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Virus & Virus-like Diseases ofCitrus & Avocado
John V da GracaTexas A&M University-Kingsville
Virus & Virus-like?Graft transmissible; Some vectored (insect, mite, fungus);Some mechanical
True virusesViroids
ProcaryotesUnknown
Major Citrus Virus & Virus-like Agents/Vectors
• Tristeza Quick decline; stem pitting - Citrus tristeza virus /Aphids• Huanglongbing (Greening) - Liberibacter spp./ Psylla• Psorosis/Scaly bark- Citrus psorosis virus/ Fungus?• Stubborn - Spiroplasma citri / Leafhoppers• Leprosis -Citrus leprosis virus / Mites• Variegated chlorosis- Xylella fastidiosa / Sharpshooters• Witches’ broom of lime - Phytoplasma / Leafhopper• Blight – cause / vector unknown• Exocortis - Citrus exocortis viroid / Mechanical• Cachexia - Hop stunt viroid / Mechanical• Tatterleaf – Citrus tatterleaf virus / Mechanical
Other Virus & Virus-like Diseases• Concave gum, Cristacortis , Impietratura• Infectious variegation, Leaf rugose• Vein enation/Woody gall (Aphids)• Satsuma dwarf, Citrus mosaic (soil vector?)• Citrus yellow mosaic (Mealy bugs)• Dweet mottle (= Citrus leaf blotch?)• Rubbery wood• Multiple sprouting• Measles• Chlorotic dwarf (Whitefly)• Indian ringspots + other ringspotdiseases• Concentric ring blotch/Zonate chlorosis (mites)• Gum pocket, gummy bark, Kassala• Corky vein• Yellow vein clearing/ Yellow mottle• Australian decline (leafhopper?)• Sudden death – NEW – SERIOUS (aphids?) Etc.
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History of Major Diseases
• 1880’s -yellow shoot disease (HLB, greening) - China
• 1890’s - blight - Florida
• 1890’s - sour orange rootstock problems - South Africa
• 1896 - psorosis described – Florida
•1930s – tristeza disease in S.America
• 1934 - psorosis graft transmitted - Florida
• 1943 - HLB graft transmitted - China
• 1946/48 - aphid & graft transmission of tristeza - Brazil
• 1965 - psylla transmission of HLB - South Africa
• 1988 - graft transmission of blight - Florida
Brown citrus aphid
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Acknowledgement ;Tim Gottwald
Tristeza destruction of trees on sour orange rootstock
• South America – approx. 40 million killed since 1930 (BCA)
• Spain – 45 million since 1960 (No BCA)• Florida – 3 million in 2000-02• Total worldwide – over 100 million• Italy – 98% on sour – decline widespread
(No BCA)• 200 million to go? (TX, Mex., Med.)
ExocortisCachexia
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Psorosis
PsyllaTatterleaf
BlightWitches’ broom disease of lime
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Citrus variegated chlorosis
Control
• Prevention :- Used certified disease-free bud/graftwood- Quarantine- Prevent mechanical spread- chlorox disinfection- Mild strain protection (eg CTV)
• Vector control ? Difficult to get 100%(eg. Biocontrolof psylla in Reunion)
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