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International Society for Infectious Diseases <http://www.isid.org>
Date: April 10, 2008
Source: Webindia123 [edited]
<http://news.webindia123.com/news/Articles/India/20080410/929033.html>
Downy mildew disease hits muskmelon crop in Punjab
Downy mildew disease, which is a limiting factor for successful
growing of various cucurbit crops, has now affected the
muskmelon crop in Punjab. According to Punjab Agricultural
University (PAU) plant pathologist Dr Chander Mohan, the disease
has attacked almost all the varieties of muskmelon grown in the
state and severely affected its yields.
Stating the reason behind the spread of the disease, he said
that farmers in the districts of Amritsar, Kapurthala, and
Nawanshahar cultivated cucumber crop under low plastic tunnels.
The temperature and humidity in plastic tunnels is favourable
for the growth of the downy mildew pathogen and the disease
first appeared in cucumber fields and then spread to the
muskmelon fields.
Elaborating the symptoms of the disease, Dr Mohan said initially
the disease appears in the form of water-soaked lesions on the
under-surface of lower leaves. The corresponding area on the
upper surface shows yellow lesions. Later, grey coloured fungal
growth develops on the underside of these lesions and is visible
only during early morning hours when there is high humidity.
These lesions later increase in size and merge with each other
giving a blighted appearance. As a result the growth of vines is
stopped thereby adversely affecting fruit yield and taste.
To control the disease, scientists have suggested spraying crops
with fungicides. Two sprays should be done at weekly intervals.
Under heavy disease risk situation, additional sprays are
recommended.
--
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[Downy mildew caused by the fungus _Pseudoperonospora cubensis_
is a devastating disease of cucurbits. _P. cubensis_ is found
worldwide, but it is usually most damaging in tropical and
subtropical areas.
Different pathogen strains with variable host preferences
(pathovars) seem to exist. By affecting the leaves and thus the
photosynthetic potential of its host, downy mildew reduces yield
and fruit quality, and it can eventually kill the host plant. If
appropriate conditions are present, plantings can be infected so
rapidly that they appear to have been frosted.
The fungus is an obligate parasite surviving on cultivated or
wild cucurbits, and volunteer plants of crops or cucurbit weeds
may serve as sources of inoculum. The disease is spread by wind,
rain splash, and mechanical means. Disease development can occur
over a wide temperature range under conditions of high humidity.
Control strategies include the use of resistant cultivars as
well as applications of protectant and systemic fungicides.
The related species _P. humuli_ causes a serious disease of
hops.
Downy mildews in other fungal genera affect grapevine,
sunflower, and a number of vegetable crops. Generally, each
downy mildew species is confined to a number of hosts.
Maps
India:
<http://www.globalsecurity.org/military/world/india/images/IndiaMap_tourism.gif>
and
<http://healthmap.org/promed?v=22.9,79.6,5>
Punjab districts:
<http://www.mapsofindia.com/maps/punjab/punjab-district.htm>
Pictures
Photo gallery of downy mildew on cucurbit species:
<http://www.ces.ncsu.edu/depts/pp/cucurbit/images.php>
Downy mildew on rockmelon upper and lower leaf surfaces:
<http://hgic.clemson.edu/factsheets/graphics/2206/downyupper700.jpg>
and <http://hgic.clemson.edu/factsheets/graphics/2206/downylower700.jpg>
Downy mildew on cucumber leaf:
<http://www.ag.ohio-state.edu/~vegnet/news/currentvn10-06_files/image002.jpg>
Links
Cucurbit downy mildew, disease information:
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_Foliar.htm>,
<http://web.aces.uiuc.edu/vista/pdf_pubs/927.pdf>
and <http://www.avrdc.org/LC/cucurbits/downy.html>
Cucurbit downy mildew pathotypes:
<http://www.ces.ncsu.edu/depts/pp/cucurbit/thedisease.php>
_P. cubensis_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=120276>
PAU Plant Pathology:
<http://www.pau.edu/departmenthome.asp>.
- Mod.DHA]
[see also in
the
archive:
2007
----
Downy mildew, cucurbits - USA: (SC), new strain 20071023.3448
Fungal diseases, vegetable crops - Canada: cucumber, potato
20070730.2442 Downy mildew, cucumber - USA (OH, MI), Canada (ON)
20070704.2120
2006
----
Downy mildew, cucumber - Canada (ON), USA (MI) 20060803.2149
2003
----
Downy mildew, squash - Italy (Latium, Umbria) 20030401.0803]
