Understand and Identify Huanglongbing Tolerance in Citrus and its Relatives
Posted August 2025
Researchers: Ozgur Batuman, Choaa El Mohtar, Amit Levy, Zhonglin Mou, Danelle K. Seymour
Contact: Ozgur Batuman, UF/IFAS SWFREC obatuman@ufl.edu
Summary:
All elite commercial citrus cultivars are susceptible to huanglongbing (HLB). However, wild relatives of citrus (such as Australian lime) tolerate HLB. One mechanism of HLB tolerance is reducing callose and reactive oxygen species (ROS) accumulation when infected with CLas. Therefore, if we understand how citrus relatives regulate callose and ROS upon infection, we can reprogram commercial citrus to respond in a similar manner, enabling tolerance in elite commercial citrus scions. In this project, we will identify citrus accessions with elevated basal callose levels, test their HLB tolerance, and identify genetic markers that will help us identify genetic defects (i.e., elevated callose and ROS accumulation) within commercial citrus, and use this knowledge for breeding purposes. One approach to rapidly introducing HLB resistance in our cultivars is using transgenic or transient expression approaches. We will use citrus tristeza viral vector (CTV) or transgenic approaches to overexpress or downregulate citrus defense genes, or combine them to make ‘Valencia’ or ‘Hamlin’ tolerant/ resistant like wild citrus and some relatives. The outcome of this project will allow us to: 1) understand better the molecular mechanisms underlying HLB susceptibility and tolerance, 2) obtain new citrus germplasms with reduced CLas-induced callose and ROS accumulation, 3) acquire potential biomarkers for conventional breeding, 4) identify citrus genes involved in defense mechanism and manipulate them with gene editing or balanced expression approaches for HLB resistance, and 5) better understand the citrus immune system leading to HLB susceptibility and tolerance.
Take Home Message:
- We will learn the regulations of citrus defense-related genes involved in HLB tolerance/resistance in citrus relatives.
- We will utilize gene expression and gene-editing strategies to decrease our cultivars’ susceptibility to HLB.
- Knowledge gained will allow us to increase HLB tolerance in both scion and rootstock citrus varieties.
