Citrus tristeza virus
The S. Tolkowsky Laboratory, Department of Virology, The Volcani Centre, Bet Dagan, Israel
R. F. Lee
University of Florida, Institute of Food and Agricultural Science, Citrus Research and Education Center, Lake Alfred, Florida 33850, USA
Disease described by Webber (1925) and
Toxopeus (1937); aphid and graft transmissibility reported by
Meneghini (1946) and
Fawcett & Wallace (1946).
- Citrus quick decline virus (Fawcett & Wallace, 1946)
- Podredumbre de las raicillas in Argentina (Zeman, 1931)
- Lime die-back virus (Hughes & Lister, 1949)
- Grapefruit stem pitting virus (Oberholzer et al., 1949)
- Hassaku dwarf virus (Tanaka et al., 1969)
A virus with flexuous filamentous particles 2000 nm long and 10-11 nm in diameter
containing single-stranded RNA. Infects a narrow range of hosts mostly restricted to
the Rutaceae. Transmitted mechanically with difficulty and in a semi-persistent manner
by a few aphid species.
Tristeza, or quick decline (Fig.1
), of many commercial varieties of Citrus
sour orange (C. aurantium)
rootstocks; the severity of symptoms depends on the virus
strain, some strains causing almost no damage. Tristeza was first recognized as a
scion/rootstock disease, no symptoms appearing in plants on tolerant rootstocks. Symptoms
include rapid wilting of trees on sour orange rootstocks, and root damage; honeycombing
often occurs immediately below the bud union on the sour orange stock. When trees decline
rapidly, a yellow-brown stain is sometimes present at the bud union and on the inner
surface of the bark patch (Fig.2
). Stunting of young trees propagated on sour orange
rootstocks occurs in Florida. Stem-pitting and loss of plant vigour occurs on grapefruit
scions in South Africa, Australia, and in the Far East (Fig.3
stem-pitting regardless of the rootstock occurs on certain sweet orange (C. sinensis)
varieties, e.g. Pera in Brazil, California and the Far East. Probably the most
devastating disease caused by the virus is dieback of limes (C. aurantifolia)
irrespective of rootstock. Certain Passiflora
species in the jungles of
South America show serious wilt symptoms.
Common in the Far East, Australia, Africa, India, South, Central and North America,
and most other citrus growing areas. Only certain parts of the Mediterranean region are
still free of the virus.
Host Range and Symptomatology
Most varieties of Citrus
and a few species in certain other genera of the
family Rutaceae, such as Aegle marmelos, Aeglopsis chevalieri, Afraegle paniculata,
Citropsis gilletiana, Microcitrus australis,
and Pamburus missionis,
(Muller & Garnsey, 1984
A majority are tolerant, however, of commonly
occurring strains of the virus. Certain Passiflora
species such as P. gracilis
(Muller et al., 1974
P. caerulea, P. incense
and P. incarnata
(Roistacher & Bar-Joseph, 1987b
are sensitive, whereas other species are tolerant or immune
(Bar-Joseph et al., 1989
Citrus aurantifolia (Key lime, Mexican lime, and various other names in different
parts of the world) is the most commonly used indicator plant. It reacts to most strains
of the virus by developing yellow flecks along leaf veins on the upper leaf surface and
water-soaked spots on the lower leaf surface. Intensity of symptoms depends on the virus
strain and the time elapsed after inoculation. Infected leaves are smaller, and may show
cupping and chlorosis. Virulent strains induce vein corking on the upper leaf surface
and may cause severe stem-pitting under the bark.
C. medica (citron) (Fig.5) and C. macrophylla (alemow) show symptoms
similar to those in C. aurantifolia.
C. sinensis (sweet orange): young plants on sour orange (C. aurantium)
rootstocks show decline, the severity depending on the virus strain.
C. aurantium (sour orange), lemon (C. limon) and grapefruit (C.
paradisi) seedlings show stunting and severe yellows when infected with seedling
yellows strains of tristeza virus.
