Agriculture Reference
In-Depth Information
Within strict protocols and predefined condi-
tions, seed lots that receive a “certified” classifi-
cation have been tested for quality and approved
for production by the certification agency. In
order for a seed lot to be approved, it must have a
high level of varietal purity and be free from, or
have minimally tolerable levels of, certain seed-
borne pathogens and a minimal amount of
other issues, like seedborne herbicide carry-over.
When possible, growers should only buy and
plant certified potato seed.
To promote early and uniform emergence
in regions with short growing seasons, seed
tubers may be pre-sprouted prior to planting.
Pre-sprouting, or chitting, requires specialized
equipment and facilities, and is often labor-
intensive. The presence of low light suppresses
sprout elongation during chitting and results
in short green sprouts. Some of the sprouts
may be removed prior to planting to reduce
stem number per plant. Disadvantages of using
pre-sprouted seed include additional expense,
equipment and labor, planter performance
issues (sprouts getting caught on equipment),
and emergence issues due to sprout injuries
during planting.
Some growers cut seed potatoes to reduce
costs, extend limited seed stocks, break apical
dominance, and reduce tuber size for improved
planter performance. Schotzko
et al
. (1983) de-
termined that the economically acceptable seed
tuber and seed piece size range for commercial
producers was
43-71
g. Seed pieces above that
range were found to be wasteful, and those
below compromised emergence. One size range
does not work for all varieties, however. The
Schotzko
et al
. (1983) seed piece weight range
was specific to Russet Burbank, which had eyes
well distributed across the tuber. Some varieties
have few eyes, which are often concentrated
near one tuber end (bud end). Seed pieces with-
out eyes (blind seed pieces) will not sprout; there-
fore, seed pieces of varieties with few eyes must
be cut large enough to ensure that at least one
eye is found on every piece.
Cut seed is either planted immediately or al-
lowed to wound heal (suberize). Suberized seed
pieces typically fare better than freshly cut seed
in adverse germination conditions such as cool,
wet soils (Secor and Gudmestad, 1993). More-
over, properly suberized seed may be stored for as
long as whole seed, which allows seed to be cut
and stored well before planting, freeing up re-
sources and management in preparation for
planting. To prevent shrinkage and rot, humid
air must flow continuously through the seed
piece pile during suberization (Secor and Gud-
mestad, 1993). Whether suberized or not, grow-
ers often treat seed tubers and pieces during or
prior to planting with a fungicide and/or sys-
temic insecticide to protect against soil- and
seedborne fungi and in-season insect pests. To
promote rapid emergence, seed is often removed
from refrigerated storage and “warmed” several
weeks prior to planting. Sanitary seed-cutting
conditions are essential for preventing disease
and bacteria transmission across or within seed
lots. Additional information on seed tuber physi-
ology, seed potato production and certification,
and insect and disease prevention may be found
throughout this volume.
6.8
In-Row Seed Piece Spacing
and Plant Population
The ideal combination of plant population, row
width, and in-row seed piece spacing for a par-
ticular variety and region is the one that pro-
duces the optimum tuber size profile (see
Table
The spatial configuration of seed pieces, and ul-
timately healthy plants, plays a major role in de-
termining the tuber size profile. Other important
and often growth-limiting factors include sea-
son length, variety, irrigation and nutrient avail-
ability, and soil type. Research has shown that
stem number per plant also affects tuber size
profile (Knowles and Knowles, 2006). In 2006,
Knowles and Knowles reported that physiologic-
ally older seed tubers produced higher stem and
tuber numbers per plant and smaller tuber size
profiles compared with physiologically younger
seed. In addition to seed age, stem number is cor-
related highly with planted seed tuber weight
(Wurr
et al
., 1992). Wurr
et al
. (1992) found
that as planted seed tuber weight increased,
stem number increased. Using planted seed
tuber weight to boost stem number might pro-
vide the desired results; however, the economics
of planting larger seed is often prohibitive
(Schotzko
et al
., 1983). Because the ability to
