Verification of new Populus nigra L. clone improvement based on their performance over three rotations
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iForest Research Article
doi: 10.3832/ifor3171-013
vol. 13, pp. 185-193
Biogeosciences and Forestry
Verification of new Populus nigra L. clone improvement based on their
performance over three rotations
Kateřina Novotná, Populus nigra is an important autochthonous woody plant that can be grown as
a renewable energy source. The possibility of its improvement through in-
Petra Štochlová, traspecific hybridization was tested. Differences in biomass production,
Vojtěch Benetka growth parameters, Melampsora larici-populina rust resistance and drought
tolerance were evaluated among 19 intraspecific hybrids from controlled
crosses, 2 clones selected from natural populations and the “MAX 4” clone (P.
nigra × P. maximowiczii). These P. nigra clones from controlled crosses were
chosen from more than 2000 hybrid individuals whose parents were selected
from natural populations in the Czech Republic. A field trial was set up in
Průhonice, Czech Republic (320 m a.s.l., 591 mm rainfall annually, mean an-
nual temperature of 9.5 °C). The planting density was 6061 plants ha -1, and
the plants were coppiced three times at 3-year intervals. The trial was irri-
gated only during its establishment. Among the clones, significant differences
were found in all the evaluated traits over three rotations. An average dry
matter yield of the best clone “MAX 4” was 12.8 t ha -1 yr-1 over three harvests.
The best black poplar clone reached up to 9.4 t ha-1 yr-1 in three harvests. Rust
resistance was constant over 9 years and high for the three P. nigra clones
(two from controlled crosses and one from natural populations). Moreover, the
best P. nigra clones from controlled crosses showed higher drought tolerance
than the “MAX 4” clone. Breeding progress was confirmed, and most of the P.
nigra clones from controlled crosses performed better than the clones se-
lected from natural populations. The trial validated the suitability of natural
populations for use as gene sources for intraspecific hybridization and as
sources of clones with traits comparable with those of interspecific clones.
These new P. nigra clones can replace allochthonous clones in areas where au-
tochthonous P. nigra populations are threatened by introgression.
Keywords: Plant Breeding, Black Poplar, Intraspecific Hybridization, Short Ro-
tation Coppice Culture, Melampsora larici-populina, Biomass Production, Tree
Regeneration
Introduction within the last 8 years and is now at 2862 these clones are Populus deltoides Marsh. ×
In recent years, the importance of fast- ha (Ministry of Agriculture of the Czech Re- P. nigra L. (= P. ×canadensis Moench), P. tri-
growing trees cultivation intensively man- public 2018). chocarpa Torr. & A. Gray × P. deltoides, P. ni-
aged as coppices with 2- to 5-year rotation Similar to those in other European coun- gra × P. maximowiczii Henry and P. maxi-
cycles and potential lifetimes of 30 years tries (Herve & Ceulemans 1996, Verwijst mowiczii × P. trichocarpa (FAO 2016); how-
(DEFRA 2004), the so-called short-rotation 2001, Langeveld et al. 2012), Czech SRC cul- ever, in central Europe, the trend in recent
coppice (SRC) cultures, has increased with tures are usually based on poplar or willow years has been to grow the “MAX 4” hy-
the increasing demand for woody biomass species, and the most commonly grown brid clone of P. nigra × P. maximowiczii
as a renewable energy source (Bentsen & poplars in Europe are primarily the result of (Štícha et al. 2016). The popularity of F1 in-
Felby 2012). This trend is apparent in the interspecific crosses. In countries with the terspecific hybridization is due to the pre-
Czech Republic, where the total SRC area highest SRC area (France, Italy and Spain), dominance of heterosis and the ease with
has increased by more than eight times the most popular parental combinations of which it can be economically exploited
through vegetative propagation (Stanton
et al. 2010).
Silva Tarouca Research Institute for Landscape and Ornamental Gardening, Publ. Res. P. nigra is an autochthonous woody plant
Inst., Květnové náměstí 391, CZ-252 43 Průhonice (Czech Republic) that covers a large area of Europe (Vanden
Broeck 2003), and its populations can be
@ Kateřina Novotná (novotna@vukoz.cz) threatened by introgression from the
aforementioned interspecific hybrid clones
Received: Jun 19, 2019 - Accepted: Mar 14, 2020 and other clones of allochthonous poplar
species (Smulders et al. 2008). The relevant
Citation: Novotná K, Štochlová P, Benetka V (2020). Verification of new Populus nigra L. causes are cultivated poplar trees grown to
clone improvement based on their performance over three rotations. iForest 13: 185-193. – the adult stage, which is the case not only
doi: 10.3832/ifor3171-013 [online 2020-05-12] for clones coming from P. deltoides and P.