A battery of five indicator plants (Mexican lime seedlings, Navel budded onto sour
orange, sour orange seedlings, Duncan grapefruit seedlings and Madam Vinous seedlings)
has been proposed to index for tristeza infection severity
(Garnsey et al., 1987).
C. aurantifolia, C. excelsa, C. hystrix, and C. macrophylla are good species
for maintaining cultures for purification purposes. C. sinensis is the best species
for maintaining virus cultures over long periods.
The virus probably has one of the most diverse ranges of strains with a wide range of
biological activities. There are four major groups of strains. Mild strains also exist
which are almost symptomless in sensitive indicator plants such as Mexican lime.
Seedling yellows strains. Cause severe stunting and yellowing of lemon, sour
orange and grapefruit. Seedling yellows is principally a greenhouse disease, but lemons
and grapefruit topworked on rootstocks carrying seedling yellows strains of tristeza virus
can show field symptoms.
Grapefruit stem pitting strains. In Australia
(Stubbs, 1964), South Africa
(Oberholzer et al., 1949), and the Far East
(Miyakawa, 1971), infected grapefruit
trees are stunted, the fruit is small and misshapen, and yields are considerably reduced;
the wood of the trunk and large limbs is pitted with longitudinal depressions; in some
instances, the main scaffold branches are twisted and distorted.
Sweet orange stem pitting strains. In Brazil, Colombia, Hawaii and the Far East,
severe isolates induce severe stem-pitting and decline in certain sweet orange varieties
regardless of the rootstock combination. With the Capao Bonito strain in Brazil
(Muller et al., 1968) and Hassaku dwarf strain in Japan
(Miyakawa, 1971), fruit size and
yield are considerably reduced.
Lime die-back strain
(Hughes & Lister, 1949). Causes vein flecking on
young leaves, severe pitting of wood of twigs and branches, stunting of trees, and
die-back with eventual death.
Transmission by VectorsToxoptera citricida,
the oriental citrus aphid, and Aphis gossypii
are the most efficient vectors
Costa & Grant, 1951
Bar-Joseph & Loebenstein, 1973
Roistacher & Bar-Joseph, 1987a
and in a few cases T. aurantii
also have been reported to
transmit the virus
(Dickson et al., 1951
Norman & Grant, 1956
). The virus
can be acquired and transmitted by aphids, usually after acquisition and inoculation
feeding periods of at least 30 min; frequencies of transmission are positively
correlated with the length of the acquisition period up to 24 h and the length of the
inoculation period up to 6 h
(Costa & Grant, 1951
Raccah et al., 1976
Transmission is in the semi-persistent manner with no latent period; infectivity is
lost within 48 h of acquisition
(Bar-Joseph et al., 1979a
Transmission through Seed
Transmission by Dodder
Reported to be transmitted by Cuscuta americana
(Knorr & Price, 1954
), but this report is not confirmed.
Moderately immunogenic. Sodium dodecyl sulphate (SDS)-immunodiffusion
(Gonsalves et al., 1978
Garnsey et al., 1979
enzyme-linked immunosorbent assay (ELISA)
(Bar-Joseph et al., 1979b
), radio-immunosorbent assay
(Lee et al., 1981
), immunofluorescent assays
(Tsuchizaki et al., 1978
Sasaki et al., 1978
Brlansky et al., 1984
), immunospecific electron microscopy (ISEM)
(Garnsey et al., 1980
Brlansky et al., 1984
), and western blotting
(Lee et al., 1987
have been used for detecting the virus. Polyclonal
antisera have been prepared in rabbits against unfixed virus particles, formaldehyde-fixed
particles, and SDS-dissociated particles
(Gonsalves et al., 1978
epitopes were suggested based on the types of serological assay in which antisera were effective
(Brlansky et al., 1984
Polyclonal antisera also have been produced in chickens
(Bar-Joseph & Malkinson, 1980
The double antibody sandwich (DAS) form of ELISA has been the most commonly used
(Bar-Joseph et al., 1979b
several modifications have been developed. Indirect ELISA systems use commercially
available goat anti-rabbit, anti-chicken or anti-mouse conjugates. Avidin-biotin
(Irey et al., 1988
) and enzyme-amplification
(Ben-Ze'ev et al., 1988
been used to increase the sensitivity of ELISA for detecting citrus tristeza virus.
