Agriculture Reference
In-Depth Information
in order to produce new improved processing
cultivars that will deliver reduced acrylamide
levels in the processed products.”
between full and no insecticide treatments for
Nadine over the
2
years of evaluations. The au-
thors concluded (with the exception of reduced
ZC symptoms in raw tubers of Nadine) that
“there was no real indication that any of the
other cultivars in the trial had any effective re-
sistance to TPP (tomato-potato psyllid) or ZC”
.
Butler
et al
. (2011) evaluated
22
potato
breeding clones and cultivars to assess whether
host genotype impacted adult potato psyllid be-
havior and transmission of liberibacter. The au-
thors reported observing significant differences
among potato germplasm for the occurrence and
duration of potato psyllid probing, the duration
of psyllid cleaning and resting, and the amount
of time psyllids spent off the potato leaflet, sug-
gesting that resistance to the insect vector of
liberibacter did exist. Reduced transmission of the
liberibacter responsible for ZC was also observed
in psyllid-resistant germplasm, as well as in three
breeding clones with no apparent resistance to
the insect vector—indicative of possible resist-
ance to the liberibacter pathogen itself.
Zebra chip disease
First described in Mexico in 1994 and subse-
quently reported in Central America, the USA
(Secor
et al
., 2006; Gudmestad and Secor, 2007)
and New Zealand (Liefting
et al
., 2008), zebra
chip (ZC) has emerged as a devastating disease
of potato. Substantial reductions in yield as well
as tuber quality have resulted in great economic
losses to this disease in potato. The primary
symptoms of ZC in the tuber include browning
of vascular tissue, flecking of internal tissues,
and discoloration of the medullary ray tissues.
These tuber symptoms become more pro-
nounced following frying of tubers for chips or
French fries, with dark striping and streaks—
thus, the designation, zebra chip disease. In New
Zealand, up to 60% losses in harvestable yield
and downgrading of the potato crop due to re-
duced starch content in tubers has been reported
(Liefting
et al
., 2008).
The disease has been associated with a bac-
terium,
Candidatus
Liberibacter solanacearum
(syn. Ca. L. psyllaurous) (Hansen
et al
., 2008;
Secor
et al
., 2009), which is transmitted by the
potato psyllid,
Bactericera cockerelli
(Šulc) (Munya-
neza
et al
., 2007). Being a relatively new disease of
potato, little was known regarding resistance in
cultivars. Muyaneza
et al
. (2011) evaluated nine
potato cultivars commonly grown in the USA for
resistance to ZC over a
2-
year period in field-cage
evaluations using liberibacter-infected potato
pysllids. Cultivars included chip and fry process-
ing types, as well as an early russeted cultivar
used for fresh consumption. In these field-cage
evaluations, none of the nine cultivars exhibited
resistance to ZC, with almost 100% of the inocu-
lated plants developing severe ZC foliar and tuber
symptoms, as well as yield reductions of 50% or
greater. An evaluation of a breeding clone and
11
potato cultivars widely grown in New Zealand
for ZC incidence under full, reduced, and no in-
secticide treatments (for control of potato psyl-
lid) identified the fresh market cultivar, Nadine,
as having reduced ZC symptoms in raw tubers
(Anderson
et al
., 2013). However, 50% and 60%
reductions in marketable yield were observed
Improved sustainable production
Improved sustainability in production has be-
come progressively more important to the potato
industry, with increasing efforts in reducing
production inputs such as pesticides and nutrient
applications. Since 2009, following the voiced
concerns of shareholders, McDonald's, the largest
global food-service retailer, has made sustainabil-
ity a priority, with their website detailing their ef-
forts and progress in improved sustainability.
Potato cultivars with host plant resistance
and a reduced need for nutrients can contribute
to reduced pesticide and fertilizer applications
during the production of the crop. As an ex-
ample of host plant resistance contributing to
greater sustainability in potato production, the
late blight-resistant processing cultivars, De-
fender and Palisade Russet (Novy
et al
., 2006,
2012) can reduce significantly the number of
applications of fungicides needed for the control
of the late blight disease. On the basis of their
data, Stevenson
et al
. made the following conclu-
sion regarding the cultivar, Defender:
Even if only 20% of Washington and Wisconsin
potato growers adopted this new cultivar,
