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International Society for Infectious Diseases <http://www.isid.org>
Date: Thu 30 Dec 2010
Source: The Hindu, Press Trust of India (PTI) report [edited] <http://www.thehindu.com/sci-tech/agriculture/article1018345.ece>
70 percent of onion crop in Maharashtra damaged by disease
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Diseases caused by unseasonal rains have ruined almost 70 percent of the kharif (July to November) onion crop in Maharashtra in 2010.
The Indian Council of Agricultural Research (ICAR) will now prepare a list of do's and don'ts for farmers to avoid such a situation in future, Umesh Shrivastava, ICAR, said. Improper action to ward of the ill-effects of untimely rains led to 2 diseases -- anthracnose and purple blotch -- infecting onion crops, he said.
Water-logging in the "flat beds" of onion fields in the state, which accounts for 30 percent of production of the staple vegetable in the country, caused the 2 diseases, resulting in widespread damage, he added. The problem was compounded by cloudy and humid weather afterwards. ICAR said that even though farmers sprayed their onions with fungicide this proved to be futile, as rains washed [it] away.
The diseases have reduced onion yields by almost 50 percent triggering a drastic shortfall which in turn drove [up] prices in retail markets.
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[Purple blotch of onion is caused by the fungus _Alternaria porri_.
Crop losses depend on environmental conditions and may range from 25 to 90 percent. The damage may continue to develop post-harvest.
Symptoms include small, water-soaked lesions with purple centres on leaves, leaf bases, and flower stalks, which expand and result in necrotic patches. The disease is favoured by high humidity and often occurs as a secondary infection on plants already affected by other pathogens or pests (for example, onion thrips). The pathogen is mostly spread with infected plant material and by mechanical means (including insects and human activities). Disease management may include fungicides, clean planting material, phytosanitation to minimise inoculum, and crop rotation.
Anthracnose of onion (also called smudge, twister) is caused by the fungi _Glomerella cingulata_ or _Colletotrichum circinans_. An additional species (_Gibberella moniliformis_) has recently been identified to be associated with a severe form of the disease in the Philippines (see link below) where up to 100 percent crop losses have been reported. Symptoms include water-soaked, pale yellow spots on leaves, which expand lengthwise until covering the entire leaf blade; affected leaves shrivel and droop. The pathogens survive on crop debris and spread occurs mainly with infected plant material and by mechanical means. Disease management may include removal of infected crop debris to reduce inoculum, crop rotation, fungicides (although effectiveness may be limited), biocontrol organisms (for example _Trichoderma_), and cultural measures (reduction of moisture in the crop). Some resistant or tolerant onion cultivars are being developed.
Maps
India:
<http://www.globalsecurity.org/military/world/india/images/IndiaMap_tourism.gif>
and
<http://healthmap.org/r/00Zs>
Maharashtra:
<http://www.indiaprofile.com/images/maps/maharashtra-tourist-map.gif>
Maharashtra districts:
<http://www.mapsofindia.com/maps/maharashtra/maharashtra.htm>
Pictures
Anthracnose symptoms on onion:
<http://www.bar.gov.ph/images/anthracnose_symptom_onion%20.jpg> (leaf) and <http://isudevcom.files.wordpress.com/2009/07/infected-onion-bulb.jpg?w=126&h=150>
(bulb), and
<http://www.infonet-biovision.org/res/res/files/626.280x185.clip.jpeg> (bulb) Onion purple blotch symptoms:
<http://vegetablemdonline.ppath.cornell.edu/Images/Impt_Diseases/72_Onion_Purple.jpg>,
<http://www.ipmimages.org/images/768x512/5364058.jpg>,
<http://www.no-dig-vegetablegarden.com/images/onion-diseases-purple-blotch.jpg>,
and via
<http://www.forestryimages.org/browse/subimages.cfm?sub=16559>
Links
Information on onion anthracnose:
<http://www.openacademy.ph/index2.php?option=com_content&do_pdf=1&id=1071>
and via
<http://www.oisat.org/pests/diseases/fungal/anthracnose.html>
Information on purple blotch of onion:
<http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2005/21hrt05a6.htm>
Information on onion purple blotch and anthracnose via:
<http://libnts.avrdc.org.tw/fulltext_pdf/eam0072.pdf>,
<http://www.nhrdf.com/htmlfiles/Onion/link6.htm>,
<http://www.infonet-biovision.org/default/ct/125/crops>, and <http://nhb.gov.in/bulletin_files/vegetable/onion/oni002.pdf>
Research on anthracnose pathogens of onion:
<http://isudevcom.wordpress.com/2009/07/15/new-anthracnose-pathogen-attacking-onions-found-study/>
_A. porri_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=215273>
_G. gloeosporioides_ taxonomy and synonyms:
<http://www.speciesfungorum.org/Names/SynSpecies.asp?RecordID=245491>
_C. circinans_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=260903>.
- Mod.DHA]
[see also:
2009
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Fungal blight, onion - India: (MH) 20090103.0024]
Topics
Species