Plate trapped antigen (PTA)-ELISA also has been applied, especially for use with
(Vela et al., 1986
Permar et al., 1990
polyclonal antibodies so far produced against citrus tristeza virus appear to react
with all strains tested
(Bar-Joseph et al., 1989
). Several monoclonal antibodies
have been produced; most have reacted with all citrus tristeza virus strains tested
(Vela et al., 1986
Gumpf et al., 1987
), but one is capable of
differentiating between severe and mild strains
(Irey et al., 1988
Permar et al., 1990
The chemical and physical properties of the particles place the virus as a member
of the closterovirus group
. No serological cross-reactivity with other members of the
closterovirus group has been reported.
Some mild strains, but not all, are capable of cross-protecting plants against severe strains
Fig.6). Mild strain cross-protection is used commercially to
protect against stem-pitting of Pera sweet orange in Brazil
(Costa & Muller, 1980)
and against stem-pitting of grapefruit in South Africa
(De Lange et al., 1981).
Stability in Sap
The virus is mechanically transmissible by slash inoculation of the bark of citron
plants using extraction procedures that maintain virus integrity
(Garnsey et al., 1977
Muller & Garnsey, 1984
This method of assay has been used to study the
stability of the virus in crude sap extracts from infected bark; the thermal inactivation
point (10 min) is about 50°C, and infectivity of sap persists for 24 h at room
temperature, 5 days at 4°C and -60°C, and for 5 years in lyophilized preparations
stored at -20°C. Infectivity is destroyed by RNase, but not by DNase. Infectivity
persists after incubation in a solution of 0.005 M EDTA, 0.5 M NaCl and 0.005 M
. The virus retained infectivity when dialysed against pH 6.0 to 9.0
buffers, then back to pH 7.6 Tris-HCI buffer, but not when dialysed at pH values lower than 6.0
(Garnsey et al., 1981
R. F. Lee & R. H. Brlansky, unpublished data).
1. Bar-Joseph et al., (1985)
Grind bark from young flushes of infected citron
plants with a mortar and pestle in the presence of liquid nitrogen; thaw frozen powder
in 0.1 M Tris-HCl, pH 7.8 (1 g bark powder/5 ml buffer), filter, re-extract pulp, combine
filtrates, centrifuge at 4000 g
for 10 min. Collect supernatant fluid and
centrifuge at 8000 g
for 5 min. Filter supernatant fluid through paper
tissue; add polyethylene glycol, M. Wt 6000 (PEG) and NaCl to final concentrations of 6%
and 1.1% (w/v), respectively. After 30-60 min at 4°C, centrifuge at 19,500 g
for 15 min. Resuspend pellet in 25 ml 0.04 M sodium phosphate buffer, pH 8.2, (PB)
for 1 h, centrifuge at 5900 g
for 10 min. Float 8 ml samples of supernatant
fluid on step gradients made by layering 1 ml each of 0, 15, 22.5 and 30% (w/v)
dissolved in a solution of PB and 10% (w/v) sucrose.
Centrifuge 2.5 h at 38,500 rev./min in a Beckman SW41 rotor at 8°C. Locate the
virus-containing fractions by EM or ELISA. For further purification, dialyse against
0.05 M Tris-HCl, pH 7.8, and centrifuge in a 10-40% sucrose gradient for 3 h at 25,000
rev./min at 4°C in a Beckman SW27 rotor; concentrate the virus particles by
ultracentrifugation and resuspend in 0.05 M Tris-HCl buffer, pH 7.8.
