1

Virus & Virus-like Diseases ofCitrus & Avocado

John V da GracaTexas A&M University-Kingsville

j-dagraca@tamu.edu

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.

2

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

3

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

4

Psorosis

PsyllaTatterleaf

BlightWitches’ broom disease of lime

5

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)