Impact of Rice Variety Development — Changes, Challenges, and Future.

Rough rice grain yield is the economic trait that has had the most genetic gain in the last 25 years.  The genetic contribution of the Arkansas rice-breeding research program was measured to be 17% by quantifying the increase in yields attributable to genetic enhancements in rice for the period 1983-2005.  The varieties released by the University of Arkansas rice breeding program experienced an increase in annual yield, and a decrease in yield variance.  In the southern rice growing states Arkansas, Louisiana, Mississippi, Missouri and Texas the average yields have increased by approximately 2289 kg ha-1 from 5071 kg ha-1 in 1984 to 7361 kg ha-1 in 2008.  This represents a 45% increase in on farm yields in the Southern US.  In California (1984-2008) the yields have increased by 998 kg/ha from 7974 kg/ha to 9318 kg/ha representing a 13% increase in on farm yields.  Another key economic trait in rice is milling yield (mg g-1 whole kernel:mg g-1 total milled rice) at 120 mg g-1 moisture.  This trait has been relatively constant over the last 25 years in the United States.   New technologies have been introduced in rice breeding including the Clearfield technology, hybrid rice and, more recently transgenic rice.