A ProMED-mail post <http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>
Date: February 2018
Source: Journal of Phytopathology [edited] <http://onlinelibrary.wiley.com/doi/10.1111/jph.12688/full>
[Ref: Q Zhao et al (2018): Identification and characterization of _Cucurbita_ gummy stem blight fungi in Northeast China. J Phytopathol, recorded first online; DOI: 10.1111/jph.12688]
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_Cucurbita maxima_ (pumpkin) is a typical cucurbit that is susceptible to gummy stem blight. In recent years, this major fungal disease has decimated pumpkin yields in Northeast China in increasingly numerous outbreaks with more rapid spread in recent years.
We conducted a systematic study of the growth and morphological characteristics of various purified strains of _Cucurbita_ gummy stem blight (GSB) fungus from across Northeast China. DNA samples of 30 isolates with distinct hyphal variations were subjected to internal transcribed spacer (ITS) sequencing. Sequence analysis resulted in identification of the isolates as _Stagonosporopsis cucurbitacearum_ and demonstrated that this is a dominant and widely distributed fungal species in this region.
Multi-site phylogenetic analysis assigned the 30 strains to 2 genotypes that aligned to 7 phenotypic types of GSB fungi. By analysing ITS conserved sequences of these phenotypically diverse groups, we found that GSB pathogens broadly shared 2 motifs that contained sequence variations unique to 2 groups in addition to common identical motifs.
This study provided useful data for rapid and accurate identification of _S. cucurbitacearum_ and diagnosis in early symptoms of GSB. It also provides tools to explore the distribution and regularity of GSB outbreaks spatially and temporally across Northeast China.
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Communicated by:
IBIS (International Biosecurity Intelligence System) <https://ibisbiosecurity.org/>
[Gummy stem blight (GSB) of cucurbits caused by the fungus _Stagonosporopsis cucurbitacearum_ (previously _Didymella bryoniae_) is a major disease of these crops. It can affect all above ground parts of plants at any stage of growth. Symptoms may include leaf lesions followed by blight and necrosis, as well as lesions and cankers with red exudate on stems that can eventually girdle the entire stem, leading to wilting and yellowing of its leaves and vines.
Seedlings and transplants may be girdled by lesions and collapse, or be so weakened by the infection that they are never productive. The fungus also causes black rot if it infects the fruits. GSB requires prolonged moisture to become established and consequently is a serious problem in regions of high rainfall and glasshouse crops.
Spores may be seed borne or spread by air currents, water from rain or irrigation systems, or by mechanical means (including insect and human activities). The fungus can survive between growing seasons in an over-wintering structure, and wild cucurbits or volunteer crop hosts may serve as pathogen reservoirs. Disease management may include crop rotation, phytosanitation (removal of inoculum sources and reservoir hosts), fungicides and use of certified GSB-free seed or transplants.
A total of 2 related species, _S. citrulli_ and _S. caricae_, also affect cucurbits with similar GSB symptoms, but they vary somewhat in host preferences and epidemiology. _S. caricae_ is the only GSB fungus that also affects a non-cucurbit host, papaya (_Carica papaya_).
Maps
China:
<http://www.beijing-travels.com/image/chinamap.jpg>
China provinces:
<http://www.chinadiscovery.com/assets/images/customer-support/maps/china-provinces-map-600.jpg>
Pictures
GSB symptoms on cucurbit leaves and stems:
<http://www.omafra.gov.on.ca/english/crops/facts/09-051wf6.jpg>,
<http://www.plantdoctor.eastwestseed.com/sites/default/files/styles/diagnosis/public/gummy%20stem%20blight_WAM%20%282%29.jpg?itok=tGpWCATu>,
<https://aggie-horticulture.tamu.edu/vegetable/files/2012/01/wmd61_61_61.jpg>
and
<https://www.apsnet.org/publications/apsnetfeatures/Article%20Images/PumpkinFig8_2.jpg>
GSB on cucurbit transplants:
<http://agdev.anr.udel.edu/weeklycropupdate/wp-content/uploads/2008/05/gummystem-300x253.jpg>,
<http://agdev.anr.udel.edu/weeklycropupdate/wp-content/uploads/2009/06/gummy2.jpg>
and
<http://www.forestryimages.org/images/192x128/1234191.jpg>
GSB on cucurbits, photo gallery:
<http://vegetablemdonline.ppath.cornell.edu/Images/Cucurbits/GummyStem/GummySB_Collage.jpg>
Links
Gummy stem blight information:
<https://www.daf.qld.gov.au/business-priorities/plants/fruit-and-vegetables/a-z-list-of-horticultural-diseases-and-disorders/gummy-stem-blight>
(with pictures)
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbit_GSBlight.htm>,
<https://www.apsnet.org/publications/apsnetfeatures/Pages/GummyStemBlight.aspx>,
<https://horticulture.com.au/wp-content/uploads/2017/02/Gummy-stem-blight-factsheet.pdf>
and
<http://edis.ifas.ufl.edu/pp280> (with pictures) _S. cucurbitacearum_ taxonomy and synonyms:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=515660>
and
<http://www.speciesfungorum.org/GSD/GSDspecies.asp?RecordID=515660>. - Mod.DHA]
[See Also:
2015
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Gummy stem blight, watermelon - USA: (FL)
http://promedmail.org/post/20150506.3344025
2012
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Gummy stem blight, watermelon - Trinidad & Tobago: (MR)
http://promedmail.org/post/20121008.1329578
2009
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Gummy stem blight, watermelon - USA: new strains
http://promedmail.org/post/20090521.1899
2007
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Downy mildew, cucurbits - USA (02): clarification
http://promedmail.org/post/20071109.3633
Downy mildew, cucurbits - USA: (SC), new strain http://promedmail.org/post/20071023.3448]
Topics
Species
