Fungal friend. Arbuscular mycorrhizal fungi produce hundreds of spores, such as the ones shown here, just outside the roots of a plant

Shannon Schechter

Better Rice Through Fungi

More than 80% of plant species make friends with a common fungus. In return for sugar, the fungus helps the plants extract nutrients from the soil. But rice plants, a primary food source for billions of people, don’t have this special relationship—and thus they don’t receive the extra boost the fungi give other plants. A new study suggests that with a little help from researchers, however, the fungus will bond with rice, increasing the plant's growth rate by up to five times.

Plant pathologist Ian Sanders hypothesized that some spores of the fungus—known as arbuscular mycorrhiza—do like rice but that they are essentially genetically out-voted by their brethren. Each fungal spore has a unique genetic makeup, he and colleagues found in previous research, so some spores may be more genetically predisposed to team up with rice than are others.

To find out if this was really the case, Sanders and colleagues at the University of Lausanne in Switzerland collected single fungal spores from fields near Zürich and cultivated them in the lab. When the fungi had matured, the researchers extracted individual spores from each parent and grew them for three generations.

The researchers then added spores from each generation to rice plants. They found that the third generation of fungi—the grandchildren—increased the plants’ growth rate by two to five times more than the other generations. Although the scientists aren’t sure why only the grandchildren had this effect , it’s likely due to the third generation’s greater genetic variability, which the scientists were able to achieve by growing individual spores in the lab, says Daniel Croll, a co-author of the study who now is an evolutionary biologist at the Swiss Federal Institute of Technology in Zürich, Switzerland. The researchers report their findings online today in Current Biology.

“It’s encouraging that the genetic manipulation of these cosmopolitan organisms could have an impact on crop production,” says James Correll, a plant pathologist at the University of Arkansas, Little Rock. But, he cautions, there are still many unanswered questions. “Even though you might show an increase on crops in a greenhouse, it may not translate to field conditions,” he says.

The researchers acknowledge that the work is far from field ready. In addition to more greenhouse studies, they plan to study the impact of the manipulated fungi on the growth rate of another food crop—cassava, a shrub whose leaves and roots are a staple for some 500 million people across the world. That study should begin in Colombia next year.