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International Society for Infectious Diseases

Date: January 2018
Source: European Plant Protection Organization (EPPO) Reporting
Service 1/2018/011 [edited]
< EPPOReporting/2018/Rse-1801. pdf>

Since 2010, a new emerging citrus decline disease has been observed in
Iran. This disease is currently widespread in the Southern part of
Kerman province where it is causing the death of approximately 10 per
cent of cultivated citrus trees. The disease has been observed on
sweet orange (_Citrus sinensis_), grapefruit (_C. paradisi_), and
mandarin (_C. reticulata_) plants grafted on Bakraee, a local citrus
variety frequently used as a rootstock. Early symptoms include pale
green leaves, no production of new sprouts, and general retardation of
growth. Late symptoms include tree decline along with reduction and
decay of the root system.

To determine the possible causes of this new decline disease, leaf and
root samples were collected in March 2017 in Southern Kerman, from 9
symptomatic and 3 asymptomatic citrus trees. Molecular tests revealed
the presence of mixed infections with phytoplasmas and liberibacter
species in symptomatic samples. Liberibacter species were identified
exclusively in roots, while phytoplasmas were found in both roots and
leaves. Further tests showed that liberibacter strains could be
attributed to '_Candidatus_ Liberibacter asiaticus' (EPPO A1 List) and
that phytoplasma strains could be attributed to '_Candidatus_
Phytoplasma aurantifolia'. Further investigations are needed to better
understand the etiology and epidemiology of this new citrus decline,
as well as to determine its potential impact on citrus production.

[Source: H Alizadeh et al (2017), Plant Disease 101, 2145
<https://apsjournals.apsnet. org/doi/full/10.1094/PDIS-05- 17-0670-PDN>]
Communicated by:

[_Candidatus_ Liberibacter asiaticus (CaLas) causes Asian greening
(huanglongbing, HLB), one of the most damaging diseases of citrus
crops. Symptoms include leaf mottling, misshapen fruits, stunting and
eventual death of trees. It is spread by the Asian citrus psyllid
(_Diaphorina citri_), as well as by grafting, with plant material and
possibly by seed. Disease management requires an integrated approach
including use of clean planting and grafting stock, elimination of
inoculum and vector control.

_Ca._ Phytoplasma aurantifolia (16SrII taxonomic group) causes
witches' broom disease of lime (WBDL). WBDL is a devastating disease
and has so far been reported from Oman (with over 98 per cent of lime
trees infected), Iran, the United Arab Emirates, Pakistan and India.
Symptoms may include abnormal chlorotic shoot proliferations, followed
by dieback of affected branches and eventual death of the tree within
a few years. The pathogen is transmitted by grafting, but an insect
vector is also suspected. Disease management of phytoplasmas is
difficult and generally includes vector control, removal of sources of
inoculum and use of certified clean planting material.

(For more information on both diseases see previous ProMED-mail posts
in the archives and links below.)

Coinfections of other phytoplasmas with CaLas have been reported
previously (examples via the links below). The report above is the
first time this particular combination has been identified. In total,
3 liberibacter (CaLas as well as the related _Ca._ L. americanus and
africanus) and at least 3 phytoplasma (including SrII, SrIX, SrI)
species have been reported to cause similar symptoms in citrus.
Further research is needed on symptomatology, epidemiology and host
impact of both single and mixed infections of these pathogens.

< maps/middle_east_and_asia/ iran_pol01.jpg>
Iran provinces:
< iran/maps/iran-political-map. jpg>

Citrus greening symptoms:
<http://www.delhidailynews. com/news_image/ 1402146122citrus-greening.jpg> ,
< content/uploads/2012/10/ citrus-greening.jpg>,
<https:// content/uploads/2016/10/ citrus_greening.jpg>
< 200904/r362894_1677317.jpg>
Witches' broom symptoms on lime:
<http://www.forestryimages. org/images/768x512/0746027.jpg >,
<http://www.forestryimages. org/images/768x512/0746054.jpg >,
<http://www.forestryimages. org/images/768x512/0746031.jpg > and
<http://www.forestryimages. org/images/768x512/0746032.jpg > (shoot,
compared with healthy)

Citrus greening information:
< greening.html>,
< plants/health-pests-diseases/ a-z-significant/citrus- greening-huanglongbing>
< SearchType=slideshowViewSlide& slideshowId=197>
Asian greening, information and taxonomy:
< datasheet/16565> and
< taxonomy/34021>
Information on lime witches' broom and phytoplasma:
< QUARANTINE/data_sheets/ bacteria/PHYPAF_ds.pdf>,
< standard/185/pm7-061-1-en.pdf> ,
< afficheN&cpsidt=3597606> and
< article/10.1007/s13562-012- 0160-z/fulltext.html>
_Ca._ Phytoplasma aurantifolia taxonomy:
< taxonomy/180978>
_Ca._ Phytoplasma taxonomy and species groups:
< taxonomy/33926>
Coinfections of CaLa with other phytoplasmas:
<https://apsjournals.apsnet. org/doi/10.1094/PHYTO-98-9- 0977>,
<http://onlinelibrary.wiley. com/wol1/doi/10.1111/jph. 12200/full> and
<https://www.sciencedirect. com/science/article/pii/ S0261219414001392>
EPPO quarantine lists via:
< QUARANTINE/quarantine.htm>
 - Mod.DHA]

[See Also:
Asian greening, citrus - China 20180208.5616524
Asian greening, citrus - Panama: 1st rep (BC) 20170707.5157200
Asian greening, citrus - Trinidad & Tobago: 1st rep 20170614.5104395
Asian greening, citrus - Mexico: (OA) 20170502.5007425
Asian greening, citrus - China: (southern) 20170120.4778384
Asian greening, citrus - Nepal: (KS) 20161129.4660906
Asian greening, citrus - Tanzania: susp 20160912.4481387
Witches' broom, lime - Oman 20141221..3047303
Viruses, virus-like pathogens - Pacific Islands 20100514.1572
Huanglongbing, citrus - Bhutan, Iran, Americas 20090415.1436
Witches' broom, lime - Iran: update 20090128.0378
Lime witches' broom phytoplasma - India 20000125.0129
and additional items on citrus greening in the archives]
............................... ...................dha/msp/lm
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