Quirky Rice May Speed
Breeding of Improved Varieties
The accidental discovery of a quirk
in a variety of Chinese rice called Zhongxin No. 1 may be a boon to breeders of
this crop. The finding may help them produce new and better rice varieties in 5
years instead of the usual 10 or more, says Richard R.-C. Wang of the
ARS Forage and Range Research Laboratory
in Logan, Utah.
Wang and colleague Xiaomei Li, formerly with Utah State University at Logan,
are thought to be the first to uncover the oddity in rice. It's known as loss
of heterozygosity, or LOH. It occurs when second-generation offspring show
fewer gene combinations than might be expected.
A research geneticist, Wang uses rice as a model for finding important clues to
the genetics of rangeland grasses, which are relatives of rice. Rice is simpler
to investigate because it has fewer genes than many of its wildland cousins,
such as crested wheatgrass, wild rye, or Indian ricegrass.
Wang and other scientists in the Forage and Range Research Laboratory
investigate grasses and other hardy native and introduced plants that could be
used in the West to stabilize erosion-prone slopes, revegetate areas denuded by
wildfire, or provide nutritious, appetizing forage for livestock and wildlife.
Wang and Li examined the genetic makeup of hybrid plants made by colleague
Jiansan Chen of the Chinese Academy of Agricultural Sciences in Beijing. While
working as a visiting scientist at the Logan laboratory, Chen made the hybrids
by pollinating Zhongxin No. 1 plants with pollen from U.S. rice plants.
The Logan scientists found that the genetic makeup of some of the
second-generation hybrids remained fixed, or constant, in subsequent
generations. "That occurred sooner than expected," according to Wang.
This speed is potentially valuable. Here's why: It often takes many years of
plant breeding before combinations of valued traits, such as salt tolerance and
improved pest resistance, for example, can become fixed in offspring of rice
"When uniform second-generation plants show the traits breeders
want," explains Wang, "that means the laborious breeding process has
likely been streamlined from many years to just a few. That's how loss of
heterozygosity could turn out to be a valuable shortcut for breeding new rice.
Having a valued trait fixed into the plant's genetic makeup early in the
breeding process is a big savings of time and money."
LOH plants have fewer versions of genes from both parents than typical, or
heterogenic, offspring. The numerous combinations of genes that normally result
in heterogenic offspring can complicate breeding.
LOH, in contrast, results in a narrower range of combinations, so it can vastly
simplify the breeding process. "We don't know what controls this genetic
mechanism," notes Wang, "but we hope to find out so that we can put
it to work in breeding new plants for the future."By
Wood, Agricultural Research Service Information Staff.
This research is part of Rangeland, Pasture, and Forages, an ARS National
Program (#205) described on the World Wide Web at