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Finding Another Key to Developing a Greening— Resistant Citrus Tree

At UF/IFAS, we are working on finding solutions for Florida’s citrus growers. This is a summary of one project made possible by state legislative funding for the UF/IFAS Citrus Initiative during the 2018-19 cycle. It documents how we are making progress and  providing Florida growers with reasonable, pragmatic solutions to successfully grow citrus in the new age of citrus greening.

Researcher: Manjul Dutt, Horticultural Sciences

IMPACT: Researchers are one step closer to developing a greening-resistant citrus variety and one that will result in long-term resistance to the disease. Progress is being made in understanding how genetically engineered citrus reacts to HLB and identifying genetically engineered rootstocks that can potentially protect trees in the future.

Citrus greening disease, also known as Huanglongbing or HLB, is the result of an infection by the bacterium Candidatus Liberibacter asiaticus. Though the concept of HLB-resistant citrus is simple, the process of developing such a variety is complex, requiring scientists to understand genetic mechanisms that increase resistance or decrease vulnerability to infection. Both goals are being pursued by horticulturalist Manjul Dutt, a research assistant scientist with UF/IFAS Citrus Research and Education Center.

In one recent study, Dutt grafted HLB-infected sweet orange scions to rootstocks that had been genetically engineered to produce a compound that confers resistance to pathogens. In this project, results indicated that the compound traveled from rootstock to scion and significantly reduced the
concentrations of HLB bacterium in the scion. A companion study showed it was possible to “turn off” a gene that naturally occurs in sweet orange and interferes with its ability to produce a greening-resistant compound. If the tree could  then produce more of the resistant compound, it could use its own natural defenses more effectively to fight greening. This discovery opens the door for Dutt and collaborators to employ CRISPR gene-editing technology and develop gene-edited citrus varieties that can effectively combat the HLB pathogen.