Agriculture Reference
In-Depth Information
savings of several million dollars due to lower
fungicide costs and fewer losses in storage could
result. Defender additionally presents a viable
alternative for organic potato producers. All
evidence to date suggests that its improved
resistance to late blight and early blight is a
long-lasting type of resistance that promises
to reduce fungicide use.
of new potato cultivars, with the Aberdeen
(Idaho) potato breeding program being refer-
enced, with variance among programs generally
occurring in the number of breeding clones
evaluated, selection intensity in each field gener-
ation, and the size of field plots and their number
of replicates in trials (Hoopes and Plaisted, 1987).
(Stevenson
et al
., 2007)
Improved efficiencies in nutrient use by po-
tato cultivars have the capacity to reduce poten-
tial groundwater contamination with nitrates
and mitigate water-quality degradation associ-
ated with phosphate runoff. Trehan (2009a,b)
found the Indian cultivar, Kufri Puhraj, to be the
most efficient in nitrogen, phosphorus, and po-
tassium use. The author concluded that the root
system of this cultivar was more efficient in
uptake of nitrogen. Observed variability in phos-
phorus and potassium efficiency among ten In-
dian potato cultivars appeared to relate to both
root uptake and plant utilization (Trehan, 2009a).
A substantial reduction in nitrogen relative to
the North American industry standard, Russet
Burbank, also has been reported for the follow-
ing potato cultivars, with percent reduction in
nitrogen relative to Russet Burbank given in par-
entheses: Alta Russet (33%), Alturas (40%), and
Bannock Russet (40%) (Novy
et al.
, 2002b, 2003;
Bizimungu
et al
., 2011).
Parental selection and hybridization
A breeder will put time and thought into the an-
nual selection of parents for hybridization in the
“crossing block”—this term is used to describe
the assemblage of parents for that year's hybrid-
izations. The value of the sexual progeny resulting
from the intercrossing of parents relies heavily
on the merit of the parents and the directed
crosses among them. The selection of parents is
based on a combination of attributes, such as
desirable agronomics, processing and sensory
qualities, as well as pest and disease resistances;
no parent has all the desired attributes, thus its
selection and hybridization with other parents
that complement its known weaknesses. Paren-
tal choices include breeding clones/cultivars
that produce higher frequencies of desirable off-
spring with certain other parents (specific com-
bining ability), or when hybridized with an array
of parents (general combining ability). Observa-
tions on parental combining ability may be
based on breeders' personal experience over
years or through statistical evaluations of pro-
geny performance (Brown and Dale, 1998; Ruiz
De Galarreta
et al
., 2006). Parents can also com-
prise breeding clones and cultivars from other
breeding programs, germplasm representing hy-
brids between adapted and non-adapted germplasm,
and potato wild species.
Parental crossing sheets that detail the strengths
and weaknesses of each parent along with par-
entage are then generated and used in decision
making regarding the crosses to be conducted,
as well as a means of tracking hybridizations to
ensure unique and non-redundant hybridiza-
tions are made. To maximize heterosis and avoid
inbreeding depression, hybridizations among
closely related parents are generally avoided.
Potato flowers used in hybridizing are per-
fect with both male (anthers) and female (car-
pels) sexual organs borne on the same flower.
16.4 Traditional Breeding
Methodologies
As discussed previously in the chapter, potato
has the unique ability for both sexual and asex-
ual (clonal) reproduction. Once a breeding clone
with enhanced characteristics relative to com-
mercially available potato cultivars is identified,
that genotype with its desirable attributes can be
propagated clonally via the tuber, allowing the
crop uniformity necessary in commercial potato
production. However, in order to develop a new
potato cultivar using traditional breeding methods,
sexual reproduction is the starting point for any
breeding program. Potato flowers, which make
potato such a beautiful crop when in full bloom
in the field, are also the instruments for the cre-
ation of new potato cultivars by the breeder via
sexual hybridization. This section presents the
methodology used by the breeder in the development
