The importance of planting certified trees that are free
of Apple chlorotic leafspot virus (ACLSV)
SS Malan. Plant Improvement Specialist, SAPO Trust, Private bag X5023, Stellenbosch, 7599. Tel: 021-8876823; [email protected]
Introduction
The symptoms on stone fruit can present as
showed ring patterns and mosaic symptoms
Apple chlorotic leaf spot virus (ACLSV) de-
pseudopox (Photograph 1) or false plum pox
(Brunt et al., 1996).
creases the growth, average fruit weight and
(Jelkman & Kunze, 1995) or as “butteratura”
yield of trees (Cosba et al., 1986). ACLSV,
in apricot and cherry. The latter was present-
Transmission
like other viruses, cannot be eliminated from
ed as severe fruit necrosis symptoms in Hun-
Grafting is known for transmitting ACLSV
plants using chemicals, in contrast to for in-
gary (German-Retana et al., 1997).
between woody hosts (Cosba et al., 1986).
stance fungi which can be reduced or elimi-
Other symptoms of ACLSV include se-
There is currently no certainty as to how
nated using fungicides. For this reason it is
vere mottling and pitting on cherry and peach
ACLSV is transmitted naturally. Seed trans-
extremely important to plant certified trees,
leaves and fruits (Desvignes & Boyé, 1989)
mission studies have been inconclusive (Poul
also referred to as blue label trees, which are
and symptoms of “viruela” on apricot (Peña-
& Dunez, 1998).
free of ACLSV, thus ensuring higher fruit
Iglesias & Ayuso, 1973). Severe graft incom-
weight and yield in an orchard on the long
patibilities may also occur due to ACLSV in-
Detection
run. ACLSV, Apple mosaic virus (ApMV),
fection in some rootstock-scion combinations
RT-PCR is more sensitive in the detection of
Apple stem grooving virus (ASGV) and Ap-
(Candresse et al., 1995). In some cultivars, like
ACLSV than DAS-ELISA by a factor of 70
ple stem pitting virus (ASPV) alone or in
Bulida, fruit show irregular sinking, grooves,
fold (Malan, 2014), but due to cost-efficiency
combination can cause significant yield re-
spots and important malformations that make
DAS-ELISA is currently the method that is
duction of fruit and reduced growth (Camp-
them unmarketable (Peña-Iglesias, 1988).
used within the South African Deciduous
bell, 1981). A yield reduction of up to 30%
Plum bark split (Lister, 1970) and peach dark
Fruit Plant Certification Scheme.
(Van Oosten et al., 1982) was reported on
green sunken mottle (Salmon et al., 2002) can
High temperatures (Candresse et al.,
the apple cultivar Golden Delicious infected
also occur. Fruit showing circular, sunken
1995; Svoboda & Polak, 2010) limits the de-
with ACLSV, ASGV and ASPV. ACLSV is
black necrotic lesions and circular ring symp-
tection of ACLSV. It could be attributed to a
governed under the South African Plant Cer-
toms were also reported from Prunus domes-
reduction in the virus titre and in general it
tification Scheme and it is required that plant
tica ‘Victoria’ (Bénédicte et al., 2004).
limits ELISA to about three months after bud
On pome fruit ACLSV is mostly symp-
break in the spring (Candresse et al., 1995).
tomless (German-Retana et al., 1997), but it
It was found that in mid-summer only 10%
can cause russet ring on apple fruits and in
of known infected trees tested positive using
ACLSV
Japan it caused top-working disease and in-
ELISA (Candresse et al., 1995).
Synonyms for ACLSV include Pear ring pat-
duced lethal decline in apple trees propagated
ACLSV levels were also found to vary
tern mosaic virus and Quince stunt virus,
on Maruba kaido (Malus prunifolia var. ringo)
between different tissue and fruit types. For
Plum pseudopox virus and Apple latent virus
rootstocks (Salmon et al., 2002) within a few
apple, flower petals and leaf material showed
type 1 (Brunt et al., 1996).
years (Kinard et al., 1996). On Malus platy-
highest virus levels in spring (Cieslinska et
carpa it caused line patterns and chlorotic
al., 1995). Uneven distribution of ACLSV in
Host Range
rings, and on Malus sylvestris cv. R12740-7A
infected trees was observed (Fridland, 1973;
ACLSV was first reported in apples from
it caused chlorotic leaf spots and stem pitting.
Poul & Dunez, 1998). In short bud sticks (5-
the USA in 1959 (Lister et al., 1965). ACLSV
On Malus sylvestris cultivar Spy, chlorotic
10 buds long) infection was usually systemic,
infects most fruit tree species, including
spots and stem pitting, chlorosis and stunting
whilst in longer bud sticks (20-40 buds long)
apricot, cherry, peach, prune, pear, plum,
occurred, whilst on Malus sylvestris cultivar
many uninfected buds were detected, espe-
apple (Lister, 1970; Nemeth, 1986; Desvi-
Virginia Crab, stem pitting occurred (Brunt
cially towards the tips (Fridland, 1983).
gnes & Boyé, 1989; German-Retana et al.,
et al., 1996). On quince variety C7/1, chlorotic
RT-PCR, especially where different vi-
1997), quince (Rana et al., 2008) and almond
rings and spots occurred, whilst on Pyronia
ruses are combined in one multiplex PCR,
(Spiegel et al., 2005).
veitchii chlorosis and stunting occurred. Pears
coupled with quick and simple RNA ex-
material distributed within the Scheme be
tested and found free from the virus.
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APR | MEI 2015
traction can potentially be used for pome
Pseudopox symptoms
and stone fruit virus certification programs.
of ACLSV detected on
However, RT- PCR assay has the risk of giv-
plums in Paarl, Western
ing false negative results caused by RNA deg-
Cape, South Africa.
radation or due to the presence of inhibitors
of the reverse transcriptase or polymerase
(Park et al., 2006).
Phylogenetic relationships
Phylogenetic trees, which are similar to a human family tree indicating all the ancestors and
their relationships, were compiled for ACLSV
extracted from different trees and areas. From
the results of the phylogenetic trees, it was
evident that South African isolates of ACSLV
were genetically highly similar (between 78.8
to 97.9%) (Malan, 2014). The South African
isolates were also compared to ones extracted
from trees in other countries and it was possible to deduce that the isolates that occur in
South Africa are similar to ones from various
countries overseas. It could thus be deduced
that the virus was imported to South Africa
in plants from different countries and not just
via a single import. Even within South Africa,
the virus isolates do not correlate with specific
geographic areas, indicating spread within the
country. The phylogenetic trees also indicated
that the majority of South African isolates of
ACLSV are not host specific and that crossinfection between pome and stone fruit is thus
possible. One fruit group could thus serve as a
source of infection for another fruit group.
Management
The best management practice for infection
with ACLSV is planting certified trees, as
these have been tested and found free from
the virus, as viruses cannot be treated with
chemicals. Certified trees with blue/candidate
labels can be obtained from a Plant Improvement Organization such as SAPO Trust or a
nursery providing such blue/candidate label
trees The important implication of the possibility of cross-infection
between fruit groups is that sanitation of
equipment between fruit groups is essential
to prevent spread of the viruses and that one
fruit group can serve as a source of infection
leaf spot virus causing plum line pattern. Acta Horticulturae,
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Lister, R. M., Bancroft, J. B., & Nadakavukaren, M. J.
(1965). Characteristics of filamentous viruses isolated mechanically from apple. Phytopathology, 55, 859.
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