Agriculture Reference
In-Depth Information
therefore not desirable, and susceptibilities are
therefore best identified early in the breeding
program as soon as adequate tubers are avail-
able for controlled inoculations.
As a clone advances in a breeding program,
with more manageable numbers and greater
seed amounts than in earlier stages, the number
of replicates in trials increases, as does the num-
ber of trial sites. This allows an assessment of a
breeding clone's merit in differing environments
and changes in its performance relative to other
trial entries. The changes in relative perform-
ance due to environmental influences are
termed genotype × environment interactions,
with Bradshaw providing a comprehensive re-
view of its impact in potato breeding (Bradshaw
1994, 2007a). Bradshaw (2007b) indicates that
early-generation selection is best practiced in en-
vironments as closely similar to those of com-
mercial production environments where a new
cultivar would be grown. Based on this assess-
ment, Bradshaw advocated that potato produ-
cing countries, when possible, should have their
own potato breeding programs to facilitate the
breeding and development of new cultivars.
Additional data on breeding clones' responses to
diseases and pests, such as viruses, late blight,
and nematodes, are also now collected during
field years
4-6;
this information being useful in
determining whether a breeding clone will be re-
tained in the breeding program or discarded.
represents the final
3
years of evaluation prior to
the release of a meritorious breeding clone as
a potato cultivar, with trial sites in the states of
California, Colorado, Idaho, Oregon, Texas, and
Washington. Similar regional trials are also
conducted by breeding programs of the north-
central, south-western, and eastern USA, with
the data collected being used by breeders in mak-
ing final determinations regarding the release of
a breeding clone as a new cultivar.
It is during evaluations in the TSPVT and
WRPVT that detailed postharvest data on pro-
cessing and sensory attributes are collected, as
well as economic analyses for the fresh and
processing value of breeding clones relative to in-
dustry standards. Data are presented in formal
reports and at meetings with potato industry rep-
resentatives present, and introduces them to the
merit of a breeding clone for consideration for
their company's use and evaluation. During the
final
3
years of evaluation in the WRPVT, con-
current production management trials of promis-
ing breeding clones are also being conducted by
researchers in the NPVDP. These trials establish
guidelines for the management of potential new
cultivars with respect to nutrients, irrigation—
western US production typically being irrigated—
and storage. The adoption of a new cultivar by the
industry is improved if management regimes to
optimize performance are also included in the
cultivar release, in extension publications, and in
presentations given at grower meetings.
Seeds of a promising clone for industry
evaluations are initially obtained from breeding
programs, concomitant with the clone being
established in tissue culture under aseptic labora-
tory conditions.
In vitro
plantlets tested and con-
firmed as being free of viruses, viroids, and
bacteria become the starting point for the produc-
tion of certified seed, as outlined by Love
et al
.
(2003). Certified seed originating from patho-
gen-free,
in vitro
plantlets is generally available for
larger-scale field evaluations by industry collabor-
ators prior to a final decision being made regard-
ing the release of a breeding clone as a cultivar.
Advanced regional trials
Dependent on there being adequate seed amounts,
breeding clones saved following the sixth field year
of evaluation in the Aberdeen program are ad-
vanced to the Tri-State Potato Variety Trials
(TSPVT), with sites in the states of Idaho, Oregon,
and Washington. Sites in the three states allow a
more comprehensive evaluation of a breeding
clone's merit for the north-western US potato in-
dustry, which produced 57% of the US potato
crop in 2012 (USDA, National Agricultural
Statistics Service, Crop Production Summary,
2012). A breeding clone having merit for release
as a cultivar is generally retained in the Tri-State
regional trial for
2
years, although clones showing
exceptional merit have been retained for just
1
year prior to advancing to the Western Re-
gional Potato Variety Trial (WRPVT). This trial
Cultivar release
Following the third year of evaluation in the
WRPVT, a decision is made regarding the merit