2. Lee et al. (1987).
Collect bark tissue and leaf midribs from young flushes of
citron, Mexican lime or C. excelsa, freeze on dry ice and pulverize in a mortar and
pestle. Homogenize the frozen tissue powder in 0.1 M Tris-HCl buffer, pH 8.4, containing
0.1% (v/v) Triton X-100 (1 g tissue/5 ml buffer). Centrifuge at 10,000 g for
20 min, collect supernatant fluid and add PEG and NaCl to final concentrations of 4.0 and
0.8% (w/v), respectively. Stir 1 h at 4°C, centrifuge at 10,000 g for
20 min. Resuspend pellet in 0.04 M potassium phosphate buffer, pH 8.0 (1.3 ml/g tissue
fresh wt). Stir suspension for 1 h at 4°C, then centrifuge at 5000 g
for 10 min. Adjust supernatant fluid to a final concentration of 5% (w/v) PEG, 1% (w/v)
NaCl, and stir 1 h at 4°C. Centrifuge mixture at 10,000 g for 15 min.
Resuspend pellet in 30 ml 0.05 M Tris-HCl, pH 8.0, stir 1 h at 4°C. Centrifuge
suspension at 5000 g for 10 min, float 5 ml supernatant fluid onto
preformed step isopycnic (PSI) gradient made by overlayering 2.0, 2.0, 2.0 and 1.0 ml
of 8.83, 17.66, 26.5 and 35.33% (all w/w), respectively, of Cs2SO4
dissolved in 0.05 M Tris-HCl buffer, pH 8.0. Centrifuge at 36,000 rev./min for 15 h at
4°C in a Beckman SW41 rotor. Identify the virus-containing fractions by ELISA and/or
ISEM, dialyse overnight against 0.05 M Tris-HCl buffer, pH 8.0, and centrifuge at 10,000
g for 10 min. Adjust volume of supernatant fluid to 22 ml with 0.05 M
Tris-HCl buffer, pH 8.0, mix with 17.0 ml of a 53% (w/w) solution of
Cs2SO4 in 0.05 M Tris-HCl buffer, pH 8.0, place in VTi50 (or
Type 60) rotor and centrifuge at 50,000 rev./min for 24 h at 4°C, then locate the
virus-containing fractions by ELISA and/or ISEM. Yields of 0.4 to 5.1
A260 units per 100 g bark tissue are obtained, depending upon virus
strain and purification host.
3. Lee et al. (1988).
Strip bark from young flushes, chop into pieces about
1-2 mm wide, and add to extraction buffer containing 0.1 M sodium citrate, pH 6.0,
with 2% Driselase enzyme, 10% sucrose, 0.5% 2-mercaptoethanol and 1 mM
phenylmethylsulphonylfluoride (1 g tissue/4 ml buffer). Shake preparation at 6°C
for 1-2 h, add 1/200 volume of 3.0 N NaOH to raise pH, and freeze at -20°C for at
least 1 h. Thaw, stir with a glass rod, filter, and centrifuge at 9000 g
for 10 min at 4°C. Add Triton X-100 to supernatant fluid to a final concentration
of 0.2%. Overlay 27 ml of the virus preparation onto a step gradient formed by layering
5 ml 25% sucrose over 5 ml 60% sucrose, both made up in 0.05 M Tris-HCl, pH 8.0.
