The world's worst agricultural weed looks a lot like the rice plant with its green stems. Sadly, early growers of rice may be blamed for unwittingly giving the barnyard grass the edge to root itself as the perfect rice imitator. 

This new research conducted by a team of researchers from the Washington University in St. Louis and Zhejiang University, China's Academy of Sciences, releases evidence that the barnyard grass may have benefitted from the cultivation practices that old farmers used to engage in. Continuous hand weeding is one of the identified practices that may have caused the spread of such weeds along the Yantze River Region about a thousand years ago. 

The barnyard grass is known in the global agricultural community as a type of invasive weed that usually grows among row of cereals and crops. They used to be easily identifiable because of their red stems, but their evolution has made it even more challenging for farmers to tell them apart from their crops. This new study was published in the Nature Ecology and Evolution journal on September 16. 

"Asia is a continent of rice farmers who despite advancements in technology, prefer to weed their farmland with their bare hands. Any of the weeds that stick out are carefully identified and removed from the crops area," said Kenneth Olsen, a Biology professor in Arts and Sciences. "Over a hundred generations has passed yet the practice of hand weeding remains the same and in place. This practice, however useful it has been has allowed some strains of barnyard grass to specialize in growing in rice fields. In fact, they have evolved to closely mimic how the rice plant looks like that it has become challenging to tell them apart from the real rice plants. This practically saved them from detection and the possible pull out."

Olsen worked in collaboration with Longjiang Fan from Zhejiang University, the corresponding author of the study who has been working on a study particularly focused on the evolution of rice genomics and the evolution of the agricultural weed. They worked together on the interpretation and analyses of the data collected. 

This study worked with the sequenced genome of the weed that mimic the rice plant and compared it with the non-mimic type of the weed. This is the initial step they took to better understand how such Vavilovian mimicry occurred. It is characterized by the adaptation of weeds to make them look a lot like the domesticated plants.

"The advent of agricultural practices  about 10,000 years ago, humans have developed a habitat for these naturally growing weeds to exploit," Olsen said. "The most successful among these  agricultural weeds are those that have evolved to escape easy detection and continue to proliferate in what they consider a fertile new environment."

Olsen openly speaks of his speculation that since US rice farmers depend highly on mechanized methods of farming, it has become even more challenging for them to detect the spread of such weeds. 

"If farmers are not in the field to do the labor by hand, these weeds will only continue to grow and simply blend in."