HUANGLONGBING (HLB) HOST RANGE AND BACTERIAL SPECIES DIVERSITY

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

2. Outline • The bacteria that cause HLB • Bacterial diversity in groves • Citrus host range of HLB

3. Three Species of Bacteria Cause HLB • Ca. Liberibacter asiaticus • only known species in Florida • Vectored by 2 psyllid species • Diaphorinacitri and Triozaerytreae (experimentally) • Heat tolerant • Found on the Indian Subcontinent, Southeast Asia, Arabian peninsula, Brazil, Louisiana and Florida

4. Ca. Liberibacter africanus • Has not been found in Florida • Vectored by 2 psyllid species • Triozaerytreae and Diaphorinacitri (experimentally) • Bacterium and vector heat sensitive • Found in many African countries, Madagascar and Yemen at higher altitudes

5. Ca. Liberibacter americanus • Newest species of bacteria that cause HLB • Not found in Florida • Vectored by Diaphorinacitri • 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

6. New Disease of Potato –Zebra Chip • Caused by a newly identified Ca. Liberibacter • Identified in New Zealand • Vectored by the potato/tomato psyllid • Bactericeracockerelli • Also damages tomatoes and peppers • From South Texas to Colorado as well as Mexico, Guatemala

7. Bacterial Diversity Study 186 samples Asymptomatic grove 177 samples HLB infected grove

8. Bacterial Diversity Study Symptomatic Groves Proteobacteriaα – proteobacteriaRhizobiales 91.5 % Ca. Liberibacter spp. are with in the Rhizobiales

9. Bacterial Diversity Study Asymptomatic Groves Proteobacteriaα – proteobacteriaRhizobiales 29 %

10. Future Directions To look atbacterial populations before and after infection in: • Psyllids • Dodder • Periwinckle • Tobacco Asymptomatic grove HLB infected grove Bacterial diversity of roots from both asymptomatic and HLB infected groves

11. HOST RANGE EXPERIMENTS Questionable whether resistance occurs in Citrus speciesand 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

12. 1 Citrusmacrophylla (Alemow) 2 Valencia Sweet Orange 3 Flame Grapefruit 4 Nulesclementine (mandarin) 5 Minneola Tangelo 6 Eureka lemon 7 Volkamer Lemon 8 Persian lime 9 Mexican lime 10 Citron 11 Carrizo 12 Poncirustrifoliata 13 Citrushalimii 14 Citrusindica 15 Citrusmicanthra var. microcarpa 16 Citrusambyllocarpa 17 Sour orange 18 Meiwa kumquat 19 Khalily 20 Citrushystrix 21 Swinglecitrumelo 22 Sun Chu Sha (mandarin) 23 Palestine Sweet lime 24 Murrayapaniculata 25 Citruslatipes 26 Cleopatra mandarin 27 Madam Vinous Sweet Orange 28 Duncan grapefruit 29 Ling Ping Yaupummelo 30 HiradoBuntan Pink pummelo 31 Siamese Sweet pummelo 32 Severiniabuxifolia Citrus varieties and relatives that have been inoculated

14. Research 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 Healthy Infected Healthy Infected Healthy Infected +++ +++ +++ Relative number of Ca. Liberibacter cells

15. Mexican Lime +++ Citruslatipes +

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

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

18. 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

19. Citrus Research and Education Center Dr. Ron Brlansky Dr. William Dawson Dr. Nian Wang