The development
of improved willow clones for eastern
North America 1
by R.F. Kopp 2, L.B. Smart 2, c.A. Maynard 3, J.G. Isebrands
and L.P. Abrahamson
2,3
i
',
[
Z
4, G.A. Tuskan
5
Effo,'_s aimed at genetic hnprovement ofSalix are increasing in Nerd'_ America. Most of these are directed towards de','eloping improved
clo,-es for b/omass production, phytoremediation, nutrient filters, and stream bank stabilization in the Northeast and Nonh-central United States. Native species are of primary interest, but a small number of clones containing non-native germplasm are also being used
m _e breeding program to provide valuable traits. Parent combinations for conu'olled crosses are being selected with the hope of maximizing the probability of producing clones exhibiting heterosis for traits of interest, such as rapid early growth, pest resistance, general adaptability, etc. The present strategy is to test as many parent clone combinations as possible, and then repeat the ruost protmstag crosses to produce large families from which the best clones will be selected for further testing. Molecular fingerprintiog
• • ._
technology will
accelerate the rate of improvement. National and international cooperation would facilitate regional clone
andbe applied to of
de;eloi_ment
promotion
willow as a bioenergy crop.
"_ "_
Key. words: Salix, biomass production,
gl_
m_ _
_
breeding, heterosis, molecular fingerprinting
Lea efforts destin_.s 'a t'am_.lioration gdn,_tique du Salix croissent sans cesse en Am_rique du Nord. La majeu,'e pattie des efforts eat
concentrSe sur le d_veloppcment de clones am_lior_.s pour la production de biomas_e, la phytorem4diation, le_ filtres d'_ldments nutritifs
et la stabilisation des rives des cours d'eau dana te nord-est et le centre-nord des Etats-Unis. L'int&at porte avant toute chose sur lea
es_ces indig_.nes, mais un petit hombre de clones contenant des cellules embryonnaires non indighnes sont 6galement utilises dana
le programme de reproduction afin d'apporter des caract&istiques int6ressantes. Lea combinaisons parentales pot:r obtenir des
descendants de proven,'mce contt'61,Sesont choisics dana le but de ma.rdrn.iserla probabilit_ de produire des clones dthnoulmnt une hdt&ogdndir6
dc_ caract_ristiqt,es int6ress-mtes, ton'mar la croiss,',.nce initiale rapide, Ia rdsistanee aux ravageurs, l'adaptabilit4 gdn4rale, etc. La slratdgie
actuelle eat de tester autant de combinaisons parentales de clones que possible, et de reproduire par la suite lea descendants lea plus
pronzetteurs pour produire des grandes families desquelles lea meilleurs clones seront choisis pour poursuivre tea tests. La technologic
_
,._
"_ ._
L
de I'empreinte digitale mol6culaire sera utilis,Se pour acc_l_rer le taux d'am6lioration. La cooNration nationale
faciliterait le d4veloppement de clones rdgionaux et la promotion du saule en tant que ressource biodnerg4tique.
Mots-clis : Salix. production de biomasse, reproduction, h6t&og4ndit6, empreinte digitale moldculaire
History of Willow Genetic Improvement
"_
o
Interest in growing and using poplars
and willows for
energy and to produce high-value chelnicals and other bio-ba..¢_,l
q-"ne dccumented
history of Salix culture in North America starts during the period from 1840-1850 when German immigrants began producing willows for basketry" in New York State
and Pennsylvania.
Early basket makers used native species,
products has increased in the United States during the past two
decades, due to unstable petroleum prices, a desire to decrease
dependency
on imported fossil fuels, and concern about the
environmental
impacts of burning fossil fuel. Exceptionally
high productivity
rates have been achieved
with hybrid
poplars in the Pacific Northwest. Nit in l!:e Nortl_,:,',st and Northcentral United States Septoria canker severely limits growth
of many hybrid poplar clones (Abrahamson
et al. 1990. Ostry
and McNabb 1990). However, Septoria is not a disease problem for willows. Because of disease problen'_s with hybrid poplars
and reports of high biomass yields acNeved with willows grown
under intensive culture systems in Europe (Stott 1984, Chrispt-imary gelaus
tersson 1986), Salix became the
of interest for
short-rotation woody biomass production in the Northeast Urtited States during the late I980s. Despite the availability
of
but
soon began
willows
fromuniformiEurope,
particularly
Saliximporting
pt_rpurea andL..planting
to increase
product
ty. The importance
of selecting clones with desirable form and
wood qualities that were adapted to local soils and pests was
recognized in the earliest days of willow culture (Hubbard 1904).
Early willow improvement
efforts in the United States ineluded field trials of 70 European
clones in the 1880s (Simpson
1898). The willow basket industry, in the U.S. reached
during the 1870s and continued until World War 1I.
a peak
._t.a
•o _
1
in the
United States
o _ _
_ eq
,.a _ _"
,., _
et interaationale
tPreseated to tl_e 21st Session of the International Poplar Commission.
ZState University
of000.Vancouver,
New York and
College
Environmental
Science and
Forestry,
Faculty
of 2Environment;d
ForestofBiology.
