Tree Improvement Program Project Report 2006 / 2007

.2.6 Enhanc ng Seed Product on n
North Okanagan Lodgepole
P ne Seed Orchards
(SPU 0719)
Chr s Walsh and Joe Webber
The OTIP SPU 0719 final report for 2005 provided a
complete summary of the lodgepole pine seed set study for
the period of 2000 to 2005. Over that period, the improved
irrigation system did not result in substantial increases
in seed yields, although cone mass and seed weights have
improved. Temperature and drought conditions during
the pre-pollination, pollination, fertilization, and embryo
development periods have not been severe, and soil
moisture content has been adequate. Crown misting has
also not been necessary. Again weather conditions during
the sensitive periods of reproductive development have not
limited either pollen uptake or fertilization and embryo
development.
There is growing concern that both seed yields and
cone numbers are declining over the last three years. This
downward trend is observed across the orchard in general
and is not associated with culture (over-watering) although
over-watering may exaggerate this trend. Lower cone
numbers may be the result of decreasing tree vigour caused
by crown shading that comes from increased tree size. Also,
cone numbers may be dropping because the sampling
points have become increasingly lower in the crown.
Although sampling now considers crown position (high and
low), cone numbers are still declining.
We have no reason to suspect pollen supply (uptake)
as the cause of the decline, especially in the upper crown
seed cones, although pollen supply in the lower crown (in
large trees) may be limiting. Since this orchard is nearing
20 years old, we must suspect the vigour of the trees as a
cause of lower cone and seed production. We also need to
consider whether insect damage to first-year cones after
harvesting can adversely affect yields the following year.
Because the pre- and post-pollination season was not
hot and dry, we abandoned monitoring cultural effects on
seed set. However, we monitored insect damage, pollen
supply to lower crown cones, and weather. Increasing lower
crown pollen supply (control crosses and SMP) did not
improve seed set, and insect losses were in the range of 10
filled seed per cone in upper crown cones. We have noted
that insect seed losses increase with heat. The year 2006 was
2
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
relatively cool during the pre- and post-pollination period
but was unusually hot and dry during June and September.
RESULTS
Lower crown pollen supply
We used both control cross pollination and SMP to
determine if pollen supply to lower crown cones was
limiting seed yields. We treated lower crown cones with
SMP in 2005 and then compared them with openpollinated
cones in upper crowns, both with and without
insect protection (bagging). We compared cones treated
with control crossing in the lower crown with OP cones in
both the lower and upper crowns.
Figures 33 and 34 show the effect of SMP on lower
crown cones for both total seed per cone (TSPC) and filled
seed per cone (FSPC). Figures 33 and 34 also show the
effect of insect protection on lower (SMP) and upper crown
cones (OP only). Increasing pollen supply (SMP) to lower
crown cones did not improve either TSPC or FSPC, but
the effect of insect protection is apparent. About 10 FSPC
were lost in the upper crown from insect predation, but the
loss was less than two for lower crown cones.
Figures 35 and 36 show the effect of control cross
pollination on lower crown cones compared to OP
cones in both the upper and lower crowns. There was a
slight decrease in FSPC (about four) from OP cones in
lower compared to upper crown cones, and control cross
pollination did not improve the number of FSPC in the
lower crown.
Meteorolog cal data
Temperature (Tsum) and vapour pressure deficit (VPDsum)
sums are shown for the irrigation block only. Tables 13 to
16 show the meteorological data for four important periods
of reproductive development in lodgepole pine. April to
mid-May represents the period of rapid second-year cone
development and pre-pollination development of the firstyear
cones. The last two weeks of May represent the period
of flowering, pollination, pollen uptake, and early pollen
development (penetration of the nucellus). June represents
the period of fertilization and early embryo development
of the second-year cones, and September is the period of
differentiation of first-year cones (although recent data on
describing the period of seed cone differentiation suggest
that it occurs much earlier).
Heat sums, vapour pressure deficits, and precipitation
vary by year and period of reproductive development.
During pre-pollination, 2006 was an average year with