by Georgia Moore
Parents worldwide hope their children will bear the best traits from each side of the family -- the genes for a certain eye or hair color, "brains" or ability.
But when researchers crossed two varieties of rice -- one from United States , the other from China -- they got much more than they expected in the hybrid offspring: a rice plant with increased photosynthesis and, therefore, dramatically increased yields.
"We have finally been able to successfully increase photosynthesis -- and couple that with an increase in yield," said Clanton Black, a UGA research professor of biochemistry. "I think we are the first people ever to do that successfully."
During five years of field testing in China and two in Arkansas, the Oryza sativa rice hybrid consistently has produced more than 20 percent higher yields than the average of the parent varieties, Black said. Last year, the hybrid crop set near record yields of 208 bushels per acre in Arkansas, where rice farmers usually expect half that amount.
One of Black's former students, Zeng-Ping Tu, bred the hybrid while in China. Tu's goal was to combine selected traits of both parents to produce a rice plant that would grow in a wide range of environments, from flat coastal areas to mountain foothills. That's why Tu chose to cross a standard commercial rice of good quality from a monsoon climate with one from the coast of Texas.
"It is a broadly adapted plant, but much more broadly adapted than Mr. Tu anticipated," Black said, referring to the plant's increased photosynthetic ability.
Photosynthesis enables plants to capture energy from light and convert it to sugar for maintenance and growth. Scientists have long searched for a way to make the process more effective.
Black, who grew up on a central Florida farm, said he's spent much of the past 35 years seeking the solution. The unexpected increase in photosynthesis in Tu's rice hybrid placed the researchers a step closer.
Most plants undergo a "midday depression" in photosynthesis to protect themselves from the brunt of the sun's intensity. But the hybrid is different.
"There is some small midday depression, but the hybrid avoids the strong inhibition of photosynthesis during the middle of the day," he said. "That means [the plant conducts] more photosynthesis and it's sort of like more interest in the bank. You're making more interest, so you grow a little faster."
The hybrid can avoid the midday depression because it contains a greater amount of carotenoids -- yellow pigments that are able to absorb light energy and dissipate it without the formation of harmful products -- than its parents.
Additionally, the hybrid increases by eight to 10 days the life span of the "flag leaf," which forms under the rice grain and produces photosynthetic products like sugar that nourish grain formation. The hybrid also develops a canopy of leaves for increased light interception more rapidly than its parents.
"It puts out what I like to call a green umbrella over the soil so that it gets the area covered in and gets maximum light interception," Black said. "Since it can do this faster, the whole plant grows quicker."
The hybrid's overall life span is six to 12 days shorter than its parents, perhaps because it grows faster and therefore completes its life cycle in less time, he said.
So far, researchers have not observed any problems with the hybrid, only benefits, Black said.
"The folks in Arkansas this year put it through quality testing, and the man who did it said it was right up there with the highest quality rices he'd seen," Black said.
In addition, the hybrid is very resistant to blast disease, a fungal disease that poses a big problem for farmers in some regions, such as the mountainous areas of China.
The hybrid currently is available in China, and several companies in Arkansas are interested in field testing it for possible marketing in the United States.
It is hard to predict, though, what impact the hybrid might have as a cash crop because rice is the most locally consumed crop in the world, Black said. Ninety-six percent of rice is consumed where it is grown, so only a small portion of the world's rice ever reaches the world market. Still, rice is the main staple of a large portion of the world's population, he added.
"If you make 20 percent more rice, you could sell more in town or on the export market," he said. "You might eventually observe that happening, but I think that's way down the road."
Even though the hybrid's economic impact may lie in the future, its scientific impact is immediate and important, Black said.
"Other hybrids could be made in a similar fashion by taking parents that have traits that are useful -- photosynthetic-type traits or yield traits -- and making other crosses," he said. "We're doing more of those crosses now with rice. You can extrapolate this to any number of crops."