Tree Improvement Program Project Report 2006 / 2007

it must be noted that the genotypes that form females late
may also be induced much later. In other words, there is a
delay in differentiation in some of the clones, which should
be reflected in the management of induction treatments,
such as pruning or hormone induction. It is likely that
the timing difference in the initiation of female strobili
varies between the five clones. Overall, they differ from
each other from two to four weeks. Initiation of female
(and lateral-shoot) buds would appear to be in mid-July.
Female strobilus differentiation likely begins in late July for
some genotypes because female buds could be observed by
August 1, 2006. Based on this observation, female strobilus
initiation is more highly variable than was previously
suspected. This means that induction treatments should be
implemented in early July if they are to maximize female
bud formation. We suggest that female strobilus induction
treatments need to be carried out in a genotype-specific
manner.
The pattern of male differentiation among the clones
selected for histological analysis showed that male initiation
and differentiation occurred before the first date of longshoot
bud collection, namely July 5, 2006 (Table 25). Male
strobilus initiation occurred at some time in June 2006.
Due to the advanced stage of development of male
strobili observed for some of the clones, it is likely
that initiation occurred even earlier. Male strobilus
differentiation is also thought to occur earlier than
previously published (Owens 2006).
Induction strategies of female buds of lodgepole pine
should take into account the information summarized
in Figure 74. Within long-shoot buds there is a marked
apical-basal gradient: typically, the bottom half developed
male and short-shoot buds, whereas the top half has either
short-shoot buds and later female buds and lateral-shoot
buds. Within each half there are also gradients, with males
mostly formed at the bottom of the bottom half. In the
upper portion, female buds and lateral-shoot buds are the
latest to form, but female buds are almost always higher up
the distal portion than lateral-shoot buds. A time factor also
comes into play because buds form in an obvious order:
males precede short-shoot buds and lateral-shoot buds,
and female buds are last. This means that induction of
female buds can occur after male buds have visibly formed
(as observed under a dissecting scope), but not long after
because the period from short-shoot bud initiation to
female bud initiation is no longer than three weeks.
A practical conclusion of this work is that when
males are readily apparent in halved long-shoot buds
T R E E I M P R O V E M E N T P R O G R A M
P R O J E C T R E P O R T 2 0 0 6 / 2 0 0 7
(longitudinally bisected leader shoot tips), it is time
to apply induction treatments to optimize female bud
initiation.
Acknowledgments
We gratefully acknowledge the assistance of Dr. Mike
Carlson and Chris Walsh of KRS in providing us with plant
material and much advice. We also appreciate the work of
Heather Anholt, who collected samples for us.
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