With three new grants totaling more than $11 million, UC Riverside is helping lead the fight against citrus greening or Huanglongbing. Because California supplies the country with 80% of its fresh citrus, and because 267,000 acres of Golden State lemons, oranges, grapefruits, and mandarins are at stake if operations are permanently lost, the USDA National Institute of Food and Agriculture is making an emergency investment in citrus disease research with three projects at UCR.
These projects focus on instilling tolerance to the disease with three different approaches: below ground, in the rootstocks, above ground in the shoots and branches, and systemically, with a peptide that would move throughout the tree.
The largest of the projects, at $6.8 million, is being led by Danelle Seymour, Assistant Professor of genetics in the Botany and Plant Sciences Department at UCR. Their focus is on breeding HLB-resistant rootstocks, and the project depends on collaboration with Kim Bowman, a citrus breeder at the USDA Agricultural Research Service in Ft. Pierce, FL.
“In Florida, nearly every single tree is infected. It’s terrible for growers, but wonderful for breeding,” Seymour says. “We can’t do this research at large scale in California because the disease isn’t as widespread here.”
The classic way to improve resistance or encourage new qualities in crops is through genetics, making crosses between one plant that has a favorable trait, and one that doesn’t. “We hope the result is better than the parents,” Seymour says. “When you work in wheat or tomato, you can do these crosses and perform evaluations every year. In citrus, it takes 10 to 15 years to evaluate a new generation of trees.”
Because of the long lag time, the research-ready trees in Florida represent an opportunity for Seymour’s team to begin examining new crosses now. The breeder, Kim Bowman, has evaluated more than 10,000 trees and unique hybrids, from which a handful will be selected for release to growers.
In addition to evaluating these select few new hybrids for their HLB tolerance, the researchers will be watching the Florida-grown trees’ responses to the different environmental conditions in California. “Can they perform well in response to different salinity levels in the soil, different humidity, as well as other pests and pathogens that we have here? We’ll find out,” Seymour adds.
Chandrika Ramadugu, a Project Scientist also in UCR’s Department of Botany and Plant Sciences, is leading a project to develop HLB-resistant scion varieties that can be grafted to rootstocks.
For trees, grafting can be equated to an organ transplant. The scion from one tree is attached to the trunk or rootstock of another with the hope of creating a new plant with combined attributes. With its grant of $3.28 million, this project will analyze second-generation hybrids that are bred for 10 years using Australian lime as a source of disease resistance.
Ramadugu will evaluate 24 novel hybrids in California, Florida, and Texas to assess resistance to HLB. Ideally, in addition to having enhanced disease tolerance, the new plants will also be able to produce good-tasting fruit.
A third project, granted $1.36 million, will utilize a peptide found in Australian finger limes that is known to impart HLB resistance. Led by Hailing Jin, Microbiology & Plant Pathology professor, the project is developing ways to infuse trees with the peptide.
“The antimicrobial peptide in the finger limes are more efficient at killing bacteria as compared to antibiotics currently used in the field, and much more stable at high temperatures,” Jin says.
Because spray applications are expensive, Jin’s project aims to spread the peptide throughout the trees’ insides.
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