Transcript Greening7May2008

CITRUS GREENING
DISEASE
Presentation by Dr. Jamba Gyeltshen,
4/06/09
1
SYNONYMS FOR GREENING
DISEASE
• South Africa
– Greening
– Yellow branch
– Blotchy mottle
• China
– Yellow shoot (Huanglongbing)
• Taiwan
– Decline (Likubin)
• India
– Die-back
• The Phillippines
– Leaf mottle
• Indonesia
– Vein phloem degeneration
2
CAUSAL ORGANISM
Two ‘Candidatus Liberobacter spp.’
– Liberobacter asiaticum
– Liberobacter africanum
Candidatus in scientific
classification is a formal word
that is placed before the genus
and species name of bacteria
that cannot be maintained in a
Bacteriology Culture
Collection. Such type of
bacteria are also known as
fastidious bacteria (nonculturable).
Their low concentration and uneven
distribution presents difficulties to
detect by conventional methods
3
DISTRIBUTION
• Spread over 24 other countries in Asia and
Africa
• In the recent years it has been confirmed
in the Americas: Brazil and USA (Florida)
• No confirmed report from middle East and
North Africa
4
ECONOMIC IMPORTANCE
• Losses difficult to estimate; sometimes
small, sometimes total loss; South Africa
30-100% crop losses recorded in some
areas.
5
SYMPTOMS
• First symptoms- yellowing along the veins
or blotchy mottle
• Sometimes chlorotic mottle resembling
zinc or iron deficiency
• Lopsided fruit that are bitter in taste and
have aborted seeds
• Premature fruit drop
• Green color retention at maturity
6
Leaf symptoms
• Pummelo (top): yellowing,
mottling, and vein corking
• Sweet orange (middle): small
in size and showing symptoms
of zinc deficiency (3 leaves);
mature, mottled leaves which
are curling outwards
• Mandarin: yellowing and
mottling
• http://www.fftc.agnet.org/librar
y/image/tn2001002f1.html
7
Symptoms on fruits
• Diseased twig with yellow
leaves and diseased fruit
of Tankan tangor. (left):
the fruit is small and pale
green in color. A healthy
green leaf and normal
large fruit are shown to
the right.
http://www.fftc.agnet.org/li
brary/image/tn2001002f4.
html
8
SYMPTOM VARIATION
• In Asia: extensive yellowing, dieback, and
decline
• In China young trees have been killed in 12 years.
• Root systems remain poorly developed
with relatively few fibrous roots
• New root growth suppressed and roots
often start decaying from the rootlets.
9
TRANSMISSION
• Experimentally transmitted by dodder to
periwinkle (Cantharus roseus)
• Consistently transmitted via grafts but not
through budding
• Insect vectors: psyllids
10
The Asian citrus psylla
• Fig. The Asian citrus psylla Diaphorina citri, which
transmits the Asian strain of the greening organism
11
Life History
• Eggs hatch in about 2-4 days.
A female lays up to 800 eggs
during her lifetime of several
months. There are five
nymphal instars. The complete
life cycle ranges from 2 to 9
weeks depending upon food
and temperature. This may
result in up to 30 overlapping
generations per year in hot
climate.
• http://ipm.ifas.ufl.edu/agricultur
al/fruit/citrus/ASP-hoy.htm
12
Asian psyllid
• Diaphorina citri – heat tolerant
» psyllids can carry the pathogen throughout their adult
life; lifespan=90 days
» 100% transmission when feeding for at least 1 hr
» PCR assays +ve 2 months after inoculation
» Symptoms developed 8 months after inoculation
» (Hung et al., 2001)
13
African citrus psyllid
• Trioza erytreae -heat sensitive
» no symptoms appear above 30 deg. C
» 32 deg. C all stages killed (lab tests);
» 27 deg. C 52% mortality
» 21 deg 9% mortality
» requires 1 day feeding; latent period 7 days
» 4% new trees affected per day
(Hung, et al., 2004)
14
Disease management
•
•
•
•
Once infected, it is difficult to control
Control of vectors
Healthy propagating materials
Quarantine
15
REFERENCES
•
da Graca J. V. 1991. Citrus greening disease. Annual Review of Phytopatholgy
29:109-136.
•
Hung, T. H., S. C. Hung, C. N. Chen, M. H. Hsu, and H. J. Su, 2004. Detection by
PCR of Candidatus Liberibacter asiaticus, the bacterium causing huanglongbing in
vector psyllids: application to the study of vector-pathogen relationships. Plant
Pathology 53: 96-102.
•
•
Hung, T. H., M. L. Wu, and H. J. Su, 1999. Development of a rapid method for the
diagnosis of citrus greening disease using the polymerase chain reaction. J.
Phytopathology 147:599-604.
•
Jagoueix, S., J. M. Bové, and M. Garnier. 1996. PCR detection of the two
‘Candidatus’ liberobacter species associated with greening disease of citrus.
Molecular and cellular probes 10:43-50.
•
Knapp, J. L., S. Halbert, R. Lee, M. Hoy, R. Clark, and M. Kesinger, 2004.
Agricultural IPM: Fruit (Citrus):The Asian Citrus Psyllid and Citrus Greening Disease.
IFAS, University of Florida. IPM Florida website
http://ipm.ifas.ufl.edu/agricultural/fruit/citrus/ASP-hoy.htm doi 11/21/04
16