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Comparison of the performance of native and invasive plants of Senecio vulgairs L.
Dandan Cheng1, *, Viet Thang Nguyen 2,3, Noel Ndihokubwayo 2,4
1 State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences,
Wuhan, Hubei, 430074, China
2 School of Environmental Studies, China University of Geosciences (Wuhan), Wuhan, Hubei, 430074,
China
3 Faculty of Biology, Thai Nguyen University of Education, No. 20, Luong Ngoc Quyen Street, Thai
Nguyen City, Vietnam
4 Ecole Normale Supérieure, Département des Sciences Naturelles, Boulevard du 28 Novembre, B.P
6983 Bujumbura, Burundi
* Corresponding author, E-mail:[email protected]
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Abstract
According to the Evolution of Increased Competitive Ability (EICA) hypothesis and Enemy
Release Hypothesis (ERH), comparing the plants from the same species, individuals from the
invasive range will outperform those from the native range. However, not all recent studies
support the prediction of these two hypotheses. In this study, we sought to test the prediction
by comparing the performance of common groundsel (Senecio vulgaris) taken from native
(Europe) and invasive (China) ranges. Those plants were grown in a greenhouse and in a
common garden, and harvested with various vegetative and reproductive traits measured. We
found that although the plants grown in the common garden grew and reproduced better than
those grown in the greenhouse, the invasive plants outperformed the native plants in relation
to most vegetation parameters (except plant height) and reproduction in both experiments; and
generally, the invasive plants allocated more proportion of biomass to root than the native
plants. However, the proportion of biomass allocated to reproductive organ and relative dry
matter content were the same between the native and invasive plants, no matter among the
plants grown in the greenhouse or in the common garden. Our study partially supported the
predictions of the EICA and ERH and indicated that evolution might have happened to S.
vulgaris invasive to China.
Key words: Evolution of Increased Competitive Ability (EICA) hypothesis, Enemy Release
Hypothesis (ERH), reproductive allocation, root/shoot ratio, dry matter content.
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1. Introduction
Biological invasions are currently one of the most important environmental issues brought by
globalization (Miller et al., 2010) and one of the major threats to biological diversity (Wilcove
et al., 1998). Facilitated by human activities intentionally or unintentionally, the biological
invasions have been the result of species exchanges between many regions throughout the
world (Rejmánek 1996; McKinney & Lockwood 1999; Garcia-Serrano et al., 2007). The
increase in threats caused by invasive species on ecosystems have led to many studies focused
on why some species significantly succeed in new environments where they are not native
(Callaway & Ridenour 2004; van Kleunen et al., 2010; Firn et al., 2011). A number of
hypotheses about invasive mechanism have been put forward from the aspects of the
interactions between plants and the biotic factors in the environments.
The Enemy Release Hypothesis (ERH) postulated that invasive plants benefit from a direct
release from natural enemies resulting in an increase in distribution and abundance (Keane &
Crawley 2002). In the absence of specialist herbivores in introduced ranges, exotic plants are
also less likely to be attacked by generalist herbivores in introduced ranges (Inderjit 2012).
Hence, resources previously allocated to plant defense in the native range might reallocate to
growth or reproduction of the exotic plant, so leading to enhanced competitiveness, as
suggested by the Evolution of Increased Competitive Ability (EICA) hypothesis (Blossey &
Notzold 1995). Moreover, the EICA emphasize that the different reallocation pattern could be
kept when the native and invasive plants of the same species were under identical growing
conditions. These combining of the two hypotheses (ERH/EICA) would improve
understanding of the phenomenon of biological invasions (Joshi & Vrieling 2005; Kambo &
Kotanen 2014).
To test the EICA hypothesis, comparative studies between native and introduced populations
of the same species are useful (McKenney et al., 2007; Handley et al., 2008; Zou et al., 2008;
Turner et al., 2014). The plant performance can be measured by various traits such as dry
biomass and plant height (Blossey & Notzold 1995), growth rate (Daehler 2003; Traveset et
al., 2008), fecundity, survival (Daehler 2003), etc. Studies in line with the EICA found that
invasive species performed better than the invasive ones (Leger & Rice 2003; Wolfe et al.,
2004; Blumenthal & Hufbauer 2007; Caño et al., 2008; Oduor et al., 2011; Turner et al. 2014).
However, some studies found that the performance of invasive plants depends mainly on the
identity of the species (Traveset et al. 2008), and the pattern that invasive species perform
better than the native one in their new ranges is not universal (Parker et al., 2013; Seipel et al.,
PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2012v1 | CC-BY 4.0 Open Access | rec: 2 May 2016, publ: 2 May 2016
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2015). Therefore, the EICA does not hold for all cases of invasive plant species (van Kleunen
& Schmid 2003; Bossdorf et al., 2004; McKenney et al. 2007). It still remains unanswered
questions related to what attributes make some species more invasive.
