In 2018, the guava root-knot nematode was discovered on a farm in northern Louisiana. It was the first — and so far, the only — sighting of the destructive pest in the state.

Though the pest has yet to spread through Louisiana as it has in other states, LSU AgCenter scientists are nevertheless trying to learn as much as possible about it so they can help farmers if more infections occur down the road.

A nematode is a microscopic worm that feeds on and damages plant roots. The guava root-knot species is particularly devastating; it can cause wilting and root galling severe enough to result in total yield losses in several crops.

Much is unknown about this pest, which is a relatively new arrival to the U.S. Originally from Asia, it was found in Florida in 2001. Ten years later, it showed up in North Carolina, where it has devastated sweet potato fields.

With the help of some high-tech tools, scientists with the AgCenter Nematode Advisory Service are studying differences between the guava root-knot nematode and the more common Southern root-knot nematode. The two are similar but can be distinguished when examined at the molecular level.

AgCenter plant pathologist Josielle Rezende is using a technique called loop-mediated isothermal amplification, or LAMP, to identify the nematodes. DNA is extracted from nematode-infected plant roots, then incubated with species-specific primers and reagents.

“If the target nematode is present, the DNA will be amplified,” Rezende said, allowing it to be detected on an instrument that monitors fluorescence.

“LAMP is a fast, sensitive and economical molecular technique that can be used for increasing the efficiency of diagnosis and management,” she said. “The LAMP assay can be performed within 1.5 hours and is a promising identification tool for the guava root-knot nematode in pest quarantine and field surveys.”

Being able to quickly identify the guava root-knot nematode is critical because of the aggressive nature of the pest.

One of the best ways to manage any pest is by planting varieties and hybrids that are not susceptible to that pest. So Rezende also is studying how different soybean varieties and corn and grain sorghum hybrids respond when exposed to the nematode.

“There is limited information about the reaction of most agronomic, vegetable and cover crops in Louisiana to the guava root-knot nematode,” Rezende said. “Screening plant varieties of different crops grown in Louisiana could identify potential sources of resistance, thus generating important data that can be applied to manage this nematode in our state.”

The nematode did not reproduce or cause galls on any of the corn or sorghum hybrids she tested in 2019. All of the soybean varieties tested, however, developed severe root galling.

Rezende said future research will try to determine if factors such as soybean maturity group affect how susceptible a variety is to the nematode.

“These data can help identify varieties that are very poor hosts and can help manage this nematode if this species develops into a future problem,” she said.

This story is featured in the Louisiana Soybean and Grain Research and Promotion Board 2020 Report.

LSU AgCenter plant pathologist Josielle Rezende stands next to the Genie II, an instrument she uses to identify species of nematodes through a technique called loop-mediated isothermal amplification. Photo by Olivia McClure/LSU AgCenter