D. HanoldA, B. KawasB and J.W. Randles{ XE "Randles, J.W." }A
A
University of Adelaide, Waite Campus, Glen Osmond, 5064, South Australia
B
ICARDA, PO Box 5466, Aleppo, Syria
INTRODUCTION
Eucalyptus camaldulensis is widely grown in Syria for land
rehabilitation, amenity, and as roadside trees. Seed was
imported repeatedly on a large scale from different locations in
Australia up to the 1970s (I. Nahal, L. Makki pers comm). This has
resulted in a national population of E. camaldulensis including
both subspecies camaldulensis and obtusa, as well as local
hybrids of the two. Around 500 000 eucalypt seedlings are being
produced annually from Syrian seed by 11 government nurseries
for distribution around the different regions.
During a visit to ICARDA by D. Hanold in October 2008, yellowing
symptoms similar to the Mundulla Yellows (MY) syndrome (1)
were noted. The MY‐like symptoms appeared to be widespread
in some locations, and preliminary surveys of several sites were
carried out to obtain further information about its distribution.
While a witches' broom disease without associated yellowing
symptoms had been described earlier from Syrian eucalypts (2),
this is the first report of a eucalypt yellowing disease from that
country.
MATERIALS AND METHODS
Based on the description of MY distribution in Australia (1), trees
not adjacent to roads as well as roadside trees were
characterised. Survey sites in the regions around Aleppo, Tel
Hadya, Ein Dara, Idleb, Tabaqah, along the road to the coast
west of Homs, and along the Damascus‐Aleppo highway were
mapped (Fig. 1).
Photographs were taken of trees at each site and additional
information recorded as available. Individual trees on the
ICARDA station (Tel Hadya) were also numbered for future
reference and leaf samples were taken to Adelaide and stored
frozen for molecular analysis. Symptomatic seedlings identified
in a nursery were planted at ICARDA together with
asymptomatic controls to observe disease progress.
RESULTS
Eucalypts with symptoms resembling the descriptors of MY
(Table 1) and including interveinal chlorosis, epicormic shoots
and asymmetric yellowing of the crown were observed in all
areas except west of Homs where only asymptomatic eucalypts
were observed. E. camaldulensis both in single and mixed
species plantings on roadsides, in paddocks, soil rehabilitation
areas, seed gardens and nurseries were affected. Symptoms
occurred on single trees adjacent to asymptomatic ones, in
clusters, and as disease gradients similar to the distribution of
MY in Australia (1).
DISCUSSION
MY is defined by characteristic descriptors distinguishing it from
yellowing disorders due to environmental factors. Its cause is
unknown, but a biotic, contagious agent has been implicated (1).
Yellowing diseases of eucalypts closely resembling the Australian
MY have also been reported from Spain and South America (1).
This is the first report of a similar syndrome from Syria and the
Middle East.
Syria has developed a large, isolated population of E. camaldulensis over the last century. Little insect or fungal
damage has been observed suggesting that many pathogens
affecting the species in Australia are absent. Nevertheless MY‐
like symptoms virtually identical to the syndrome in Australia are
present. Further epidemiological and phenotypic, as well as
molecular comparison of Syrian and Australian symptomatic E.
camaldulensis is needed and may provide information on
aetiology and possibly origin of the disease.
Figure 1. Map of Syria.
Table 1. Comparison of the Syrian eucalypt yellowing disease (SEY) with
descriptors of MY (1).
Descriptors SEY MY
Leaf symptoms: interveinal chlorosis distortion of leaf margins necrotic pin spots no dead leaves on twigs
+ + + + + + + + Epicormic shoots + + Twig dieback + + Disease stages:
early (yellow patches in foliage) medium (yellow epicormic shoots) late (overall tree dieback)
+ + + + + + Affected trees next to healthy ones
Trees of all ages affected No recovery observed Not cured by pruning
Symptoms in paddocks and roadsides
+ + + + + + + + + + ACKNOWLEDGEMENTS
We gratefully acknowledge the support of I. Nahal and B. Bayaa,
Aleppo University; L. Makki, Syrian Department of Agriculture; A.
El‐Ahmed, R. Brettell, S. Kumari and the staff and management
of ICARDA.
REFERENCES
1. Hanold D, Gowanlock D, Stukely MJC, Habili N, Randles JW (2006) Mundulla Yellows disease of eucalypts: descriptors and preliminary studies on distribution and etiology. Australasian Plant Pathology 35, 199–215.
2. Bos LM, Makkouk KM, Bayaa B (1990) Witches' broom and decline of Eucalyptus, a serious disease in Syria, likely caused by mycoplasma. Arab Journal of Plant Protection 8, 135–133.