1 ForestryDrive.SyraSeptea-ber
24-=8.
Was_tington,
t_'SA
cuse. NY 13210
_
:_Stat¢University of New York College of Environmental Science and
•_ I_ Forestry, Faculty of Forestry, 1 Forestry Drive, Syracuse. NY 13210
"_USDAForestHighway
Setwice Notah
Central Research
Station, ForestrySciences Labo_ato_y.5985
K, R.hinetaadcr.
W15450t
_OakRidge Nation,'dLaboratory, Environmental Scicr.cesDivision. P.O. Box
2008 Mail Stop 6422, Oak Ridge. TN 3783t
_i
MARCH/APRIL
improved
clones
from Europe,
improvementclones
of willows became
necessary
to obtaingenetic
locally-adapted
that
express irlcrease.d average production
rates, improved growth
ing
theand
economic
attractiveness
of resistance,
growing willows
bioenform,
improved
levels of pest
therebyforirnprovergy and bio-based products.
Willows are also being planted in North America for purposes other than bioenergy
with increasing
frequency.
PIaytoremediation
is an emerging
technology
being used for
remediation
of contaminated
soils and filtration
of water
throughout
North America
(Isebrands
2000) and Europe
20Or, VOL. 77, NO. 2, TIlE FORESTRY CHRONICLE
257
(l'ctUu 1999).Phyt(w_nlcdiutioninvolves Ihedirect u._ct)f planls
Ic_decrease risks from contaminated soil. sludge, .,,cdiments,
and ground water by contaminantremoval,degradatk_n,_'rconfil_emcnt(US EPA I1598).Willows (5olL_spp.k_dc_lgwith [x'.pku_
([_OlmlU._spp.), are tile most COllll'll()l'l[y
usedtrec species I'¢w
phytoremcdia[ion, due to their rapid growth zate, ease of
prc,pagation, and denlonsuated cont,mlinant uptake c_pability. Willows are currently under study acrossNorth America
for a v:uiely of i_hytt,remediation and rip_u'ianbuffer strip applications (Isebrands and Ka,nosky 2001_.
WiIlo_,s are widely used in riparian management in North
America. Dormant willows are planted as cuttings, D_sts,
and brush rnattre.sses Ior stream bank stabirization fSchultz et el.
2(XY,.)).
Willows :u'e also used to stabilize reservoir btmk.s.Re,arch
on using willows for purification of waste-water and sludge
ha.sbccrt in progress in Sweden since the 19S0s,and SaIL_climes
have been shown to be effective for removing large quantities
of nutrients from land-applied wastes in Europe (Perttu and
Kowalik 1997) and even tl'te removal of caesium fronl radiocontaminated soils (Sennerby-Forsse et el. 1993). Nutrient illlet.,;COmlX_d ofgntsses have been succe._fully u.scd Ibr d,_x.'adcs
in North America (Young et el. I980), but planting willows
in filter strips is relatively new. Genetic improvement through
selection and breeding may be _2cess_y to develop clonc.ssi:ccifically for planting in filter strips and clones tirol are more effeclive for stream and reservoir bank stabilization,
Tile Salix Gerl|lplasni
Resource
in North
AIII_'L'Jca
North America contains a Salix germplasm resource floatis
large, rich in genetic diversity, and virtually unexplored
(Zsuffa 1988). About 70 willow species are native to Nu_th
America (Fowells 1965). In addititm, willow species inu'c.nluccd
from Europe, including S. elba and S. purpureo, have become
naturalized in the Northeast and North-central United States
and Southeast Canada (Voss 19_5i. Many native, naturalized
and introduced species have desirable traits for biomass production, phytoremediation, nutrient filters, and stream bank
stabilization, but few of them have been tested across a wide
variety of geographic areas or site types (Table l).
A genetically dive_.'sewillow breeding population is nece.sszuy
to provide sufficient variation from which clones can be
developed that are adapted to a wide variety of purposes and
site conditions in eastern North America. A broad genetic base
in tile breeding population will ensure flexibility in the b_'ceding program and the potential to adapt to changes in types of
sites desired for planting and/or pest problems. Maintaining
a genetically diverse germplasm collection is critical for tlie
long-tern] success of willow breeding efforts (Eriksson et el.
198,1). From t 987 through 1999, researchers at the State
University of New York College of E_vironmental Science
and Forestry (SUNY-ESF) assembled a breeding population
of willow containing more than 500 clones. Most of the
clones caste from Ontario, Canada (developed by co-operators at the University of Toronto) and from wild stands across
New York and Pennsylvania. and are of species native or naturalizcd in the Northeast. Ilowever, bccause many of the
clones are closely related and several species are representcd by a small number of clones, the genetic diversity in this
collection will be expanded in order to sustain a king-term breeding program.
2.88
The overall goal of our will(_w breeding D)pulatiun devclopmcnl efl'_wl is lu us.,,cmblea large and diver.,,c germpln.,,m
collection thai _,,ill permit continuous iu_l'WOVernents
over
many breeding generations. Specific goals include doubling
II'te number (fl" S. erio_ cFlufla cIiilleS I'rom. approxinl_ltclv
100 to 200 and expanding the number of S. pttrpureo c{ones
from 20 to 150.Ba._d oil genetic diversity estimates fL;r S.eri.
