- During physiological ageing of seed potatoes, the stored tuber
undergoes certain biochemical changes which cause the breaking of
dormancy and the initiation of bud growth. The ageing process can
be manipulated through storage temperature and duration. Higher
temperatures usually accelerate seed tuber ageing. In order to
define the process of physiological ageing and develop optimum
ageing treatments, seed potatoes were stored at 4.4°C and then
warmed to either 10.0°C (1984) or 15.6°C (1985) for 0, 2, 5, and 8
weeks prior to planting. Levels of total, reducing, and sucrose
sugars, respiratory activity, free amino acids, soluble protein,
and phosphorylase activity were monitored weekly. Field studies
were conducted to determine the effects of seed storage temperature
and duration on plant development and yield. Three sites with
different lengths of growing season were selected.
Warming seed to 10.0°C and 15.6°C greatly accelerated sprouting
ability in storage. Apical dominance was evident in seed which had
been stored for long periods at these elevated temperatures.
Total, reducing, and sucrose sugars declined during storage at
10.0°C, indicating both a suppressing effect of elevated temperature on sugar fractions and increasing metabolic energy demands.
Conversely, both reducing and total sugars increased over time in
seed held at 4.4°C, eventually reaching a constant level. Sucrose
declined to a minimum and then fluctuated randomly with additional
time at this temperature. Phosphorylase activity increased dramatically approximately five weeks after testing began in tubers stored at both 4.4°C and 15.6°C. Activity then declined two weeks later and remained constant throughout the study. Free amino acids
decreased to a low level during storage at both temperatures,
reached a constant state, and then slowly increased with additional
storage time. Soluble protein levels initially increased during
storage, but then declined. Respiratory activity, as indicated by
the production of formazan, remained fairly constant throughout
storage at both temperatures.
Plant stands were not affected by storage temperature. Seed
warmed to 10.0°C and 15.6°C generally emerged faster and established a canopy earlier in the season than seed held at at 4.4°C.
Differences in plant size and canopy density diminished rapidly as
the season progressed. Numbers of aboveground stems per hill
increased with time at 10.0°C and 15.6°C. Storage treatment did
not affect time of tuber set or plant senescence.
Storage treatments significantly affected yields at one loca
tion in 1984. Seed held continuously at 4.4°C produced more
undersized tubers than any other treatment at Corvallis (medium
Treatments significantly affected yields at all three sites in
1985. At Powell Butte (short season), seed held at 4.4°C yielded
more than seed warmed to 15.6°C, and produced significantly higher
yields of U.S. No. 1 tubers than any other treatment. Seed warmed
at 15.6°C for 2 weeks yielded significantly more culls than any
other treatment. At Corvallis, (medium length season) seed stored
at 15.6°C for 5 weeks produced significantly higher total yields
than any other treatment. Yields of U.S. No. 1 tubers at Hermiston
(long season) were higher for seed held continuously at 4.4°C,
while seed warmed at 15.6°C for 5 weeks produced more undersized
tubers than any other treatment.
It appears that length of growing season, plant growth
patterns, and plant types combine to determine yield response to
seed conditioning. Seed conditioned at higher temperatures emerged
early, produced large numbers of aboveground stems per hill, and
performed best in an area with a medium growing season, but did not appear to be well suited for areas of either short or long seasons.
Seed held continuously at 4.4°C emerged late, produced few above-ground
stems per hill, and produced higher U.S. No. 1 yields than
seed conditioned at the higher temperatures, in areas with a long
or short season. Powell Butte (short season) experienced a late
spring frost in 1985. It is possible that due to less advanced
foliage growth at the time, plants from seed held at 4.4°C were not
as severely damaged as the plants from warmed seed, explaining high
yields produced by cool stored seed in this short season area.