A Review of the Citrus Greening Research and Development Efforts Supported by the Citrus Research and Development Foundation Fighting a Ravaging Disease (2018) / Chapter Skim
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Pages 5-20
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From page 5... ...
First detected in Florida in 2005, HLB is now widespread in the state and threatens the survival of the Florida citrus industry despite substantial allocation of research funds by Florida citrus growers and federal and state agencies. In Florida, HLB research is overseen by the Citrus Research and Devel opment Foundation (CRDF)
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; the complexity of pathogen, vector, and host interactions; the lack of a good model system; as well as the current approach to HLB research. CURRENT KNOWLEDGE OF HUANGLONGBING PATHOGEN, VECTOR, AND HOST AND THEIR INTERACTIONS HLB is a disease of citrus associated with bacteria that are spread by a sucking insect, the Asian citrus psyllid.
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Trapping data indicate no consistent ACP seasonal movement patterns, necessitating continuous monitoring. Vector–Host Interactions ACP infests species in at least 10 genera in the family Rutaceae (which contains about 160 genera including Citrus)
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were established in loridaF to promote regional coordination of insecticide applications, but their effective ess is limited by low grower participation in some areas. Mod n els predict that reducing ACP populations during critical times can decrease HLB spread, but even 100% CHMA participation would not likely slow HLB progression because refugia for vector and pathogen exist in abandoned groves and backyard trees.
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From page 9... ...
Research on HLB Vector–Host Interactions CRDF funded projects to screen citrus germplasm for traits affecting ACP attractiveness, quantify impacts of citrus species and flushing on ACP traits, and identify ACP overwintering habitats and alternative hosts. Other studies were designed to understand Cleopatra mandarin and trifoliate o range resistance to ACP and CLas, respectively; to identify semio hemicals c impacting psyllid–host interactions; and to examine plant structures inter fering with ACP feeding.
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From page 10... ...
NIFA and CRB fund projects to identify candidate resistance genes in resistant or tolerant citrus relatives for gene editing to produce non-GE HLB-resistant citrus cultivars. Research on HLB Pathogen–Vector Interactions CRDF-funded projects aimed to characterize and interrupt CLas movement within, and interactions with, ACP.
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From page 11... ...
Research on HLB Host–Pathogen Interactions CRDF funded projects aimed at identifying host genes highly up regulated in resistant versus susceptible citrus varieties; identifying and mapping HLB resistance gene(s) in Poncirus; curating genomic sequences of CLas, ACP, and citrus; and bioinformatically analyzing proteins of each species to predict their interactions.
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From page 12... ...
MAC has supported research on cultural management, such as removing abandoned groves, reducing irrigation water pH, applying thermotherapy or mulches, and intensive grove management. Research on Diagnostics No current CRDF-funded projects directly address CLas diagnostics, but a past project investigated optical sensing to screen seedlings for HLB resistance.
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From page 13... ...
These factors influence the likelihood of implementation and success of future HLB management approaches, as shown by studies, funded by other agencies, on grower participation in CHMAs as well as surveys on grower willingness to plant GE citrus and consumer willingness to purchase GE products. NOTABLE OUTCOMES, PITFALLS, AND FUTURE DIRECTIONS Key research findings and recommended future research are listed here to highlight areas in which the committee found that progress had been made and to point to research efforts the committee believes should be continued or initiated.
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Recommendations for Future Research • Characterize additional CLas effectors and identify and function ally analyze host targets, applying new knowledge to novel HLB management tools. • Identify and characterize new critical citrus genes or gene products that are targets of CLas.
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• Potentially useful levels of resistance were identified in citrus rela tives for incorporation into breeding programs. Host Resistance: Genetic Engineering • Numerous transgenic citrus expressing genes that may confer HLB resistance were produced and are being tested.
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• Increasing citrus density in orchards can decrease the rate of HLB spread. • Multiple inoculations of infected trees exacerbate HLB impact on fruit yield and quality.
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From page 17... ...
Recommendation 3.3: CRDF should consider establishing an infrastructure enhancement project to assess field testing needs for all citrus disease and insect research and validation activities and to design plans to meet those needs by enhancing current field test sites, establishing new field test sites, and/or developing collaborations with citrus growers to use production orchards for testing.
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Recommendation 3.4: Consider specific funding for the development of sets of management approaches that can be combined in different ways, optimized, and validated for use in different locations and conditions. Finding 3.5: Plant pathologists, sociologists, and economists are using modeling to assess the complex interactions that characterize HLB; however, no CRDF funding has directly supported research on economic and sociological factors that impact decision making and behaviors of growers, processors, and the public and can influence the adoption and success of future HLB management efforts.
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From page 19... ...
Recommendation 4.2: Continue to support the development and application of gene modification, including gene editing, focusing on targets mediating molecular interactions among plant, bacteria, and vector. Conclusion 4.3: HLB research is hampered by the lack of standardized methods and parameters for measuring, evaluating, and analyzing factors including vector transmission rates, fruit yield, plant tolerance/resistance, citrus variety performance, antibacterial compound effectiveness, and diag nostic assay evaluation.
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From page 20... ...
Recommendation 4.6: CRDF should consider working, together with representatives of other agencies at the national and state levels, to create an overarching HLB research advisory panel to develop a fresh systems approach to HLB research prioritization and the strategic distribution of resources for research leading to effective HLB management.
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