Relative values

日期:2019-03-07 06:09:10 作者:亓柰 阅读:

By Andy Coghlan UNLIKELY marriages between scrawny wild species of rice and their commercial relatives are boosting rice yields by a staggering 10 to 20 per cent. Researchers say this approach has also produced other unexpected benefits, including protection against a virus. The news has prompted calls from environmental campaigners to adopt the technique as an alternative to genetic engineering. “If you do it by natural methods, we have no problem with that,” says Benedikt Haerlin, Greenpeace’s genetic engineering coordinator in Berlin. “This could be extremely effective, and you don’t need to get genes from daffodils or microorganisms.” Susan McCouch of Cornell University, New York, explained the technique and unveiled her team’s results on 16 November at a conference organised by Nature Biotechnology in London. There are many thousands of known strains of rice, McCouch says, of which only 25 per cent are used commercially. Normally, plant breeders only exploit a “wild” trait, such as disease resistance, if it is obvious in the wild relative. McCouch, however, reasoned that the huge number of genes present in wild species should include some that would be useful to their cultivated relatives. So in the early 1990s, she and her colleagues started crossing wild species with no outward signs of valuable traits with good breeding lines of Oryza sativa, the rice species grown commercially. All commercial varieties of rice derive from two sativa subspecies, japonica and indica. Japonica varieties are favoured in China, Japan and the rest of Southeast Asia. They produce stubby, sticky grains. Indica varieties have longer grains and are generally grown elsewhere. “Mainstream colleagues told us it was preposterous to try crossing with wild relatives,” says McCouch. But by the mid-1990s, she had boosted yields of a valuable Chinese breeding line of sativa by 18 per cent after crossing it with a bizarre-looking wild rice species, O. rufipogon. “It’s native to Malaysia, grows 2 metres tall, and shatters easily, spilling its grains,” says McCouch. Since then, the programme has expanded, involving teams from Korea, Indonesia, Colombia, Brazil and the Ivory Coast. Now, McCouch is awaiting the results of crosses between a dozen sativa varieties and three wild species, including O. rufipogon. The other wild species— O. glaberrina and O. barthii—are from Africa. Preliminary findings from five crosses suggest that yields have increased by 10 to 20 per cent, McCouch said. And one cross turned out to be resistant to the Hojablanca virus, which devastates rice crops in Latin America, despite the fact that neither parent was resistant. McCouch thinks that there must be new interactions occurring between proteins and genes from the different parents, even though they succumb to the virus individually. The team is combing through the DNA of the hybrid plants to identify the genes that imparted the improved traits. “If you know what the gene sequence is, you can go back into the wild populations and look for more beneficial variations,