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Apical bud removal increased seed yield in hemp ( Cannabis sativa L.)

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Acta Agriculturae Scandinavica, Section B - Soil & Plant Science
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In plants, apical dominance prevents the development of lateral shoots. It can be overwhelmed by apical bud defoliation, allowing numerous lateral buds to develop into more lateral branches carrying more fruits and possibly increasing seed yield. This study tested this hypothesis on five hemp (Cannabis sativa L.) cultivars in a 2-year field experiment. In comparison to the intact ones, the defoliated plants developed several lateral shoots. The hemp seed yield was significantly influenced by the year of production, the apical bud removal, and the cultivar. The average two-year seed yield of the defoliated plants (715 ± 47 kg/ha) was significantly higher than the yield of the intact plants (568 ± 35 kg/ha). Absolutely the greatest effect of apical bud removal on the seed yield was observed for the cultivar ‘Novosadska konoplja’, where increase was 225 kg/ha (25%); a slightly smaller difference occurred for the cultivar ‘Uniko-B’ (183 kg; 30%), followed by ‘Juso-11’ (140 kg/ha; 27%) and ‘Bialobrzeskie’ (128 kg/ha; 29). Cultivar ‘Beniko’ presented the smallest difference with apical bud removal – 58 kg/ha (15%) yield increase We maintain that hemp producers can achieve a larger seed yield not only by selecting an appropriate cultivar and row distance but also by removing apical buds.
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Apical bud removal increased seed yield in hemp
(Cannabis sativa L.)
Darja Kocjan Ačko, Marko Flajšman & Stanislav Trdan
To cite this article: Darja Kocjan Ačko, Marko Flajšman & Stanislav Trdan (2019) Apical bud
removal increased seed yield in hemp (Cannabis�sativa L.), Acta Agriculturae Scandinavica,
Section B — Soil & Plant Science, 69:4, 317-323, DOI: 10.1080/09064710.2019.1568540
To link to this article: https://doi.org/10.1080/09064710.2019.1568540
Published online: 13 Jan 2019.
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Apical bud removal increased seed yield in hemp (Cannabis sativa L.)
Darja Kocjan Ačko, Marko Flajšman and Stanislav Trdan
Biotechnical Faculty, Department of Agronomy, University of Ljubljana, Ljubljana, Slovenia
ABSTRACT
In plants, apical dominance prevents the development of lateral shoots. It can be overwhelmed by
apical bud defoliation, allowing numerous lateral buds to develop into more lateral branches
carrying more fruits and possibly increasing seed yield. This study tested this hypothesis on ve
hemp (Cannabis sativa L.) cultivars in a 2-year eld experiment. In comparison to the intact ones,
the defoliated plants developed several lateral shoots. The hemp seed yield was signicantly
inuenced by the year of production, the apical bud removal, and the cultivar. The average two-
year seed yield of the defoliated plants (715 ± 47 kg/ha) was signicantly higher than the yield of
the intact plants (568 ± 35 kg/ha). Absolutely the greatest eect of apical bud removal on the
seed yield was observed for the cultivar Novosadska konoplja, where increase was 225 kg/ha
(25%); a slightly smaller dierence occurred for the cultivar Uniko-B(183 kg; 30%), followed by
Juso-11(140 kg/ha; 27%) and Bialobrzeskie(128 kg/ha; 29). Cultivar Benikopresented the
smallest dierence with apical bud removal 58 kg/ha (15%) yield increase We maintain that
hemp producers can achieve a larger seed yield not only by selecting an appropriate cultivar
and row distance but also by removing apical buds.
ARTICLE HISTORY
Received 10 September 2018
Accepted 7 January 2019
KEYWORDS
Cannabis sativa; cultivars;
defoliation; height of plants;
seed yield
Introduction
Industrial hemp (Cannabis sativa L.) for harvesting in
the European Union, is a plant with a brous stem
and is a non-food raw material (European Commission
2000; Weightman and Kindred 2005). However, nutri-
tional qualities of hemp seed, rich in both oils and pro-
teins (Callaway 2004a), are recognised as alimentary
advantages (Andre et al. 2016) and lead to intensive
seed production (Salentijn et al. 2015). Demand for
cold-pressed oil, other foodstus and dietary sup-
plements made of hemp seeds has increased with
the recognition that consumption of hemp seed pro-
ducts may help prevent the emergence and develop-
ment of various diseases in humans (Rodriguez-Leyva
and Pierce 2010) and favourably inuences the
growth and development of domestic animals,
especially poultry (Khan et al. 2010).
In hemp seed production, several constraints
decrease seed yield, and dierent cultivation tech-
niques are continuously tested (e.g. plant density, N
fertilising and sowing time). One of the approaches
to enhance yield in some agriculture crops is the
apical bud removal (defoliation). Apical dominance
seems not to be auxin related and is likely governed
by high sugar demand, which serves to slow the
growth of the axillary buds below (Mason et al.
2014). Once apical buds are removed, lateral shoots
massively develop. Studies on the reactions of plants
to apical bud removal include a variety of plant
types, including trees, ornamental shrubs, grapevines,
some garden crops and eld crops (Lortie and
Aarssen 1997). In vegetable fruits, such as paprika,
tomatoes, aubergines, cucumbers, pumpkins and
melons, apical buds are regularly removed to increase
yield (Salisbury and Ross 1992). In hemp, however, con-
troversial information exists regarding hemp response
to defoliation (Small et al. 2007; Leonte et al. 2015;
Baldini et al. 2018), demonstrating that besides
edapho-climatic conditions, seed yield is also
inuenced by the cultivar and applied agro-technique
measurements (e.g. plant density). This research
determined the seed yield and plant height in
response to apical bud removal for ve hemp cultivars
in comparison with the yield from intact plants. It was
hypothesised that plants with apical buds removed
would produce a higher seed yield than the intact
plants.
