HUANGLONGBING (HLB) HOST RANGE AND
BACTERIAL SPECIES DIVERSITY
HUANGLONGBING (HLB) HOST RANGE AND
BACTERIAL SPECIES DIVERSITY
Dr. Megan DewdneyDr. Megan DewdneyAssistant Professor and Extension Assistant Professor and Extension SpecialistSpecialist
OutlineOutline1. The bacteria that cause HLB
2. Bacterial diversity in groves
3. Citrus host range of HLB
1. The bacteria that cause HLB
2. Bacterial diversity in groves
3. Citrus host range of HLB
Three Species of Bacteria Cause HLB
Three Species of Bacteria Cause HLB
• Ca. Liberibacter asiaticus– only known species in Florida
• Vectored by 2 psyllid species – Diaphorina citri and Trioza erytreae
(experimentally)
• Heat tolerant • Found on the Indian Subcontinent,
Southeast Asia, Arabian peninsula, Brazil, Louisiana and Florida
• Ca. Liberibacter asiaticus– only known species in Florida
• Vectored by 2 psyllid species – Diaphorina citri and Trioza erytreae
(experimentally)
• Heat tolerant • Found on the Indian Subcontinent,
Southeast Asia, Arabian peninsula, Brazil, Louisiana and Florida
• Has not been found in Florida
• Vectored by 2 psyllid species– Trioza erytreae and Diaphorina citri
(experimentally)
• Bacterium and vector heat sensitive• Found in many African countries,
Madagascar and Yemen at higher altitudes
• Has not been found in Florida
• Vectored by 2 psyllid species– Trioza erytreae and Diaphorina citri
(experimentally)
• Bacterium and vector heat sensitive• Found in many African countries,
Madagascar and Yemen at higher altitudes
Ca. Liberibacter africanus
Ca. Liberibacter africanus
Ca. Liberibacter americanus
Ca. Liberibacter americanus
• Newest species of bacteria that cause HLB– Not found in Florida
• Vectored by Diaphorina citri• Disease is not as severe as when caused
by Asian species• Heat tolerant• Only found in Brazil currently• Is not found in citrus as often as in the past
• Newest species of bacteria that cause HLB– Not found in Florida
• Vectored by Diaphorina citri• Disease is not as severe as when caused
by Asian species• Heat tolerant• Only found in Brazil currently• Is not found in citrus as often as in the past
New Disease of Potato –Zebra Chip
New Disease of Potato –Zebra Chip
• Caused by a newly identified Ca. Liberibacter– Identified in New Zealand
• Vectored by the potato/tomato psyllid – Bactericera cockerelli
• Also damages tomatoes and peppers• From South Texas to Colorado as well as
Mexico, Guatemala
• Caused by a newly identified Ca. Liberibacter– Identified in New Zealand
• Vectored by the potato/tomato psyllid – Bactericera cockerelli
• Also damages tomatoes and peppers• From South Texas to Colorado as well as
Mexico, Guatemala
Bacterial Diversity StudyBacterial Diversity Study
Asymptomatic Asymptomatic grovegrove
HLB infected HLB infected grovegrove
177 177 samplessamples
186 186 samplessamples
PhylumPhylum ClassClass OrderOrder Order Order %%
ProteobacterProteobacteriaia
αα - - proteobacteriaproteobacteria
RhizobialesRhizobiales 91.591.5
UnclassifiedUnclassified 4.54.5γγ - -
proteobacteriaproteobacteriaEnterobacteriaEnterobacteria
lesles1.1 1.1
BacteroideteBacteroidetess
UnclassifiedUnclassified UnclassifiedUnclassified 5.65.6
FirmicutesFirmicutes BacilliBacilli BacillialesBacilliales 0.50.5
Bacterial Diversity StudyBacterial Diversity StudySymptomatic GrovesSymptomatic Groves
ProteobacteriaProteobacteria αα – – proteobacteriaproteobacteria RhizobialesRhizobiales91.5 %91.5 %
CaCa. Liberibacter spp. are with in . Liberibacter spp. are with in the Rhizobialesthe Rhizobiales
PhylumPhylum ClassClass OrderOrder Order Order %%
Proteobacteria α - proteobacteria
Rhizobiales 29
Unclassified 3.2β -
proteobacteriaBurkholderiales 15.6
γ - proteobacteria
Pseudomonodales
Xanthomonadales
5.9
Unclassified Unclassified 0.5Bacteroidetes Unclassified Unclassified 43.0Actinobacteria Actinobacteria Actinomycetales 0.5
Deinococcusthermus
Deinococci Deinococcales 2.2
Bacterial Diversity StudyBacterial Diversity StudyAsymptomatic GrovesAsymptomatic Groves
ProteobacteriaProteobacteria αα – – proteobacteriaproteobacteria Rhizobiales Rhizobiales 29 % 29 %
Future DirectionsFuture DirectionsTo look at bacterial populations before and after infection in:•Psyllids•Dodder•Periwinckle•Tobacco
To look at bacterial populations before and after infection in:•Psyllids•Dodder•Periwinckle•Tobacco
AsymptomaAsymptomatictic
grovegrove
HLB HLB infectedinfected grovegrove
Bacterial diversity of roots from both asymptomatic and HLB infected groves
Bacterial diversity of roots from both asymptomatic and HLB infected groves
HOST RANGE HOST RANGE EXPERIMENTSEXPERIMENTS
Questionable whether resistance occurs in Questionable whether resistance occurs in Citrus Citrus speciesspecies and relativesand relatives
Lots of ‘tolerance’ in greenhouse, but plants Lots of ‘tolerance’ in greenhouse, but plants eventually dieeventually die
Even if tolerant citrus species are found, Even if tolerant citrus species are found, tolerance tolerance cannot be moved into commercial cannot be moved into commercial scions by scions by conventional breedingconventional breeding
Citrus varieties and relatives that have been inoculated
Citrus varieties and relatives that have been inoculated
11 CitrusCitrus macrophyllamacrophylla (Alemow)(Alemow)
22 Valencia Sweet OrangeValencia Sweet Orange33 Flame GrapefruitFlame Grapefruit44 Nules clementine Nules clementine
(mandarin)(mandarin)55 Minneola TangeloMinneola Tangelo66 Eureka lemonEureka lemon77 Volkamer LemonVolkamer Lemon88 Persian limePersian lime99 Mexican limeMexican lime1010 CitronCitron1111 CarrizoCarrizo1212 PoncirusPoncirus trifoliatatrifoliata1313 CitrusCitrus halimiihalimii1414 CitrusCitrus indicaindica1515 CitrusCitrus micanthramicanthra var. var.