trichocarpa but also for interspecific hy-
Communicated by: Gianfranco Minotta brids of P. ×canadensis-type that can spon-
taneously interbreed with P. nigra (Benetka
© SISEF https://iforest.sisef.org/ 185 iForest 13: 185-193
Novotná K et al. - iForest 13: 185-193
et al. 2002b). The contamination of P. nigra resistance genes, plant breeders now focus production value comparable to that of
iForest – Biogeosciences and Forestry
gene pools has led to restrictions on inter- their efforts on quantitative resistance commercial hybrid poplar clones when
specific hybrid cultivation in certain loca- genes, for which selection is slower but the parental clones originate from contrasting
tions (Ministry of the Environment of the risk of a sudden loss of resistance is re- conditions (Benetka et al. 2012).
Czech Republic 1992). duced (McDonald 2010). The aim of the present study was: (i) to
The original autochthonous species P. ni- Another goal in poplar breeding has verify whether black poplar clones originat-
gra is not commonly grown in its pure arisen with the projected dryer summer cli- ing from intraspecific hybridization (con-
form, and few cultivars are available. Fur- mate in Central-Western Europe (Schär et trolled crossings) of parental trees from lo-
thermore, these clones are usually selected al. 2004, Seneviratne et al. 2006, Kreuzwie- cal populations were improved in yield and
from natural populations (IPC 2000). Ac- ser & Gessler 2010). Poplars are especially growth traits and leave rust resistance in
cording to previously published studies sensitive to water deficiency and could be comparison with selected clones from nat-
(Nielsen et al. 2014, Verlinden et al. 2015), threatened by these climatic extremes. The ural populations; (ii) to verify whether their
P. nigra clones are the least productive, al- growth of their leaves and shoots is af- performance was comparable with that of
though certain clones derived from geneti- fected by water shortage (Monclus et al. commercial interspecific hybrid clones; and
cally pure P. nigra produce yields compara- 2009), affecting the total biomass, leaf (iii) to choose black poplar clones that are
ble to or exceeding those of interspecific area, shoot height and diameter (Monclus convenient for growing in SRC systems un-
hybrid clones (Benetka et al. 2002a, Al Afas et al. 2006). Therefore, these traits are der suboptimal conditions.
et al. 2008, Dillen et al. 2013). Additionally, used as indicators of drought, and their
pure P. nigra clones are not commonly evaluation can be used to select genotypes Materials and methods
grown because of their generally reported with higher drought tolerance.
susceptibility to leaf rust caused by Mel- A prerequisite for successful breeding for Materials
ampsora larici-populina Kleb., which is the resistance to drought is variability in the Twenty-one clones of P. nigra L. ssp. nigra
case in Western Europe (Steenackers 1972). traits observed in the genus Populus L.; from the black poplar breeding program-
M. larici-populina leaf rust is one of the namely, in P. nigra, variability was observed me of Silva Tarouca Research Institute for
main diseases of cultivated poplars and can between populations originating from con- Landscape and Ornamental Gardening,
cause severe damage and economic losses trasting climatic conditions within Europe Publ. Res. Inst. (Czech Republic), including
(Frey et al. 2005). This disease negatively (Viger et al. 2016). There are consistent 19 clones originating from 9 intraspecific
affects biomass production (Gastine et al. genotypic differences in the water-use effi- hybrid combinations (Benetka et al. 2012),
2003, Benetka et al. 2012, Štochlová et al. ciency (WUE) of poplar species and hy- were used in a field trial. These clones were
2015), resulting in yield losses of up to 66% brids, along with a lack of correlation be- chosen among 2227 individuals for their
in P. nigra clones (Štochlová et al. 2015). tween the WUE and productivity of poplar good yield potential and high level of resis-
The resistance of P. nigra to M. larici-pop- clones (Marron et al. 2005, Monclus et al. tance to M. larici-populina leaf rust
ulina shows a quantitative inheritance 2005, 2006, Navarro et al. 2018). This indi- (Benetka et al. 2012). An additional, leaf
(Dowkiw et al. 2012), as demonstrated by a cates that there is the potential for the se- rust-susceptible intraspecific clone (98/37)
genetic analysis of this trait (Benetka et al. lection of poplar clones that combine high was only used to confirm rust infection and
2005). This type of resistance does not en- WUE and high productivity, which would represented an additional rust source. The
sure complete resistance but produces be an advantage for the growth of poplar parental trees used in our crossings were
more durability than qualitative resistance. trees in moderately drought-prone areas plus trees selected from natural popula-
In contrast, the qualitative resistance that (Braatne et al. 1992, Jones et al. 2016). tions, and crosses were performed be-
occurs in some P. deltoides clones ensures The black poplar clones used in studies by tween parents from different climatic and
complete or near-complete resistance to Benetka et al. (2002a, 2014) and Dillen et al. geographic regions, with their genetic di-
some M. larici-populina strains (Pinon 1992, (2013) were derived from natural popula- versity previously confirmed by microsatel-
Dowkiw & Bastien 2004), although this re- tions and did not represent the products of lite DNA analysis (Benetka et al. 2012).