_,cephala,approximately 150 clones collected fr_m a b,'oad
get,graphic range should conlain most of the alleles present
in the species (Aravanopoulos et aL 1999,_. Up to 75 ckm_zs
(_t"both S. hwida and 5: nigra, and a small number of clones
of other SatL_ species will be collected. Clones from non-native
species will be obtained frm'n colleagues in Asia z_ndEurope
to provide additional useful genes th_tt may be incorpt)rated
into production clones through advanced-generation breeding.
Efforts to expand our willow germplasm collcction began
in July 20(X).We co[lcctcd If'A)willow chilies fio,n native stands
across New York. Obits, Permsylvania, Connecticut. and
Massachusetts and propagated them in a greenhouse for
field-planting during spring 2(X) I. Trees were selected bused
on vigour, forltl, itftd insect and disease resistance relative to "
other trees of the same Sl.Vecicsin tile i,umcdiale vicinity, Mt_st
of the clones collected thus far were identified as S. eriocephala
and S. puq_urea with smaller numbers of S, ha'ida and S. ni£ra
also included. Colleclions will be ct)mplclcd in Michigan, Minnesota and Wisconsin during 2001.
All of the new clones collected for this project wilt be
planted in observation trials on two sites, one in New Yo_'kand
the othcr in Wisconsin. The purposcx of these trials are: 1) tO
assess the phenotypic variability in _ew clones collected
from a wide geographic region. 2) to determine how the
clones perform in locations distant fi'om Lh¢ir origin, and 3)
to identify clones for future breeding vmfk v,ith desirable traits.
The trials will also serve as clonul archives duplicated on _wo
sites to minimize the chance of losing clones. Intra- anti
inter-specific hybrid clones produced in our previous breeding efforts will be included in d_cse ui_ds to compare _,'ith clothes
collected from native stands. Production clones cur,'ently
being planted will also be included in ihese trials to serve as
cuntrols ("cotnmerciai checks").
Cloncs will be selected for use in the first parental generatiou based on measurements and observations completed
during the first and second growing seasons after the initial
coppice. Selection criteria will vary, dependhlg on the desired
end-use of the clones. Statistical analyses will be used tt_
determine if clonal differences exist in initial height growth,
average stem diameter, sttx_l dry weight, number of stems per
.stool, disease and/or insect resistance,-and
ci'own form
(Table 2) and if clone-by-site interaction is large. If large cloneby-sile interactions _u'eobserved, then sel_tion of superior clones
,.,.,illbe _':complished in a .__i!e-sl.',c.cifit'.
mariner. 1.2J'gev,'u'iabitity
will be maintained in Ihe base breeding populatitm t_) allow
selection tbr nun_erous end-uses.
Background
on Genetic
Illil}rOVelllent
of
Willow ill North
America
A limited ,'mxountof willow breedittg and selection has been
conducted in North America. Native species were bred in the
1980s by researchers at the University of Toronto to produce
F t inu'a- and interspccific hybrids for biocnergy production
(Mosseler 1985). Controlled breeding of S. eriocephala and
MARS/AVRIL 2001, VOL. 77, NO. 2, TI-IE FORESTRY CHRONICLE
Table 1, Clas.sil_cation
otSalix
species testcd in biomass
Sectional
Ctas.,_il3cat[o n 1
production
Species
Subgenus Sah.x
H:lmbotti,_n=e
S. an,ygdaloides
S. nigra Marsh
Aridel ss.
trials in the Northeast
or North-central
United States.
Form
Native Range
tree
tree
.N.C. USA
Eastern USA
Salix
S. alba L.
S. fragilis L.
u¢e
tree
Central Europe
Central Europe
Subalbae
S. marmrdona Koidz.
tree
Northern China
Salicaster
S. hici(la Muhl.
shrub
Eas:ern N. America
Longifoti_e
S. exig,,a Null.
shrub
North America
S. bebbiana Sur_.
S. discolor" .Muhl.
S. petiolaris Smith
shrub
shl'ub
shrub
transcontineata/
NorLh America
North America
Vimcn
S. dasychtdos Wimm.
S. pcllita Anderss.
S. sachalhrensis Schmidt.
S. vimmalis L.
tl'ee
shrub
shrub
shrub
C. Europe to E. S:beria
E. Can_,da
Japan
C. Europe to E. Siberia
Cordatae
S. eriocephala
.shrub
North America
Helix
S. n,iyabeana Seeman
S. purpt_rea L.
shrub
shrub
E. Siberia, China
Europe
Subgenus V_.:r_
Vettix
_Secdonal classification
according
Muhl.
to Dora ( 1976_.
