*Devious Phloem Intruder* Candidatus *Liberibacter Species Causing Huanglongbing: History… DOI: http://dx.doi.org/10.5772/intechopen.105089*

Antibiotics alone or combined with other bactericides have also shown to be effective against citrus HLB. However, antibiotics need to evaluate their phytotoxicity before their commercial use. The combination of thermotherapy and antibiotics, plant defense activators, and thermotherapy provides controlled HLB management efficiency. The formation of nanoemulsion in water in oil (W/O) and/or oil in water (O/W) could offer a practical methodology for the targeted delivery of antimicrobial compounds to the phloem of citrus by foliar spraying method to control citrus HLB. In addition, transgenic orange cultivars over-expressing the *AtNPR1* gene exhibited enhanced resistance to HLB. Transcriptome analysis between susceptible, tolerant, and resistant citrus varieties provides new insights into HLB tolerance by revealing defense-related genes, biological pathway signaling, hormones, transporters, carbohydrate metabolism, phloem-related genes, and secondary metabolism. In addition, some potential targets have also been identified, such as *DMR6-like* and *NPR1-like* genes for future HLB-tolerant citrus breeding [171]. Epibrassinolide as a foliar spray in HLB-affected plants improved the immunity against *Candidatus* Liberibacter asiaticus in the greenhouse and citrus field. However, further studies on the impact of eBL and nanoemulsion loaded with antibiotics in HLB-affected citrus plants are warranted to understand the complexity of citrus pathophysiology and fruit productivity. Researchers have investigated many control strategies to combat *Candidatus* Liberibacter species, but no effective management strategies have been developed. More studies are needed to investigate a sustainable and environmentally friendly strategy to control citrus HLB in the form of an antimicrobial agent in citrus groves. Meanwhile, biotechnological approaches such as transgenic, gene editing, and hostinduced gene silencing may provide an unprecedented opportunity for long-term HLB management tools.

Based on the extensive prevention strategy experiments in the citriculture field by Chinese farmers, it has been shown that the control of HLB disease can be carried out in the three-pronged approach.


Nanotechnology-driven farming is still early, but it is an exciting and challenging field of research to be developed in the future, especially if the proper emphasis is placed on understanding the fundamental interactions between nanoscale materials and crop plants [172]. Future nanotechnology will enable the development of biosensors for early diagnosis of disease, new methods for suppression of disease pathogens in field and greenhouse conditions, and new molecular tools for understanding pathogenic mechanisms in pathogens and plants [173]. Nanotechnological investigations in phytopathology have increased dramatically over the last decade. Nanomaterials can be engineered as biosensors to diagnose plant diseases and as a

means of delivery of genetic material, probes, and agrochemicals. Nanotechnology has been incorporated into disease management strategies, diagnostic tools, and molecular tools. Nanotechnologies could provide an alternative treatment to citrus farmers to be integrated into their existing HLB management programs in the citrus groves.