Common groundsel (Senecio vulgaris, Asteraceae), a herbaceous plant native to Europe, is
suggested to be of autotetraploid originating from Senecio vernalis (2n = 20) in southern
Europe (Kadereit 1984). Senecio vulgaris can complete its life cycle in a short time, 8 weeks;
and an average of 38300 seeds are produced in each of its generation (Kempen & Graf 1981).
Genetic variability, short generation time, the capacity for large – scale seed production and
rapid germination throughout the year, are all characteristics of successful weed invaders
(Holzmueller & Jose 2009 and references therein). The ingestion of S. vulgaris and other
species of this genus has been implicated as a possible cause of liver toxicity in livestock
(Wiedenfeld 2011), because the plants of S. vulgaris contains high amount of pyrrolizidine
alkaloids which cause liver toxicity in livestock and human beings (Borstel et al., 1989).
Some biotype of S. vulgaris can resist herbicides such as simazine, atrazine (Radosevich &
Devilliers 1976), atrazine, bromacil, pyrazon, buthidazole (Fuerst et al., 1986) and linuron
(Beuret 1989). Therefore, S. vulgaris is considered as a troublesome weed, especially in
horticulture where frequent cultivation occurs (Holt & Lebaron 1990).
Senecio vulgaris, first recorded in China in 19th century, mainly distributes in north – eastern
and south – western China, and may cause great damages to agricultural plants (barley, rape,
strawberry, etc.), fruit trees and lawns in low latitudes in central China (Li & Xie 2002; Xu et
al., 2012). The morphology of S. vulgaris plant is similar to some other Senecio species used
as Chinese traditional medicinal plants, so it could bring high risk to health if they are used as
medicine by mistake (Yang et al., 2011).
In this study, we carried out experiments in a greenhouse and in a common garden with S.
vulgaris plants from the native (Europe) and invasive (China) range. We investigated whether
the hypotheses ERH and EICA can explain the biological invasion of S. vulgaris in China by
comparing the performance between native and invasive S. vulgaris plants under the identical
growing conditions. We addressed the following questions: (1) Do invasive S. vulgaris plants
grow and reproduce better than the native ones? (2) Are there any differences between native
and invasive plants in relation to reproduction and underground/above ground allocation? (3)
Are there any differences between native and invasive plants in relation to dry matter content?
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2. Materials and Methods
2.1. Plant resources
Six native and six invasive populations of S. vulgaris were sampled in Europe and China in
2012 and 2013 (Table 1). Three mother plants were chosen from each population, and the
seeds were collected from the mother plants. The seeds were air – dried and stored at room
temperature in paper bags until sowing. The collected seeds were grown for the second
generation in a climate room, and resulting seeds of the first flower head per plant were used
in the experiment. The maternal effects in S. vulgaris would be strong and influence seeds
germination and plant size (Aarssen & Burton 1990; Figueroa et al., 2010). . We would like to
remove the maternal effects by using the seeds from second generation plants grown in the
climate room, instead of those collected from field.
2.2. Experimental design
We used 24 good seeds for each mother plant in this study. The total of selected seeds was 24
× 12 × 3 = 864. Four seeds of each mother plant were sown in one cell of the 12 cell boxes
(size of one cell: 3.7 × 3.7 × 6 cm) filled with a moistened substrate of coconut peat
(Zhenjiang Jingkou District Green Island Horticultural Development Center, Zhenjiang,
Jiangsu, China) mixed with sand (1:1 by volume). The sowed seeds were moistened every day
by using a small sprayer, and were germinated in a climate chamber (12h dark/12h light at
24oC, relative humidity 80%). The first seedlings appeared two days after seed sowing.
Seedlings emergence was carefully observed and recorded every day. The seedlings were
transferred to the greenhouse at the fourth day after sowing. Then, one week later, seedlings
that had two true leaves were transplanted, each seedling was grown in one pot (8 × 8 × 9 cm)
filled with substrate prepared as described above.
The 0.5 liter pots containing seedlings were randomly put in blocks under a roof of net to
protect them from insects (Figure S1). The seedlings were watered one time within two days.
When plants had 5 – 8 leaves, two groups of seedlings similar in size were formed. To form
each group, 3 plants from each mother plant were chosen (Figure S2). The total plants were
108 and were randomly placed in each group. One group was left in the greenhouse and the
other one was placed in the common garden. The plants were watered 3 times every week.
The plants in the greenhouse were treated with a solution of liquid pesticide Leguo 0.19%
(Lianyungang Dongjin Chemical Co., Ltd., Jiangsu, China) 2 – 3 times per week with a small
sprayer.