sistance can be suddenly overcome any type of selective breeding. Newly re- Two other P. nigra clones (202 and 301)
(Dowkiw et al. 2012). Due to the transitory leased clones arising from cross-pollination selected from a set of approximately 200
nature of resistance based on qualitative might be promising and have a potential plus trees originating from natural popula-
tions (Benetka et al. 2007) were chosen as
reference clones based on long-term yield
trials (Benetka et al. 2014) to evaluate the
improvement in P. nigra clones from con-
trolled crosses. Furthermore, clone 202 is
one of the parental trees of several tested
P. nigra clones (00/234, 00/237, 00/239, and
00/274). In addition to these two clones,
the “MAX 4” clone, an interspecific hybrid
of P. nigra × P. maximowiczii, was used as a
reference clone.
Locality and experimental design
The trial was established at the Silva Ta-
rouca Research Institute for Landscape
and Ornamental Gardening in Průhonice,
Czech Republic (Central Bohemia – 49° 59′
26″ N, 14° 34′ 40″ E) in spring 2009
(Benetka et al. 2012). The plantation site is
in a flat location at an altitude of 320 m
a.s.l. facing slightly towards the south, and
it consists of arable land that was grassed
over before the establishment of the plan-
Fig. 1 - Monthly cumulative precipitation (blue bars) and average temperatures (black tation. The soil type is modal brown earth
points) during the experimental period (2009-2017). found on loess, and the ground water level
186 iForest 13: 185-193Verification of P. nigra clones
is approximately 2.1 m deep. The location is
iForest – Biogeosciences and Forestry
Fig. 2 - Lang’s
a suitable but rather dry area with frequent
rain factor within
drying winds. The trial was not fertilized
the experimen-
and was irrigated only before the establish-
tal period (2009-
ment of the plantation and at sapling plant-
2017) and the cli-
ing, respectively. The monthly average
mate type with
temperatures and cumulative precipitation
respect to
during the 2009-2017 experimental periods
Lang’s rain fac-
are shown in Fig. 1, and Lang’s rain factor is
tor in the Czech
shown in Fig. 2. The mean annual tempera-
Republic (Minář
tures and mean annual cumulative precipi-
1948).
tation were 9.0, 9.5 and 9.9 °C and 643.6,
601.4 and 528.8 mm in first (2009-2011),
second (2012-2014) and third (2015-2017) ro-
tations, respectively.
One-year-old saplings, obtained by culti-
vating 0.2 m-long hardwood cuttings, were
cut at a height of 0.5 m and planted with a
planting machine at a spacing of 3.0 × 0.55 were counted and their diameters were rust incidence was calculated based on an
m (i.e., a plant density of 6061 plants per measured. The shoot with the highest di- annual rust evaluation over a nine-year pe-
ha) in spring 2009. A randomized block de- ameter in each plant was considered the riod.
sign with two to five (predominantly four) main shoot. Before the second and third
blocks for each P. nigra clone and eight harvest, the combined total cross-sectional Statistical analysis
blocks for the “MAX 4” reference clone area (TCA) of all measured shoots was cal- Statistical evaluations were carried out
was used, and four or five plants of each culated and expressed as the sum of the using software R (R Core Team 2019) or
clone were included in each block. Border per plant area in mm2. In the autumn be- Statistica® v. 11.0 (StatSoft Inc., Tulsa, OK,
rows were planted around the experimen- fore harvesting, plant mortality was deter- USA). Clones (fixed factor) and blocks (ran-
tal plot to prevent any border effect, and mined as the percentage of dead plants rel- dom factor) were used as the independent
the plot was also fenced to prevent brows- ative to the total number of plants planted. variables, and the parameters of the num-
ing by wild animals. The incidence of M. larici-populina leaf ber of shoots per plant, diameter of the
rust was evaluated under field conditions, main shoots, TCA, DMIP and dry matter
Measurements in a previous study (Štochlová et al. 2015) yield per unit area were used as the depen-
Biomass was harvested three times, and virulences 2, 3, 4, 5 and 7 were detected on dent variables in linear mixed-effects mod-
these harvests were separated by a three- test clones. Evaluations were made using a el of ANOVA (Bates et al. 2015). The param-
year interval. Plants were coppiced in Feb- 6-point scale ranging from 0 = no symp- eter mortality was not statistically evalu-
ruary 2012 for the first time, in January 2015 toms of rust infection on the leaves to 5 = ated due to its minimal variability. The
for the second time, and in February 2018 all leaves necrotized or shed (Štochlová et square root transformation (Anděl 1998)
for the third time. Individual plants were al. 2015) at least once during a vegetation was applied to the number of shoots per
cut by hand with a chainsaw at a height of period (April-September). The point values plant to obtain an approximately normally
approximately 0.1 m above the ground at presented are the means of the point eval- distributed variable. When a significant dif-
the first harvest and at ~0.05 m above the uations performed for each replication in ference was found, a post hoc comparison
previous cut at the following harvests. Dur- mid-August, and the mean point value of was carried out using Tukey’s test. The
ing the harvests, the fresh woody above-
ground biomass produced by all plants of a
given clone in each block was pooled and
weighed. To simultaneously estimate the
dry weight yield, a representative sample
of the harvested material (equally from 1-,
2- and 3-year-old part), including the main
and lateral shoots, was collected from each
block and weighed separately. The size of
these samples ranged from 300 to 1000 g
depending on the diameter of the shoots.
