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International Society for Infectious Diseases <http://www.isid.org>
Date: 7 November 2008
Source: Business Standard [edited]
<http://www.business-standard.com/india/storypage.php?autono=339418>
Mildew hits maize in TN
Maize production in Tamil Nadu (TN), which accounts for 83 per
cent of the country's maize production, has been hit by the
downy mildew disease, according to Tamil Nadu Agricultural
University.
India has the world's 5th largest maize acreage with over 7
million hectares (17.3 million acres) and it is the 3rd most
important cereal. This year [2008], maize production has been
hit in Coimbatore, Udumalapet, Darapuram, Odanchatram, Dindigul,
and Theni, the major districts that cultivate maize, due to the
infestation of downy mildew disease.
The downy mildew group of fungi is seedborne. It affects plant
development as infestation is at the early stage (30 days) of
crop development. The disease could intensify when the relative
humidity is high and could be a major constraint in maize
production, according to university's release.
Maize has gained in popularity with farmers in Tamil Nadu as a
more remunerative crop and simple management practices, and
farmers have begun to cultivate 2-3 crops in a year. Continuous
cropping and congenial environment has led to development of
pests.
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[Downy mildews are important maize pathogens in many tropical
regions of the world. They are particularly destructive in Asia,
where losses in excess of 70 per cent have been documented.
Around 10 different species of downy mildew fungi in the genera
_Peronosclerospora_, _Sclerospora_, and _Sclerophthora_ have
been reported to affect maize. In India, a number of these
pathogens occur, but _P. sorghi_ (sorghum downy mildew) and
_Sclerophthora rayssiae_ (brown stripe downy mildew) are
considered common.
Symptoms of the different downy mildew species on maize are
similar, although they can vary with plant age, climatic
conditions, and host germplasm. Infection at the seedling stage
results in stunting, chlorosis, and premature plant death.
Infection of older plants results in leaf symptoms of mottling,
chlorotic streaking, lesions, and may produce white striped
leaves that eventually shred. 'Downy' growth often occurs on
leaves and is more common on the lower leaf surface. Plants may
be stunted, tiller excessively, have malformed tassels and ears,
and may not produce seed.
Downy mildew spores are spread within a crop mainly by splashing
rain, wind, or mechanical means. The fungi survive between crops
on infected plant material or alternate weed hosts. Some of the
maize pathogens can also be seedborne, although this is largely
restricted to seed that is fresh and has a high moisture
content. Downy mildews are usually controlled with fungicides.
Maps
India:
<http://www.globalsecurity.org/military/world/india/images/IndiaMap_tourism.gif>
and
<http://healthmap.org/promed?v=22.9,79.6,5>
Tamil Nadu districts:
<http://www.mapsofindia.com/maps/tamilnadu/tamilnadu-district.htm>
Karnataka districts:
<http://www.mapsofindia.com/maps/karnataka/karnataka.htm>
Pictures
Maize with downy mildews:
<http://www.cimmyt.org/Research/maize/maizepathologyresearch/Images/path1.jpg>
and
<http://cril.cimmyt.org/gallery/main.php?g2_view=keyalbum.KeywordAlbum&g2_keyword=maize&g2_itemId=365>
Information on maize downy mildews:
<http://maizedoctor.cimmyt.org/index.php?id=233&option=com_content&task=view>,
<http://www.ikisan.com/links/ap_maizeDisease%20Management.shtml>,
<http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.py.15.090177.001341>,
and
<http://cril.cimmyt.org/gallery/main.php?g2_view=keyalbum.KeywordAlbum&g2_keyword=maize&g2_itemId=153>