S. sericea by researchers at Vassar College in Poughkeepsie,
NY yielded intra- and interspecific hybrids, which were used
in studies on herbivore preference and gene introgression
(Roche arid Fritz 1997, Hardig et al. 2000). Our group initiared a progr,'u'n of controlled willow breeding in I998 to produce wilIows for bioenergy or conversion to high-value
chemicals. Native and introduced species were used to produce F 1intra- and interspccific progeny in 1998, and some of
these clones were crossed in 2(X30 to produce F 2 progeny (Kopp
et al. 2000). Thus, very few multiple-generation,
structured
Salix pedigrees exist today that could be useful in gene
ticularly potato leaf'hoppers (Empoascafabae
Harris), cause
substantial damage and associated poor growth of this species
in the Northeast and North-central United States (Kopp2000).
Preliminary information from an unreplicated field u'ial suggests that progeny of crosses between S. vimina/is and S.
miyabeana, an Asian species, may be less susceptible to
potato leafhopper attack. If substantiated,
S. viminalis
germplasm may contribute to the production of high-yielding
hybrid clones for use in North America once genes for resistance to potato leafhopper can be introduced.
expression studies.
lnterspecific hybridization of willows may yield superior
clones through the combination of desirable traits, hcterosis.
and greater phenotypic stability it1varied environments (Stettier et al. 1996). Many examples of successful interspecific
hybridization with willows have been reported (Argus 1974,
Hathaway 1977. Zsuffa er al. 1984, Larsson 1998). However, interspccific hybridization of willow species native to
North America generally resulted in F I hybrid progeny,
which often had decreased vigour and poor survival, though
some individuals exceeded the growth of either parent (Mosseler 1990). S. eriocephala females failed to yield viable
seed in any interspeciflc hybridization attempts in studies cornpleted by Mosseler (1990) or Kopp (2000), S. eriocephala is
known to be difficult to hybridize when it is the pistillate parent because of inhibition of pollen tube growth (Mosseler 1989).
These findings suggest that S. et_ocephaIa males should be used
in interspecific hybridization efforts with this species.
Vigorous growth by S. vhrlinalis in northern Europe is
well documented (Gullberg 1993, R/Snnberg.W_istljung and
Gullberg 1996, Larsson 1998), but various insect pests, par-
Role
of Biotechnology
in Willow
Tree
Improvement
Application of biotechnology to willow tree improvement
may accelerate the rate of genetic gain. Recently developed
molecular techniques may enable willow breeders to narrow the pool of candidate breeding trees, so that effort is not
wasted on crosses that have low probability ofproducing dcsirable progeny. Molecular markers can help to characterize populations, estimate genetic variability within and among wild
or generated populations, and identify individuals at a young
agethatwillexpmssau'aitatmatudty
(Dinus andTuskm_ 19971.
Molecular fingerprinting can be used to produce genetic
maps for traits ofit_terest. A genetic map including restriction
fragment length polymorphism (RFLP), sequence-tagged
sites (STSs), and RAPD markers was produced for a hybrid
poplar family dcrved from all inbred F2 family (Bradshaw et aL
1994).This m,apwas used to identify quantitative trait leci (QTLs)
with large effects on growth, form, and phenology (Bradshaw
arid Stettler 1995). Similar techniques may be applied to willow breeding. We have generated populations of Fj and F,2_
proge-
MARCH/APRIL 2001, VOL. 77. NO. 2. THE FORESTRY CHRONICLE
289
"l'2dflc
2.'l','aits,,r il,{crt',_t
r.r witl,w I_immL_._
produdiou.
Mcnsurational
Traits
Biomass
prtKlu,:tion"
Ste.mhci_hl"
Stemdiamctur
_
Numberuf_tcm_
"_
Stoo[
form_
.SurvivaP
',V_md
densit)
_
Logcncl';.dclargu I'andlics. Mo¢'cthan 12t) relatively .,,m:dlFurlsib I'amilicswere prtxJuccdby controlled D_flinution Irom 199,
V,
tO2(XX)
(K(Jpp
2(X_)).
P,ogenyfromd],:sc
cross,:s
are CUll'12{lll
b¢illg testedhi field trials. More crosses to identify l'u;ourabl¢
l'h.,,sic,l,_gical
TraiLs
Syl!elxic_lr,ouImxluc_ic,v"
In_ect_u._¢el_libihly:'
Patho_ca
m_cg_tinili
W'
i"a[]lilycombiJmtio(',s
(approxitrv.ltely50) wilt r'e comple:edwhen
Mammalbro',,,s:Rt,._¢el;tibility
_
flowers and juvenile growth atld [_cst resistance data are
t[e."bicide
tolerance
_
available
ti0mclones
collected
orprc.KIuced
from1.993
to2(Y]I.
Foliagechemistry
t'
Parentclone combinations will be selected to ma;<irrlizt2the
Cuticle
lhicknes#chemistr.'.
_'
I.c_f_,,-e_"
probability of generating progeny exhibiting heterosis for
Leafniu'ogea percenu,gc _'
biomass
productioll or other traits of interest. Molcculur
Leaf_,eightJunit area_
fingerprint data may also be usedto identify particular parent
Photosynthesis rate_'
combinations that ,'ue likely to yield desirable clones based on
13utlburM
d
ale
t_
i]laxhllizillg the alllOUlltof molecular diversity" alllOnl2 crossed
Growthccs_ali,tlil
dineI"
genotypes.
