[VIPS] Crown ideotype for hybrid poplar
'Toby' H D Bradshaw
toby at u.washington.edu
Wed Oct 4 18:46:14 EST 1995
There was considerable discussion at the recent International
Poplar Symposium (IPS; point your Web browser at
http://poplar1.cfr.washington.edu for more information) on
ideotype breeding of hybrid poplar to maximize
productivity in short (4-9 years) and medium (10-20 years)
rotation plantations under intensive culture. To continue the
discussion beyond the end of the meeting, and to include as
many new participants as possible, I would like to have a
Virtual International Poplar Symposium (VIPS). Hence,
the [VIPS] in the header.
Of many possible elements to be included in an ideotype
for a domesticated tree growing in a monoclonal stand,
crown architecture is one element with the potential for
strong input from various disciplines, including anatomy,
physiology, evolutionary biology, ecology, and genetics.
The two Populus species most often involved in commercial
hybrid poplar plantations in Pacific Northwestern North
America are P. trichocarpa (black cottonwood; PNW native)
and P. deltoides (eastern cottonwood; from eastern and central
NA). These species have very different crowns:
P. trichocarpa P. deltoides
hang large small
tilt small large
sylleptic many few
proleptic small large
branch steep flat
light high lower
apical high lower
F1 hybrids between P. trichocarpa and P. deltoides are
intermediate for many of these crown characters, and
superior to either parental species in growth (at least in the
Pacific Northwest) and light interception. However, there is
nothing to indicate that the F1 hybrids have optimized
crowns for productivity, and so there is a strong interest in
understanding the critical components of a crown ideotype.
Ideotypes can be formulated on purely theoretical grounds,
then tested empirically by breeding and selection. The
ability to clonally propagate ideotypes (and their sub-
optimum relatives) gives these experiments considerable
Several key questions should be answered in order to
formulate a crown ideotype:
1) Which crown characters (e.g., leaf orientation, branch
number) are most influential in light interception?
2) Which Populus species can contribute to the net
improvement of each important crown architecture trait?
3) How do crown ideotypes vary across latitude (i.e.,
changes in sun angle), or gradients of temperature, or
changes in light intensity, or other physical features?
4) What is the evolutionary/ecological reason for the
difference in crown structure between P. trichocarpa and P.
5) How do crown ideotypes differ between short rotations
for pulpwood and medium-length rotations for veneer or
6) How much of the variation in crown traits is genetic, and
how much is due to phenotypic plasticity?
Toby Bradshaw | (206)616-1796 (voice)
Center for Urban Horticulture | (206)616-1826 (FAX)
Box 354115 | toby at u.washington.edu
University of Washington | 47.39.496N 122.17.404W
Seattle WA 98195 | Will make linkage maps for food.
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