Agriculture Reference
In-Depth Information
turnaround time frame for producing early-
generation material. Plantlets are easy to bulk
up, but must be hardened properly prior to
transplanting them in the field. Producers must
take care in transplanting the stocks, to avoid
root damage, and to place the plantlet properly
in the field soil. Plants must be hydrated and a
transplant fertilizer used during the planting to
help the roots grow. Transplants must send roots
into the fertilizer zone within a short period of
time to be successful. Normally, plants in the
12-
15 cm range with good roots are appropriate.
Plants should be planted with only the top two to
three leaves showing above the soil line. Irriga-
tion should be immediate and proper transplant
techniques used until the plants have begun to
grow in the field and reached the
25-
35 cm
range in height.
Since plantlets are extremely susceptible to
extreme weather such as hail, row covers may be
used during their early growth. After plants are
actively growing, producers can make rows,
hand weed, etc. Once the plants are fully estab-
lished, producers should avoid mechanical op-
erations to prevent disease spread and root
pruning (Stark and Love, 2003). One major con-
cern regarding the use of plantlets in the field is
the fact that they tend to remain juvenile longer
into the season and usually have only one stem.
This makes them ideal candidates for vectors
and in-season spread of viruses like PVY.
It is essential that starting material originate
from disease-free,
in vitro
plantlets produced
under normal aseptic conditions.
Sprouts derived from tubers
After clean, disease-free tubers (such as minitu-
bers) have sprouted, the young sprouts can be
removed from the mother tubers and transplanted
in the greenhouse to produce plants or in the field
to produce seed potatoes. In specialized green-
house or screenhouse facilities, the tubers can be
sprouted and the sprouts collected for planting.
When enough seed tubers are not available, this
method can increase the multiplication rate four
to five times, allowing up to 525 kg of seed tubers
planted for each hectare (Yan
et al
., 1999).
8.7
Field Production
Field production of seed potatoes is more compli-
cated than raising commercial table-stock pota-
toes. While many of the principles are similar,
the seed requires additional steps to ensure dis-
ease issues do not become problematic. Also, seed
potato growers must produce a crop suitable for
seed the following year while meeting the re-
quirements of the certification process.
The use of early-generation, fully tested
tissue culture stocks has greatly improved the
chances of a grower starting properly, with large
numbers of pre-basic or nuclear seed stocks
(first year in the field). However, the high cost of
production, which includes the laboratory phase
(whichever system is used), the growth phase
(greenhouse or screenhouse), and the small size
of the minitubers, which limits yield, results
in pre-basic seed that is useful only for the seed
producer. Additionally, having seed stocks of the
appropriate physiological age with uniform
growth characteristics and quick germination is
critical for commercial operations (Iritani and
Thornton, 1984; Bryan, 1989).
Field selection is the first criteria a seed
grower must meet. In many countries, the soil
must first be tested for the presence of specific
pests such as potato cyst nematode or root-knot
nematode (NAK, 2013; Sather
et al
., 2013). If the
results are negative, then a grower may be able
Single leaf cuttings to produce
minitubers
Single leaf cuttings from tissue culture, disease-
tested plantlets can also be used to produce mini-
tubers. Haapala (2005) and Haapala
et al
. (2008)
discuss the cost-effectiveness and minituber in-
crease potential by using
in vivo
production of
single-node leaf buds or other small plant material.
The cuttings are placed into growing rooms in flats
containing non-sterile soil in a low-light, protected
environment and allowed to root and grow, and
then cut again within about
3
weeks. Because of
their size, space requirements are minimal (up to
500 cuttings m
-2
), with up to
100,000
progeny
produced within 6 months from a single cutting.
After obtaining the needed numbers, the plants
can be planted into a greenhouse or similar clean
production environment to produce minitubers.
