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Thursday, March 26, 2009

Early Blight, New Strains, Potato Crop, Canada

A ProMED-mail post

ProMED-mail is a program of the
International Society for Infectious Diseases

Date: Tue 17 Mar 2009
Source: Manitoba Co-operator [edited]
Click on title above to see article;

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."

Communicated by:

[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

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.


Pictures of early blight
On potato leaf:

On potato tubers:

On tomato fruit:

Early blight fact sheets (with pictures):
, and

Management of potato diseases including early blight:

_A. solani_ taxonomy:

Information on strobilurins:
. - Mod.DHA]

[see also:
Blight & undiagnosed disease, potato, chilli - Bhutan 20090211.0612
Leaf blight, potato - Bangladesh: (KH) 20090121.0255
Fungal diseases, potato - Bangladesh 20080107.0091]
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