Storage Temperature Affects Sexual Potato Seed Dormancy

Abstract

Sexual potato ( Solanum tuberosum L.) seeds require many months of afterripening in dry storage to completely lose dormancy and germinate readily at >25C. We examined the relationship between storage temperature and seed dormancy, as assessed by the percentage of germination after 4 days. Two F 1 hybrid lots of `Desiree' × 7XY.1 were used; one seed lot was produced by carefully removing half of the developing tubers from the mother plant during seed development, and the control remained undisturbed. Seeds were stored with 3.4% moisture (dry-weight basis) at 10, 20, 30, 40, and 50C and were tested eight times during 29 months for daily germination at 27/40C (21/3 h) for the first 8 days, followed by 6 days at 17C. After 29 months of storage, final germination was <97% only when control seeds were stored at 50C, in which germination was 72%. Germination after 4 days increased curvilinearly with increasing storage temperature, and both seed lots similarly lost dormancy (germination >90%) after 10 months at 40C. Optimum germination levels were maintained after 29 months at 40C. Seeds stored at 50C never completely lost dormancy, and after 7 months of storage, germination at 4 days gradually decreased to zero. Dormancy was eventually lost after 29 months in most seeds stored at <40C, and differences between seed lots suggest that removing tubers from the mother plant increased dormancy. We conclude that dry potato seeds can be safely afterripened at temperatures up to 40C; lower temperatures slow the rate of dormancy loss, and higher ones are detrimental to seed quality.

