LSU AgCenter plant pathologists are screening crop varieties to see if any of them have traits that deter the guava root-knot nematode, an aggressive pest that recently has become a major concern in other states.
Nematodes are microscopic worms that stunt plants’ growth, make them wilt and turn yellow, and cause galls on the roots. Those symptoms interfere with water and nutrient uptake, limiting plant development and yield potential.
So far, the guava root-knot nematode has been detected in just one location in Louisiana — a sweet potato field planted with material from North Carolina, where the pest is widespread.
The nematode also has been found in South Carolina and Florida. It has been devastating to sweet potatoes, but attacks other vegetables and agronomic crops such as soybeans.
In an effort to identify sources of resistance before a potential guava nematode outbreak in Louisiana, AgCenter plant pathologist Josielle Rezende is studying how varieties of soybeans, grain sorghum, cotton, corn and sugarcane respond when exposed to these nematodes.
“This will give us a good indicator to work with in the field in case this nematode becomes a problem in soybeans,” she said.
AgCenter plant pathologist Chris Clark is leading a similar effort with Louisiana sweet potato varieties.
“We are doing this research to be ahead of the problem,” he said.
Their work is done within the confines of a laboratory and a greenhouse on the LSU campus to avoid introducing the pest into Louisiana soil.
“We normally wouldn’t like to make recommendations on resistance based on greenhouse tests,” Clark said. “We would like to have field tests too, but it’s not possible.”
In addition to studying varietal resistance and susceptibility, Clark and Rezende are learning more about the guava nematode biology and ecology. Much about it remains unknown. For example, it’s not clear whether the aggressiveness of guava nematode populations varies by location or other factors, Clark said.
The guava nematode is similar to the Southern root-knot nematode, which is common in Louisiana, but seems to be more destructive. Rezende said sweet potato varieties that can tolerate the Southern root-knot nematode appear to be susceptible to the guava root-knot species.
Farmers can send soil samples to the AgCenter Nematode Advisory Service to determine whether their fields have a nematode infestation and, if so, which species is present. To contact the lab, call 225-578-5724.
The best way to control any type of nematode is rotating fields to nonsusceptible crops. Nematicides also are effective but field-wide applications are expensive.
“That will be a last resort for farmers,” Rezende said.
LSU AgCenter plant pathologists Josielle Rezende, left, and Chris Clark, right, stand next to equipment and plants used in their work related to the guava root-knot nematode. They are screening crops for nematode resistance. Photo by Olivia McClure