The samples were dried at 105 °C until their
weights were constant, and the average
dry matter weight of the individual plants
(DMIP), expressed as kg yr-1, was calculated
from the weight of the harvested fresh
biomass from a given block, multiplied by
the appropriate value of the percent dry
matter, and divided by the number of
plants in a given block and by the length of
the rotation. The total dry matter yield per
unit area (ha) and the percentage of living
plants were then calculated.
At the end of first rotation cycle before
harvesting, the main shoot diameter was Fig. 3 - Mean value of the dry matter yield for the five best P. nigra clones from con-
measured with a digital calliper at a height trolled crosses (02/455, 02/477, 02/456, 02/371, 02/286), P. nigra reference clones from
of 0.5 m above the ground. In the follow- natural populations (202, 301) and the P. nigra × P. maximowiczii reference clone “MAX
ing rotation cycles before harvesting, all 4” within the first (I.), second (II.) and third (III.) rotations. The bars represent the
shoots thicker than 0.01 m at this height standard errors of the mean values.
iForest 13: 185-193 187Novotná K et al. - iForest 13: 185-193
contingency. All results are presented us-
iForest – Biogeosciences and Forestry
Tab. 1 - P-values of the linear mixed-effects model of ANOVA (effects of the clone or ing a significance level of α < 0.05.
block on dependent variables) in the first (I.), second (II.) and third (III.) rotations.
(TCA): total cross-sectional area; (DMIP): dry matter weights of individual plants. Results
Variable Rotation Block Clone Biomass production
Diameter of strongest shoot I. > 0.5Verification of P. nigra clones
from that of the “MAX 4” clone in the third
iForest – Biogeosciences and Forestry
harvest. Both black poplar reference
clones exhibited lower mean values than
most of the P. nigra clones from controlled
crosses, although significant differences
were not found in any of the harvests. De-
scendants of clone 202 exhibited up to 22%,
34% and 11% higher DMIP values than did
their parent during the first, second and
third harvests, respectively (Tab. S1 in Sup-
plementary material). The DMIPs were
very strongly correlated with the TCA in
both the second and third harvest (R =
0.877, p < 0.001 and R = 0.918, p < 0.001, re-
spectively).
Similar to the DMIP results, the “MAX 4”
clone showed the highest dry matter yield
per unit area in all harvests (Fig. 3, Tab. S1
in Supplementary material) because negli-
gible mortality was observed during the
trial (Tab. 2). The biomass yields of most
black poplar clones were significantly low,
only the 5 above mentioned P. nigra clones
Fig. 4 - Percentage differences in the dry matter yield for the five best P. nigra clones
did not differ from the interspecific refer-
from controlled crosses (02/455, 02/477, 02/456, 02/371, 02/286), P. nigra reference
ence clone in the third harvest. The highest
clones from natural populations (202, 301) and the P. nigra × P. maximowiczii reference
increment of dry matter yields per unit
clone “MAX 4” between subsequent harvests. Different letters are related to the
area between the first and second harvest
results of multiple comparisons of the mean ranks through a post hoc test. The bars
was observed in the “MAX 4” clone (i.e.,
represent the standard errors of the mean values.
