University of Arkansas Division of Agriculture researchers are working to determine if cross pollination between herbicide-tolerant rice and red rice will become a problem for producers.

Seeds of Stuttgart strawhull red rice that flowered at the same time with herbicide-resistant rice, in experimental weed control plots, are being screened for presence of resistant individuals among the offspring.

“Both plants are self-pollinating, so any cross-pollination would be low in occurrence,” said Nilda Burgos, weed scientist, Arkansas Agricultural Experiment Station. “But they are from the same genus and species, so they are genetically compatible.”

The study began when rice plants and red rice weeds flowered at the same time in a test plot at the Division of Agriculture's Rice Research and Extension Center near Stuttgart. The plots were part of an efficacy study, conducted by UA Ph.D. student Tomilea Dillon, for Clearfield rice and imazephapyr herbicide, marketed for resistant rice as Newpath. Clearfield, developed by breeders at Louisiana State University, is tolerant to imazephapyr.

“Because the plants flowered simultaneously, there was a possibility that cross-pollinization could have produced red rice with the herbicide-tolerant gene.”

A small percentage of the red rice plants survived the herbicide treatments, she said, and seeds from those survivors were planted in greenhouses at Stuttgart and Fayetteville. Burgos and Dillon treated those plants with imazephapyr and, again, some survived.

“The survival rates for these red rice plants was still small, between 0.8 percent and 0.04 percent,” Burgos said. “The next step will be a molecular study this spring to see if herbicide-tolerant hybrids were produced.

“The nature of rice and red rice plants is such that even if hybridization is possible, it will be at very low rates of occurrence and well within manageable levels.”

David Gealy, weed physiologist for the USDA Agricultural Research Service, will test for hybridization using genetic markers he has identified for rice primers. At the same time, Burgos and Division of Agriculture colleagues will develop gene-specific markers that would indicate if the survivor plants contain the herbicide-resistant gene.

If the plants are herbicide-tolerant hybrids, further tests will be conducted to see if the tolerant gene has any effect on the plants' hardiness; that is, would they be more or less likely to survive in nature.

Even if imazephapyr-tolerant red rice hybrids are possible, farmers will be able to manage the weeds with conventional production methods, Burgos said.

“Rotation with soybeans, which require different herbicide treatments, will still be an effective means of controlling red rice,” Burgos said. “At this point in our research, I'm confident that this is not an alarming development.”


Fred Miller is a science writer for the Arkansas Agricultural Experiment Station.