_rraits that will bc IJlr_;IglJl'¢d I.,{l Ii'_'C$ lit illl _11_ '¢..
bTrait_'hm _ill be measuredastime a,_drundtn_permit.
After large numbers of families contailling small null'lburs of Dogeny ha',e bccn ev_duated in the field, five to !(l crosses will be selected that are likely to yield progeny exhibiting
ny, which may be amenable to molecular mapping, and are
currently developing AFLP and microsatellite markers fer
w il low.
Genetic transformation
research with Salix is not as
advm]ced ,as for Pop,/us.hl
Sweden, transforrttmioil of a
limited numbcr of Salix clones was successful using Agrobacterium lumefaciens, but phmtlets could not be produced from
transformed calli (Vah:tla el al. 1989). SalLr lucidu.was transformed using A. tumeJ'aciens and planllets were produced, but
the transferred genes were not stable (Xing 1995). EfFerts to
develop a transformation system for Salix are in progress at
SUNY-ESF. Genes controlling
flowering in Salix will be
'
identi fled, with the objective of altering their expression in transgenie pkmts to prtx.luce clones d_atdo not fk)wer. As noted al:x)ve,
this strategy m.ight then be used to essentially eliminate the possibility of introgression of genes from introduced species
into natural populations of willow through cross-pollination,
outstanding performance. These selected crosses will be
repeated to produce families with large numbers of progeny.
Data from small families produced fl'om 1998 to 2000 will be
available in 201)I,so that the first set orcrosscs to paxJuce large
families will be made during 2002. A second set of ._elected
Willow Breeding Strategy for the Northeast
and North-central
United States and Southeast Canada
ed cuttings for clone-site trials that will be established using
operational spacing and cultural practices on at least two
sites.
Basic genetic studies are necessary to obtain heritabiiity
estimates for traits (ff
interest. Progeny tests conl2tiaing 3,1fullsib S. eriocel)lrtht fatnilies from an. g x 7 factorial mating design
completed during 1998 were established in 20(X) to provide
these estimates (Kopp 2(XX)).Ten randurnly selected seediings
fiom each family and the p,'u-entswere vegetatively propagated
and dorm,'u_t,hardwcxx.Icuttings were pl,'mted in replicated tests
at LaFayette and Tully, NY. These tests will perntit estimates
of general Combining ability, specific combining ability,
additive and non-additive genetic variance components and
genotypc-by-environment interactio, ror any traiL,_ofinletest.
Advanced-generation
breeding strategies, i.e., F3 and
beyond, are not clearly defined at this point in willow development. "Ihere ,aremultiple, equally likely alternatives da:ttmay
ultimately prove useful. It is unlikely that insighl_ into which
alternative should be pursued will come from breeding programs in any other woody species. Even with Popuh_s, the generation intervals are considerably longer than with SalL_. As
a result, a willow breeding program ,,,,'ill face decisions on
advanced-generation breeding well before most tree breeding
programs are into their F., generation. Therefore, concessions need to be made early in the formation of any willow
improvement progt'am that will 1) allow llexibility in pursu-
We have devised a strategy for the genetic irul)rovemertt of
willows wi(h the goal of rapidly prt}ducmg clones that are adapted to growtl_ in intensively cultured biomass plantings in the
Northeast and North-cemral United States and Southeast
Canada (Fig. I ). The system can be used to produce clones for
other purposes by altering the selection criteria. This strategy is based on our initial results and from reports on improvemeat efforts in Sweden and Canada. Brietly. the strategy
assumes that hybrid vigour for growth rate or other traits of
interest can be obtained by controlled intra- and inter-specific
mating and depends on identifying specific favourable cornbinations of parents. Because reliable prediction of desirable parent clone ct)mbinations is not currently possible,
lmge numbers of crosses u,ill bc completed yielding many farotiles with small numbers of progeny, which will be field tested (Fig. I). Crosses that appear promising will be repeated to
produce large numbers of progeny. [tigh selection intensity
will be applied to these large families and selected individuals will be vegetatively propagated, resuhing in large genetic gain.
Efforts are in progress to identify crosses that have polential to generate exceptional progeny and are worth repeating
290
crosses to produce lm'ge families wilt be completed when new,
promising parent combinations are identified.
Selection of exceptional individuals to be propagated for Olx'rational plantings should ideally be from families exhibiting large
variability with 500 or more individuals (Tuskan 1997L Such
families will be evaluated in the field in a non-replicaled
scrccaing
l'hcontop
5% of the l:,rogeny
in each
familycomwill
be selectedtrial,
based
measurements
of trai_,_of
interest
pleted at the end of the first coppice-growing season, l,arge
nu tubers of clonal replicates froth each selected clone will be
prcxluced using small one- or two-bud cuttings, then mmspl;mted
to
a fertilized,
irrigatedot_chad
cuttingwill
orchard.
Dormant
one-year-old
stem.sflora
the cutting
be h,'wvest_I
to provide
urucx.,rt-
MARS/AVRIL 20OI, VOL. 77. NO. 2. TI IE f:()RESTI,IY CHRONICL,E
are taken to reduce the risk of introduced willows becoming
F'estsor ofintrogression of their genes into the native gene pool.