Centrifuge at 19,000 rev./min for 15 h at 4°C in a Beckman SW28 rotor. Collect 1.5
ml fractions from the bottom of the tube, and locate the virus by ELISA; it is usually
in the second and third fractions. Pool virus-containing fractions and layer onto a 1.5
x 7 cm column of Bio-gel A-15, 100-200 mesh; collect 1 ml fractions in tubes containing
0.25 ml 25% sucrose in 0.05 M Tris-HCl buffer, pH 8.0. The virus elutes in the void
volume; pool virus-containing fractions and adjust to 22.5 ml with 0.05 M Tris-HCl
buffer, pH 8.0, then mix with 17.5 ml of 3 molal Cs2SO4 made
in 0.05 M Tris-HCl buffer, pH 8.0. Centrifuge at 50,000 rev./min for 18 h at 4°C
in a Beckman VTi50 or Type 60 rotor. Locate virus-containing fractions by ELISA, combine
and dialyse against 0.05 M Tris-HCl, pH 8.0, containing 10% sucrose, then centrifuge at
9000 g for 10 min at 4°C. Layer supernatant fluid onto a preformed
step gradient made up of 2 ml each of 0.5, 1.0 and 1.5 molal Cs2SO4
in 0.05 M Tris-HCl buffer, pH 8.0. Centrifuge at 36,000 rev./min for 15 h at 4°C in
a Beckman SW41 rotor. Fractionate tubes, combine virus-containing fractions, dialyse
against 0.05 M Tris-HCl buffer, pH 8.0, containing 10% sucrose, and then centrifuge at
8000 g for 10 min at 4°C.
Other purification procedures have been reported by
Bar-Joseph et al., (1970),
Bar-Joseph et al., (1972), and
Gonsalves et al., (1978).
Properties of Particles
Sedimentation coefficient (s20,w
) determined in sucrose density
gradients: 140 ± 10 S at zero depth
(Bar-Joseph et al., 1970
(Bar-Joseph et al., 1972;
Tsuchizaki et al., 1978);
1.12 ± 0.01 not corrected for light-scattering
(Lee et al., 1987).
Buoyant density: 1.328 g/cm3 in CsCl after formaldehyde fixation
(Bar-Joseph et al., 1972);
1.2570 g/cm3 unfixed in Cs2SO4
(Lee et al., 1987).
Particles are very flexuous filaments 10-11 nm in diameter and 1900-2000 nm in length
visible in leaf dip preparations, or in large numbers in bark dip preparations, mounted in phosphotungstate
(Bar-Joseph et al., 1976
). They are well preserved in
ISEM in which antisera prepared against unfixed whole virus diluted 1/500 with 0.02 M
Tris-HCl buffer, pH 8.0, are used to coat parlodion-coated grids. Grids for ISEM are
positively stained for 1 min on drops of 5% uranyl acetate in 50% ethanol, rinsed for
20 sec in 95% ethanol, and air-dried (Lee et al., 1987
Particle CompositionNucleic acid:
RNA, non-segmented, single-stranded, M. Wt about 6.5 x
or 20 kilobases
(Bar-Joseph et al., 1979a
Bar-Joseph et al., 1985
and without a poly-A tail at the 3' end (M. Ballas & M.
Bar-Joseph, unpublished data). The RNA in the particles is positive sense
(Lee et al., 1988
Protein: Two proteins are associated with purified preparations of Florida
strains: a major coat protein (CP1) of 23,000 daltons and a minor coat protein (CP2)
of 21,000 daltons, present in a ratio of 5/1 (CP1/CP2). The amino acid composition of
CP1 for a severe Florida strain is reported as: (molar ratio) lys 17; his 4; arg 8; asp
22; thr 12; ser 16; glu 13; pro 5; gly 24; ala 16; cys 1; val 13; met 1; ile 8; leu 20; tyr 4; phe 4
(Lee et al., 1988). Recent analysis of the coat proteins of strains
from Spain and Israel indicate M. Wt of 27,000-28,000 and 26,000 for CP1 and CP2, respectively
(Dulieu & Bar-Joseph, 1990;
Guerri et al., 1990).