© 2019 Informa UK Limited, trading as Taylor & Francis Group
CONTACT Stanislav Trdan stanislav.trdan@bf.uni-lj.si Biotechnical Faculty, Department of Agronomy, University of Ljubljana, Jamnikarjeva 101, Ljubljana
SI-1000, Slovenia
Supplemental data for this article can be accessed at https://doi.org/10.1080/09064710.2019.1568540
ACTA AGRICULTURAE SCANDINAVICA, SECTION B SOIL & PLANT SCIENCE
2019, VOL. 69, NO. 4, 317323
https://doi.org/10.1080/09064710.2019.1568540
Materials and methods
Plant material
For the analysis of apical bud removal, ve cultivars were
chosen (Table 1), which were studied in 2000 and 2001,
when hemp production was being reintroduced in Slove-
nia (Kocjan Ačko et al. 2002). Since no hemp cultivars that
are intended specically for seed production are mar-
keted, farmers sow the available cultivars, which are envi-
sioned for producing stems and bres (Ranalli 2004; Vogl
et al. 2004). In comparison with the hemp grown for
bres, wherein, producing long and thin stems requires
sowing with 12- do 15-cm row spacing (Schumann
et al. 1999; Young 2005), the production of hemp seed
normally involves 25- to 60-cm rows. This spacing
enables plants to develop lusher and branched inores-
cences and thereby increase seed yield.
Field experiment
The eld trials on the ve hemp cultivars occurred in the
laboratory eld of the Biotechnical Faculty in Ljubljana
(46°04N, 14°31E, 299 m elevation), where the soil is
medium deep and silty-clay. Soil pH was 7.0 and the
level of K
2
O and P
2
O
5
was in the optimum range (20
30 mg K
2
O 100 g of soil
1
and 1325 mg P
2
O
5
100 g of
soil
1
). Plots were established on 20 April 2010 (from
now on referred to as year 1) and 24 April 2011 (from
now on referred to as year 2). The trial was arranged as
a randomised complete block design with three repli-
cates. The basic plot covered 5 m
2
(1 m × 5 m). Seeds
of each cultivar were sown manually at a row spacing
of 25 cm (4 rows) and a distance of 20 cm per row (25
plants per row) at a depth of 1.5 to 2.5 cm. A density of
approximately 100 harvested female or hermaphrodite
plants per basic plot was ensured, by placing two
seeds in the same spot. All seeds did not germinate; if
two plants grew close together, the weaker one was
cut. Since the sex of dioecious cultivars (Novosadska
konoplja,Juso-11) was unrecognisable before the
emergence of owers, the desired number of 100
female plants (unisexual plants in the case of monoe-
cious cultivars) per basic plot was regulated until the
middle of the generative period.
In the years before the experimental sowing of hemp,
the eld, which was fertilised with approximately 20 t of
animal manure per hectare, was used for growing pota-
toes; the pre-sowing treatment of the hemp eld
involved using 40 kg of NPK per hectare (applied in a
15:15:15 formulation). The presence of weeds, due to
wider row spacing in the trials, was reduced rst with
inter-row hoeing and, subsequently, with occasional
manual weeding. The growth and development of
hemp were monitored until the apical buds appeared
at the beginning of reproductive (owering) phase.
Then, the removal of the apical buds (defoliation) was
carried out manually in the middle of June, in the
growth stage 2000, according to the decimal code devel-
oped by Mediavilla et al. (1998). Simultaneously, the
height at which the apical buds were removed was
measured. The control treatment was non-defoliated
plants. The nal height of the plants was determined at
harvest on 5 and 6 September in year 1 and 2, respect-
ively. Inorescences of the hundred plants from each
plot were cut manually and placed in paper bags
before oven drying at 40 to 50°C. The seeds were
removed from the inorescences, by shaking and thresh-
ing while other materials were removed with sieves and
blown o. Seeds from the individual cultivars were
weighed, and the seed yield was calculated in kilograms
per hectare at 10% moisture.
In year 1, total monthly precipitation was lower than
the long-term average (19852010), except for August,
when rainfall was 176 mm (39 mm above the long-
term average). Temperatures were similar to the long-
term average, except in June and July, when it was
higher by 1.2 and 1.6°C, respectively. Year 2 had extre-
mely low precipitation in April (38 mm) and August
(43 mm), and high rainfall in July (157 mm). Tempera-
tures were mostly above the long-term average; at
most by 2.2°C, in August (Figure 1).
Statistical methods
Data on the seed yield (kg/ha) and nal plant height
(cm) of the ve hemp cultivars were analysed by the
general analysis of variance (ANOVA) to test the
eects of the year, cultivar, defoliation treatments and
their interactions and by individual ANOVA, to assess
the eects of cultivar and defoliation treatment within
each year. The averages were separated by Student
NewmanKeuls multiple range tests at p< 0.05. Before
analysis, each variable was tested for homogeneity of
the treatment variances. If the variances were non-
homogeneous, data were transformed to log(y) before
ANOVA. All statistical analyses were performed with
Statgraphics Plus for Windows 4.0 (Statistical Graphics
Corp., Manugistics, Inc.). Data are presented as untrans-
formed means ± SE.
Table 1. List of origin, ecotype and sexual type of used cultivars.
Cultivar Origin Ecotype Sexual type
BenikoPoland Northern, low-hemp Monoecious
BialobrzeskiePoland Northern, low-hemp Monoecious
Juso-11Ukraine Middle European hemp Dioecious
Novosadska konopljaSerbia Southern, high-hemp Dioecious
Uniko-BHungary Middle European hemp Monoecious
318 D. KOCJAN AČKO ET AL.
Results
Morphological appearance of the plants after the
defoliation
During the growth and development of the hemp,
special attention was paid to the transition from vegeta-
tive to generative development. The short cultivars Bia-
lobrzeskieand Benikoformed buds at the height of 70
to 80 cm while the other three, taller cultivars, formed
buds at the height of 90 to 100 cm. The defoliation
occurred rst in the taller cultivars (Novosadska
konoplja,Uniko-Band Juso-11) and then a week
later in both short cultivars (Bialobrzeskieand
Beniko). After apical bud removal, the plants formed
lateral shoots, which eventually lengthened and
strengthened considerably. The majority of plants devel-
oped from two to three lateral shoots, with only a few
forming four to six such shoots. The lusher inorescences
of the plants without apical buds acquired mass than the
intact plants, but no stems broke under the weight of the
seeds.
