: etn 750 (technical)
Florida Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
J. W. Sites, Dean for Research
University of Florida, Gainesville
A* A* COOK
Introduction ....... ....3............ 3
Virus Diseases ...........4.. .. ..-
Bunchy Top ........ .... .. .. .. 4
Leaf Curl ... ....- -- .......
Papaya Mosaic ... ..... .. .. .... 5
Papaya Ringspot ..... ... .. .. 8
Spotted Wilt -- .........- .. ........ 9
Tobacco Ringspot -. .. .. 12
Yellow Crinkle ............ .. 13
Other Virus-like Diseases of Papaya .14
Literature Cited .. ..................... 15
VIRUS DISEASES OF PAPAYA
A. A. Cook1
Papaya (Carica papaya L.) (13)2 is widely grown in trop-
ica' and semi-tropical latitudes for the edible fruit with delicate
taste. The extensive adaptation of this plant and wide accept-
ance of the fruit offer considerable promise for papaya as a
commercial crop for local and export purposes.
Virus diseases of papaya have been reported from nearly
every continent where the crop is grown, and, in many areas,
severely restrict profitable production. Early publications re-
lating tu these diseases emphasize descriptions of symptoms
observed on naturally infected plants and the common names
applied to them by the investigators. Partly because of geo-
graphic separation, a concerted study and comparison of the
diseases from different areas has not been made. Confusion
,about the identity and diagnostic characteristics of specific
diseases has arisen because of different environmental condi-
tions, disease descriptions from varieties of unknown or un-
related pedigrees, and/or information relative to inconsistent
aspects of syndromes or causes.
A review of existing information about virus diseases of
papaya and related observations of investigators was published
in 1949 (39). A number of reports since then have contributed
significantly to identification of some of the diseases and causal
viruses. Some of these recent publications were mentioned in
the review of Frossard (28).
It is unfortunate that the term "mosaic" has been used both
to describe a type of symptom associated with more than one
disease as well as the common name for a single disease caused
by a distinct, infectious entity. Identification of diseases from
symptoms alone can be quite misleading because of the simi-
larity of syndromes induced by different viruses. In this resume
an attempt was made to relate virus diseases of papaya, pre-
viously described under various names, according to definite
characteristics: i.e., transmissibility by insects, distinctive visi-
ble symptoms (latex flow), virus particle morphology, phys-
1Professor (Plant Pathologist), Department of Plant Pathology, Univer-
sity of Florida, IFAS, Gainesville, Florida, 32601.
2Numbers in parentheses refer to Literature Cited.
ical properties of the causal viruses, and diagnostic host rank
This compilation is intended to serve as a basis for consist"
use of common names of the diseases and to encourage fourth
definitive study of them.
Bunchy top disease was first reported in 1931 from Pue
Rico where it was recognized as the most prevalent of the v'
diseases affecting papaya (23, 24). The disease has been
ported since that time from a number of Caribbean Isl
(Cuba, Haiti, Jamaica, and Trinidad) where it is a major I
lem (1, 14, 66).
Infected plants first exhibit a faint mottling in the upp
leaves which is soon followed by a decided reduction and ye
lowing of laminae. Internodes become progressively shortene,
petioles become stiffened, nearly horizontal and shortened, ar
often show oily-appearing spots. Subsequently there is comply
cessation of apical growth, which, with the shortened int(
nodes, serves to impart a "bunchy top" appearance. Failure oi
latex to exude from wounds on diseased leaves, petioles, stems,
or fruits is a diagnostic characteristic of this disease. Infected
plants are often killed.
Incidence and dissemination of bunchy top disease is de-
pendent on the presence of the leafhopper vector Empoasca
papayae Oman (3, 45, 60). Transmissibility of bunchy top by
grafting and the leafhopper vector has been established (16).
Mycoplasma-like bodies have been found in the sieve tubes and
phloem parenchyma cells of bunchy top infected plants but not
in healthy plants (65).
Application of insecticide to reduce the incidence of the leaf-
hopper vector is recommended. Control has been achieved by
topping infected plants below the point where latex exudes after
wounding (16). The resulting axillary shoots appear to be un-
infected. Complete remission of symptoms has been obtained
after six weeks by soil drenches of 100 ppm chlorotetracycline
or tetracycline hydrochloride at 3-day intervals (65).
This disease, first recorded from Madras in 1939 (59), has
caused losses in both dooryard and commercial plantings but
.parently is confined to India and the Philippines (57).