The RNA can be translated in vitro
in rabbit reticulocyte lysates to produce
a product of about 26,000 daltons which is precipitated by antiserum to virus particles
(Lee et al., 1988
Sequence homology between strains was compared using cDNA from a library obtained by random priming
(Rosner et al., 1983). Six of nine strains hybridized with all
the tested cDNA clones, the three other strains hybridized differentially
(Rosner & Bar-Joseph, 1984);
two of these cDNA clones were able to detect a specific virulent strain
in Florida by differential hybridization
(Rosner et al., 1986). cDNA libraries
also have been prepared by oligo dT tailing; two clones from these libraries were selected
that together represent 70% of the CTV genome with a 2200 bp overlap between the two clones
Calvert et al., 1986,
A full length replicative form of 13.3 x 106 daltons (Fig.7) has been
found by extraction, purification, and polyacrylamide gel analysis of dsRNA
(Dodds & Bar-Joseph, 1983).
Also present are a number of subgenomic dsRNA species whose size
and relative amount depend on virus strain and host (Fig.7)
Dodds et al., 1987).
These dsRNA molecules have been denatured and translated in vitro in
a rabbit reticulocyte lysate system. The translational product of a 0.8 kbp dsRNA
co-electrophoresed with the viral coat protein and was immunoprecipitated by virus-
specific antisera (Dulieu & Bar-Joseph, 1990).
Relations with Cells and Tissues
Flexuous filamentous particles occur in large numbers in phloem cells but not in other
cells. Aggregates of virus particles, called chromatic cells
) or inclusion bodies
(Christie & Edwardson, 1977
), are often found in parenchyma or
parenchyma-like cells adjacent to sieve tubes in the phloem. These inclusion bodies
stain purple with Azure A (Fig.8
), appearing as cross-banded structures
Fluorescent antibody staining techniques have been used to detect inclusion bodies in situ
(Brlansky et al., 1988
). Quantitative differences in number of
inclusion bodies between mild and severe strains have been reported in certain hosts
such as Mexican lime and C. hystrix
). Necrosis occurs at the
bud union as a result of destruction of phloem tissues in trees on sour orange
rootstock which are undergoing quick decline.
Ecology and Control
Once introduced into a citrus-growing area, tristeza virus is spread naturally by
aphids and becomes endemic. Introduction into new areas can be prevented by quarantine
measures and budwood certification schemes. The development of rapid detection methods
for tristeza virus has facilitated large-scale surveys and eradication schemes which
have enabled virus incidence to be suppressed to low levels; survival of the virus in
wild hosts has not appeared to present a problem. In some instances, such schemes have
prolonged the use of sour orange as a rootstock. In areas where tree losses occur on
sour orange rootstocks, replants are usually grown on tristeza-tolerant rootstocks
such as rough lemon, Rangpur lime, trifoliate orange or trifoliate hybrids. Resistance
to stem-pitting strains of tristeza virus is not available in commercially acceptable
grapefruit, sweet oranges or limes, and mild strain cross-protection is presently the
only method available for control of these strains.
Citrus blight, a disease of unknown aetiology, results in decline symptoms in
trees on sour orange rootstocks similar to those induced by tristeza virus. Tristeza
decline on sour orange rootstocks can be differentiated from blight by the syringe injection test
(Lee et al., 1984
); tristeza-affected trees take up water in
the trunk wood whereas blight-affected trees do not.
Citrus greening, a disease caused by a fastidious, phloem-limited bacterium, is
endemic in many of the citrus-growing areas where tristeza virus also is endemic, and
its symptoms are often similar to those of tristeza. Greening can be diagnosed by
grafting to seedlings of mandarin orange, a differential indicator which does not react
to tristeza virus.
- Bar-Joseph & Loebenstein, Phytopathology 63: 716, 1973.
- Bar-Joseph & Malkinson, J. Virol. Meth. 1: 1, 1980.
- Bar-Joseph, Loebenstein & Cohen, Phytopathology 60: 75, 1970.
- Bar-Joseph, Loebenstein & Cohen, Virology 50: 821, 1972.
- Bar-Joseph, Loebenstein & Cohen, Proc. 7th Conf. int. Org. Citrus Virologists: 39, 1976.
- Bar-Joseph, Garnsey & Gonsalves, Adv. Virus Res. 25: 93, 1979a.