Inuence of the year of production, defoliation
and cultivar on the seed yield and the nal height
of the plants
Hemp seed yield was signicantly inuenced by the year
of production, defoliation and cultivar (p< 0.0001). The
average 2-year seed yields were greater for defoliated
plants than for non-defoliated plants (715 ± 47.0 vs 568
± 35 kg/ha), although the eect was more pronounced
in year 2 than year 1 (year × treatment interaction; p=
0.0125), for which, average hemp seed yields were 712
± 47 and 570 ± 35 kg/ha, respectively. Across years,
yields also diered by cultivar (year of production × the
cultivar interaction, p= 0.013). Cultivar yields decreased
in the order Novosadska konoplja(996 ± 50 kg/ha) >
Uniko-B(697 ± 37 kg/ha) > Juso-11(595 ± 43 kg/ha) >
Bialobrzeskie(502 ± 27 kg/ha) > Beniko(418 ± 12 kg/
ha) (Supplementary material, Table S1) and a signicant
dierence in yield was conrmed in all cultivars.
Plant height was also inuenced by the year of pro-
duction, defoliation and cultivar (p< 0.0001). Plant
height was greater in year 2 (148 ± 4 cm) than year 1
(126 ± 4 cm), although year-to-year variation in this
response varied by cultivar (cultivar × year interaction;
p< 0.0001). Regarding plant height, the rank of the culti-
vars from signicantly tallest to signicantly shortest was
Novosadska konoplja(165 ± 4 cm) > Uniko-B(140 ±
7cm) > Juso-11(132 ± 7 cm) > Bialobrzeskie(128 ±
5cm)>Beniko(122 ± 4 cm). The cultivars also displayed
dierent responses to defoliation according to the year
(year of production × defoliation interaction, p=
0.0122), revealing that plants with removed buds were
signicantly shorter (126 ± 4 cm) than the intact plants
(149 ± 3 cm) (Supplementary material, Table S2). Finally,
there was a 3-way interaction among the year of pro-
duction, defoliation and cultivar (p= 0.0065).
Comparison of seed yield and the nal height of
defoliated and non-defoliated plants
In both years of the study, defoliation treatments
aected the seed yield of almost all cultivars signicantly.
Figure 1. Mean monthly air temperature and total monthly precipitation during the eld experiment and the long-term average
ACTA AGRICULTURAE SCANDINAVICA, SECTION B SOIL & PLANT SCIENCE 319
In year 1, defoliation treatment (vs non-defoliation) sig-
nicantly increased seed yield only for Novosadska
konoplja(979 ± 46 vs 793 ± 6 kg/ha) and Uniko-B(717
± 50 kg/ha vs 557 ± 2 kg/ha). In year 2, the eect of defo-
liation was signicant for all cultivars, except for Beniko
(474 ± 7 kg/ha vs 408 ± 8 kg/ha) (Figure 2). For average
seed yield of both years of the study, the strongest
eect of defoliation was observed for Uniko-B,in
which, apical bud removal enhanced seed yield by 30%
(183 kg/ha) as the average of the 2 years. There was a
slightly weaker eect of defoliation on Bialobrzeskie
(29%; 128 kg/ha), Juso-11(27%; 140 kg/ha) and Novo-
sadska konoplja, which had the highest absolute yield
dierences (225 kg/ha), reected by a 25% yield increase.
Benikoseed yield only increased 15% (58 kg seed/ha)
(Supplementary material, Table S1). Plant high of all cul-
tivars signicantly decreased by defoliation treatments in
both years of the study, except year 2, in which the
height of cultivar Uniko-Bwas not aected by defolia-
tion (Figure 3). The highest decreases in plant height
(on average of both years of the study) were observed
for cultivar Bialobrzeskie(23%; 26 cm) and Juso-11
(23%; 27 cm), followed by Beniko(21%; 23 cm) and
Uniko-B(15%; 19 cm; p= 0.030). The height of the
highest cultivar Novosadska konoplja(165 ± 4 cm)
decreased by 13% (20 cm; p= 0.002).
Discussion
Hemp is cultivated for the biomass and seeds. With the
present production technology, hemp seed yield per
unit of area can vary considerably, with maximum
yields up to 2400 kg/ha in Europe (Tang et al. 2016;
Campiglia et al. 2017). Recent data show that farmers
in Slovenia produce 200 to 1600 kg of hemp seed per
hectare while yields of beginner farmers are usually
smaller than expected (Flajšman et al. 2017). The
average hemp seed yield in this study of 641 kg/ha,
means that yield could still be improved. However,
weather conditions were seen to aect seed yield. Year
2 favoured seed production, and average seed yield
was 142 kg/ha higher compared with year 1. The pro-
nounced weather eect also reected in the plant
height, with a dierence in average plant height of
15% (22 cm) in favour of year 2 (Supplementary material,
Tables S1 and S2). Although year 2 had less total precipi-
tation from April to September (443 mm) than year 1
(513 mm), the rainfalls were better distributed through-
out the growing season, especially, June and July
(active vegetative growth of plants) in year 2 had more
rainfall than in year 1. Besides, temperatures were
higher compared to the long-term records, except in
July (Figure 1). Conversely, in year 1, June was dryer
and July had a higher temperature in comparison to
the long-term data. Heavy precipitation in August prob-
ably impacted negatively on ripening of the seeds and
decreased the yield in this year.
The agrotechnical measure of defoliation in hemp is
frequently performed in practice, to derive cannabinoids,
terpenes and phenol substances from the resinous tri-
chomes of female blossoms (Andre et al. 2016). The
process technologically diers from the seed production
dealt with in the current study. Hemp seed production is,
operationally, usually occurs without apical bud removal.
In both cases, the removal of apical buds produces lateral
buds that form an inverse pyramidal crown with a great
Figure 2. The inuence of the year of production and defoliation treatments (D defoliation, ND non-defoliation) on cultivars seed
yield. The mean yields of the cultivars were separated by a StudentNewmanKeuls multiple range test (p< 0.05) among defoliation
events within each year. The dotted line separates years. The values carrying the same letters do not dier signicantly.
320 D. KOCJAN AČKO ET AL.
potential for producing secondary metabolites (Green
2003; Andre et al. 2016) and seeds.
