Fungal and Bacterial Disease Aspects in Potato Production - The Potato: Botany, Production and Uses - page 190

greatly the choice of cultivar, agronomic prac-
tices, and crop protection decisions. Daccache
et al . (2012) reported that by the 2050s, the
area of land that was currently well or moder-
ately suited for rain-fed production would de-
crease by 88 and 74%, respectively, due to the
increased likelihood of dry conditions.
As mentioned above, it is predicted that
global climate change will result in a significant
increased risk of late blight epidemics on all con-
tinents where potatoes are grown (Hijmans et al .,
2000). In some areas of the USA, the patterns of
rainfall are changing and winters are getting
milder, leading to conditions that are more con-
ducive for the initiation and development of
potato late blight epidemics; for example, in Mich-
igan (Baker et al ., 2004). One way to counter this
problem will be through the use of disease risk
forecasting models (Wharton et al ., 2008).

have shown that these resistant isolates are now
widespread throughout the USA (Fairchild et al .,
2013) and Canada.
In 2009, A. solani isolates from potato were
discovered with resistance to boscalid (Wharton
et al ., 2012a). The succinate dehydrogenase in-
hibitor (SDHI) fungicide, boscalid (FRAC group 7),
was released for use on potato in 2003 (Stammler
et al ., 2007) and was readily adopted by many
growers in the USA as an alternative to the QoI
fungicides for the control of early blight. The
emergence of resistance to boscalid is worrying
as, recently, the US-EPA has registered several
new fungicides containing active ingredients
with similar chemistries to boscalid. Penthi-
opyrad (Fontelis, Vertisan, DuPont Crop Protec-
tion) and flyopyram (Luna, Luna Tranquility,
Bayer CropScience) are two such compounds
that are also in FRAC group 7. These studies
show the need for increased education programs
to promote the use of resistance management
strategies in the application of these products.

Fungicide resistance

Fungicide resistance in potato pathogens has be-
come a major issue in recent years, as the indus-
try has moved to mostly specialized single-site
mode of action and translaminar fungicides
(MacDonald et al ., 2007; Olanya et al ., 2009;
Horsfield et al ., 2010; Venkataramana et al .,
2010; Cooke et al ., 2011; Taylor et al ., 2011).
This has been typified by the rapid development
of resistance to the QoI fungicides (FRAC
group 11) in the Alternaria pathogens on potato.
The QoI fungicides work by disrupting respir-
ation in fungal cells by binding to the so-called
Qo site (the outer quinol-oxidation site) of the
respiratory enzyme complex, cytochrome bc 1 . As
a result of this narrow mode of action, there is
an inherent risk for the development of patho-
gen resistance. Since 1999, the persistent and
intensive use of azoxystrobin and other QoI fun-
gicides alternated with chlorothalonil on com-
mercially grown potato crops in the Midwest
and throughout the USA has increased the se-
lection pressure for the development of QoI fun-
gicide resistance in A. solani (Pasche et al ., 2004).
As a result, the efficacy of these fungicides has
started to decline, and isolates of A. solani with
reduced sensitivity or complete resistance to QoI
fungicides have now been identified (Pasche and
Gudmestad, 2008). Furthermore, field surveys

Molecular disease diagnostics

Detection and identification of potato pathogens
is dependent on a diverse range of techniques
and skills, from traditional culturing and taxo-
nomic skills to modern molecular-based methods.
The wide range of methods employed reflects the
great diversity of potato pathogens and the
different parts of the plant that they may infect.
A typical disease diagnostic laboratory usually
has the capacity to perform morphological iden-
tification using microscopical methods, methods
for detecting proteins from pathogens such as
enzyme-linked immunosorbent assay (ELISA) or
electrophoresis, methods for detecting fatty
acids, molecular methods identifying the nucleic
acids such as polymerase chain reaction (PCR),
and last, traditional bioassays such as inocula-
tion of test plants, or isolation on selective media
followed by morphological identification. A decline
in funding and the availability of trained staff to
perform traditional techniques is a significant
issue for maintaining the critical mass required
to deliver this type of service.
Generic methods that can be used to iden-
tify a number of different pathogens can help
with the capacity maintenance and sustainability