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99HORTSCIENCE, VOL. 31(1), FEBRUARY 1996
HORTSCIENCE 31(1):99–101. 1996.
Storage Temperature Affects Sexual
Potato Seed Dormancy
Noël Pallais
Department of Physiology, International Potato Center, P.O. Box 1558,
Lima, Peru
José Santos-Rojas
Instituto Nacional de Investigación Agropecuaria, Casilla 24-0, Remehue,
Osorno, Chile
Rosario Falcón
Department of Physiology, International Potato Center, P.O. Box 1558,
Lima, Peru
Additional index words. Solanum tuberosum, afterripening, seed quality, true potato seed
Abstract. Sexual potato (Solanum tuberosum L.) seeds require many months of afterripening
in dry storage to completely lose dormancy and germinate readily at >25C. We examined
the relationship between storage temperature and seed dormancy, as assessed by the
percentage of germination after 4 days. Two F1 hybrid lots of ‘Desiree’ x 7XY.1 were used;
one seed lot was produced by carefully removing half of the developing tubers from the
mother plant during seed development, and the control remained undisturbed. Seeds were
stored with 3.4% moisture (dry-weight basis) at 10, 20, 30, 40, and 50C and were tested
eight times during 29 months for daily germination at 27/40C (21/3 h) for the first 8 days,
followed by 6 days at 17C. After 29 months of storage, final germination was <97% only
when control seeds were stored at 50C, in which germination was 72%. Germination after
4 days increased curvilinearly with increasing storage temperature, and both seed lots
similarly lost dormancy (germination >90%) after 10 months at 40C. Optimum germina-
tion levels were maintained after 29 months at 40C. Seeds stored at 50C never completely
lost dormancy, and after 7 months of storage, germination at 4 days gradually decreased
to zero. Dormancy was eventually lost after 29 months in most seeds stored at <40C, and
differences between seed lots suggest that removing tubers from the mother plant
increased dormancy. We conclude that dry potato seeds can be safely afterripened at
temperatures up to 40C; lower temperatures slow the rate of dormancy loss, and higher
ones are detrimental to seed quality.
afterripening in dry storage and potato seed
dormancy. Removal of developing tubers from
the mother plants during seed production was
tested as a technique to increase seed quality;
therefore, the influence of this effect on the
results also was investigated.
Materials and Methods
This study was conducted at the Interna-
tional Potato Center in Lima, Peru, from Feb.
1992 to Oct. 1994 using two F1 hybrid potato
seed lots of ‘Desiree’ x 7XY.1. Seed was
produced by hand-pollinations in Osorno,
Chile, by the Instituto de Investigaciones
Agropecuarias in Apr. 1991, according to the
recommended practice for high-quality seed
(International Potato Center, 1987). Both seed
lots were produced and harvested under simi-
lar conditions. In one lot, about half of the
developing tubers were carefully removed from
the mother plants after pollination (–TUBER),
and the other lot served as control (CON-
TROL).
Seeds had been stored at ≈15C (±5C) for 11
months before the other treatments were started.
Seed moisture content, determined with a
Sartorious infrared dryer (model YTC01L;
Sartorious, Goettingen), at that time was 6.8%
in CONTROL and 7.1% in –TUBER. A total
of 155 g and 230 g of CONTROL and
–TUBER seeds, respectively, was produced.
Each lot was separated with a seed blower
(model 1; Hendrickson Enterprises) at three-
fourths setting into high- and low-density
sublots; 48% of the CONTROL and 53% of
the –TUBER seeds fell in the high-density
fraction. Only high-density seeds were used
for treatments. Seeds were dried by sealing
with fresh silica gel at 22C until both lots
attained 3.4% (±0.05%) moisture content; how-
ever, –TUBER seeds took a few days longer
than CONTROL seeds to reach this level.
Random seed samples sufficient for each evalu-
ation were immediately sealed in separate
aluminum packages and stored in tempera-
ture-controlled (±2C) dark incubators at 10,
20, 30, 40, and 50C.
Evaluations consisted of germination tests
conducted at ≈3, 4, 7, 10, 14, 19, 24, and 29
months of storage. Before testing, seeds were
humidified to a uniform moisture content of
13% by placing them in a sealed environment
above water at 22C for 24 h. Germination tests
consisted of four replications of 100 seeds
each placed evenly over dry Whatman no. 2
filter paper in 9-cm petri dishes. Seeds were
hydrated with 5 ml of deionized water before
placing them in an incubator at 27C for 21 h
and at 40C for 3 h. Although official rules for
testing potato seeds are not available, 3 h at
40C was included to provide a diurnal stress
similar to that which might be encountered by
seeds at midday when sown under field condi-
tions. Water was added as needed. On the
eighth day of the germination test, tempera-
ture was lowered to a constant of 20C; how-
ever, 17C was used in the 29-month test.
Hydrated seeds usually were placed in the
germination environment at the beginning of
the 27C cycle, but in the 14- and 24-month
tests, seeds were placed at 27C for only a few
hours before the 3-h cycle at 40C. Germina-
tion was counted daily for 12 days at the first
sight of radicle emergence, and for 14 days in
the 29-month test. Germinating seeds were
exposed to laboratory light and temperature
(22C) for ≈20 min during daily evaluations.
Results were summarized by presenting
data on 1) germination percentages after 4
days for each germination test, and 2) final
germination percentages after 14 days in the
29-month test. Analyses of variance (ANOVA)
were performed after arcsin transformations
of the data to determine significance with a
completely random design and a two-way
factorial arrangement (seed lot × storage tem-
perature) (Steel and Torrie, 1980). Percent-
ages of germination were presented according
to the results of ANOVA and transformed data
were submitted to quadratic regression analy-
sis (best-fit model) with storage temperature
as the independent variable.
Results and Discussion
Storage temperature had a profound effect
on potato seed dormancy as estimated by the
percentage of germination after 4 days at 27/
40C (Fig. 1). The germination responses to
increasing storage temperature were predomi-
Use of sexual potato seeds is increasing as
an alternative to seed tubers for propagating
potatoes in developing countries (Pallais,
1994). Seeds that germinate readily only at
17C (±3C) are considered dormant and not
appropriate for sowing a crop of potatoes,
whereas nondormant and high-quality seeds
germinate readily at ≥27C (Pallais, 1995a,
1995b). Gibberellic acid is not completely
effective in promoting uniform germination of
dormant seeds and optimum seedling growth
at >25C (Pallais et al., 1990, 1991). Potato
seed dormancy is released progressively dur-
ing afterripening in storage, and seeds should
always be stored at <5% moisture content on
a dry-weight basis (Pallais, 1995a, 1995b;
Pallais and Espinola, 1992). High storage tem-
perature and low seed moisture content can be
used to speed seed dormancy loss during
afterripening (Pallais, 1995a, 1995b). Our
objective was to determine the relationship
between increasing temperature during
Received for publication 17 Jan. 1995. Accepted for
publication 10 Oct. 1995. We thank Bill Hardy for
his editorial suggestions. The cost of publishing this
paper was defrayed in part by the payment of page
charges. Under postal regulations, this paper there-
fore must be hereby marked advertisement solely to
indicate this fact.

