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International Society for Infectious Diseases <http://www.isid.org>
Date: 17 March 2009
Source: Manitoba Co-operator [edited]
<http://www.manitobacooperator.ca/issues/ISArticle.asp?id=97433&PC=FBC&issue=03172009>
Potato blight develops fungicide resistance
Samples taken last summer [2008] by provincial potato
specialists and ag chem firm Bayer CropScience show "widespread"
presence of fungi that have mutated to resist the fungicides
used most often to control them. Of 113 isolates of _Alternaria
solani_, the cause of early blight in potatoes, Bayer said over
80 percent carried the F129L mutation that causes "reduced
sensitivity to strobilurins."
Strobilurins "don't work as well as they have in the past."
Early blight leaf tissue samples were collected during the
summer of 2008 in Alberta, Manitoba, Ontario, and Prince Edward
Island [PEI].
"Initial results confirm that mutant strains are widespread in
Alberta, Manitoba, and Ontario, which is not surprising given
the widespread distribution of mutants in the United States,"
said Rick Peters, Agriculture and Agri-Food Canada. "To date,
PEI is the only area that we've surveyed where all samples were
still sensitive to strobilurins, likely due to the less frequent
use of strobilurins in this province."
"We're putting our heads in the sand if we ignore this growing
issue," said potato pest specialist Tracy Shinners-Carnelley of
Manitoba Agriculture, Food and Rural Initiatives. "When the risk
for early blight is high, use the available tools appropriately
in a planned program. And if strobilurins are part of that
program, they must be tank mixed with a protectant fungicide."
--
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[Early blight of potato and tomato is caused by the fungus
_Alternaria solani_. It causes leaf spots and tuber blight on
potato, and leaf spots, fruit rot, and stem lesions on tomato.
The disease can occur over a wide range of climatic conditions
and can result in complete defoliation and severe yield losses.
The pathogen often causes no visible symptoms until plants
approach maturity. It is spread with infected plant material
(including tubers, transplants and seed), by mechanical means,
wind, and rain. Solanaceous weeds and volunteer crop plants may
serve as pathogen reservoirs. Disease management includes use of
certified clean propagation material, fungicides, crop rotation,
and use of cultivars with reduced susceptibility.
Strobilurins are strongly antifungal agents produced by fungi.
Being derived from natural products, strobilurins are considered
environmentally safe. Like several other fungicide classes, they
have single-site activity and therefore pathogens must be
expected to develop resistance or tolerance over time.
The finding that many strains of _A. solani_ with increased
tolerance levels to this important group of fungal control
agents have emerged is of major concern to potato and tomato
industries worldwide.
Furthermore, it highlights the importance of rotating or mixing
chemical classes for management of all fungal pathogens, as
suggested above, to reduce the risk of resistant strains
emerging.
Maps
Canada:
<http://www.lib.utexas.edu/maps/americas/canada_pol_1986.gif>
and <http://healthmap.org/promed/en?v=55.4,-101.9,4>
Pictures of early blight
On potato leaf:
<http://www.ag.ndsu.edu/pubs/plantsci/hortcrop/pp1084-4.gif>
On
potato tubers:
On
tomato fruit:
Links
Early blight fact sheets (with pictures):
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_EarlyBlt.htm>,
<http://www.aces.edu/pubs/docs/A/ANR-1052/ANR-1052.pdf>,
<http://ohioline.osu.edu/hyg-fact/3000/3101.html>,
and <http://www.ndsu.nodak.edu/instruct/gudmesta/lateblight/basic_frame3.htm>
Management of potato diseases including early blight:
<http://archives.eppo.org/EPPOStandards/PP2_GPP/pp2-02-e.doc>
_A. solani_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=444460>
Information on strobilurins:
<http://www.answers.com/topic/strobilurin>,
<http://grounds-mag.com/mag/grounds_maintenance_strobilurin_fungicides_natures/index.html>,
and
<http://www.ibwf.de/ibwf_his&act_en.htm>. - Mod.DHA]
[see also
in the
archive:
Blight & undiagnosed disease,
potato, chilli - Bhutan 20090211.0612 Leaf blight, potato -
Bangladesh: (KH) 20090121.0255
2008
----
Fungal diseases, potato - Bangladesh 20080107.0091]