The results of this study conrm the high inuence of
the cultivar on seed yield (deviation from 35% to + 55%
from average yield), as stated previously by other authors
(Callaway 2004b; Vogl et al. 2004; Tang et al. 2016).
Besides, a statistically positive inuence of apical bud
removal on the seed yield in all cultivars in both years
of the experiment occurred. This phenomenon has
been reported for cotton plants (Gossypium hirsutum L.)
as well (Sadras 1996; Bednarz and Roberts 2001). Further-
more, cultivar origin is related to seed yield. Southern
ecotype Novosadska konopljayielded the highest
(996 ± 50 kg/ha), followed by both middle European eco-
types Uniko-B(697 ± 37 kg/ha) and Juso-11(595 ±
43 kg/ha), and then the northern European cultivars Bia-
lobrzeskie(502 ± 27 kg/ha) and Beniko(418 ± 12 kg/
ha). In addition, there was no connection between culti-
var origin and its response to defoliation since both
middle European ecotypes reacted with the highest per-
centage increase, and both northern European cultivars
reacted inconsistently. The response of the southern
ecotype Novosadska konopljato defoliation was mod-
erate compared with the other cultivars. It is likely that
northern European cultivars, when grown in the area of
origin, would show enhanced yield and the defoliation
impact would be improved. However, in year 2, when
seed yields were higher relative to year 1, the eect of
defoliation was more pronounced in all cultivars.
This study showed that defoliation caused an average
25.9% increase in seed yield. Small et al. (2007) tested a
hypothesis that insect damage of the main stem of
hemp may be benecial for seed yield. In that work, 62
hemp accessions were planted in a eld previously culti-
vated with corn infested with European corn borer (ECB).
After the ECB invasion of hemp plants, the upper part of
the main stems was destroyed, causing very strong
branching. The results were a substantial increase in
biomass production (20%) and 9% decrease in plant
height. Seed yield was assessed but not quantied,
although, seed productivity was signicantly positively
correlated (r= 0.33) with the percentage of ECB-
damaged plants. Small et al.s(
2007)study veried the
positive eect of naturally occurring defoliation by ECB
invasion. However, the benecial inuence of insect
damage on hemp production is dicult to assess since
insect infestation cannot be controlled and its large out-
breaks could annihilate hemp crops.
Seeding density could have a crucial role in the
success of increasing seed yield by plant defoliation.
The current trial used a very low plant density of 20
plants per m
2
at harvest (row spacing of 0.25 m, and
inter-plant distance of 0.2 m). Instead, Baldini et al.
(2018) sowed 130 viable seeds per m
2
at 0.15 m inter-
row spacing and noticed a 34.5% (190 kg/ha) decrease
in seed yield after defoliation of eight monoecious
hemp cultivars, grown for multipurpose use. It is very
likely that the comparatively wider growing space in
the current experiment allowed defoliated plants to
occupy more space, develop more intensive branching
and, consequently, more seed yield. Planting density
could be highly associated with the success of defolia-
tion. This assumption was endorsed by Leonte et al.
(2015), who tested three defoliation treatments (non-
defoliation, cutting once and cutting twice) on three
monoecious hemp cultivars at two dierent row
Figure 3. The inuence of the year of production and defoliation treatments (D defoliation, ND non-defoliation) on cultivarsnal
height. The mean heights of the cultivars were separated by a StudentNewmanKeuls multiple range test ( p< 0.05) among defolia-
tion events within each year. The dotted line separates years. The values carrying the same letters do not dier signicantly.
ACTA AGRICULTURAE SCANDINAVICA, SECTION B SOIL & PLANT SCIENCE 321
distances (25 and 50 cm) at very low sowing rate (6 kg/
ha). Although both the year of cultivation and cultivar
inuenced seed yield, a wider row distance with an
increasing number of defoliations increased seed yield
by around 10%, on average.
In the current work, defoliated plants were 18.3%
shorter than the non-defoliated plants for the 2-year
average, which represents an advantage for mechanised
seed harvesting. Apical bud removal was considered to
have been timed appropriately (mid-June), which was
conrmed by the intensive growth of lateral buds into
inorescences and, together, produced more seeds
than apical buds of intact plants. Based on the study
results presented, the removal of apical buds is rec-
ommended as an economically important agrotechnical
measure in the production of this widely useful eld crop
(Bassetti et al. 1998; Struik et al. 2000; Amaducci et al.
2015; Kocjan Ačko 2015, Andre et al. 2016; Fike 2016).
Acknowledgement
This research was partly supported by grants from the Slove-
nian Research Agency, research programme P4-0077. The
authors are thankful to the reviewers for their collaboration
and valuable advices, which helped to improve this manuscript.
Disclosure statement
No potential conict of interest was reported by the authors.
Notes on contributors
Dr. Darja Kocjan Ačko is an assistant professor-researcher in the
Dept. of Agronomy at the Biotechnical Faculty, University of
Ljubljana (Slovenia), where she works since 1985. Her experi-
ence areas are crop production, organic farming and nutritional
composition of plants. She has mentored over 70 Bsc and Msc
diploma thesis.
Dr. Marko Flajšman is a researcher in the Dept. of Agronomy at
the Biotechnical Faculty, University of Ljubljana (Slovenia) since
2012. His research topic is crop production, mainly hemp and
soybean.
Dr. Stanislav Trdan is a full professor-researcher in the Dept. Of
Agronomy at the Biotechnical Faculty, University of Ljubljana
(Slovenia), where he works since 1997. His research interests
are focused on environmentally acceptable plant protection,
especially in the eld of agricultural entomology. He has pub-
lished more than 80 refereed articles.
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ACTA AGRICULTURAE SCANDINAVICA, SECTION B SOIL & PLANT SCIENCE 323
... Axillary bud development depends on the production and translocation of indole-acetic acid (IAA) produced in the plant's apical meristem. In hemp, apical bud removal allowed numerous lateral buds to develop, resulting in a yield increase (Kocjan Acko et al., 2019). According to Bauer et al. (1976), removing terminal bud increased the proportion of reproductive development compared to vegetative growth, but seed yields were unchanged in Urbana, IL, USA. ...
