Stuttgart, Arkansas, USA
December 6, 2010
University of Arkansas Division of Agriculture research on the effects of high nighttime temperatures on rice grain yield and quality has identified genetic differences in rice varieties that were less affected by the heat than other varieties. The findings could lead to future development of more heat-tolerant rice varieties, said Paul Counce, a plant physiologist based at the Division's Rice Research and Extension Center near Stuttgart.
The summer of 2010 was the hottest on record in Arkansas, as measured by average daily temperatures over a 24 hour period, Counce said. The difficulty of keeping fields adequately irrigated contributed to the lowest statewide rice yields since 2001, which the U.S. Department of Agriculture estimated at 142 bushels per acre. Another likely factor was high nighttime temperatures, Counce said. Rice millers also reported that grain quality was significantly below average.
Research in the Division of Agriculture's Rice Processing Program on the effect of high temperature on rice yield and quality has identified genes that appear to be associated with tolerance to high temperatures, Counce said.
It has been documented that the flowers on rice plants do not open properly when the temperature is above 95 F, which hinders pollination and results in blank hulls with no grain inside and smaller, lighter kernels, Counce said. However, nighttime temperatures are usually moderate during flowering in late spring or early summer.
Research over several years by Counce and others in the Rice Processing Program has documented that blanks and lower-quality kernels can also result from high nighttime temperatures during the grain-filling stage in mid-summer, which occurred frequently in 2010.
The research team studied the genetic coding of enzymes that carry out the grain filling process and found that the enzyme starch synthase appears to be most affected by nighttime temperatures. In one of the rice varieties least affected by high night temperatures, the genes that code expression of starch synthase were relatively unaffected by night temperature, Counce said.
These findings suggest that it might be possible to incorporate specific genes for increased tolerance of high night temperatures into future rice varieties, Counce said.
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