Non-native clones or their progeny will be used in biomass plant-
I
BreedlngPoptaatlon
!
could spread by natural vegetative propagation. Pollen-pistil
incongruhy and asynchronous flowering prevents successful
ings andinterspccific
natural
not in riparian
hybridization
areas, so there
anaong
is little
manychance
willowthat
species
they
(Mosseler 1989). The potential for hybridization of inh'_xluced
species with natives will also be evaluated prior to clone
Controlled
Breedlng
__
:
f
"_'-,
{" ManyCrosses ',
Molecular
Technlques_ _)
release.
Trees (Mosseler
produced by
interspecific
f0equently
do not flower
1990),
so effortshybddiTation
are in progress
to idcn,_ FieldTesting
tify species
thatcharacteristics.
can be bred and
infertile
progeny
withcombinations
desired growth
In yield
addition,
production clones may be rendered sterile through the use of geaet-
Co,_rolledBreedlng
,,..._e
Vam_../"--*
Test
/,
\oper_lonaw
\jCtones_'_,._,_
Fig. 1. Generalized willow breeding strategy for the Northeast and
North-central United States.
ing alternative strategies and 2) quickly determine the appropriate advanced-generation
approach,
Today, there is considerable debate on whether willow
advanced-generations
should be formed using simple recurrent selection, reciprocal recurrent selection or to abandon these
strategies altogether for random wide crossing among unrelated individuals. Information on fieId performance, intrafamily phenotypic variability, and molecuIar diversity will allow
us to choose front among one of these three alternatives. For
example, if heterosis is mainly the result of overdominance and
intrafamily phenotypic variances are high. then reciprocal recurrent selection may be the most appropriate advanced-goneration strategy.
Based on conservative estimates, it is expected that the strategy described above will initially result in 10 re 20% g_ins in
biomass production each generation. Willow breeding in
Sweden completed since 1987 yielded clones with 10 to 20%
increases in biomass production compared with commercial
check clones (Larsson 1998). Because most of the clones currently being used in operational biomass plantings in New York
were sclcctcd from wild populations or from F z populations
that had been tested in small plots on a minimal number of sites.
ic transformation in an effort to eliminate
native stands (Strauss et al. 2000).
_ene tlow into
Conclusions
Willow genetic improvement in North AmeAca is at an early
stage of development. Breeding wit', willows native to North
America plus several naturalized and non-native species h_
been completed, providing a starting point for future breeding activities. The breeding strategy described above may be
modified as new information becomes available. Critical
assumptions of the proposed strategy are that hcterosis can be
obtained by mating appropriate pairs of clones and controlled
matings will resuIt in families with large variability. Success
of the breeding program depends on assembling a collection
of genetically diverse germplasm. Collection efforts are
focused on native species gathered from a broad geographic
range, but a limited number of non-native clones are desired
to maximize genetic diversity and breeding options. Cooperation with willow breeders around the world is desired,
so that germplasm can be exchanged, although environmental stewardship will be a pt'iority when considering Ire'go-scale
deployment of non-native material.
Acknowledgements
The authors wish to thank the agencies that are financially supporting this research including the New York State
Energy Research and Development Authority, the Oak Ridge
National Laboratory, managed by UT-Battelle, LLC, for the
U.S. Department of Energy under contract DE-AC0500OR22725 and the United States Department of Agriculture.
References
Ahraham_on, l..P., KH. White, C,A- Nowak, R.D. Briggs and DJ.
Robison.
1990. Evaluating
hybrid field
poplar
clonal
growth2 l:potential
in
a three-year-old
genetic selection
trial.
Biomass
101-114.
improvements exceeding 10% to 20% are anticipated. Hybrids
between Populus trichocarpa and P. deltoides showed more
than twice the growth rate of either parent (Stettler et al.
1988). Identifying willow species combinations resulting in
similar levels of heterosis may be possible,
The strategy described above includes importing nonnative willow species to North America as well as making use
of naturalized species. Importing non-native willows is
Aravanopoulos, F.A., K.H. Kim and I.. Zsuff'.,. 1999. Genetic diversity of superiorSalLrclones selected for intensive foresu'yplantatious.
Biomass and Bioenergy 16: 249-255.
Argus, G.W. 1974.An experimental study of hybddizarion and pollinadon in Salix (willow).Canadian JoumaI of Botany 52:1613-1619.
Bradshaw, H,D,andR.F, Stetfler,199$.Moleculargeneticsof growth
and development in Populus. IV. Mapping QTI.s with Ire'goeffects
on
form. and phenology traits in a forest tree. Genetics
139:growth,
963-973.
desired, because some species or clones have unique traits and
presumably unique alleles that are not present in the native species,
All imports are completed under strict compliance with
USDA guidelines as pollen, seeds, or dormant unrooted cuttings, so the risk of pest introduction is minimized. Many steps
Bradshaw, H.D., M. Villar, B.D. Watson, K.G. Otto, S. Stewart
and R.F. Stettler. 1994. Molecular genetics of growth and devel°pmentinP°pulus'Ill'Agencdclinkagenmp°fahybfidp°plarc°m"
posed of RFLP. STS, and RAPD markers. Theoretical and Applied
Genetics 89:167-178.
