Agriculture Reference
In-Depth Information
been used between the in vitro stages of plantlet
growth and minituber production. The growing
period was extended and a hardening period
was introduced with low temperatures during
the in  vitro growth, resulting in up to 97% more
minitubers than when no induction period was
used. Van der Veeken and Lommen (2009) dem-
onstrated that planting density affected minitu-
ber production; at low planting densities, higher
numbers of tubers were initiated, but they were
somewhat smaller.
When produced in a greenhouse, the facil-
ity must be cleaned and disinfected, as well as
items used for planting, including benches, pots,
trays, etc. The facility must be sanitary and in-
sect free, and must be maintained with strict
sanitation for all personnel entering the green-
house. The production cycle can take place at any
time during the year, but often the costs associ-
ated with maintaining the greenhouse become
prohibitive during the cooler winter months
due to heating, and plant growth may not be
as successful. Supplemental lighting may help
with growth during the off-season times. Potting
mixes are varied, but must originate from sterile
sources with no soilborne pathogens or weeds.
Insect control is essential to prevent the move-
ment of viruses into the stocks. Additionally,
certification officials must inspect the plants
(usually twice during their growth) to verify
cultivar, growing conditions, greenhouse suit-
ability, and tuber identification, among other
considerations (Sather et al ., 2013).
At harvest, representative tuber samples
are taken for pathogen testing. Harvested mater-
ial is stored in open mesh bags, typically in large
coolers with appropriate humidity and airflow,
similar to typical commercial potato storage. It is
understood by the producers that the minitubers
may need longer storage times to enhance
dormancy break and/or to fit the timing of
greenhouse production with subsequent field
production. A good discussion of these factors is
presented by Stark and Love (2003).
Minitubers should be sized prior to plant-
ing, for ease in planting and to keep emergence
uniform. Producers should be aware of minitu-
bers' slower emergence than tubers from field-
grown crops, due to their longer dormancy. Also,
strict sanitation and isolation are critical to keep
diseases and pests from the initial field crop.
Sanitation also includes using land suitable for
production of the earliest-generation material,
soil that has been tested and found free of major
soilborne pests, rotating land formerly used for
field-grown potatoes, and incorporating proper
insect control techniques.
Microtubers
Improving the efficiency of minituber produc-
tion by microtubers is a reliable, year-round
laboratory solution, and negates the use of plant-
lets. The method was first studied in the late
1970s and early 1980s, and was implemented
shortly thereafter in China and the Republic of
Korea (Donnelly et al ., 2003). Microtuber pro-
duction is a method of producing small tubers
in  vitro from tissue culture plantlets. They have
many uses, and today most countries and insti-
tutions use microtubers in commercial seed
production.
Microtubers can be produced year-round,
have high productivity per square meter ( 200,000
microtubers m −2 ), are a convenient size for storage
and transportation, and when replacing plant-
lets, maintain uniformity during emergence in a
greenhouse setting. However, the microtubers
should be past dormancy break and ready to grow.
One method described by Ewing et al . (1987) was
simply to cut the tubers in half to assist in dor-
mancy break.
Microtubers have also been used in the field
rather than minitubers. While research has
been conducted on the use of microtubers in this
way (Kawakami et al ., 2003; Pruski et al ., 2003),
they tended to be later in growth and had reduced
yields. Other disadvantages of using microtubers
for field growth are the need for a longer grow-
ing period due to increased dormancy and the
requirement for specialized techniques for plant-
ing. Also, there tends to be a lower success rate
in adapting microtubers to field conditions be-
cause of their size (Liu et al ., 2006; Qui, 2009).
Plantlets for field production
Plantlets may be used for field production, and
although risky due to adverse weather and other
factors, can be quite successful. Growers often
use plantlets when there is a need for a quick
 
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