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The experiment was conducted from 2nd April to 4th June in 2014. The average daily
temperature of this period was: 21.2oC with a maximum of 32oC on sunny days and minimum
of 11oC during night. The rainfall averaged 156 mm in April, 114 mm in May, and 51 mm in
June; with the total of 31 rainy days, 27 cloudy days and 6 sunny days.
2.3. Plant harvesting and measurement
Plants were harvested individually when each of them had the first matured capitulum, or
when any plants were died because of rain or disease. Various vegetative and reproductive
characters were measured at harvest. We counted the number of leaves and branches of each
plant, measured height (the distance from the base of the stem to the apical meristem of a
plant). Each plant was cut into three parts: (1) stem and leaves, (2) root and (3) capitula. The
stem and root of each plant were separated from its root crown by scissors. The capitula were
separated at their stalks. The fresh weights of the three parts of each plant were separately
measured at harvest by using a scale (AdventureTM OHAUS). The plant samples were dried at
50oC in 2 consecutive days by a heat dry machine and then the dry weight of each samples
were separately measured by another scale (METTLER TOLEDO) due to its high sensitivity
to low weight.
2.4 Data analysis
The vegetative characters analyzed in this study were: height, number of branches and leaves;
fresh and dry weight of shoot, root, and whole plant. The reproductive characters were: the
number of capitula, fresh and dry weight of capitula. The ratio between root fresh/dry weight
and shoot fresh/dry weight were computed to assess how the plants allocated their resources
to biomass of shoot and root. The proportions between capitula fresh/dry weight and whole
plant fresh/dry weight were also calculated to assess how the plants allocated their biomass to
reproductive organ. The dry matter content of the plant was analyzed by using the percentage
of shoot/root dry weight to shoot/root fresh weight.
To check the differences between ranges, populations and mother plants, plant trait
parameters were analyzed with a three – level nested ANOVA with range, population nested
within range, and mother plant nested within population. The nested ANOVA tests were
conducted for plants grown inside the greenhouse and in the common garden, separately.
The data on the vegetative and reproductive characters were analyzed with Principal
component analysis (PCA) to show the differences between plants grown in the greenhouse
and those grown in the common garden. The results of the PCA also showed the differences
between the native and invasive plants grown in the identical conditions.
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All analyses were performed in R version 3.1.2 (R Core Team 2014).
3. Results
3.1. Difference between the greenhouse and common garden experiments
We used Principal component analysis (PCA) to examine the difference between plants
grown in the greenhouse and in the common garden. PC1 explained 51%, PC2 explained 23%
and PC3 explained 9% of the variation in the data. More than 90% of the total variation was
accounted for the first 5 PCs. The plot with PC1 and PC2 and loading plots showed that plants
grown in the two places are different in relation to most performance parameters (Figure 1).
In general, the plants grown in the common garden perform better than those grown in the
greenhouse.
3.2. Greenhouse experiment
Among the plants grown in the greenhouse, the invasive plants were bigger than the native
ones, because the plants from the invasive populations produced more number of branches
and leaves, and more vegetative biomass (fresh/dry weight of shoot, root, and whole plant)
than those from native populations. Actually, of all the vegetative parameters, only height was
not significantly different between the native and invasive plants. Moreover, the invasive
plants had more reproduction output than the native ones in relation to the number and
fresh/dry weight of capitula (Table 2, Figure 1).
The invasive and native plants did not differ in respect of reproductive allocation (the
proportion of biomass allocated to reproductive organs), root/shoot ratio in fresh biomass, and
dry matter content. However, the invasive plants had significantly higher root/shoot ratio in
dry biomass than the native ones (Table 2).
Generally, significant differences were found at the population level but not at the mother
plant level. Plants from each population were different in vegetative parameters (height,
number of branches and leaves, fresh/dry weight of shoot, root and whole plant) and
reproductive output (number of capitula and fresh/dry weight of capitula). However, those
trait parameters did not differ between mother plants within populations (Table 2).
3.3. Common garden experiment
The native and invasive S. vulgaris plants did not differ again in relation to their height. The
number of branches leaves and capitula were not significantly different between the invasive
and native plants as well. However, the invasive plants produced more vegetative and
reproductive biomass than the native ones.
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No significant difference was found between the native and invasive plants in respect of
reproductive allocation or relative dry matter content. However, the invasive plants had
significantly higher root/shoot ratio than the native ones (Table 3).
4. Discussion
Although the plants grown in the common garden performed better than those grown in the
greenhouse, when we compared the native and invasive plants for the two experiments
separately, the trends pattern are the same: higher vegetative, reproductive biomass and
root/shoot ratio was found in invasive plants, and no significant difference were found in
relation to the reproduction allocation and dry matter content.
