Super-Root Mutants for HLB

Murcott on a super-root mutant clone of UFR-1 shows HLB symptoms on the lower leaves, but not on new growth on the top.

A citrus nursery employee has found super-root mutants that might offer hope for developing trees that are less susceptible to HLB. The employee is Beth Lamb, a tissue culture expert at Phillip Rucks Citrus Nursery. University of Florida Institute of Food and Agricultural Sciences citrus breeder Jude Grosser tells about her discovery.

“She discovered some mutants of some of the UFRs (University of Florida rootstocks), and she calls them super-root mutants because they’re producing up to twice as much feeder roots as the original clones,” Grosser says. “Feeder root loss is a big problem when trees get infected with HLB, so a rootstock that produces more feeder roots might have a better chance of dealing with the disease.”

Lamb shared some of the mutants with Grosser, who grafted HLB-infected Murcotts to them. Grosser uses Murcotts as an indicator plant for HLB “because it reacts more quickly and more severely (to HLB) than sweet orange,” he explains. “The second flush came out completely normal on three of these (Murcotts on super root mutants), very healthy” and with no HLB-causing bacteria in the new flushes. He says that is “remarkable for a highly susceptible variety like Murcott. So, it seems the rootstock is doing something to mitigate the disease.”

Grosser has since put these trees in the field. “It’s going to be really interesting to see what happens with the spring flush,” he says.

HLB is the greatest production problem the Florida citrus industry has ever faced. Many growers and researchers believe the ultimate solution to HLB is development of trees that are resistant to the disease.

About the Author

Tacy Callies

Editor of Citrus Industry magazine