title: Infection Density Dynamics of the Citrus Greening Bacterium "Candidatus Liberibacter asiaticus" in Field Populations of the Psyllid Diaphorina citri and Its Relevance to the Efficiency of Pathogen Transmission to Citrus Plants.
abstract: Huanglongbing, or citrus greening, is a devastating disease of citrus plants recently spreading worldwide, which is caused by an uncultivable bacterial pathogen, "Candidatus Liberibacter asiaticus," and vectored by a phloem-sucking insect, Diaphorina citri. We investigated the infection density dynamics of "Ca. Liberibacter asiaticus" in field populations of D. citri with experiments using field-collected insects to address how "Ca. Liberibacter asiaticus" infection density in the vector insect is relevant to pathogen transmission to citrus plants. Of 500 insects continuously collected from "Ca. Liberibacter asiaticus"-infected citrus trees with pathological symptoms in the spring and autumn of 2009, 497 (99.4%) were "Ca. Liberibacter asiaticus" positive. The infections were systemic across head-thorax and abdomen, ranging from 10(3) to 10(7) bacteria per insect. In spring, the infection densities were low in March, at ∼ 10(3) bacteria per insect, increasing up to 10(6) to 10(7) bacteria per insect in April and May, and decreasing to 10(5) to 10(6) bacteria per insect in late May, whereas the infection densities were constantly ∼ 10(6) to 10(7) bacteria per insect in autumn. Statistical analysis suggested that several factors, such as insect sex, host trees, and collection dates, may be correlated with "Ca. Liberibacter asiaticus" infection densities in field D. citri populations. Inoculation experiments with citrus seedlings using field-collected "Ca. Liberibacter asiaticus"-infected insects suggested that (i) "Ca. Liberibacter asiaticus"-transmitting insects tend to exhibit higher infection densities than do nontransmitting insects, (ii) a threshold level (∼ 10(6) bacteria per insect) of "Ca. Liberibacter asiaticus" density in D. citri is required for successful transmission to citrus plants, and (iii) D. citri attaining the threshold infection level transmits "Ca. Liberibacter asiaticus" to citrus plants in a stochastic manner. These findings provide valuable insights into understanding, predicting, and controlling this notorious citrus pathogen.
authors.affiliation: Okinawa Prefectural Plant Protection Center, Yaeyama Branch Office, Ishigaki, Okinawa, Japan Okinawa Prefectural Agricultural Research Center, Itoman, Okinawa, Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Ukuda-Hosokawa
authors.affiliation: Okinawa Prefectural Plant Protection Center, Naha, Okinawa, Japan.
authors.forename: Yasutsune
authors.initials: Y
authors.lastname: Sadoyama
authors.affiliation: Okinawa Prefectural Yaeyama Agriculture, Forestry and Fisheries Promotion Center, Ishigaki, Okinawa, Japan.
authors.forename: Misaki
authors.initials: M
authors.lastname: Kishaba
authors.affiliation: Kagoshima University, Faculty of Education, Laboratory of Zoology, Kagoshima, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kuriwada
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Anbutsu
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo, Japan Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan t-fukatsu@aist.go.jp.
authors.forename: Takema
authors.initials: T
authors.lastname: Fukatsu
mesh_terms: D000825:Animal Structures / Q000382:microbiology; D000818:Animals; D058491:Bacterial Load; D002957:Citrus / Q000469:parasitology*; D018562:Disease Transmission, Infectious; D006430:Hemiptera / Q000382:microbiology*; D010935:Plant Diseases / Q000382:microbiology*; D010944:Plants; D012230:Rhizobiaceae / Q000302:isolation & purification*; D012621:Seasons
references.citation: Proc Biol Sci. 2003 Dec 22;270(1533):2543-50
references.pmid: 14728775
references.citation: Mol Ecol. 1999 Nov;8(11):1935-45
references.pmid: 10620236
references.citation: Appl Environ Microbiol. 2003 Mar;69(3):1428-34
references.pmid: 12620825
references.citation: Annu Rev Phytopathol. 2003;41:483-500
references.pmid: 12730387
references.citation: Mol Cell Probes. 2008 Jun;22(3):139-50
references.pmid: 18400468
references.citation: Plant Dis. 2009 Mar;93(3):257-262
references.pmid: 30764183
references.citation: Int J Syst Evol Microbiol. 2005 Sep;55(Pt 5):1857-1862
references.pmid: 16166678
references.citation: Phytopathology. 2008 May;98(5):592-9
references.pmid: 18943228
references.citation: Annu Rev Entomol. 2010;55:247-66
references.pmid: 19728837
references.citation: Curr Biol. 2013 Aug 5;23(15):1478-84
references.pmid: 23850282
references.citation: PLoS Pathog. 2012;8(3):e1002610
references.pmid: 22457628
references.citation: Appl Environ Microbiol. 1998 Oct;64(10):3599-606
references.pmid: 9758773
references.citation: Int J Syst Evol Microbiol. 2000 Nov;50 Pt 6:2119-2125
references.pmid: 11155987
references.citation: J Econ Entomol. 2013 Feb;106(1):25-35
references.pmid: 23448011
references.citation: PLoS One. 2013 Dec 04;8(12):e82612
references.pmid: 24349319
references.citation: Int J Syst Bacteriol. 1994 Jul;44(3):379-86
references.pmid: 7520729
references.citation: Annu Rev Phytopathol. 2008;46:243-71
references.pmid: 18422428
references.citation: J Econ Entomol. 2010 Oct;103(5):1531-41
references.pmid: 21061950
references.citation: Annu Rev Phytopathol. 2010;48:119-39
references.pmid: 20415578
references.citation: Annu Rev Entomol. 2013;58:413-32
references.pmid: 23317046
references.citation: J Invertebr Pathol. 2003 Mar;82(3):167-75
references.pmid: 12676553
references.citation: Annu Rev Entomol. 2006;51:91-111
references.pmid: 16332205
references.citation: Phytopathology. 2009 Feb;99(2):139-44
references.pmid: 19159305
references.citation: Proc Natl Acad Sci U S A. 2012 Jul 24;109(30):12213-8
references.pmid: 22783015
references.citation: Phytopathology. 2008 Apr;98(4):387-96
references.pmid: 18944186
references.citation: Mol Plant Microbe Interact. 2009 Aug;22(8):1011-20
references.pmid: 19589076
references.citation: J Invertebr Pathol. 2014 Jan;115:55-61
references.pmid: 24211673
references.citation: PLoS One. 2012;7(11):e50067
references.pmid: 23166822