-Symptoms consist of a severe distortion caused by crinkling
id curling of the leaves, the margins of which are rolled down
id inward. Affected leaves become leathery and brittle with
listed petioles and dark green, thickened veins that appear
'ore noticeable because of accompanying vein-clearing. Dis-
sed plants cease growing, become unproductive, and eventually
Leaf curl has been transmitted by a white fly (Bemisia
-ci Gen.) and grafting but not by mechanical inoculation
Presumed to be caused by a virus, the disease has been
.mitted to tomato (Lycopersicon esculentum Mill.) and
co (Nicotiana tabacum L.). The susceptibility of tobacco
apaya leaf curl and papaya to tobacco leaf curl disease
impted the suggestion that both diseases were caused by the
bacco leaf curl virus.
Roguing of infected plants and routine application of insec-
.:ies for insect control are recommended until more specific
trol procedures have been determined.
As indicated in the introduction, there is much contradictory
information in the literature, particularly that relating to dis-
mases given the common names "mosaic" and "ringspot". Here-
n, diseases that include mottling of the leaves, no reduction of
latex flow from wounds, and are not transmitted by aphids are
considered under the designation papaya mosaic. Distinctive
symptoms on selected host plants (Table 1) and defined morpho-
logical and physical properties of the associated virus (Table 2)
further serve to distinguish this disease (56). Papaya mosaic
was reported from Florida in 1962 (19, 21) and now is known
to occur also in Venezuela (22). Losses incurred by mosaic
have not been assessed.
Affected bearing plants exhibit a mottling of leaves that
does not vary in severity much during different seasons of the
year. Seedling plants develop vein-clearing followed by rugosity
of laminae and later a distinct mottling. After infection is
systemic in young plants, growth is retarded and laminae of
leaves produced become progressively reduced and filiform.
Symptoms are usually absent on petioles, stems, and fruits.
The virus that causes papaya mosaic can be transmitted
mechanically but not by aphids (21, 71). Expressed juice from
Table 1. Host ranges and symptoms of viruses infectious on Carica papaya.'
Papaya Papaya Spotted Tobacco
ringspot mosaic wilt ringspot
Amaranthus caudatus L' L
Antirrhinum majus N M M/N M
cv. Super Tetra
Apium graveolens M M
Arachis hypogaea M N
Beta vulgaris L S
Brassica campestris N
Brassica oleraceae M/N N
Callistephus chinensis N M/N M
cv. Blue Wonder
Capsicum annuum N M/N M/N
cv. California Wonder
Capsicum frutescens N M/N M/N
Carica cauliflora M M
Carica goudotiana M/N M/K
Carica monoica M K
Carica papaya M M M M
Carica parviflora K
Carica pubescens M
Carica quercifolia N N
Cassia occidentalis N L
Chenopodium amaranticolor N L L/M
Celosia argentea L
Citrullus vulgaris M/N M/N M
Crotalaria spectabilis N M
Cucumis melo L/M/N M/N M
Cucumis melo M
Cucumis sativus M/N M/N N M
cvs. A & C, Chicago Pick-
ling, National Pickling,
Marketer, Ohio MR17
Cucurbita pepo M N M
cvs. Jack-O-Lantern and Small
Cucurbita pepo M N M
cvs. Cocozelle Bush, Early Pro-
lific, Straightneck, Yellow
Cyclanthera pedata M M
Datura stramonium N M M/N
Emilia sonchifolia M
Table 1. Host ranges and symptoms of viruses infectious on Carica papaya
Papaya Papaya Spotted Tobacco
ringspot mosaic wilt ringspot
Glycine max N M/N
Gomphrena globosa N L L L/M/N
Gossypium hirsutum N
Jacaratia mexicana N N/K
Luffa acutangula M
Luffa cylindrica N
Lupinus sp. M M
Lycopersicon esculentum N N M M
cv. Bonny Best
Melothria pendula M M
Momordica charantia N N
Nicotiana glutinosa N M M/N
Nicotiana rustica N M M
Nicotiana tabacum N N M M/S
cvs. Kentucky 35, Kentucky 151
Passiflora edulis N N
Petunia hybrida M M/N
Phaseolus lirr N M
cv. Hendei sh
Phaseolus vu N N M/N M/N
cvs. Bounti o, Scotia
Pisum sativur N M/N M/N
cv. Little M_/M
Phytolacca ar Ilicana L L
Sesamum in< cum M
Sicana odoritera N N
Solanum melongena N N M M
cv. Black Beauty
Spinacia oleracea N L/M/N L/M/N
Tetragonia expansa N L/N L/M
Tropaeolum majus M M/N
Vicia faba M M
Vigna sinensis N M M/N
cv. Ramshorn Blackeye
Vinca rosea S
Zinnia elegans N S M M/N
1 Bunchy top disease known to be infectious only on C. papaya; Isabella mosaic
and feather leaf diseases not established as virus-induced; leaf curl virus in-
fectious on Lycopersicon esculentum and Nicotiana tabacum but not Gossy-
plum hirsutum; yellow crinkle disease known to be infectious only on Datura
stramonium, Lycopersicon esculentum and Trifolium repens; cucumber virus 9
not known to infect C. papaya in nature. For references not listed in text,
see Footnote 1, Table 2.