6.1 t ha-1 yr-1), for which the yield of the sec-
ond harvest increased by approximately
54% relative to that of the first harvest (Fig. tions was 12.8 t ha-1 yr-1, while this value in Growth traits
4). In the P. nigra clones, the yield incre- the black poplar clones ranged between The growth traits were measured at the
ment ranged between 0.3 and 3.8 t ha -1 yr-1, 5.8 and 9.4 t ha-1 yr-1. The black poplar refer- end of the vegetation period just before
and the yield in the second harvest in- ence clones (202, 301) were among the each harvest, and significant differences
creased by approximately 32% on average. clones with the lowest annual production were observed in all the evaluated traits
In one P. nigra clone (02/378), the yield in- (Tab. S1 in Supplementary material). (Tab. 1, Tab. S2 in Supplementary material),
creased by approximately 62%. However,
the yield increment of the black poplar ref-
erence clones was below average. The dif- Fig. 5 - Mean value
ferences in the dry matter yields per unit of (a) the main
area between the “MAX 4” clone and the shoot diameter,
best P. nigra clones increased in the second (b) the number of
harvest, with the highest-yielding P. nigra shoots and (c) the
clones exhibiting dry matter yields per unit TCA (total cross-
area that were approximately 71% (clone sectional area) for
00/274) and 66% (clone 02/455 – Tab. S1 in the five best P.
Supplementary material) of those of the in- nigra clones from
terspecific reference clone in the first and controlled crosses
second harvests, respectively. The dry mat- (02/455, 02/477,
ter yields per unit area decreased in the 02/456, 02/371,
third harvest (Fig. 3, Tab. S1). The yields in 02/286), P. nigra
the third harvest relative to that in the first reference clones
harvest were equivalent in one clone and from natural pop-
even lower in 13 clones. These clones in- ulations (202, 301)
cluded both reference P. nigra clones and and the P. nigra ×
the “MAX 4” reference clone, although its P. maximowiczii
yield remained 10% higher than the best reference clone
black poplar clone (02/455). The yield de- “MAX 4” within
crease between the second and third har- the first (I.), sec-
vest was significant in 13 clones, with the ond (II.) and third
highest decrease in the most productive (III.) rotations.
“MAX 4” clone (Fig. 4), while the decrease The bars repre-
in low-yielding black poplar clones was in- sent the standard
significant (Tab. S1 in Supplementary mate- errors of the
rial). The percentage of yield decrease be- mean values.
tween the second and third harvest of the
“MAX 4” reference clone was significantly
higher than that of some high-yielding P.
nigra clones (Fig. 4).
The average annual production of the
“MAX 4” reference clone over three rota-
iForest 13: 185-193 189Novotná K et al. - iForest 13: 185-193
with the independent variable of clone harvest and ranged between 2692 and Dowkiw et al. 2012). The first step was the
iForest – Biogeosciences and Forestry
having the greatest effect. A significant 4738 mm2 with highest TCA observed in P. selection of natural P. nigra populations to
block effect was observed only in TCA. nigra clone 02/455. Compared with the obtain plant material with high genetic di-
The diameter of the main shoot was the parental clone, the descendants of clone versity, and extensive crossing of geo-
highest in all clones before the first har- 202 showed up to 50% and 31% higher TCA graphically different genotypes generated
vest, followed by that before the second values during the second and third harvest, intraspecific hybrid populations, from
and third harvest (Fig. 5a, Tab. S2 in Supple- respectively, and the lowest values were which the selection was made (Benetka et
mentary material). The “MAX 4” clone had observed in both black poplar reference al. 2012). The current study focused on the
the greatest mean diameter of the main clones. selection of clones with favourable bio-
shoot before all three harvests at 68.2, mass production, higher M. larici-populina
62.8 and 48.8 mm, respectively, and it dif- Health status resistance and drought tolerance. Com-
fered significantly from all P. nigra clones in Plant mortality was negligible after the pared with the previous research of Bas-
the second and third rotation. The best P. establishment of the trial (Tab. 2). Before tien et al. (2014), the selection was per-
nigra clones had main shoot diameters of the first harvest, only one clone (02/103) formed based on field evaluations, without
68.1, 47.5 and 34.7 mm in the three rota- exhibited 5% mortality. Before the third the use of molecular markers and labora-
tions, respectively, with clone 02/455 show- harvest, it exhibited 10% mortality, and two tory evaluations of rust resistance.
ing the best results in the first two rota- additional clones (02/40, 02/102) exhibited
tions and 02/264 showing the best results 5% mortality. Biomass production
in the third rotation. Both P. nigra clones The occurrence of M. larici-populina leaf In this study, the P. nigra clones from con-
selected from nature were among the rust was evaluated under field conditions trolled crosses showed higher growth and
clones that showed the lowest main shoot (Tab. 2). The particular dates of rust inci- yield parameter values than did the clones
diameter in all three rotations. Compared dence evaluations were positively corre- selected from natural populations that had
with the parental clone, the descendants lated with themselves (R = 0.382-0.741, p < previously been confirmed to be suitable
of clone 202 exhibited greater shoot diam- 0.001). The results show that the rust inci- for SRC plantations (Benetka et al. 2014,
eters during the first, second and third har- dence is strongly dependent on the clone; Štochlová et al. 2019). The best intraspe-
vests of up to 16%, 29% and 4%, respectively the Pearson’s coefficient of contingency cific descendants of clone 202 displayed up
(Tab. S2 in Supplementary material). Simi- was C = 0.692, p < 0.001. to 34% greater dry matter yield per unit
lar to the main shoot diameter, higher av- Although the lowest rust incidence was area and up to 29% greater shoot diameter
erage shoot diameters were found before observed in the “MAX 4” reference clone, for the main shoots compared with their
the second harvest than the third harvest, some of the individual black poplar clones parent during the second harvest. In P.
