CORVALLIS, Ore. - Field tests have shown that a new system of planting different varieties of rice plants can dramatically reduce problems with the most important fungal disease of rice, with implications for greater rice production around the world and m ore food for literally billions of people.
Studies done in Yunnan Province of China, the results of which were just published in the journal Nature, show that losses to the fungal disease "blast" can be almost eliminated in some of the types of glutinous rice in which it was the most severe proble m, at times destroying entire crops.
"This approach was really a phenomenal success, much more effective than anyone predicted," said Chris Mundt, a professor of botany and plant pathology at Oregon State University and co-author on the study. "This is not a new concept, but it's a sound app lication of ecological principles to crop agriculture and it was astounding to see the scope of disease reductions that were a result."
It may also be possible to dramatically reduce the use of chemicals on a sustainable basis and significantly increase the income rice farmers are able to earn from the same area of land, researchers say.
Rice is a primary food and leading source of caloric intake for more than half of the world's population, and is clearly the most important single food crop on Earth.
But rice production has historically struggled with blast, a fungus that causes lesions on rice plants, reduces yields and in severe cases can kill the entire plant. Total crop losses are possible, especially when the crop year is unusually cool and wet, and a 20 percent loss in rice yield is routine, Mundt said.
Blast can affect either the glutinous, or more "sticky" varieties of rice, experts say, and the non-glutinous varieties that are the types most commonly sold in groceries around the world. Different varieties have been developed in attempts to find some t hat showed more natural resistance, but the fungus often overcame that resistance within a short time. And use of chemicals to control blast has become both pervasive and expensive, especially considering that this is a cheap, mass-produced crop for use a s a dietary staple.
Normally, rice producers in China might choose to produce about 20 percent glutinous varieties to meet market demands, Mundt said, but in some regions problems with blast have caused growers to almost give up trying to grow the glutinous rice varieties.
In the United States, Mundt is an expert on fungal diseases of crops. He has had considerable success mixing different types of wheat and barley varieties to reduce plant disease problems in those crops. When he spoke about these approaches to some crop s cience experts in China, they became interested in trying the same concepts with rice.
Researchers say that the blast pathogen specializes in particular "genotypes," or varieties of rice, some of which are glutinous and some of which are non-glutinous. During the past few years they used several known varieties of rice in one of the largest experiments on rice ever conducted, interspersing rows of one type of rice with other types to slow down the movement of blast fungi through the field.
The results amazed researchers. The yield losses to blast in glutinous varieties of rice dropped an average of 94 percent. The losses in non-glutinous varieties dropped by 25 percent the first year of the experiment and by 55 percent the second year.
"That's another part of this study that was so encouraging," Mundt said. "The results of the approach actually worked better the longer we did it and the more acreage on which the system was used. Some theoretical studies in the past have predicted that t he benefits of crop diversification should actually increase as the approach is used on a larger spatial scale, but this is one of the first large experiments to clearly demonstrate that concept."
Deep concerns over the problems with blast and desire for increased rice production in this province of China, Mundt said, caused growers to show an extraordinary level of voluntary cooperation with the experiments. The amount of land on which the approac h was tested quadrupled from the first year to the second year.
At the same time, growers who had been using fungicides from three to eight times a year to fight blast reduced their chemical use to a single treatment the first year of the experiment, and no chemicals used at all in the second year. Overall, gross inco me per hectare of rice in this region of China went up by an average of 15 percent, Mundt said, and this does not even include the substantial reduction in fungicide costs.
Collaborators with OSU on this research included the Yunnan Agricultural University, with funding support of $1.3 million over three years from the Asian Development Bank. The project was proposed and organized by the International Rice Research Institute .
"There's evidence and good reason to believe we can sustain these results," Mundt said. "Scientists will also continue to develop new, blast-resistant varieties of rice that should further assist with this approach of crop diversification. This should cle arly be good for the environment, good for rice farmers and a major step forward for feeding people around the world."