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[80]. A significant secondary contributor to the genetics of current apple varieties is the
European crabapple,
Malus sylvestris
[79] which may also possess important resistant genes
lost in the modern varieties.
Several studies of
M. sieversii
material collected from geographically and climatologically
different sites in Kazakhstan have concluded that significant genetic diversity can be captured
in small-sized sub-populations of these site collections [81, 82]. In a subsequent study of the
Kazakhstan collection, Richards et al. [83] concluded that differentiation in genetic diversity
was greater among individual families than among sites and that gene diversity and allelic
richness varied significantly among collection sites. The use of this material to study drought
responses in apple at the morphological and genetic levels without the complication of grafted
rootstocks provides the cornerstone of our approach to identifying novel drought resistant
mechanisms or factors contributing to drought susceptibility.
Figure 1.
Malus sieversii
collection sites in Kazakhstan [after 80].
Research Course:
In order to isolate and characterize genes responding to drought from a
commercially important cultivar as a standard for comparison, we used SSH on cDNA
prepared from 'Royal Gala' subjected to a moderate-severe drought. Genes identified by this
method were further characterized for their expression in various tissues under drought
treatment or in fully watered controls.
To begin analyzing
M. sieversii
lines for drought responsiveness, we first surveyed core
populations of individuals collected from xeric site 6 and later, xeric site 9 for WUE using stable
carbon isotope composition (δ
13
C) to identify individuals with better WUE. Morphological
features, e.g. leaf area, leaf length, stomatal density and number of leaves per current year's
branch length were evaluated [84]. Individuals showing δ
13
C extreme values were then
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