Screening Malus seedlings for cold resistance
Date
1988-08
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Degree Level
Masters
Abstract
Cold stress is the most important factor limiting the northern
expansion of Malus cultivation, and breeding for improved cold
resistance is time-consuming and laborious. Members in the genus Malus
are characteristically heterozygous and reveal a high variability in
the hardiness of their seedlings. This study was conducted to develop
an appropriate acclimation routine to identify cold hardy transgressive
segregants from Malus seedling populations. The effects of frosts (16 hours at -3°C) and lag-times (10 and 11 days at +3 to +5°C), short (8
hour) day and cool (+3 to +5°C) temperature exposures, and different
screening temperatures (-20, -30, and -40°C) were investigated on
seedlings grown in a greenhouse from open-pollinated Golden Delicious
(Malus pumila), Antonovka (Malus baccata) X (Malus pumila) and Rescue
Crab (Malus baccata) X (Malus pumila).
Differentiation in hardiness response of the seedling populations
was not achieved until after exposure to short days at cool
temperatures for six weeks. Further population differentiation was
achieved by exposure to one or more frosts compared to no frost
exposures. Rescue gave a 74% increase in survival, Antonovka a 62%
increase, and Golden Delicious a 51% increase, when compared to
survival with no frosts.
After the acclimation response had been initiated by exposure to
short days at cool temperatures, up to 11 days in the same conditions
caused no significant decrease in hardiness. Additionally, no
significant decrease in survival was observed in seedlings held at cool
temperatures and short days for up to 10 days after a frost exposure.
Hardiness levels of acclimated and non-acclimated seedlings agreed
with known inherent hardiness responses for all three cultivars
evaluated. Cultivar seedling response to different freeze temperatures
was pronounced. For crosses representing a full range of cold
hardiness capabilities, a screening temperature close to -30°C was
found to be most effective. The response of the different cultivar
seedlings to the three different freeze temperatures indicated that the
screen could be tailored to fit the minimum survival requirements of a particular region.
A binomial form of regrowth data collection, percent seedling
survival, was determined to be the most efficient and precise measure
of evaluation. The controlled three-step freeze procedure and thawing
rate that was developed, will facilitate rapid, repeatable screening of large numbers of progeny. An examination of replication means revealed
that the probability of survival was influenced by when the seedlings
grew in the greenhouse. It is recommended that, for subsequent
screens, all the material should be grown at the same time.
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Citation
Degree
Master of Science (M.Sc.)
Department
Horticulture
Program
Horticulture