In the expansive fight to save Florida citrus from HLB, the tiniest molecular factors may have the biggest impact.
At least that’s one of the guiding principles that Dr. Manjul Dutt, assistant professor at the Citrus Research and Education Center in Lake Alfred, is using in his ongoing research to create citrus trees that are naturally highly resistant to the HLB bacteria that causes citrus greening.
“We have been tasked to look at this issue from a genetic point of view,” Dutt says. “We are using all of our available tools in order to find the best solution toward more resistant and robust citrus in order to help growers overcome this huge problem.”
This means looking in relatively unlikely places to spur on his research. Recently, Dutt began examining finger limes, a relatively — new specialty crop in Florida — that seem to be naturally HLB-resistant.
“We are working to understand the mechanism of resistance in those limes, in order to identify genetic elements that can be used to develop more improved sweet oranges and grapefruits,” says Dutt.
Dutt is also using peptides and proteins as tools for understanding how to make citrus trees better able to resist greening.
He says he is getting ready to start field trials for HLB-resistant rootstocks.
“What these peptides and proteins do is make the tree primed and ready to resist the bacteria,” says Dutt. “Plants are naturally able to resist pathogens, what we are trying to do is help the plant be more robust, to have a better, stronger immune system in place.”
Dutt took an NPR1 gene from Arabidopsis plant — a common plant from the mustard family that had been identified as promoting resistance to greening — and inserted a gene into a citrus plant, which resulted in a higher level of resistance to citrus canker and greening.
His upcoming field trial combines some of these other results in ways to make the citrus tree naturally more resistant. The focus is more on the rootstock and not on leaves, scion, or bud.
“When a bacterial pathogen like HLB is introduced, the first thing it does is travels down into the rootstock, not up into other parts of the tree,” Dutt says. “If we are able to modify the rootstock to be more resistant to the bacteria, it will be ready to lead the fight against the bacteria, while the bud, and the fruit that comes from it, is relatively protected from the bacteria’s impact.”
He says the field trial will also use integrated management practices, including sprays, fertilization and irrigation practices currently used to minimize the impact of the HLB.
Dutt said he hopes to get the trees for this experiment into the field by next year. The trial will last three to five years in order to examine the fruit quality.
NPR1 is just one gene, and researchers are looking at a number of other genes, says Dutt.
“We are also examining wild citrus, which seems to be naturally resistant to HLB, and trying to understand how the genes and pathways work together to make the tree more durable. If we can identify those genes, it would help us in multiple ways.”