... Terminal bud clipping resulted in higher yields than control in both years ( Figure 1). Previous studies reported similar results in sesame and hemp crops (Kokilavani et al., 2007;Kocjan Acko et al., 2019;Siddagangamma et al., 2018), whereas no such effect was observed in soybean (Bauer et al., 1976). Removal of the shoot apex (decapitation) increased yield in several legume species (Davis, 1982 and early clipping (3744 kg ha −1 ) resulted in higher yields compared to the control (2792 kg ha −1 ) in 2018. ...
... In addition, the removal of the terminal bud exerts physiological changes manifested by increased cytokinins and IAA (Ibrahim et al., 2021). Elongation and lateral growth occur once the terminal bud is clipped and the lateral buds grow into new branches (Kamble et al., 2015;Kocjan Acko et al., 2019;Singh et al., 2013). Clipping the indeterminate plants at V4 and R1 growth stages did not affect the yield loss compared with previous defoliation studies at the R5 growth stage (Fehr et al., , 1981Goli & Weaver, 1986). ...
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Soybean [Glycine max (L.) Merr.] is one of the four major staple crops and the world's most important vegetable protein source. Very little information is available on the performance, yield, and cultivars of soybean when choosing a cultivar to grow in Pacific Northwest (PNW). Of the oilseed crops, soybean appears to have the best potential to be grown at a profit (high yields) in PNW when considering the high input costs for irrigated crops. The present study was conducted to determine if terminal bud clipping would increase yields of soybean cultivars under irrigated conditions in 2‐year field experiments. Five soybean cultivars were planted in four‐row plots with rows 0.13 m apart. Plots were replicated four times with two treatments (early clipping and late clipping) and control in a randomized complete block design. Data regarding yield and growth traits were recorded using standard procedure. Soybean yield was significantly influenced by the year of production and terminal bud clipping, whereas cultivars showed no effect. Early and late clipping resulted in a 15% and 18% increase in yields in 2018, whereas late clipping resulted in a 16% yield increase in 2019 compared to control. Terminal bud clipping resulted in shorter plants and reduced lowest pod height, lodging, and maturity compared with the control. Lodging and maturity decreased with late‐maturing cultivars. Finally, results suggest that terminal bud clipping increases soybean yields. Early maturing cultivars (maturity group 0.4) are unsuitable for PNW due to the lowest pod height.
... The seed yield is differentiated not only by choosing the appropriate variety and row spacing but also by the removal of apical buds (Ačko, Darja, and Trdan 2019). Heading reduces plant height (which facilitates mechanized harvesting) and, indirectly, can also reduce the sowing norm (Bajić et al. 2022). ...
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Industrial hemp cultivation was restricted years ago in most countries, thus wiping out centuries of science and genetic resources. It is only since the 1990s that hemp has been experiencing its renaissance, which is nowadays driven by new cultivation strategies. The objective of review was to compile and summarize the latest hemp research and achievements. The focus was on research from 2018 to 2023. VOSviewer software was used to define the main research areas and trends. Most articles were discussed, among others determination average yield loss due to water stress (8.7 Mg ha⁻¹) and due to low temperatures (0.4 Mg ha⁻¹); yield increase up to 25% achieving by rejecting the smallest seeds; or definition the optimum dose of sewage sludge application (25 Mg ha⁻¹). Regarding composition and properties: identification caflanone flavonoid (selective activity against certain neoplasms); determination of 71 compounds (monoterpenes, sesquiterpenes and CBs) in the EO; determination antioxidant capacity of EO (63 mg TE g⁻¹ and 438 mg TE g⁻¹); or comparison the content of EO from monoicous, female and male inflorescences (0.10%, 0.15% and 0.07% respectively). The current possibilities of using, e.g. for phytoremediation or for bioenergy, were presented. Also knowledge gaps and the areas for future research were identified.
... Each cannabis plant has a vast assortment of active compounds that vary in composition, concentration and ratio with environmental factors, genetic background and even morphospatial position of the plant (Danziger and Bernstein, 2021). Unfortunately, there are only few rigorous studies assessing the effect of plant architecture modulation treatments and other methods for obtaining standardized cannabis cultures (Kocjan Ačko et al., 2019). As such, preclinical studies usually use SCs or purified cannabis oil and clinical studies are usually forced to use the few cannabis-based produce that are already approved and standardized. ...
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Cannabis enjoyed a “golden age” as a medicinal product in the late 19th, early 20th century, but the increased risk of overdose and abuse led to its criminalization. However, the 21st century have witnessed a resurgence of interest and a large body of literature regarding the benefits of cannabinoids have emerged. As legalization and decriminalization have spread around the world, cancer patients are increasingly interested in the potential utility of cannabinoids. Although eager to discuss cannabis use with their oncologist, patients often find them to be reluctant, mainly because clinicians are still not convinced by the existing evidence-based data to guide their treatment plans. Physicians should prescribe cannabis only if a careful explanation can be provided and follow up response evaluation ensured, making it mandatory for them to be up to date with the positive and also negative aspects of the cannabis in the case of cancer patients. Consequently, this article aims to bring some clarifications to clinicians regarding the sometimes-confusing various nomenclature under which this plant is mentioned, current legislation and the existing evidence (both preclinical and clinical) for the utility of cannabinoids in cancer patients, for either palliation of the associated symptoms or even the potential antitumor effects that cannabinoids may have.
... Nevertheless, many studies, not only concerning dioecious species, show that a tradeoff exists between generative and vegetative growth and reproduction (e.g., [50,[74][75][76]). The removal of generative buds, flowers, or fruit, in most cases, stimulates vegetative growth [1], especially in females [28], and plants with removed buds can increase their dry weight in periods when control plants cannot [55]. ...