and the best diameters in these harvests showed an equally low incidence. The ×canadensis, Dillen et al. (2009) obtained
were found in the “MAX 4” clone, at 30.5 mean point value of leaf rust incidence in an increase of 26.5% in the 2-year-old shoot
and 24.6 mm, respectively. The average the “MAX 4” clone was 0.4 ± 0.1 over 9 diameter, and Marron & Ceulemans (2006)
shoot diameter of the P. nigra clones years, and the mean point values in the reported an increase of 23.3%. These results
ranged between 17.0 and 22.5 in the sec- black poplar clones showing minimal rust cannot be compared due to the different
ond rotation and 16.2 and 19.0 mm in the incidence (00/234, 02/477 and 202) were study conditions involved, although the ob-
third harvest (Tab. S2 in Supplementary between 0.7 ± 0.1 and 1.0 ± 0.1. In contrast, served increases are satisfactory from a
material). The average shoot diameters of the clones showing the poorest results for breeding perspective.
the P. nigra clones were 26% to 44% and 23% this parameter were 02/383, 02/371, and Higher growth parameter values of the
to 34% smaller than that of the “MAX 4” 02/40, with mean point values 2.1 ± 0.1. The tested P. nigra clones in comparison with
clone before the second and third harvest, susceptible clone 98/37 showed the high- clones used in Štochlová et al. (2015) were
respectively. est values of rust incidence over all 9 years achieved under the same rust disease at-
After the first harvest, the number of with a mean point value of 2.8 ± 0.1. tack, thereby excluding different effects of
shoots per plant increased due to coppic- In the year with the highest rust inci- the pathogen and confirming that breed-
ing and varied greatly. The number of dence (2011), the mean point values for ing progress has been achieved through in-
shoots was greater in the black poplar most of the clones with the highest resis- traspecific hybridization. The lower values
clones than in clone “MAX 4” (Fig. 5b, Tab. tance did not exceed 2 points, while the obtained for clones from natural popula-
S2 in Supplementary material) and ranged clones that showed the highest rust inci- tions could be affected by the water
between 5.9 and 14.2 shoots per plant. The dence had 3 or more points. The suscepti- regime at the locality, which is character-
mean number of coppiced shoots in the P. ble clone 98/37 received 3.8 points. ized by lower ground water levels and pre-
nigra clone with the greatest shoot num- cipitation, potentially revealing drought
ber (02/476) was 2.4 times higher than that Discussion tolerance in the best P. nigra clones from
of the interspecific reference clone “MAX The performance of 19 P. nigra clones controlled crosses.
4” just before the second harvest. In the originating from intraspecific crossings In this study, many black poplar clones
third rotation, the number of shoots in all were compared to that of 2 clones from were evaluated, although the presented
clones was higher than that in the second natural populations and the interspecific data were obtained in small plots at only
rotation, and the lowest number of shoots clone “MAX 4” in SRC systems over three one locality. However, a similar trial with
was observed in the “MAX 4” clone at 7.4, three-year rotations. The P. nigra clones the same clones has been established by
while the highest number was found in used in the current study are the result of the Central Institute for Supervising and
clone 02/476 at 16.1. more than 20 years of breeding, the goal of Testing in Agriculture at Stachy, Czech Re-
Total cross-sectional area (TCA) accounts which was to obtain genotypes suitable for public (South Bohemia – 49° 06′ 06″ N, 13°
for the number of shoots and their diame- biomass production that could replace in- 39′ 60″ E) in 2010. The plantation site is lo-
ters. In this trial, the TCA values ranged be- terspecific Populus hybrids threatening au- cated at an altitude of 742 m a.s.l. and
tween 2867 and 5764 mm2 before the sec- tochthonous P. nigra species through gene slopes slightly towards the northeast, and
ond harvest and showed high variability, introgression (Heinze 1997, Benetka et al. it was used as pasture land before the es-
particularly among the tested clones (Fig. 2002b, Vanden Broeck et al. 2005, Smul- tablishment of the plantation. The soil is
5c, Tab. S2 in Supplementary material). The ders et al. 2008). The other goal was to ob- dystric Cambisol on paragneiss with a pH
“MAX 4” clone exhibited the highest TCA tain clones resistant to existing virulences from 6.2-6.5. The average annual tempera-
value in the second harvest. Before the of M. larici-populina in the Czech Republic, ture is 6.4 °C (in growing period 14.2 °C),
third harvest, the TCA values were lower in in which the resistance would be stable, as and the average cumulative precipitation is
most of the clones than before the second expected in P. nigra (Legionnet et al. 1999, 742 mm (growing period 378 mm). The
190 iForest 13: 185-193Verification of P. nigra clones
plantation was harvested for the first time which depends on the amount of nutrient was not dependent on the amount of pre-
iForest – Biogeosciences and Forestry
in autumn 2015. A significant strong corre- storage, and the incidence of M. larici-pop- cipitation (Benetka et al. 2014). An increas-
lation (R = 0.666, p = 0.001) was found be- ulina. The decrease in the growth rate of ing yield in the third or fourth rotation was
tween rank of clones according to the plants with rust incidence from 1 to 2.25 also confirmed in other experiments in
yields at Stachy and the average annual dry points (using the same point evaluation) some clones (Al Afas et al. 2008, Dillen et
matter production in Průhonice. Among was not important, and the higher rust inci- al. 2013).
