Provisia Rice Will be Valuable for the Louisiana Rice Industry

Steve Linscombe

LSU AgCenter

H. Rouse Caffey Rice Research Station/Southwest Region

Provisia rice will be an important asset for the Louisiana rice industry. This technology will provide a second source (along with Clearfield technology) for the control of weedy rice in a commercial rice field.

Since rice production began in the late 19^th century in the coastal prairies of southwest Louisiana, one of the biggest constraints to production has been red (weedy) rice. Red rice is a noxious weed in rice that causes yield and quality reduction, exacerbates lodging and harvest difficulty and makes for a very unsightly production field. One significant difficulty with red rice is that it is very closely related to commercial rice, belonging to the same species –Oryza sativa.

This means that it has been essentially impossible to develop a conventional herbicide that will control red rice and not harm the commercial crop. However, what if you could develop a type of rice that is resistant to a herbicide that will normally kill rice as well as weedy rice?

This is exactly what was done over 20 years ago. Dr. Tim Croughan, who is retired from the rice station, approached this by using mutation breeding. This is where rice seed are exposed to an agent that will cause changes in the DNA. Dr. Croughan exposed billions of rice seed to a chemical that is known to cause mutations, then planted these seeds and sprayed the resulting plants with a herbicide called imazethapyr which was a soybean herbicide at that time known to kill rice. After several years of these efforts, he found rice plants that were not killed by the herbicide. These plants were used to breed varieties that could be sprayed with imazethapyr which led to the development of Clearfield rice technology. This technology is based on the use of these resistant varieties and imazethapyr (trade name NewPath) herbicide. Later a similar herbicide, imazamox (tradename Beyond) was also labeled for use with this technology. The Clearfield technology was first made available for Louisiana rice producers in 2002 and has become a very important part of our rice system. Over the last ten years well over 50% of the Louisiana rice acreage has been planted with Clearfield varieties where NewPath and Beyond herbicides can be used to control weedy rice and other weeds.

This technology has allowed our rice producers to dramatically change the way they grow rice. Prior to this technology most Louisiana rice was water-seeded as a means of suppressing germination of red rice seed in the soil. Now our producers can dry seed and encourage red rice germination because they have herbicides that can kill it. There is, however, a major issue with this technology that stems from the fact that the commercial crop and weedy rice are so closely related. Rice and red rice can cross, which means that pollen from a Clearfield rice variety can pollenate a red rice plant (or vice-versa) which can then create a weedy rice plant that is also resistant to these herbicides. This has occurred over the years and has led to many fields having such a high population of resistant weedy rice, that the Clearfield technology is essentially ineffective for controlling red rice.

How can this be addressed? How about developing a different herbicide resistance system that is based on a different herbicide that will also kill red rice including those plants that contain the Clearfield gene.

This is exactly what Provisia rice is. It is also based on mutated rice plants that are resistant to a herbicide that will kill non Provisia rice. In this case the herbicide is quizalofop which is also an older soybean herbicide. Provisia technology was developed by BASF. The original mutated rice plants that are resistant to Provisia herbicide were not agronomically and grain quality adapted for Louisiana rice production. BASF provided these original plants to the rice station breeding program about 4 ½ years ago to allow us to incorporate the resistant gene into rice varieties adapted for Louisiana production. The first of these varieties (PVL01) was grown for seed on about 1,200 acres in the southern U.S. this year. The Provisia herbicide was recently labeled by the USEPA for use in rice so the technology will be available on a limited basis in 2018. PVL01 will be a good introductory variety for use with this technology. While its yield potential is not as high as our best current varieties, it is acceptable and the variety has outstanding grain quality. The variety is susceptible to blast disease and an effective blast fungicide properly timed will be needed when growing the variety.

The introduction of Provisia rice technology will be very important to the Louisiana rice in the future. Having two different herbicide resistant technologies that will allow for rotation should extend the overall life of weedy rice control well into the future.

This project was partially supported by USDA National Institute of Food and Agriculture.

Permission granted September 15, 2017 by B. Leonards (LA Farm & Ranch) to republish article on www.lsuagcenter.com.

A seed production field of PVL01.