2 K = lethal infection; L = localized infection on inoculated leaves, no systemic
infection; M = systemic infection (mottle); N no symptoms (not suscep-
tible); S = infected but symptomless. More than one letter for virus-host re-
sponse indicates variation in symptoms according to cultivar or virus strain
tested or distinctive symptom types in a single syndrome.
infected leaves remains infectious after more than 180 days
in vitro but is inactivated by exposure for 10 minutes to 73-78
C. and dilution greater than 2 x 10-4. The average length of
virus particles is 533 millimicrons (34, 40, 41). Carcia cauliflora
Jacq., C. goudotiana. (Triana & Plaunch.) Solms, C. pubescens
Lenne & Koch, Cyclanthera pedata Schrad., Melothria pendula
L., Cucumis sativus L., Cucurbita melo L., Citrullus vulgaris
Schrad., Antirrhinum majus L., and Sesamum indicum L., are
susceptible and develop systemic mosaic symptoms. Vinca rosea
L., and Zinnia elegans Jacq. are infected systemically but re-
main symptomless (26). Infection by mosaic is lethal to Carica
monoica Desf., C. parviflora (DC) Solms, and Jacaratia mexi-
cana A. DC. Gomphrena globosa L. and Cassia occidentalis L.
produce localized necrotic lesions on leaves inoculated with
mosaic virus, but lesions on inoculated leaves of Chenopodium
amaranticolor Coste & Reyn. remain faintly chlorotic.
Control for papaya mosaic has not been determined but the
possibility for development of resistant varieties or hybrids has
not been investigated adequately.
Virus diseases of papaya reported since 1929 from Africa
(42), Australia (61, 62), the Caribbean area (1, 2, 14, 29, 66),
Florida (19, 20), Hawaii (35, 36, 38, 54), India (17, 18, 30,
63), and South America (44, 67), have been given a variety of
common names. On the basis of gross characterization (severe
malformation of laminae, no reduction of latex exudation from
wounds, and transmission by mechanical means and by aphids)
it is probable that several of the syndromes described were
manifestations of the disease herein considered as papaya ring-
spot. Although losses attributed to papaya ringspot have not
been assessed, it has been considered a major disease in many
Infected plants first exhibit chlorosis in the youngest leaves,
which is soon followed by vein-clearing, rugosity, and a prom-
inent mottling of the laminae. Decided malformation and re-
duction of the laminae, which may become extremely filiform,
appears later. Characteristically, elongated, dark green streaks
develop on petioles and the upper half of the stem, but may
eventually involve the entire trunk. These streaks commonly
follow closely after, but do not precede, the appearance of foliar
symptoms. Infected plants become stunted, petioles are short-
ened, and fruit set is severely reduced as the disease progresses.
The flavor and aroma of fruits that are set subsequent to infec-
tion are noticeably affected (36). Flow of latex from wounds
on infected plants is not affected but rings, either green or dark
brown, may be found on fruit.
Symptom expression is most severe in cool weather, and
foliage produced during summer months may be nearly symp-
tomless. Disagreement among investigators concerning host
range of the causal virus (10, 19, 26, 71) may be indicative of
virus strain differences, fluctuation of virus titer in vivo, or
efficacy of inoculation techniques utilized. A mild strain of the
virus has been reported (21).
Papaya ringspot virus is transmitted mechanically and by
grafting as well as by a number of aphids including Aphis
spiraecola Patch, A. gossypii Glover, A. craccivora, Koch, A.
rumicis Linn., and Myzis persicae Sulz (4, 5, 7, 8, 40, 44, 45,
50, 51, 55, 56, 58, 71). M. persicae can acquire the virus during
a feeding period of 10 seconds and infect a healthy plant by
feeding for the same length of time. The virus is inactivated
by exposure of infectious sap at 55 C. for 10 minutes, by dilution
greater than 10-3, or after standing 8 hours at room tempera-
ture, and is serologically related to watermelon mosaic (6, 9,
33, 49). Average length of virus particles is 780 millimicrons.
