HUANGLONGBING (HLB) HOST RANGE AND BACTERIAL SPECIES DIVERSITY Dr. Megan Dewdney Assistant Professor and Extension Specialist

Outline 1.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 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 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 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 Study Asymptomatic grove HLB infected grove 177 samples 186 samples

PhylumClassOrder Order % Proteobacteria α - proteobacteria Rhizobiales91.5 Unclassified4.5 γ - proteobacteria Enterobacteriales1.1 BacteroidetesUnclassifiedUnclassified5.6 FirmicutesBacilliBacilliales0.5 Bacterial Diversity Study Symptomatic Groves Proteobacteriaα – proteobacteriaRhizobiales91.5 % Ca. Liberibacter spp. are with in the Rhizobiales

PhylumClassOrder Order % Proteobacteriaα - proteobacteriaRhizobiales29 Unclassified3.2 β - proteobacteriaBurkholderiales15.6 γ - proteobacteriaPseudomonodales Xanthomonadales5.9 Unclassified 0.5 BacteroidetesUnclassified 43.0 Actinobacteria Actinomycetales0.5 DeinococcusthermusDeinococciDeinococcales2.2 Bacterial Diversity Study Asymptomatic Groves Proteobacteria α – proteobacteria Rhizobiales 29 %

Future Directions To 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 Asymptomaticgrove HLB infected grove grove Bacterial diversity of roots from both asymptomatic and HLB infected groves

HOST RANGE EXPERIMENTS Questionable whether resistance occurs in Citrus species and relatives Lots of ‘tolerance’ in greenhouse, but plants eventually die Even if tolerant citrus species are found, tolerance cannot be moved into commercial scions by conventional breeding

Citrus varieties and relatives that have been inoculated 1Citrus macrophylla (Alemow) 2Valencia Sweet Orange 3Flame Grapefruit 4Nules clementine (mandarin) 5Minneola Tangelo 6Eureka lemon 7Volkamer Lemon 8Persian lime 9Mexican lime 10Citron 11Carrizo 12Poncirus trifoliata 13Citrus halimii 14Citrus indica 15Citrus micanthra var. microcarpa 16Citrus ambyllocarpa 1Citrus macrophylla (Alemow) 2Valencia Sweet Orange 3Flame Grapefruit 4Nules clementine (mandarin) 5Minneola Tangelo 6Eureka lemon 7Volkamer Lemon 8Persian lime 9Mexican lime 10Citron 11Carrizo 12Poncirus trifoliata 13Citrus halimii 14Citrus indica 15Citrus micanthra var. microcarpa 16Citrus ambyllocarpa 17Sour orange 18Meiwa kumquat 19Khalily 20Citrus hystrix 21Swingle citrumelo 22Sun Chu Sha (mandarin) 23Palestine Sweet lime 24Murraya paniculata 25Citrus latipes 26Cleopatra mandarin 27Madam Vinous Sweet Orange 28Duncan grapefruit 29Ling Ping Yau pummelo 30Hirado Buntan Pink pummelo 31Siamese Sweet pummelo 32Severinia buxifolia

Healthy Infected Research ResultsResearch Results –No citrus cultivar or relative found to be resistant to HLB –Some cultivars more tolerant to HLB –Symptoms less severe Cleopatra mandarin Citrus macrophylla Persian lime Relative number of Ca. Liberibacter cells

Citrus latipes + Mexican Lime +++

Sun Chu Sha (mandarin) +++ Volkamer Lemon +++

Valencia Sweet Orange +++Khalily/Carrizo Flame Grapefruit ++

Conclusions 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 Dr. Ron Brlansky Dr. William Dawson Dr. Nian Wang Dr. Ron Brlansky Dr. William Dawson Dr. Nian Wang