microcarpamicrocarpa1616 CitrusCitrus ambyllocarpaambyllocarpa
11 CitrusCitrus macrophyllamacrophylla (Alemow)(Alemow)
22 Valencia Sweet OrangeValencia Sweet Orange33 Flame GrapefruitFlame Grapefruit44 Nules clementine Nules clementine
(mandarin)(mandarin)55 Minneola TangeloMinneola Tangelo66 Eureka lemonEureka lemon77 Volkamer LemonVolkamer Lemon88 Persian limePersian lime99 Mexican limeMexican lime1010 CitronCitron1111 CarrizoCarrizo1212 PoncirusPoncirus trifoliatatrifoliata1313 CitrusCitrus halimiihalimii1414 CitrusCitrus indicaindica1515 CitrusCitrus micanthramicanthra var. var.
microcarpamicrocarpa1616 CitrusCitrus ambyllocarpaambyllocarpa
17 Sour orange18 Meiwa kumquat19 Khalily20 Citrus hystrix21 Swingle citrumelo22 Sun Chu Sha (mandarin)23 Palestine Sweet lime24 Murraya paniculata25 Citrus latipes26 Cleopatra mandarin27 Madam Vinous Sweet
Orange28 Duncan grapefruit29 Ling Ping Yau pummelo30 Hirado Buntan Pink
pummelo31 Siamese Sweet pummelo32 Severinia buxifolia
17 Sour orange18 Meiwa kumquat19 Khalily20 Citrus hystrix21 Swingle citrumelo22 Sun Chu Sha (mandarin)23 Palestine Sweet lime24 Murraya paniculata25 Citrus latipes26 Cleopatra mandarin27 Madam Vinous Sweet
Orange28 Duncan grapefruit29 Ling Ping Yau pummelo30 Hirado Buntan Pink
pummelo31 Siamese Sweet pummelo32 Severinia buxifolia
Healthy Infected Healthy Infected Healthy Infected
• Research ResultsResearch Results– No citrus cultivar or relative found to be No citrus cultivar or relative found to be
resistant to HLBresistant to HLB– Some cultivars more tolerant to HLBSome cultivars more tolerant to HLB– Symptoms less severeSymptoms less severe
Cleopatra mandarinCleopatra mandarin Citrus macrophyllaCitrus macrophylla Persian lime Persian lime
+++ +++ +++Relative number of Ca. Liberibacter cells
CitrusCitrus latipeslatipes++
Mexican LimeMexican Lime++++++
Sun Chu Sha (mandarin)Sun Chu Sha (mandarin)++++++
Volkamer LemonVolkamer Lemon++++++
Valencia Sweet OrangeValencia Sweet Orange++++++
Khalily/CarrizoKhalily/Carrizo
Flame GrapefruitFlame Grapefruit++++
ConclusionsConclusions• 3 species of Ca. Liberibacter are
thought to cause HLB• Only one species is found in Florida• There is good association between
symptoms and Ca. Liberibacter spp.• Citrus species vary in their symptoms
of HLB• The severity of symptoms is not always
associated with the number of Ca. Liberibacter in a plant
• 3 species of Ca. Liberibacter are thought to cause HLB
• Only one species is found in Florida• There is good association between
symptoms and Ca. Liberibacter spp.• Citrus species vary in their symptoms
of HLB• The severity of symptoms is not always
associated with the number of Ca. Liberibacter in a plant
Citrus Research and Education Center
Citrus Research and Education Center
Dr. Ron Brlansky Dr. William Dawson
Dr. Nian Wang
Dr. Ron Brlansky Dr. William Dawson
Dr. Nian Wang