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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Publications at this Location » Publication #336649

Research Project: Horticultural, Physiological, and Genetic Factors Affecting Sustainable Citrus Production

Location: Citrus and Other Subtropical Products Research

Title: CLas population dynamics in citrus and ACP

item McCollum, Thomas
item Gottwald, Timothy
item Hall, David

Submitted to: Journal of Citrus Pathology
Publication Type: Abstract Only
Publication Acceptance Date: 12/20/2016
Publication Date: 5/18/2017
Citation: Mccollum, T.G., Gottwald, T.R., Hall, D.G. 2017. CLas population dynamics in citrus and ACP. Journal of Citrus Pathology. 4(1):29/45.

Interpretive Summary: Huanglongbing (HLB) poses a serious threat to citrus production world wide. Understanding the relationship between populations of Candidatus Liberibacter asisaticus (CLas) and development of HLB disease is essential for developing effective management strategies for the disease. We have determined how CLas populations change and move systemically in citrus trees following inoculation by grafting or by Asian citrus psyllids (ACP) inoculations. Graft inoculation results in much greater incidence of systemic CLas infection than does ACP inoculation and systemic movement occurs more rapidly in graft inoculated than in ACP inoculated plants. Changes in CLas titer over time following inoculation suggest that many nascent infections actually never proliferate and lead to systemic infection and HLB symptoms, indicating that prophylactic rather than curative treatments will likely be the most effective approach to HLB control.

Technical Abstract: Relationships between CLas titer in ACP, CLas transmission by ACP to citrus, changes in CLas titer following infection, systemic movement of CLas in citrus and eventually expression of HLB symptoms, are all critical to HLB disease development. Incidence of CLas systemic infection (based on qPCR detection) was less than 50% one month after inoculation (MAI) for 171 citrus nursery trees graft inoculated with CLas. Four MAI 95% of the graft inoculated trees were systemically infected. CLas titer throughout the trees also increased with MAI. One MAI, most infected leaves had CLas titers of ca. 100 genomes/100•mg-1 total nucleic acid (TNA), by 10 MAI ca. 50% of the plants had CLas titers between 105 and 106 genomes/100•mg-1 TNA. CLas titers in the range of 102 to 103 genomes/ 100•mg-1 TNA were less frequent than those lower or higher. At 10 MAI, 100% of plants with CLas titers in excess of 103 genomes/100•mg-1 TNA were HLB symptomatic. Adult ACP infected with CLas were also used to inoculate citrus. Essentially 100% of ACP adults tested CLas positive, with titers in infected ACP adults most frequently ca. 103 copies per insect, although infrequently, CLas titer in some ACP reached 106 copies per individual insect. CLas was detected in citrus shoots ca. 21 days following exposure to CLas infected ACP; after an additional 15 day incubation the incidence of detection increased to nearly 100% along with CLas titer. HLB symptoms became visible ca. four months following exposure to CLas infected ACP. Our results indicate that development of systemic CLas infection and HLB symptoms in graft inoculated plants differ considerably from ACP inoculated plants. However, temporal changes in CLas titer over time were similar in graft and ACP inoculated trees. In no case were HLB symptoms observed when CLas titer was less than 103 genomes 100•mg-1 TNA.