HORTSCIENCE, VOL. 31(1), FEBRUARY 1996100
SEED TECHNOLOGY
Table 1. Effect of temperature during 29 months of
storage on percentage of final germination in
two potato seed lots.
Storage Germination (%)
temp Seed lot
(°C) CONTROL –TUBER
10 100 100
20 100 100
30 100 100
40 99 100
50 72 97
ANOVAzMean square P
Seed lot (S) 145.6 0.0068
Temperature (T) 9370.9 <0.0001
S × T 105.3 0.0100
Error 17.2
zAnalysis of variance after arcsin transformation of
the data: best-fit model Q = quadratic component for
CONTROL, y = 83.4 + 1.8x – 0.04x2, r2 = 0.84 at P
< 0.001; and for –TUBER, the regression responses
were nonsignificant (P < 0.05).
1). After 29 months of storage, final germina-
tion was ≥97% for all treatments, except when
CONTROL seeds were stored at 50C, then
germination was ≈25% lower. These results
agree with Simmonds’ (1968) observations
that potato seed viability is preserved in stor-
age under either cool or dry conditions.
The results also agree with a previous sug-
gestion that potato seed production would be
influenced by the stronger sink strength of
fast-developing tubers (Pallais, 1987). Seed
viability (Table 1) and germination rate (Fig.
1) of CONTROL seeds declined faster than
those of –TUBER seeds during storage at 50C.
Because a greater resistance to unfavorable
storage conditions is used to test for differ-
ences in vigor between seed lots (Mathews,
1980), one might conclude that removing tu-
bers from the mother plants should increase
the vigor of seeds produced by such plants.
However, because seed deterioration is as-
sumed to begin only after seed dormancy is
lost (Osborne, 1982; Simmonds, 1968), the
results also might be explained if CONTROL
seeds were less dormant than –TUBER seeds
when the experiment started. This situation
was supported clearly by the results of germi-
nation at 4 days, when seeds were stored at low
temperature (10 and 20C), because germina-
tion rate increased more slowly for –TUBER
seeds than for CONTROL seeds (Fig. 1) and
low temperature preserves potato seed dor-
mancy (Simmonds, 1963). The intensity of
potato seed dormancy is positively correlated
with tuber dormancy of the mother plant
(Simmonds, 1963, 1964), and tuber removal
might have increased dormancy-enhancing
factors in sexual seeds.
The importance of using only optimum-
quality seeds for evaluating the potential of
this new sexual alternative for propagating the
potato crop cannot be overemphasized. After
sufficient and proper storage, potato seeds
lose dormancy and can germinate very quickly
(4 days) at high temperature (≥27C).
We conclude that raising storage tempera-
ture to 40C safely accelerated the rate of dor-
mancy loss in dry potato seeds, whereas stor-
age at 50C was detrimental to seed quality.
increased when seeds were stored at <40C,
and after 29 months only –TUBER seeds stored
at 10 and 20C had not fully attained germina-
tion levels of >90% (Fig. 1). These results
support a previous conclusion that high tem-
perature and low moisture can be used to
shorten the period of afterripening required by
dormant potato seeds (Pallais, 1995a). More
importantly, these results clearly indicate that
dormant, dry seeds could be safely afterripened
at temperatures up to 40C. Nonetheless, the
total germination of dry potato seeds was
affected little by storage temperature (Table
nantly curvilinear, and significant interactions
between seed lots occurred after 14 months of
storage. Most seeds were still dormant after 3
months of storage, as judged by germination
levels that were <50%. Both lots had lost
dormancy (germination >90%) similarly after
10 months of storage at 40C (Fig. 1). Germina-
tion at 4 days was >90% for both lots at 10, 19,
and 29 months of storage at 40C. But 50C
apparently was detrimental to seed quality
because, after 10 months of storage, germina-
tion rate declined before it reached optimum
levels (Fig. 1). Germination rate gradually
Fig. 1. Effect of storage temperature on percentage of potato seed germination after 4 days at 27/40C (21/
3 h) when tested after 3, 7, 10, 14, 24, and 29 months of storage in two seed lots produced in mother plants
with (–TUBER) and without (CONTROL) tubers removed. There were no significant interactions
between seed lots in the 3-, 4-, 7-, and 10-month tests, and data of significant (P < 0.05) interactions
between seed lots were provided for the 14-, 19-, 24-, and 29-month tests. Quadratic regression curves
(best-fit model) were generated after arcsin transformations to fit the data. Levels of significance at P
< 0.01 and 0.001 are denoted as ** and ***, respectively. Seeds were placed in the germination environment
at the beginning of the 27C cycle, except in the 14- and 24-month tests, when seeds were placed under
27C for only a few hours before the 3-h cycle at 40C.

101HORTSCIENCE, VOL. 31(1), FEBRUARY 1996
Removal of developing tubers from the mother
plants during seed production does not appear
to increase seed quality because dormancy
was enhanced.
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