Host range of the ringspot virus (10) includes, in addition to
C. papaya, C. monoica, and varieties of Cucurbita pepo L., C.
pepo var. melopepo L., C. sativus, and C. vulgaris.
Attempts to control papaya ringspot through application of
insecticides for control of aphid vectors have not been success-
ful. Neither roguing infected plants nor isolation of papaya
plantings has given satisfactory control. Development of re-
sistant varieties appears to be the most likely possibility for
effective control (27).
A disease of papaya caused by the spotted wilt virus was
first observed on the island of Kauai (Hawaii) in 1962 and
later on the islands of Hawaii and Oahu (68). Plantings with
90% infection have been noted, and the disease was largely
responsible for abandonment of the crop in some areas of the
Premature defoliation of infected plants is characteristic.
Defoliation is accompanied by severe chlorosis and necrosis
Table 2. Characteristics of some viruses infectious to papaya. ''
Transmitted by '
PpyVirus ood-~ 7--~ .0 o20 > -- s s2 .
mosaic 533 Aphis craccivora
Papaya rod P 56 x78 10 0.3 i+ MyAPHIS GOSSYP
PaBunchpaya rod 56 1x103 0.3 + + EMAPHIS GOSSYPIIAPAYAE
ring- 780 APHIS CRACCIVORA
spot APHIS NERII
1. Chamberlain, E. E. 1954. New Zealand Department of Scientific and
Industrial Research Bulletin 108. 255 p.
- 2. Gibbs, A. 1969. Advances in Virus Research 14:263-328.
3. Hollings, M. 1959. Annals of Applied Biology 47:98-108.
4. Kahn, R. P., H. A. Scott and R. L. Monroe. 1962. Phytopathology
5. Thornberry, H. H. 1966. U.S.D.A. Agriculture Handbook No. 307, 446 p.
2 Feather leaf not demonstrated to be virus induced.
SPositive transmission (+) and by insect species in capital letters; no trans-
mission by insect species in lower case letters.
4 B = bundle, circular and pinwheel; P = particulate.
SNot demonstrated in papaya.
of apical leaves. Dark green areas that appear water-soaked
are found on petioles and stems with green or gray circular
spots on young fruit. Mature green fruit exhibit dark green
ringspots 1-3 cm in diameter which persist on fruit colored
at maturity. Necrotic, light-colored, hard areas may be found
in the flesh of ripe fruits. Latex exudes from wounded tissues.
Strains of the virus have been distinguished (15), but in-
fectivity of individual types to papaya has not been determined.
Host range of the virus is exceptionally wide and includes spe-
cies in 35 different families; viz., several members of the Com-
positae, Cruciferae, Leguminosae, Solanaceae, and Umbelliferae.
It is transmissible mechanically as well as by four species of
thrips, Thrips tabaci Lind., Frankliniella schultzei Trybom, F.
fusca Hinds, and F. occidentalis Pergande. T. tabaci can ac-
quire the virus during a feeding period of 15 minutes or more
on an infected plant but is unable to transmit the disease to a
healthy plant until 4-18 days later. They remain infective for
a period ranging from 24-43 days after the virus-acquisition
feeding. Several weed plants, including Emilia sonchifolia DC
(31), are susceptible and may serve as sources of inoculum.
The nearly isometric virus particles have an outer mem-
brane layer and sometimes a tail-like structure (37). The virus
is quite unstable in plant sap and is rendered non-infectious by
exposure for 10 minutes at 46 C. or above, or remaining 12
hours or less at room temperature, and is rapidly inactivated at
pH 5.5 or below.
A weed control program to eliminate sources of inoculum
and routine application of insecticides to reduce thrip infesta-
tions should be followed in areas where spotted wilt is a prob-
lem. Removal of tops from infected plants has been reported
as a successful control measure (68). Resistance in papaya va-
rieties or species has not been adequately investigated.
Tobacco ringspot virus has been found to infect C. papaya
experimentally (48) and to occur naturally on this plant in
the Rio Grande Valley (43). Plants infected when young wilt
and develop terminal necrosis before they are killed.