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Dioecious species differ in the pattern and intensity of male and female reproductive investments. We aimed to determine whether female shoots deprived of generative buds show biochemical features, indicating their less-pronounced reproductive effort. For this purpose, the same branches of mature Taxus baccata females were deprived of generative organs. In the second and third years of the experiment, measurements were made in every season from the control and bud-removed shoots of females and control males. Bud removal caused an increase in nitrogen concentration almost to the level detected in the needles of male specimens, but only in current-year needles. Moreover, differences between male and control female shoots were present in the C:N ratio and increment biomass, but they disappeared when bud removal was applied to females. Additionally, between-sex differences were observed for content of phenolic compounds, carbon and starch, and SLA, independent of the female shoot reproductive effort. The study revealed that nitrogen uptake in seeds and arils may explain the lower nitrogen level and consequently the lower growth rate of females compared to males. At the same time, reproduction did not disturb carbon level in adjacent tissues, and two hypotheses explaining this phenomenon have been put forward.
... In hemp, apical dominance prevents the development of lateral shoots (branching of the inflorescence). It can be suppressed in two ways: the removal of apical meristems (Ačko et al., 2019) and the use of phytohormones that affect the height and lateral branching of plants, leading to increased seed yield, as proved in other crops, such as Solanum tuberosum L. (Kumlay, 2014), Moringa oleifera Lam. (Brockman et al., 2020). ...
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Hemp (Cannabis sativa L.) is a species sensitive to the influence of exogenous growth regulators, both in the treatment of vegetative plant tissues and in vitro culture. 1-naphthylacetic acid, indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid, kinetin, 6-benzylaminopurine (BAP), gibberellic acid (GA3), ascorbic acid and nicotinic acid of exogenous origin in the studied concentrations and doses caused a change in the content of cannabinoids in plants of the variety USO 31. Ascorbic acid, auxins and GA3 significantly reduced the content of cannabinoids, whereas nicotinic acid and cytokinins increased it. Under the influence of nicotinic acid and BAP, a higher content of cannabinoid compounds was stably manifested during each of the three years of processing and it is inherited by at least one generation of descendants. An additional method to increase the level of non-psychotropic cannabinoids may be the treatment of vegetative plant tissues with cytokinin BAP (the concentration of 40 mg/l, the consumption rate of 30 ml/m2, the phase of growth and development BBCH 51), which, in contrast to high concentrations of nicotinic acid, significantly increased the content of cannabidiol, and, to a lesser extent, tetrahydrocannabinol. The selection traits of the hemp - stem total length, mass and fiber content, seed productivity and sex determination significantly increased under treatment. A wide range of possibilities for phytohormones of exogenous origin in regulating cannabinoid accumulation, morphogenesis of hemp plants and their productivity was confirmed. Different hemp genotypes may have different responses to plant growth regulators and concentrations, which should be established in each case.
... Intriguingly, borer damage to main stems may benefit production in grain crops by stimulating branching (Small et al. 2007). Ačko et al. (2019) also reported similar and cultivar-specific responses to apical bud defoliation. ...
Chapter
Industrial hemp (Cannabis sativa L.) has considerable potential as a sustainable crop for numerous existing industrial and consumer products, with many more likely still to be realized. Much early excitement about this ancient crop arose from its assumed capacity to supply renewable feedstocks (e.g., fibers, grain, biomolecules) for numerous uses, both with little environmental “footprint” and the ability to be recycled or upcycled. Although many tout hemp as the solution for all things, such enthusiasm should be tempered by issues of historical precedent and of scale. First, the lack of research investment during the decades-long restriction in the West ensures that time will be needed to develop sustainable hemp production systems. Even as these systems are developed, there are questions about the capacity to grow sufficient amounts of hemp to meet the needs for an array—and large volume—of products. Still, there is room for guarded optimism that as the crop comes “on line,” it will receive the research needed to make the plant a viable resource for farmers and society. This review explores hemp sustainability issues in agronomic and systems contexts and touches on some of the attendant challenges to scale-up.
... T had, in general, three longer branches with terminal inflorescences, with a higher spatial distribution of the shoots and inflorescences per area (data not shown), forming a "rhombus" shape. Similar architecture modulation were also found for drug-type cannabis [29] and for fiber-type cannabis genotypes [54]. In both references, topping generated a higher number of side shoots, thus more top terminal inflorescence biomass than the control plants (not pruned). ...
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The definition of optimum harvest and pruning interventions are important factors varying inflorescence yield and cannabinoid composition. This study investigated the impact of (i) harvest time (HT) and (ii) pruning techniques (PT) on plant biomass accumulation, CBD and CBDA-concentrations and total CBD yield of a chemotype III medical cannabis genotype under indoor cultivation. The experiment consisted of four HTs between 5 and 11 weeks of flowering and three PTs-apical cut (T); removal of side shoots (L) and control (C), not pruned plants. Results showed that inflorescence dry weight increased continuously, while the total CBD concentration did not differ significantly over time. For the studied genotype, optimum harvest time defined by highest total CBD yield was found at 9 weeks of flowering. Total CBD-concentration of inflorescences in different fractions of the plant’s height was significantly higher in the top (9.9%) in comparison with mid (8.2%) and low (7.7%) fractions. The T plants produced significantly higher dry weight of inflorescences and leaves than L and C. Total CBD yield of inflorescences for PTs were significantly different among pruned groups, but do not differ from the control group. However, a trend for higher yields was observed (T > C > L).
