Friday, January 30, 2015

The International Rice Genebank: a galaxy of rice traits awaits full exploration

LOS BAÑOS, Philippines - The International Rice Genebank housed at the International Rice Research Institute (IRRI) is a virtual universe that contains most traits rice breeders need, according to Ruaraidh Sackville Hamilton, an evolutionary biologist who provides scientific leadership in the genetic conservation of rice.

“The diversity in the Genebank is massive,” Dr. Sackville Hamilton said during his presentation at the recently concluded IRRI-Global Rice Science Partnership (GRiSP) Asia Science Week, held here from 26 to 30 January. “There is diversity for almost every conceivable trait, almost every conceivable development objective,” he added.

Case in point: early-flowering rice.

Increasing average daytime temperatures is one way climate change is affecting rice production. Rice scientists at IRRI have determined that extremely higher temperatures, particularly during the flowering stage, are associated with lower yields. In most rice varieties, the peak of flowering takes place between 09:30 and 11:30 in the morning when the temperature is well on its way up. Even an hour’s exposure to heat stress at this time can be sufficient to induce sterility— and temperatures above 36°C can cause inadequate pollination resulting in empty panicles.

One proposed solution for this problem was developing rice varieties that flower earlier in the day when temperatures are cooler. “Everyone said there was no early-flowering trait in rice,” Dr. Sackville Hamilton said. “But Greg Howell, former IRRI plant physiologist, and his team found it.”

Ironically, the Genebank’s strength—the genetic diversity it holds—also presents some challenges. “The problem we face is the huge amount of diversity that we have in the Genebank,” he said. “We don’t know which accessions contain the genes breeders need, and finding them is often difficult.”

Screening this vast collection for particular traits is very labor intensive. Finding the desired trait isn’t as straightforward as looking for a needle in a haystack. That would be easy. It’s really more like looking for a needle that may not even be in a haystack. Or looking for a needle in a haystack of objects that look pretty much like needles. Dr. Howell and his team painstakingly combed through 4,200 domesticated and wild rice types at the Genebank, spending numerous hours observing the samples, and found the early-flowering trait in 590 accessions.

Currently, the Genebank provides breeders with many accessions to evaluate. But usually they can only afford what Dr. Sackville Hamilton calls a “quick and dirty” phenotypic screening. “It is not surprising that very few accessions get past the breeders’ initial screen,” Dr. Sackville Hamilton said. “We have been distributing 30,000 to 40,000 samples a year for evaluation since 1985. About 85% of the accessions (types of rice) have been evaluated at least once, but only about 5% have actually been incorporated into breeding programs."

“In the future we need to work on building the system to estimate breeding value from genotype, and then we will be able to feed more detailed knowledge to the breeders,” he said.

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