped 1.11 million acres, in keeping with the U.S. Division of Agriculture’s Nationwide Agricultural Statistical Service (NASS).

All rice manufacturing for the state is forecast at 81.2 million hundredweight, down 5% from the August forecast and down 11% from final yr’s manufacturing of 91.1 million hundredweight, NASS reported. The all-rice yield for 2022 is forecast at 7,500 kilos per acre, down 50 kilos from August and down 130 kilos from final yr.

Weedy rice infestations trigger an estimated $45 million in financial losses within the U.S. annually from yield losses and lowered grain high quality, in keeping with a analysis paper co-authored by Burgos and her collaborators at Washington College. Losses quantity to a whole bunch of tens of millions of {dollars} worldwide.

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Weedy rice is identical species as cultivated rice, Burgos stated. As a result of they’re so intently associated, the cultivated and weedy crops can cross pollinate within the subject, an motion known as “outcrossing.” By this motion, often known as gene movement, weedy rice can get hold of genetic traits from its extra civilized relative.

One of many modifications gene movement made to the weed is that pink rice is not at all times pink nor at all times medium grain, therefore its new moniker.

The potential for outcrossing raised concern for the event of herbicide resistance in fields generally planted with imidazolinone herbicide-tolerant rice varieties, Burgos stated. Often called Clearfield varieties, they permit farmers to plant their fields after which apply herbicides to kill weedy rice and different weeds with out harming their crops. Imidazolinone herbicides are generally known as ALS herbicides as a result of they kill weeds by inhibiting acetolactate synthase, a key enzyme in plant development.

Burgos recognized ALS herbicide-resistant weedy rice in some Arkansas fields at the very least 20 years in the past, about the identical yr Clearfield know-how was launched. These resistant weeds have been collected from a subject that had by no means earlier than been planted with Clearfield rice.

Burgos collaborated with Washington College Ph.D. scholar Marshall Wedger, now a postdoctoral researcher there, and his graduate advisor, Kenneth Olsen, professor of biology, to determine the pathway to resistance for weedy rice in Arkansas. The query they wished to reply was whether or not the resistant weeds Burgos recognized in Arkansas fields resulted from outcrossing or from evolutionary stress attributable to fixed herbicide functions.

Wedger is the lead creator of a analysis paper co-authored by Burgos and Olsen about their findings. It has been revealed within the Nature on-line journal, Communications Biology.

Whereas a Ph.D. scholar, Wedger acquired a Graduate Fellowship Grant from the Nationwide Science Basis to analyze the genetic mechanisms of resistance in weedy rice. He got here to Arkansas and Burgos helped him acquire seed samples from six Arkansas farms the place she had recognized ALS resistance in weedy rice.

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Burgos grew the seed and examined the crops for ALS resistance. She recognized the resistant weeds and scored their degree of resistance. The identical samples have been shared with Wedger at Washington College.

Wedger used whole-genome sequences of 48 weedy rice crops to point out how herbicide resistance advanced by gene movement from crop rice. Nearly all different instances of herbicide resistance in agricultural weeds end result from collection of tolerant crops within the weed inhabitants.

Burgos stated managed crosses, utilizing related marker traits, and whole-genome sequencing may observe which route gene movement is happening. “Analysis has proven that the dominant gene movement is from the crop to the weed,” she stated.

“Prior to now 20 years, weedy rice has gone from being very genetically distinct from U.S. crop varieties to these days largely being derived from crop-weed hybridization,” Olsen stated. “The weeds are grabbing sure traits from the crop which might be useful to them, together with herbicide resistance.”

“As a de-domesticated weedy relative, weedy rice has at all times been in a position to outcross with cultivated rice. Based mostly on our outcomes, this capability to interbreed is what led to many of the herbicide resistance that we see immediately,” Wedger stated.

Burgos stated their findings affirm what she present in rice fields some 20 years in the past. “It’s like déjà vu. I’ve seen this earlier than,” she stated.

“A lot of the resistance was decided to come back from outcrossing with Clearfield rice,” Burgos stated. “However we found a low frequency of resistant weedy rice attributable to herbicide stress.”

Wedger’s whole-genome sequencing was in a position to distinguish between resistant weedy rice that resulted from outcrossing with cultivated rice from people who resulted from one other mechanism. Outcrossing resulted in different shared genetic mutations moreover the herbicide resistance, Burgos stated. The absence of these secondary shared mutations indicated when resistance got here from herbicide stress.

The sort of herbicide pressure-induced resistance happens when ALS herbicides are used repeatedly on a subject. Weedy rice that’s not killed by the common functions spreads its seed, producing extra weeds that may tolerate the herbicide functions. The method continues till there’s a secure inhabitants of herbicide-resistant weedy rice.

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Burgos stated the unintentional improvement of herbicide-resistant weedy rice by herbicide stress resulted in the identical mutation occurring within the weeds that offers Clearfield rice its resistance. Nevertheless, different genetic mutations present in Clearfield rice weren’t shared in these weedy rice crops, indicating they didn’t end result from outcrossing.

“This implies there are two pathways to the mutation that ends in ALS herbicide resistance,” Burgos stated. Intensive use of ALS herbicides to manage weedy rice in different crops utilized in rotation with rice may result in resistance even when ALS-resistant Clearfield varieties usually are not planted within the rotation.

The report’s authors agree that adaptation of weedy rice to herbicide utility serves for instance of the risks of counting on single strategies of management for agricultural pests.

“How rapidly a resistant weedy rice inhabitants builds up to some extent the place the herbicide is not helpful depends upon how the producer manages the herbicide-tolerant rice know-how,” Burgos stated. “There are finest administration practices pointers that assist growers keep away from resistance evolution for a very long time, if carried out.”

Avoiding a buildup of herbicide-resistant weedy rice begins with zero tolerance weed administration, Burgos stated. “Don’t go away something in your subject. And don’t overlook the perimeters of the fields.”

Growers often clear up their fields totally, however some neglect the perimeters and ditches, Burgos stated. The next yr, weedy rice sprouts up on the borders of rice fields and spreads in from the perimeters.

Additionally, weedy rice seed that drops in water within the ditches will get carried to different areas and might sprout up wherever.

Rotating Clearfield rice with standard varieties may gradual gene movement and inhibit improvement of herbicide-resistant weeds, Burgos stated. Rotate rice with different crops, like soybeans, and the completely different weed management methods used with these crops may help maintain rice fields clear. She additionally advises rotating weed management methods.

“Ensure, no matter you employ, you allow no weedy rice within the subject,” Burgos stated.