Clearfield Rice Was Game Changer

Steven Linscombe  |  9/22/2015 7:07:09 PM

Original mutated resistant line from which the Clearfield technology was developed.

The Rice Research Station has been in existence since 1909. During that 106-year history, there have been numerous examples of new technologies that have benefitted the Louisiana rice industry as a result of research conducted at the facility. Perhaps one of the best examples is the continual development of new, improved rice varieties made available to Louisiana rice producers. In its history, the research station has developed and released 50 new rice varieties. In the history of Louisiana rice production, the vast majority of acreage planted has been seeded with varieties developed at the station. Rice variety development always has been and always will be one of the primary research areas at the station.

However, one of the most important developments to come from the station in recent years has been the introduction of Clearfield rice. This technology has probably had more impact on Louisiana rice production than any other new technology that has resulted from the station’s research efforts. This technology allowed for the chemical control of red (weedy) rice in a rice production field for the first time ever. Red rice is a noxious weed in rice production and is a close genetic relative of commercial rice, actually belonging to the same taxonomic species (Oryza sativa) as cultivated rice. Because they are so closely related, it is extremely difficult to develop a herbicide that will kill red rice without injuring commercial rice if used in the same field.

In the 1990s, Dr. Tim Croughan, a researcher at the Rice Station, conducted research to create a mutant to solve this problem. He treated rice seed with the chemical ethyl methane sulfonate (EMS), which is known to cause mutations. He then subsequently grew out the treated seed and sprayed the resulting plants with the herbicide imazethapyr, which is known to kill both red rice and rice. After many attempts he had a plant that survived and later attempts yielded additional surviving plants. Through the use of the mutating agent (EMS), he had successfully developed rice plants resistant to imazethapyr herbicide.

Rice breeders at the Rice Station then took these mutated plants and through conventional breeding techniques developed agronomically-adapted rice varieties that could be grown successfully in Louisiana. However, these varieties contained the gene for resistance to imazethapyr herbicide. So now, rice fields where the soil was infested with red rice seed could be seeded with one of these varieties. Then both the seed of the planted variety and the red rice seed in the soil would germinate. The field could then be sprayed with imazethapyr herbicide, which would kill the red rice plants without harming the plants of the resistant variety.

Now for the first time ever anywhere in the world, the technology was available to kill red rice in a commercial rice field without harming the seeded rice plants. It took several years for the breeding work to be conducted and for the herbicide to be registered for use in rice by the U.S. Environmental Protection Agency. The technology was licensed under the name Clearfield and the imazethapyr herbicide used in the system is called NewPath. The first commercial production of Clearfield rice in Louisiana was in 2002.The use of this technology grew after the initial introduction, and by 2012, more than 65 percent of the rice acreage in the southern U.S. was seeded with Clearfield varieties and hybrids. Since 2002, the Rice Research Station has released nine Clearfield rice varieties (both long- and medium-grain) for use by Louisiana rice producers. This technology has dramatically improved yield as well as quality of the rice produced on many Louisiana rice fields.

In addition, this technology has changed the way many Louisiana producers grow rice. Prior to Clearfield rice, most farmers water-seeded rice as a means of culturally controlling red rice. With this system, a field would be flooded and then worked in the water with an implement to destroy any existing vegetation, including any germinated red rice. Sometime later, the field would be broadcast-seeded with an airplane. After a few days to allow for germination and growth, the field would be drained for a short time to allow the roots of the small seedlings to penetrate the soil. The field would then be reflooded before the soil was allowed to crack. The small rice plants would then be allowed to grow through the shallow flood. This system can minimize red rice by depriving the red rice seed in the soil of oxygen, which is needed for germination. This system only suppressed red rice at best and sometimes was not very successful in doing so.

With Clearfield technology, famers can dry-seed (drill or dry-broadcast) fields. Not only does this system do a much better job of controlling red rice, it also allows for a reduction of the red rice seed in the soil. Remember that the water-seeding system depended on preventing buried seed from germinating, where dry-seeding allows for red rice seed germination after which the NewPath herbicide kills the red rice plants.

There are other advantages of the dry-seeded system. In the water-seeded system, when the fields are drained to allow the seedlings to anchor into the soil, there was often a high level of suspended soil particles in the water that moved into the receiving stream. Not only could this increase sediment levels in the stream but could also sometimes significantly decrease the dissolved oxygen levels. This is typically much less of an issue with dry-seeding, which makes this system more environmentally sound. Under some conditions, the dry-seeded system also reduces the total amount of irrigation water necessary to grow the rice crop. Some seedling diseases are more common in water-seeded rice as well.

In summary, the availability of Clearfield rice has been a game changer in Louisiana rice production in more ways than one.

Permission granted September 15, 2015 by B. Leonards (LA Farm & Ranch) to republish article on www.lsuagcenter.com.
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