MARCH/APRIL 2001, VOL. 77, NO. 2. THE FORESTRY CHRONICLE
291
Chrk'_le|'ssot), L. 1986. IIigh tcchnolog,y hit-mass pn_ductkm by SalLr
c:_ol_es on a samly _oil in southcru Sweden. "]'rce Physiology 2:
261-272.
Dimls, R.J. m_d G.A. Tuskan. 1997. Integration of molecu I::.."and
classical genetics: a synergi_lic approach to tree impruv,_J::cr, t.
USD,\ Forest Sczvice Gellet:tl Technical Rept_rt RM-GTR-297.
Chapter 29: 220-235.
Dorn, R.D. 1976. A sync_psis tfl'Amcric_,'_ 5t;/Lt. Canadian Jc".:'r:tal
of Botany 54: 2769-2789.
Eriksson, (;., U. Gul[berg and 1l. Kang. 1984. Breeding strategy
lc_rshort rot;_ti¢_J_
wo_×ly sfx.'cics, hs K. Perttu (ed.). Ecology and .klana__cla_ent of Forest Bion'mss Producti(Jn Systems. Report 15. pp.
199--216. Swedish University of Agricultura[ Sciences, L'ppsala.S-redc;_.
l;ox_ dfs, I[.A. 1965. Silvics ofTrces ot the United States. Agricu[t't,al 1[andbook 271. USDA Forest Ser',ice. Washit_gton. DC. 762 p.
Gullberg, U. 1993. Towards making willows pilot species fi'r coppieing production. ]'he Forestry Chronicie 69:721-726.
llardig, 1-'.M., S..J. Brunsreld, R.S. Fritz, 51. Morgau aud C.M.
Orians. 2000. Morphological and molecular evidence for hybridizat[on and i,m'ogressiot_ in a willow (Salix) hybrid zone. Molccul,'u"Fx'ology 9: 9-24.
llallmway, R.L. 1977. E,"uly growth of SalL_mats_ukula x al&t I:l_,'lxkLg.
New 2'xaland Journal of Forestry Science 7:207-213.
Hubbard, W.F. |904. The basket willow. USDA Bureau of Forestry
Bulletin No. ,16. itX)p.
[sebrands, J.G. 2000. Activities related to poplar and willow culti',ution and utilization. Report of Ihe Natiomd Poplar Commission
.f the USA. Peficxl: 1_,,,x)(>-2tL_O.
2t '_Session of the Intcntational Poplar
Comll_ission. Portland, Oregon, Septembcr 24-30. 20()0. 13 p.
[sebrm_ds, J.G. mid D.F. Karnosky. 2001. Environmemal benefits
of t_l:[at culture. In D.[. Dicknmnn et al. reds.). Poplar Cnl{ure in
N't_rth Amen'ion. N'RC Rc._earch Press, Ottawa, Ontario. Canada (in
Riinnt}er_.Wfislljtmg. A.C. nnd Lt, Gullbcrg. 1996. Genetrc relafion.shil'_s}.xztweengrowth chmaclcr'_ in 5ttlix riminalis grown in Sweden. Theoretical and Applicd Genetics q3: 15-21.
Schultz, R.C.. J.P. Collelli0 T.M. lsenhar[, C.O. M'arqttez, W.W.
Simpkins and C.J. Ball. 2000. Ripari,'ut forest buffer praclice,_./,1
W.J. Rictveld. R.F. Fisher a'_d II.E. Garrcll (re.Is.). North America_t
Agrofi_rcstry: An Integrated ScieJwe and Practice. pp. 1S9-2,_2.
American Society of Agroltomy. Madison, W[.
Seunerhy-Forsse,
L., D..Melln and K. Rosen. 1993, Uptake and
distributi_m of radiocesium in fast-growing S_llix t'imhutli_. Journ._i
of Sustainable Forestry I: 93-103.
Shnpson, J.M. 1898. Osicr_.'ulture. Unitc_.lStatcs Ekzp:.utmcmof Agdculture Bulletin No. [9.27 p.
Slcttler, R.F., R.C. Fenn, P.F.. Hcihnart and B.J. S/anion. 1988.
P_Tmlus trich_pcarpa x Popuhts deltoides hybrids f_r short ro_ati_m
culture: variation patterns and 4-year field pcrl't_rmancc Canadian
Journal of Forest Research 18: 745-753.
SteHler, R.F., L. Zsuffa at_.d R. Wu. 1996. The rule _)fhybridiz-tcon in the genetic manipulation oi"Popuhh_. h_ R.F. Stcttler. I'I.D. Brudshaw Jr., P.E. tleih-nan and T.M. 1linckley (eds.). Biology of P¢q_uhts and Its Implications for Management and Conse_waltoa. P:_'t 1,
Chapter 4. pp. 87-I 12. NRC Re._,'u'ch P_css, National Rose,arch Counoil of Canada. Ottawa, ON.