the best-performing clones under marginal dence in plants from the end of August did As a result of the drought, the yield de-
growing conditions were clones 02/456, not negatively affect the shoot thickness crease between second and third harvest
02/455 and 02/383 (Reininger et al. 2015); (amount of nutrient storage – Štochlová et was the highest and was significant in the
therefore, two of the three best clones al. 2015). These findings indicate that the most productive “MAX 4” clone, while the
from both trials are the same, thus con- incomplete rust resistance observed in cer- decrease in low-yielding black poplar
firming their high adaptability. However, tain P. nigra clones is sufficient to defend clones was non-significant. The same re-
clones with a distinct rank were observed against the decrease in biomass yield sponse was achieved even in poplar geno-
in this study, including clones 02/383 and caused by rust. In the current trial, a lower types originating from P. deltoides and P.
301, which may be less sensitive to mar- rust incidence in comparison with that in trichocarpa (Monclus et al. 2009). In con-
ginal growing conditions and lower tem- the study of Štochlová et al. (2015) was ob- trast, the yield decrease of some high-yield-
peratures (at Stachy) and present much served in 2009 and 2010, although the trials ing black poplar clones was significantly
better growth than that observed in the were situated very close to each other. In lower than that of the “MAX 4” clone, indi-
current trial (at Průhonice). In contrast, 2011, the rust incidence in both trials was cating their higher drought tolerance com-
clone 02/477 belonged to the clones with a comparable (resistant clones 97/152 and pared with “MAX 4” clone. It will be very
low yield under marginal growing condi- 97/157 were evaluated as 2.25 points and interesting to observe the biomass yield
tions; therefore, this clone likely requires susceptible clone as 4.33 points). This dif- tendency and differences among intraspe-
better growing conditions. Nevertheless, ference could be explained mainly due to cific black poplar clones and reference
further evaluations of the best clones must the use of different clones, with a low clones in a series of years with continuous
be made via field tests using larger plots in number of susceptible clones in the cur- low Lang’s rain factors.
more localities to determine the genotype rent study and a looser spacing. According
× site interactions of the clones. to several years of field observations, the Prospects and utilization
The interspecific clone “MAX 4” per- stability of the higher rust resistance was The current study indicates a high poten-
formed better for most of the evaluated confirmed in the best clones. These clones tial for further intraspecific P. nigra breed-
traits. The species combination giving rise were even better than clones with higher ing. Obtaining clones that are relatively
to the “MAX 4” clone appears to be very levels of rust resistance identified in a pre- highly resistant to M. larici-populina is high-
efficient compared with other interspecific vious work (Štochlová et al. 2015). How- ly valuable and can disprove the notion of
combinations (Zamora et al. 2013). Ob- ever, a high variability in leaf rust suscepti- the unsuitability of P. nigra in SRC cultures
served differences in evaluated traits can bility was observed among the tested due to its susceptibility to this pathogen.
be important for selection of right harvest- clones, which supports the notion of resis- In particular, pure P. nigra and P. tricho-
ing method and rotation length (optimal tance based on several quantitative trait carpa clones appeared to be most suitable
diameter of main shoots for mechanical loci (Legionnet et al. 1999, Benetka et al. for growth under suboptimal conditions
harvesting), wood assortment and its uti- 2005, Štochlová et al. 2015). Intraspecific (i.e., planted on degraded land – Dillen et
lization (chips, logs, pulp, etc. – Marron et clones with a high level of resistance were al. 2013), which meets the requirements for
al. 2012). Also differences in growth and identified, which are important for follow- growing SRC cultures in areas that are not
yield traits can affect wood properties as up resistance breeding programmes be- suitable for intensive agricultural produc-
higher number of shoots in P. nigra clones cause rust-resistant clones could achieve tion.
