US researchers said Tuesday they have found a resistant strain of wheat that can reduce nematode numbers in soil and protect the next rotation of tomato plants.

Root-knot nematodes cause crop losses around the world, and they can be difficult to control. Once they are present in soil, they can survive winter in a fallow field and infect plants during the next growing season.

The resistant wheat, however, serves as a trap crop to trick the nematodes into starting their life cycle but then prevents them from reproducing, according to researchers at the University of California, Davis, who described it in the journal Crop Science as "a better option than leaving the field fallow."

"Once nematodes commit to being a parasite, they have to complete their life cycle," Valerie Williamson, lead author of the study, said in a statement. "If they don't reproduce, the population dies out."

Finding crops resistant to nematodes may be difficult due to the pest's wide range of hosts, and trap crops are often plants that are less valuable to farmers. The researchers said they had tried a number of different rotation crops before turning to wheat.

The researchers were surprised to find a strain of wheat called Lassik into which a resistance gene had been inserted. They then grew Lassik wheat and used some of the soil to plant tomato seedlings. The wheat had the effect they were hoping for -- the tomatoes grown in soil from the resistant wheat plots were less damaged by nematodes.

"If farmers use a wheat that does not have the resistant genes, more nematodes survive, and they'll be there when they plant tomatoes," Williamson said. "But if they plant the resistant wheat, there won't be as many nematodes in the soil."

The researchers said the results offer a promising option for reducing nematode damage and they will next verify the findings on a larger scale.