Weedy rice is an agricultural pest that has a worldwide economic impact. It is an aggressive weed that outcompetes cultivated rice, resulting in output losses worth billions of dollars worldwide. A study provides new insights into the genetic modifications that give weedy rice an advantage over cultivated rice in tropical places of the world.
Rice feeds the globe. However, a marijuana that resembles another has numerous advantages. Crop losses caused by weedy rice in the United States might feed an additional 12 million people each year.
A study from Washington University in St. Louis provides new insights into the genetic modifications that give weedy rice an advantage over farmed rice in tropical regions of the world. According to a study published in Nature Communications, one of weedy rice’s secret weapons is its promiscuity: it frequently crossbreeds with naturally present wild rice in the area.
This study was carried out by biologist Kenneth Olsen, the George William and Irene Koechig Freiberg Professor of Biology in Arts & Sciences, in collaboration with partners in China, Malaysia, and Thailand. The researchers examined whole-genome sequences from 217 wild, weedy, and cultivated rice samples and discovered that wild rice hybridization with weeds contributed significantly to the evolution of Southeast Asian weedy rice.
Our study highlights how adaptive introgression – in other words, gene flow – from wild species can contribute to agricultural weed evolution. We’ve known that this process occurs for some time. But this is the first study to provide a detailed genomic characterization of the phenomenon.
Kenneth Olsen
“In the case of rice, the barriers to gene flow between the crop and its wild relatives are quite low compared to other crop species,” Olsen said. “These porous borders in rice can facilitate the evolution and adaptation of weedy crop relatives.”
Overall, the genetic diversity of rice planted in Southeast Asia is higher than in the United States. There is a huge market demand for rice in this part of the world, and climate and environmental factors also play a role in the choices that farmers make when planting rice.
“Farmers in mainland Southeast Asia – including Thailand, Myanmar, and Vietnam – and most of the island regions of Indonesia, Philippines, and parts of Malaysia grow a wide range of lowland and upland rice varieties,” said B.K. Song, a Malaysian weedy rice researcher is another corresponding author of the new study. “These include modern elite varieties and traditional landraces.”
Southeast Asian rice farmers have moved toward using some of the same mechanized planting technologies that are used by industrial rice farmers in the U.S. today. But once in the ground, rice seedlings planted in Southeast Asia rub elbows with wild rice plants that are still found alongside cultivated rice fields today. This is something that doesn’t happen in U.S. rice fields.
“The common wild rice progenitor, Oryza rufipogon, is not present in the temperate zones, including the United States, northeastern Asia, and Europe,” Song said. “Crossing between cultivated and wild rice in U.S. fields is impossible.”
In their latest study, Olsen and his colleagues discovered that hybridization between wild rice and weedy rice in Southeast Asia has allowed some weeds to grow more suited as agricultural weeds, providing them a competitive advantage over cultivated rice plants. Some weeds, for example, are quite effective at disseminating their seeds in rice fields because they carry wild rice gene copies that lead seeds to shatter easily from the grain stalk.
The genomic results also revealed that Southeast Asian weedy rice developed its tricks via a variety of evolutionary pathways that ran concurrently, including some weeds that de-domesticated or became feral, after beginning as cultivated rice, as well as those that changed as a result of crossing with wild rice.
“Our study highlights how adaptive introgression — in other words, gene flow — from wild species can contribute to agricultural weed evolution,” Olsen said. “We’ve known that this process occurs for some time. But this is the first study to provide a detailed genomic characterization of the phenomenon.
“It’s important to recognize that crop domestication is an incremental evolutionary process and not a single-step event,” he went on to say. “Similarly, I believe we run the risk of oversimplifying the situation by classifying every rice plant as wild, weed, or crop.” The true dynamics are even more complex.
So, the global struggle against weedy rice continues as many fronts as there are fields.
Tonapha Pusadee, another research co-author, stated, “In Thailand, there are numerous methods for managing the weedy rice invasion in cultivated rice fields. For example, some farmers trim the panicles or use a chemical to remove weedy rice, which is taller than cultivated rice. Some farmers choose to keep the fields fallow for a few years.