- Bar-Joseph, Garnsey, Gonsalves, Moscovitz, Purcifull, Clark & Loebenstein, Phytopathology 69: 190, 1979b.
- Bar-Joseph, Gumpf, Dodds, Rosner & Ginzburg, Phytopathology 75: 195, 1985.
- Bar-Joseph, Marcus & Lee, A. Rev. Phytopath. 27: 291, 1989.
- Ben-Ze'ev, Frank & Bar-Joseph, Phytoparasitica 16: 343, 1988.
- Brlansky, Phytophylactica 19: 211, 1987.
- Brlansky, Garnsey, Lee & Purcifull, Proc. 9th Conf. int. Org. Citrus Virologists: 337, 1984.
- Brlansky, Lee & Garnsey, Pl. Dis. 72: 1039, 1988.
- Calvert, Ph.D. Thesis, University of Florida, Gainesville, 60 pp., 1987.
- Calvert, Lee & Hiebert, Phytopathology 76: 1090, 1986.
- Calvert, Lee & Hiebert, Phytopathology 77: 1743, 1987.
- Christie & Edwardson, Monogr. Ser. Fla agric. Exp. Stn No. 9, 150 pp., 1977.
- Costa & Grant, Phytopathology 41: 105, 1951.
- Costa & Muller, Pl. Dis. 64: 538, 1980.
- De Lange, Van Vuuren & Bredell, Subtropica 2(5): 11, 1981.
- Dickson, Flock & Johnson, J. econ. Entomol. 44: 172, 1951.
- Dodds & Bar-Joseph, Phytopathology 73: 419, 1983.
- Dodds, Jordan, Roistacher & Jarupat, Intervirology 27: 177, 1987.
- Dulieu & Bar-Joseph, J. gen. Virol. 71: 443, 1990.
- Fawcett & Wallace, Calif. Citrogr. 32: 88, 1946.
- Fulton, A. Rev. Phytopath. 24: 67, 1986.
- Garnsey, Gonsalves & Purcifull, Phytopathology 67: 965, 1977.
- Garnsey, Gonsalves & Purcifull, Phytopathology 69: 88, 1979.
- Garnsey, Christie, Derrick & Bar-Joseph, Proc. 8th Conf. int. Org. Citrus Virologists: 9, 1980.
- Garnsey, Lee & Brlansky, Phytopathology 71: 218, 1981.
- Garnsey, Gumpf, Roistacher, Civerolo, Lee, Yokomi & Bar-Joseph, Phytophylactica 19: 151, 1987.
- Gonsalves, Purcifull & Garnsey, Phytopathology 68: 553, 1978.
- Guerri, Moreno & Lee, Phytopathology 80: 692, 1990.
- Gumpf, Zheng, Moreno & Diaz, Phytophylactica 19: 159, 1987.
- Hughes & Lister, Nature, Lond. 164: 880, 1949.
- Irey, Permar & Garnsey, Proc. Fla St. hort. Soc. 101: 73, 1988.
- Knorr & Price, Rep. Fla agric. Exp. Stn No. 195, 1954.
- Lee, Proc. Fla St. hort. Soc. 97: 53, 1984.
- Lee, Timmer, Purcifull & Garnsey, Phytopathology 71: 889, 1981.
- Lee, Marais, Timmer & Graham, Pl. Dis. 68: 511, 1984.
- Lee, Garnsey, Brlansky & Goheen, Phytopathology 77: 543, 1987.
- Lee, Calvert, Nagel & Hubbard, Phytopathology 78: 1221, 1988.
- Meneghini, Biologico 12: 285, 1946.
- Miyakawa, Bull. Tokushima hort. Exp. Stn 4: 1, 1971.
- Muller & Garnsey, Proc. 9th Conf. int. Org. Citrus Virologists: 33, 1984.
- Muller, Rodriguez & Costa, Proc. 4th Conf. int. Org. Citrus Virologists: 64, 1968.