SI.oll, K.G. 1984. Improving the. bioma_ lX_lcntkdof willow by scleetion and breeding. In K. Perttu (ed.). Ecology and Management of
F, rcst Biomass Production Systems. Report 15. pp. 233--260
Swedish University of Agricultural Science, Uppsala. S,.,.'cdc,L
Slrau,_s, S.I I., K. Raffa and P. LLst.21)00. Edfics and trans,,onto p[anrations. Journal of Forestry 98: 47-48.
Tuskan, G.A. 1997. Clonal forestry, heterosis and advancedgeneration breeding. Proceedings of the 24th Bi.ennial Southern
Forest Tree huprovemcnt Conference. ()tlando. FI.,, June t}'-I 2.
1997. pp. 390.--392.
press).
Kopp, R.F. 2000. Genetic improvement of SalL_ Using Traditiona[ Breeding and AFLP Fingerprinting. Ph.D. Disserlation. State
U_fivers[ty of New York College of Environmental Science and
Forestry, Syracuse, NY. [75 p.
Kopp, R.F., I,.B. Smarl, L.P. Abrahamson,
C.A. Maynard and
J.G. lsebramls. 2000. Gc_]ctit: iHtprtwemcm olSalLt" tbr the NL_rtheast and North-Central
United States. bt J.G. Isebrands and J,
Richardson
(compi.lers).
USDA Forest Service North Central
Research Station General Technical Report NC-215.21 s_Session of
the International Poplar Commission (IPC 2000) Poplar and Willow
Culture: Meeting the Needs _f Society and the Environment.
l,ars.',ou, S. 1998. Genetic improvemem of wiltow for short-rotation
coppice. Biomass and Biocnergy 15: 2.'g.-26.
Mosseler, A. 1985. An overview of Salix breeding in Otltario. Procecdings of the 2IYt' Meeting of fl_eCanadiaq TreeImprovement As._ciation. August I9-22, 1995, Quebec City. QC. pp. 142-150.
Mosseler, A. 1989, lnterspccific pollen-pistil inco_gruity in Salix.
Canadian ]ournal of Forest Research 19:1161-I 168.
.Mo&_eler, A. 1990. Hybrid performance and species crossability relatmnships in willows (Salix). Canadian Journal of B(_tany 68:
2329--2338.
Ostry, _,I.E. and II.S. MeNabb. 1990. Minimizing disease i_Liury
to hybrid poplars. Jonrnal of Environme_tal tlotticulture 8: 96--9S.
Pertlu. K.L. 1999. Environmental and hygienic aspects of v.illow
coppice in Sweden. Biomass and Biocnergy 16: 29t-297.
l'cr1,tn, K. and P.J. Kowalik. 1997. Sali,c vegetation filters for
purification of waters and soils. Biomass and Bioenergy 12: 9-19.
Roche, B.M. and R.S. Fritz. 1997. Geuetics of resistance of SalL,:
sericea to a diverse community of herbivores. Evolution 51:
1490--149S.
U.S. Environntenlal
Proleeliou Agency !EPA). 1998, A ¢itiz_'n's
guide to phytoremediation. EPA 542-F-98-t}11. Tech_ology Fact Sheet.
Office of Solid Waste and Emergency Response 15102G). 6 p.
Vahala, T., P. Slabel and 'r. Eriksson. 1989. Genetic transforlnation or willows (Salix spp.)by,'lgr_bacterium
tumtfacicns. Pbnt Cell
Reports 8: 55-58.
Vuss, E.G. 1985. Michigat_ Fk_ra: A _uide to the tdemil"tc:!tit_t _t_O
occurrence of the native and naturalized sccd-plant_ oi"[he St:_te. Part
II. Dicots (Saururaceae-Cornaceac).
Cranbr_a_k Institute of Science. Ann Arbor, M[. 724 p.
Xing, Z. 1995. Genetic _ransl'ormation and regeneration of willows (SalLr spp). Ph.D. Dissetlation, SUNY College of Envixtnament."d
Science and Forestry. Syracuse, NY. 13(I p.
Young, R.A., 3_'.I hmtrods and W. Anderson. 1981,).Effcctivencs_
of vegetated buffer strips in cumrulling pollution from feedlo:
runoff. Journal of Environmental Quality 9: 483-4,",17.
Zsuffa, I, 1988. A review of progress in _lecling and breeding Noah
American Salb: species for energy plantations at the Faculty uf
Forestry, University of Toronto. Canada. h_ternation.',l Energy
Agency Proceedings from Willow Breeding Symposium August
31-September 1, 1987. Research Notes 41: pp. 41-51. Swedish
Uuiversity of Agricultural Sciet_ces, Uppsala, Sweden.
Z.sufra, L., A. Musseler and Y. Ruj. 1984. F'rosl"x'cts for int_r:-q',eeific hybridization in willow for biornass productiou, h_ K. Pcrttu {cd.).
Ecology and Management of Forest Bit_naass Pt'cductio_ Systems.
Report 15. pp. 261-281. Swedish University of Agricultur_d Sciences,
Uppsala. Sweden.
292
MARS/AVRIL
2001, VOL. 77. NO. 2, TI IE FORESTRY
CHRONICLE