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p> The pitcher plant ( Nepenthes mirabilis (Lour.) Druce) is a unique plant listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix II and is protected in Indonesia. Conventional propagation of N. mirabilis is difficult and takes a longer time. Therefore, in vitro culture method is proposed. This study aimed to determine the best and most economical media formulation and agar concentration for N. mirabilis micropropagation. This research has been carried out experimentally using a completely randomized two-factor factorial design . The first factor was the media formulation (full-strength Murashige and Skoog (MS), half-strength MS, half-strength MS + AB mix, and AB mix) and the second factor was agar concentrations (6, 8, and 10 g l-1). Twelve treatment combinations were obtained and repeated 5 times to produce 60 experimental units. The explants were apical microshoots (1.5 cm long with 5 leaflets). The cultures were incubated at 24 ℃ under continuous light for 16 weeks. The parameters measured included shoot emergence time, number of shoots, number of leaves, and shoot length. The data were analyzed using variance analysis followed by Duncan’s multiple range test at a 95% confidence level. The results showed that half-strength MS medium resulted in the highest number of shoots and leaves and the longest shoot length, whereas adding 8 g l-1 agar resulted in the fastest shoot emergence time. Half-strength MS medium solidified with 8 g l-1 agar could produce many N. mirabilis (Lour.) Druce microshoots to support both conservation and microfloriculture development. </p
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Cannabis sativa L. is an ancient crop used for fiber and seed production and not least for its content of cannabinoids used for medicine and as an intoxicant drug. Due to the psychedelic effect of one of the compounds, tetrahydrocannabinol (THC), many countries had regulations or bands on Cannabis growing, also as fiber or seed crop. Recently, as many of these regulations are getting less tight, the interest for the many uses of this crop is increasing. Cannabis is dioecious and highly heterogenic, making traditional breeding costly and time consuming. Further, it might be difficult to introduce new traits without changing the cannabinoid profile. Genome editing using new breeding techniques might solve these problems. The successful use of genome editing requires sequence information on suitable target genes, a genome editing tool to be introduced into plant tissue and the ability to regenerate plants from transformed cells. This review summarizes the current status of Cannabis breeding, uncovers potentials and challenges of Cannabis in an era of new breeding techniques and finally suggests future focus areas that may help to improve our overall understanding of Cannabis and realize the potentials of the plant.
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Since plant organs sense their environment locally, gradients of micro-climates in the plant shoot may induce spatial variability in the physiological state of the plant tissue and hence secondary metabolism. Therefore, plant architecture, which affects micro-climate in the shoot, may considerably affect the uniformity of cannabinoids in the Cannabis sativa plant, which has significant pharmaceutical and economic importance. Variability of micro-climates in plant shoots intensifies with the increase in plant size, largely due to an increase in inter-shoot shading. In this study, we therefore focused on the interplay between shoot architecture and the cannabinoid profile in large cannabis plants, ~2.5 m in height, with the goal to harness architecture modulation for the standardization of cannabinoid concentrations in large plants. We hypothesized that (i) a gradient of light intensity along the plants is accompanied by changes to the cannabinoid profile, and (ii) manipulations of plant architecture that increase light penetration to the plant increase cannabinoid uniformity and yield biomass. To test these hypotheses, we investigated effects of eight plant architecture manipulation treatments involving branch removals, defoliation, and pruning on plant morpho-physiology, inflorescence yield, cannabinoid profile, and uniformity. The results revealed that low cannabinoid concentrations in inflorescences at the bottom of the plants correlate with low light penetration, and that increasing light penetration by defoliation or removal of bottom branches and leaves increases cannabinoid concentrations locally and thereby through spatial uniformity, thus supporting the hypotheses. Taken together, the results reveal that shoot architectural modulation can be utilized to increase cannabinoid standardization in large cannabis plants, and that the cannabinoid profile in an inflorescence is an outcome of exogenous and endogenous factors.
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Given the growing interest in multipurpose hemp crop, eight monoecious cultivars were compared in a two-year trial for quantitative and qualitative yield in a Mediterranean environment characterized by a temperate and humid climate with hot summers. All hemp cultivars were evaluated for yield potential of (i) seed plus stem at seed maturity, and (ii) essential oil yield from inflorescences harvested at full flowering. The second goal was set to test the ability of cultivars to supply new seeds after the removal of inflorescence at full flowering. Among the cultivars, Fedora obtained the best results for seed (0.79 and 0.52 t ha−1) and vegetable oil yield (0.17 and 0.09 t ha−1) normally and with inflorescence removed plants, respectively. Futura, conversely, showed the best results for inflorescence (3.0 t ha−1), essential oil (9 L ha−1), and stem yield at seed maturity (8.34 t ha−1), as means across the two years. The cultivars studied generally reached the grain-filling stage during a period that was drier and warmer than the average of the same multi-year period, and this negatively affected seed quality. The oil fatty acid composition was mainly composed of polyunsaturated fatty acids (75% on average) and not affected by the cultivar. In conclusion, although the hemp grower should always clearly know the main production objective of the crop, the monoecious cultivars available today allow a multipurpose use of hemp crop, improving the sustainability of the cultivation activity.
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Cannabis sativa L. is an important herbaceous species originating from Central Asia, which has been used in folk medicine and as a source of textile fiber since the dawn of times. This fast-growing plant has recently seen a resurgence of interest because of its multi-purpose applications: it is indeed a treasure trove of phytochemicals and a rich source of both cellulosic and woody fibers. Equally highly interested in this plant are the pharmaceutical and construction sectors, since its metabolites show potent bioactivities on human health and its outer and inner stem tissues can be used to make bioplastics and concrete-like material, respectively. In this review, the rich spectrum of hemp phytochemicals is discussed by putting a special emphasis on molecules of industrial interest, including cannabinoids, terpenes and phenolic compounds, and their biosynthetic routes. Cannabinoids represent the most studied group of compounds, mainly due to their wide range of pharmaceutical effects in humans, including psychotropic activities. The therapeutic and commercial interests of some terpenes and phenolic compounds, and in particular stilbenoids and lignans, are also highlighted in view of the most recent literature data. Biotechnological avenues to enhance the production and bioactivity of hemp secondary metabolites are proposed by discussing the power of plant genetic engineering and tissue culture. In particular two systems are reviewed, i.e., cell suspension and hairy root cultures. Additionally, an entire section is devoted to hemp trichomes, in the light of their importance as phytochemical factories. Ultimately, prospects on the benefits linked to the use of the -omics technologies, such as metabolomics and transcriptomics to speed up the identification and the large-scale production of lead agents from bioengineered Cannabis cell culture, are presented.
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Significance It is commonly accepted that the plant hormone auxin mediates apical dominance. However, we have discovered that apical dominance strongly correlates with sugar availability and not apically supplied auxin. We have revealed that apical dominance is predominantly controlled by the shoot tip’s intense demand for sugars, which limits sugar availability to the axillary buds. These findings overturn a long-standing hypothesis on apical dominance and encourage us to reevaluate the relationship between hormones and sugars in this and other aspects of plant development.
