Volume 30 Number 1 Article 10 Pages: 12-13
Year 1976 Month 1
Title: Assessment of and Screening for winterhardiness in Peach
Author: R.E.C. Layne
Citation
Abstract:
The overwintering response of
peach flower buds to cold stress was
studied from 1969 to 1975 to determine
what factors were important in
assessing and screening peach seedlings
for bud hardiness.
We found
that bud injury outdoors occured least
frequently in Stage 1 (October to December),
most frequently in Stage 2
(January to mid March) and was intermediate
in Stage 3 (mid March to
mid May).
We determined from controlled
freezing tests that peach buds deacclimated
and reacclimated in response
to outdoor temperatures at a faster
rate in Stages 1 and 2 ,than in Stage
3. Peach buds also attained greater
levels of bud hardiness in Stage 2 than
Stage 1 or 3. Genetic discrimination
of bud hardiness was best in Stage
2. Discrimination of bud hardiness
was improved if plant material for
controlled freezing tests was collected
from outdoors during periods of cold
weather and tested the same day.
Routine screening of seedlings way
therefore conducted in Stage 2 during
periods of cold weather.
It was important to include cultivars
of known hardiness as standards
in each freezing test so that meaningful
comparisons could be made from
one freezing run to another.
The
standards were used as the basis for
selection or rejection of seedlings.
Thus, seedlings that were comparable
or superior to 'Redhaven' in bud hardiness
were retained and those that
were comparable or more bud tender
than 'Loring' were discarded.
Controlled freezing tests were conducted
on detached scions of the previous
season's growth.
A sample size
of 5 scions per selection per test temperature
was adequate.
It was best
to equilibrate plant material at -5°C
for 1 hour before cooling to the desired
temperatures.
A cooling rate of
5°C per hr was effective in discriminating
different levels of bud hardiness.
Scions could be removed as soon as
the test temperatures were attained.
It was best to thaw scions slowly at
4C in a water saturated atmosphere
and to assess bud injury 1 or 2 days
later, than to thaw slowly or quickly
in a dry atmosphere, because cold injury
symptoms were sometimes difficult
to distinguish from dessication injury.
It was best if test temperatures
differed by increments of 2°C or less
to improve accuracy in LT50 determinations.
Differences in bud hardiness
at each test temperature were
tested for statistical significance by
Analysis of Variance, and the means
were compared by Duncan's Multiple
Range test.
A computer program was
written that performed the analyses
and tabulated the summarized data.
The procedures described were efficient,
effective, and reliable in identifying
cold hardy peach selections.
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