- Muller, Costa, Kitajima & Camargo, Proc. 6th Conf. int. Org. Citrus Virologists: 75, 1974.
- Norman & Grant, Proc. Fla St. hort. Soc. 69: 38, 1956.
- Oberholzer, Mathews & Stiemie, Sci. Bull. Dep. Agric. S. Afr. No. 287, 17 pp., 1949.
- Permar, Garnsey, Gumpf & Lee, Phytopathology 80: 224, 1990.
- Price, CMI/AAB Descr. Pl. Viruses No. 33, 4 pp., 1970.
- Raccah, Loebenstein & Bar-Joseph, Phytopathology 66: 1102, 1976.
- Roistacher & Bar-Joseph, Phytophylactica 19: 103, 1987a.
- Roistacher & Bar-Joseph, Phytophylactica 19: 179, 1987b.
- Rosner & Bar-Joseph, Virology 139: 189, 1984.
- Rosner, Ginzburg & Bar-Joseph, J. gen. Virol. 64: 1757, 1983.
- Rosner, Lee & Bar-Joseph, Phytopathology 76: 820, 1986.
- Sasaki, Tsuchizaki & Saito, Ann. phytopath. Soc. Jpn 44: 205, 1978.
- Schneider, Citrus Virus Diseases, Univ. Calif. Press, Berkeley, 73, 1959.
- Schneider, A. Rev. Phytopath. 11: 119, 1973.
- Stubbs, Aust. J. agric. Res. 15: 752, 1964.
- Tanaka, Shikata & Sasaki, Proc. 1st int. Citrus Symp: 1445, 1969.
- Toxopeus, J. Pomol. hort. Sci. 14: 360, 1937.
- Tsuchizaki, Sasaki & Saito, Phytopathology 68: 139, 1978.
- Vela, Cambra, Cortes, Moreno, Miquet, Perez De San Roman & Sanz, J. gen.Virol. 67: 91, 1986.
- Webber, Sci. Bull. Dep. Agric. S. Afr. No. 6, 106 pp., 1925.
- Zeman, Physis, Augsburg 19: 410, 1931.
Sweet orange (C. sinensis) tree on sour orange (C. aurantium)
rootstock showing quick decline caused by infection with a virulent strain of tristeza virus.
Yellow-brown stain as sometimes seen at the bud union of trees on sour orange
rootstocks and showing tristeza quick decline.
Severe stem-pitting on the trunk of a grapefruit (C. paradisi) tree
caused by a stem-pitting strain of tristeza virus.
Corking of the leaf veins on the upper leaf surface of a Madam Vinous
sweet orange indicator plant infected with a stem-pitting strain of tristeza virus.
(Above), Flecking along the veins of a citron (C. medica) leaf
infected with tristeza virus. (Below), Healthy leaf.
Mild strain cross-protection in Eureka lemon (C. limon): A,
non-inoculated; B, protected with a non-seedling yellows strain and challenge-inoculated
with a virulent seedling yellows strain; C, inoculated with the virulent strain at the
same time as plant B was challenge-inoculated.
Double stranded (ds) RNA extracted from C. excelsa plants infected
with virulent (T36 and T3) and mild (T30) Florida strains and electrophoresed on a
polyacrylamide gel. The replicative form (RF) is indicated by an arrowhead. DsRNA
preparations from healthy tobacco (H TOB) and from tobacco infected with tobacco mosaic
virus (TMV) are included for size comparison.
Light micrograph of inclusion bodies (arrowheads) in phloem cells associated
with tristeza virus infection. Stained with Azure A. Bar represents 10 µm. (Photo
courtesy of R. H. Brlansky.)
Electron micrograph of a thin section of a phloem cell of Mexican lime (C.
aurantifolia) infected with tristeza virus, showing the banded structure of the
inclusion bodies. Bar represents 500 nm. (Photo courtesy of R. H. Brlansky.)
Electron micrograph of purified tristeza virus particles negatively stained
with uranyl formate. Bar represents 100 nm.