Huanglongbing (HLB) is the most devastating disease of citrus in the U.S. Economic losses over the past five years in FL alone amount to over $1 billion per year, with nearly 5,000 jobs lost annually. The U.S. citrus industry is in dire need of new citrus cultivars with stable and broad-spectrum resistance/tolerance to HLB as well as desirable horticultural characteristics, crop yield, and fruit quality. The other major citrus states are at high risk for a similar disastrous situation if suitable remedies are not forthcoming soon. Neither a simple cure nor successful management strategies have been identified even after 15+years of the disease presence in Florida. Previous efforts to create new HLB resistant/tolerant cultivars were focused on conventional hybrid breeding or the development of transgenic plants. Unfortunately, the approaches used in those projects are inadequate to meet the current crisis because of the lack of sources of resistance in citrus, time constraints associated with citrus breeding and genetic engineering, and regulatory obstacles for transgenic citrus. Meanwhile, more than 15 years of HLB epidemics and tens of millions of infected trees in groves across Florida provide an unprecedented opportunity and high probability for selecting new mutant scions that are resistant or at least highly tolerant. Over the past years, our group has selected multiple citrus varieties with field resistance or tolerance to HLB from Florida groves. A recent study showed that HLB is a pathogen-triggered immune disease. These natural variants may have HLB resistance/tolerance through evasion of the immune response or loss of susceptibility genes. Although the exploitation of natural resistance/tolerance provides a key solution to developing new HLB-resistant/tolerant citrus scions and rootstocks, it still requires a significant amount of time to confirm stable resistance of the selected varieties. It is critical to develop rapid methods to shorten the selection process, to provide solutions within a shorter time frame to ensure the survival of the citrus industry, especially in Florida. Furthermore, there are many available sequences of citrus genomes, including several HLB-resistant/tolerant citrus plants and their counterparts that our group and others have sequenced. It is critical that we can integrate all genome-based information to understand the HLB-resistant/tolerant or susceptibility-related genes.

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Acknowledgement

This work was supported by the US National Institute of Food and Agriculture (NIFA), Grant Number 2023-70029-41309.