could lead to a higher proportion of bark higher biomass production (Dillen et al.
and therefore differences in combustion 2013, Štochlová et al. 2015). Moreover, P. Conclusions
heat (Geyer et al. 2000, Benetka et al. nigra is one of the parents of most of the In the present study, the significance of
2002a). most commonly grown poplar clones; natural populations (subpopulations) as a
The biomass production of new P. nigra therefore, the best P. nigra clones could be source of genetic diversity for further P. ni-
clones coming from controlled crosses was used for other interspecific crosses. gra breeding was confirmed. It was shown
higher than production of clones from nat- that the first generation of controlled, in-
ural population in the study by Benetka et Drought tolerance traspecific cross-pollination among se-
al. (2014) with exception of the third har- Both low amounts of precipitation and lected clones of P. nigra was effective and
vest of certain clones grown in optimal orhigh temperatures characterized by a low convenient for breeding with the goals of
marginal conditions. This difference couldLang’s rain factor during the third rotation high biomass yields and resistance to M.
be explained by different growing condi- (Fig. 2) enabled the evaluation of the larici-populina. It was shown that P. nigra
tions, the lower amount of precipitation in
drought resistance in the trialled clones, al- can be a genetic source of durable resis-
the third rotation, and different spacing.though the trial was not established with tance to this pathogen.
The intraspecific hybridization success is
this goal. The biomass yield of the black Most P. nigra clones from controlled
evident compared to the results of other poplar clones and “MAX 4” in the present crosses exhibited higher values of all evalu-
studies in which black poplar clones were study decreased in the third harvest in ated traits than those of clones selected
also used (Dillen et al. 2013, Benetka et al.
comparison with that in the second har- from natural populations. Three high-yield-
2014, Nielsen et al. 2014, Verlinden et al.
vest. This is in contrast to the results ob- ing clones (02/455, 02/477 and 02/456) that
2015). However, different growing condi- tained at the Rosice site (Benetka et al. were highly resistant to leaf rust and had
tions, spacing and management were im- 2014), in which a similar spacing was used higher drought tolerance were selected
plemented, and the best black poplar and the biomass yield was the same or and can be recommended for growth in
clones showed mostly comparable or even higher in the third or fourth harvest than in SRC cultures mainly in specific areas. Fur-
higher biomass yields. the second harvest. The observed decrease ther intraspecific breeding of P. nigra has
in Průhonice in the present study was considerable potential, although the inter-
Rust resistance caused by drought, whereas at the Rosice specific clone “MAX 4” performed better
In a previous work by Štochlová et al. site, the soil was always sufficiently sup- than did most of the P. nigra clones. The P.
(2015), a negative correlation was demon- plied with groundwater coming from a nigra clones presented herein will be used
strated between the shoot thickness, nearby river, and therefore, plant growth in further intraspecific breeding cycles with
iForest 13: 185-193 191Novotná K et al. - iForest 13: 185-193
the goal of further yield increases. The pos- mes. Tree Genetics and Genomes 8: 1073-1084. -
iForest – Biogeosciences and Forestry
(2005). Variability and population biology of
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Acknowledgements three different environments over four rota- 99.0063
The authors gratefully acknowledge D. tions. iForest 7: 233-239. - doi: 10.3832/ifor1162- Gastine F, Berthelot A, Bouvet A, Servant H, Roy
Reininger from the Central Institute for Su- 007 B (2003). La protection phytosanitaire du culti-
pervising and Testing in Agriculture (Brno, Bentsen NS, Felby C (2012). Biomass for energy var “Beaupré” - est-elle efficace? [Plant protec-
Czech Republic) for detailed locality de- in the European Union a review of bioenergy tion of the cultivar “Beaupré” - is it effective?].
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manuscript, as well as the anonymous re- fluence of soil water on the physiological and Populus clones. Wood and Fiber Science 32:
viewers for their comments on previous morphological components of plant water bal- 375-384. [online] URL: http://wfs.swst.org/in
versions of the manuscript. ance in Populus trichocarpa, Populus deltoides dex.php/wfs/article/view/413
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1339. - doi: 10.1093/treephys/tpp075 Miscellaneous Publications no. 1221, USDA For- (III.) harvests.
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tion in transpiration of coppiced poplar during permanent waterlogging on the growth of eters.
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culture. Global Change Biology Bioenergy 10: ulus maximowiczii A. Henry × P. nigra Linnaeus) Link: Novotna_3171@suppl001.pdf
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iForest 13: 185-193 193You can also read