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The renewed interest in industrial hemp (Cannabis sativa L.) is due to its large number of applications and for the wide range of agro-environmental conditions under which it can be cultivated. Two-year field experiments (2007 and 2008 growing seasons) were carried out in a Mediterranean environment of central Italy with the aim of assessing the impact of genotype, plant density and N fertilization on hemp yield, in terms of stems, inflorescences and seeds. The treatments consisted in: (a) seven genotypes (Epsilon68, Fedora17, Felina32, Ferimon, Futura75, Santhica27, and Uso31); three plant density (40, 80, and 120 plants m⁻²); two N fertilization levels (50 and 100 kg of N ha⁻¹). Physiological parameters, plant height, stem weight and diameter, inflorescence yield, seed yield and the characteristics of hemp and weed aboveground biomass were recorded. High plant density resulted in shorter plant height compared with low plant density (−41%) as the hemp plants tended to reach the reproductive stage early at high density. At full flowering, stem yield ranged from 3.4 to 8.0 t ha⁻¹ of dry matter and was positively correlated with the duration of vegetative phase, which tended to be high in the intermediate flowering genotypes (Epsilon68, Futura75 and Santhica27). Stem diameter was inversely correlated with plant density (6.7, 5.8 and 5.2 mm at 40, 80 and 120 plants m⁻², respectively). Conversely to stem yield, inflorescence and seed production proved to be higher in the early flowering genotypes (Fedora17, Felina32, Ferimon and Uso31) and increased as plant density increased. High N fertilization level had a positive impact on stems rather than inflorescence and seed yields (on average +28%, +17% and +4% in 100 kg of N ha⁻¹ compared with 50 kg of N ha⁻¹ fertilization level, respectively). Farmers should consider making a dual-purpose production of stems and inflorescences or stems and seeds, even if it is clear that yield is related to the choice of genotype. Further research should be carried out to find various genotypes as well as flexible agronomical practices that are able to improve both traditional (stems) and innovative (inflorescences and seeds) hemp yields under Mediterranean conditions.
Article
Hemp (Cannabis sativa L.) has been a species of value to humans for much of our history given its broad adaptation and multiple uses. The plant is thought to have originated in Eurasia but has been carried to much of the rest of the world, largely for use as a fiber crop. Declining needs for fiber and competition from other plant fiber sources began to reduce demands for hemp. In turn, concern over psychotropically potent forms of hemp (i.e., marijuana) would lead to the crop's effective prohibition during much of the 20th century. Growing recognition of the many uses for hemp beyond the traditional rope, cordage, and canvas has helped revive interest in the crop, and a majority of US states have reduced restrictions to allow research with the plant. Although hemp now appears on the verge of returning to favor in the United States, there will be much to learn to make it a viable crop competitive with other commodities. Variety and photoperiodicity, site suitability, end use (grain, fiber, or dual purposes) and management, and the interactions of these factors will have a strong impact on crop productivity and suitability for post-harvest use. In addition, the harvest and processing technologies (particularly for fibers and essential oils) that are needed to optimize the plant's value are limited or lacking in the United States. Disease and pest issues are often considered of little concern for hemp, but these likely will grow as the plant's range expands. Opportunities for hemp have increased with the recognition that the crop offers growing and diverse uses for not only its fibers, but for its seed grain and essential oils as well. Several studies indicate that hemp grains are nutritious as feed and food additives and its essential oils are of interest given a number of pharmacologically beneficial properties. Although full of promise given its numerous potential benefits and uses, building markets for these products will be a critical (and likely slow) part of hemp's development into a useful agronomic species for US growers.
Article
Interest in hemp as a multi-purpose crop is growing worldwide and for the first time in 2015 it was cultivated in Europe on more than 20.000 ha as a dual-purpose crop, for the seeds and for the fibre. In the present study, fibre and seed productivity of 14 commercial cultivars were tested in four contrasting European environments (Latvia, the Czech Republic, France, Italy). At full flowering, the stem yield ranged from 3.7 Mg ha−1 to 22.7 Mg ha−1, the bast fibre content ranged from 21% to 43%, and the bast fibre yield ranged from 1.3 Mg ha−1 to 7.4 Mg ha−1. When harvesting was postponed from full flowering until seed maturity, the stem yield of monoecious cultivars significantly increased but in dioecious cultivars it decreased at all tested sites, except for Italy. Only the early cultivars Fedora 17 and Markant produced seed in the most northern location Latvia. The seed yield ranged from 0.3 Mg ha−1 to 2.4 Mg ha−1 in Italy, France and the Czech Republic. The cultivar effect on stem and seed yield was mainly determined by the genetic variation in time of flowering. Stem yield at full flowering was strictly related to the duration of the vegetative phase while seed yield was lowest in the late flowering cultivar. The late cultivar CS is suitable for stem and fibre production as it had the highest stem yield at full flowering in all locations. Both Fedora 17 and Futura 75 are candidate cultivars for dual-purpose production in Italy, France and the Czech Republic, with Fedora 17 being more suitable for seed production and Futura 75 for fibre production.
Article
Larger plants tend to be more branched than smaller plants in some species. The nutrient diversion hypothesis for apical dominance proposes that the apical meristem of a plant acts as a strong metabolic sink, depriving nutrients from latent axillary meristems and thereby promoting strong directional (e.g., vertical) growth with little branching. Hence, larger plants may be more branched because they may have more resources that cannot all be sequestered by the apical meristem, leaving an excess available for branch production from axillary meristems. However, larger plants may also be more branched because they incur greater damage from herbivores that disrupt apical dominance. Hence, the availability of nutrients may be a confounding factor for studies of response to herbivory through effects on apical dominance. In order to distinguish these effects, we applied nutrient and water supplementation to two natural populations of Verbascum thapsus in which herbivores were excluded to test the hypothesis that nutrition level, including water, plays a role in determining the extent of branching. We used a full factorial experimental design involving three levels of resources (control, water, and water with fertilizer) and shoot apex removal. Both a single-season experiment and a two-season experiment were performed, the latter involving only the three levels of resources as treatments. Branching was increased by shoot apex removal and was enhanced by the addition of nutrients but only in clipped plants. Thus, the nutrient diversion theory does not solely explain the strong apical dominance exhibited by V. thapsus, an alternative hypothesis involving weevil herbivory is indicated that may further explain the growth form and branching patterns in this species.