Virus particles are isometric and measure approximately 28
millimicrons (64). Infectivity is lost by dilution of sap from
infected plants more than 10-4, storage at room temperature for
more than 6-10 days, and exposure to 65 C. or above.
The virus is readily transmitted mechanically and by the
nematode Xiphinema americanum Cobb, which can acquire the
virus within 24 hours. A wide range of plants are susceptible
to infection, including species in the Cucurbitaceae, Legumino-
sae, and Solanaceae, and seed transmission of the virus is not
uncommon but has not been demonstrated in papaya.
Soil application of nematocide prior to planting is recom-
mended, and roguing of infected plants as they appear will
serve to minimize the supply of inoculum. Weed hosts in and
around papaya fields should be eliminated.
The disease known as yellow crinkle has caused yield losses
estimated at 10-30%c in some years since it was first reported
from Australia in 1931 (39). The disease is not known to occur
One or more crown leaves develop translucent interveinal
areas near the margins, although the remainder of affected
leaves are normal in appearance (12, 25). The youngest leaves
usually do not exhibit such symptoms, but instead become yel-
low with margins turned under, and laminae are often much
reduced in size. The translucent areas drop out, making affected
leaves quite irregular in shape, often resembling the effects of
insect feeding. Epinasty of petioles of older, yellowed leaves
precedes eventual dropping of almost the entire foliage except
a tuft of small leaves at the top of the trunk. Coarse, enlarged
leaflike structures are produced in place of petals and other
floral structures, and affected plants bear little or no fruit
In the field, young plants are more susceptible to attack
than older plants, and most extensive losses are experienced in
the first twelve months following planting. New infections have
not been noted during cooler months, and random incidence of
the disease in the field is common.
Attempts to transmit the disease by mechanical inoculation
have been unsuccessful. The causal agent of yellow crinkle is
the tomato big-bud virus, which has been transmitted from to-
mato to papaya by dodder (Cuscuta australis Hook.) but not
by grafting from papaya to papaya. It is transmitted by the
leafhopper Orosius argentatus Evans (53). The disease also
affects white clover Trifolium repens L. and Datura stramonium
Specific control measures have not been devised, but it is ad-
visable to rogue diseased plants since they will bear no fruit and
can only serve as a source of inoculum (46). For new planta-
tions, placing of three or more plants at each location provides
for roguing of infected plants that appear during the first 12
months as well as the selection of female trees for production.
Isolation of seed-beds and production fields from susceptible
crops, including tomato and white clover, and routine control
for dodder infestation is recommended.
Other Virus-like Diseases of Papaya
Two diseases of papaya in Puerto Rico include mottling of
leaves as a major symptom, but insufficient information is avail-
able to relate either to any of the diseases described herein.
"Cucumber virus 9" has been transmitted experimentally to
papaya (11) but is not known to infect papaya in nature. The
disease known as "Isabella mosaic" does occur on papaya in
nature, but the causative agent has not been determined.
A syndrome referred to as "die-back" in Puerto Rico (4),
Trinidad (14), and Australia (12, 61, 62) also is characterized
by absence of latex to exude from wounds and may be another
manifestation of the bunchy top diesase. Although sporadic in
occurrence, it is the most serious disease of papaya in Australia,
where affected plants are first observed to have more compact
foliage at the crown. Apical leaves assume a slightly chlorotic
appearance and soon begin to shrivel. As the disease progresses,
all of the leaves may be dropped, and fruit set prior to infection
becomes softened and either ripens abnormally or falls while
The disease described by Da Costa (25) can be fatal to
young trees, while older trees often recover. It is characterized
by necrosis of crown leaves and die-back of two feet or more of
the apical portion of the trunk. Because the causal agent has
not been determined, the relation of this disease to bunchy top
remains in question.
A disease herein designated "feather leaf" was reported
from Tanganyika in 1944 (69, 70), where it was observed in-
frequently. Similar symptoms were observed by the author in
Trinidad in 1970, but only in seedling plants. Leaves on mature
plants are restricted to the crown and are considerably reduced
in size. They have a leathery texture and reduced number of
lobes, often with distorted and uneven laminae. Narrow bands
on either side of larger veins are clear and nearly translucent,
imparting a herring-bone effect, and orientation of smaller veins
may be noticeably disorganized. Leaves are commonly lighter
in color than on unaffected plants, with angular patches of dark
green tissue delimited by smaller veins. The cause of these
symptoms has not been established. Symptoms may be indis-
tinguishable from mite damage.
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