Posters
36 New host records for ‘Candidatus Phytoplasma aurantifolia’ in Australia
J.D. Ray{ XE "Ray, J.D." }
Australian Quarantine and Inspection Service, Marrara, NT, 0812
INTRODUCTION
Phytoplasmas are unculturable wall‐less prokaryotes within the
class Mollicutes that infect plant phloem vessels and are
transmitted by phloem feeding insects (2). They are implicated in
diseases of a wide range of plant species. Symptoms of
phytoplasma infection include reduced leaf size ‘little leaf’,
yellowing of leaves, proliferation of stems leaves and flowers
(witches’ broom) and floral abnormalities (1, 3).
Plant health surveys were carried out by the Australian
Quarantine and Inspection Service (AQIS) in northern Western
Australia (northern WA) and the Northern Territory (NT) from
2006 to 2008. This paper reports on the new host records of
phytoplasma collected during these surveys.
MATERIALS AND METHODS
Plants exhibiting symptoms of phytoplasma infection (little leaf
or witches’ broom) during plant health surveys in northern WA
and the NT from 2006 to 2008 were collected for diagnostic
confirmation. Plant parts with symptomatic new growth were
collected into plastic bags and kept cool. Within 2 days of
collection leaf petioles and midribs were excised from the
symptomatic material, dehydrated over anhydrous CaCl2 and
stored at 4°C where possible.
Samples were forwarded to Bioscience North Australia, Charles
Darwin University for molecular analysis. Sample analysis
included polymerase chain reaction (PCR) assays using universal
phytoplasma specific primers. Strain analysis was performed by
restriction fragment length polymorphism (JR153, KN11) or by
sequencing (JR428, JR429).
RESULTS AND DISCUSSION
‘Candidatus Phytoplasma aurantifolia’ is reported for the first
time associated with disease of Ipomea aquatica, Jatropha gossypifolia, Ocimum basilicum and Canavalia rosea (Table 1).
These new records were all detected in WA whilst no new
records were detected in the NT during this time. These
phytoplasma records represent a diverse host range.
‘Ca. .P. aurantifolia’ has a wide host range across a diverse group
of plant families and is widespread throughout Australia. The
suggested Australasian/Asian origin of this phytoplasma may in
part explain its success in harsh environments and wide host
range (1, 3).
All new records were obtained in northern WA which has a
particularly harsh climate. During surveillance it was observed
that some species of annual plants infected with phytoplasma do
not produce seed and remain green for longer than the same un‐
infected hosts (Ray, personal observation). Perhaps the
occurrence of a diverse host range for ‘Ca. .P. aurantifolia’ is a
survival mechanism for both the phytoplasma and the leaf
hopper vectors by providing live host material during periods
when other hosts have died, the creation of a green bridge.
Table 1. Details of new host records for ‘Ca. .P. aurantifolia’ in Australia.
Species, Common name Location Strain Coll. No.
Ipomea aquatica, Kangkung Broome, WA TBB JR153 Jatropha gossypifolia, Bellyache bush Cable Beach, WA SPLL‐V4 JR428 Ocimum basilicum, Lemon basil Wattle Downs, WA TBB JR429 Canavalia rosea, Beach bean Lombadina Beach, WA SPLL‐V4 KN11 ACKNOWLEDGEMENTS
Thanks to Karen Gibb, Anna Padovan and Claire Streten of
Bioscience North Australia, Charles Darwin University for
diagnostics. Andrew Mitchell and Kirsty Neaylon (AQIS) are
gratefully acknowledged for some collections, and A. Mitchell for
identifying plant specimens.
REFERENCES
1. Davis RI, Jacobson SC, De La Rue SJ, Tran‐Nguyen L, Gunua TG, Rahamma S (2003) Phytoplasma disease surveys in the extreme north of Queensland, Australia, and the island of New Guinea. Australasian Plant Pathology. 32; 269–277.
2. IRPCM Phytoplasma/ Spiroplasma Working Team—Phytoplasma
taxonomy group (2004) ‘Candidatus Phytoplasma’, a taxon for the wall‐less, non‐helical prokaryotes that colonize plant phloem and insects. International Journal of Systematic and Evolutionary
Microbiology. 54: 1243‐ 1255.
3. Schneider B, Padovan A, De La Rue S, Eichner R, Davis R, Bernuetz A, Gibb K (1999) Detection and differentiation of phytoplasmas in Australia: an update. Australian Journal of Agricultural Research. 50; 33–42.