Generally, biomass is a good parameter to investigate plant performance and competitive
ability of plant (Gaudet & Keddy 1988; Zou et al. 2008). . Hence, increasing of the vegetative
and reproductive biomass in invasive S. vulgaris plants indicates that the invasive plants
performed better and had higher competitive ability than the native plants. Higher vegetative
and reproductive biomasses in invasive populations have been also reported in some previous
studies on Senecio genus. For instance, in the climate room and experimental garden, invasive
populations of S. jacobaea (from North America, Australia, and New Zealand) displayed
significantly higher vegetative and reproductive biomass compared to the native S. jacobaea
populations (from Europe) (Joshi & Vrieling 2005). The invasive genotypes of S. pterophorus
from Spain showed higher dry biomass than those from native range (from South Africa)
(Caño et al. 2008).
The greater root/shoot ratio of the invasive plants suggests that they could probably have
higher potential of regrowth than the native ones. And it also indicated that the invasive plants
could produce more pyrrolizidine alkaloids (PAs), because PAs are known to be produced in
root of S. vulgaris before they are translocated to other parts of a plant (Hartmann et al., 1989;
Sander & Hartmann 1989). Hence, it is predicted that the invasive populations could have
higher potential of regrowth and defense against generalist herbivores compared to the native
ones.
Reproductive allocation (proportion of biomass allocated to reproductive organs) was not
different between ranges in both experiments, suggesting that although the invasive
populations reproduced more vigorous than the native ones, the invasive populations focused
on increasing the competitive ability rather than the reproductive organs. Dry matter content
is considered as a mechanical defense product (Doorduin & Johanna 2012). Hence, dry matter
content of plants is considered as quantitative defense against herbivores. The result shows
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that there was no difference in the quantitative defense between the two origins. This
suggested that there might be no shifting defense evolution happened in invasive S. vulgaris
in China.
The genetic variation happened to S. vulgaris in introduced ranges in relation to habitat type
and population size (Müller-Schärer & Fischer 2001); and S. vulgaris originated from
different habitats also revealed a genetic differentiation among habitats (Leiss & Müller-
Schärer 2001). The species used in the present study, Senecio vulgaris, was first recorded in
China in 19th century (Xu et al. 2012). This long period of time could provide a chance for
natural selection to act on S. vulgaris in the invasive range. The native S. vulgaris also
underwent natural selection in the native range which is different from the natural selection in
the invasive range. In addition, its short life – span in 8 weeks in good conditions (Kempen &
Graf 1981) could bring a good chance for the natural selection with a strong effect on the S.
vulgaris. The difference in natural selection between ranges led to the genetic differentiation
in some characteristics of plants. In our study case, the significant difference in vegetative,
reproductive characters and proportion of biomass allocated to root/shoot among ranges could
be a result of genetic differentiation which may play an important role in the invasion success.
Therefore, it is expected that a possible chance of evolution happened to the invasive
populations of S. vulgaris.
Results of this study are consistent with the predictions of the EICA and ERH, suggesting that
S. vulgaris in China might evolve to grow and reproduce vigorously, which contributes to the
invasion success of S. vulgaris in introduced ranges. Further studies would confirm this by
genetic analysis of the origination of the invasive populations of S. vulgaris in China and the
genetics base of performance, especially of growth of this species. We also plan to investigate
the PA variation and the resistance to herbivories among the native and invasive S. vulgaris.
Acknowledgements
Colleagues are thanked for their help during the experiment carried out at Hubei Academy of
Forestry, Wuhan city, Hubei province, China. Colleagues and students in the School of
Environmental Studies in CUG and Institution of Biology in Leiden University are also
thanked for their help in seed collecting, plant rearing and harvesting plants.
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Table 1. Information of the locations and collected times for Senecio vulgaris seeds
Range Country Location Coordinates Collected time
Native
Spain Barcelona Lat 41.67 Lon 2.73 06/2012
Switzerland Fribourg Lat 46.79 Lon 7.15 07/2012
The Netherlands Leiden Lat 52.17 Lon 4.48 10/2013
Germany Potsdam Lat 52.40 Lon 13.07 06/2012
Poland Puławy Lat 51.40 Lon 21.96 07/2012
Scotland St. Andrews Lat 56.33 Lon -2.78 05/2012
Invasive China
Fuyuan, Heilongjiang Lat 48.37 Lon 134.28 06/2013
Hegang, Heihongjiang Lat 47.33 Lon 130.30 06/2013
Siping, Jilin Lat 43.17 Lon 124.38 07/2013
Tongjiang, Heihongjiang Lat 47.98 Lon 133.17 06/2013
Yichun, Heihongjiang Lat 47.72 Lon 128.79 07/2013
Lijiang, Yunnan Lat 26.89 Lon 100.23 09/2013
PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2012v1 | CC-BY 4.0 Open Access | rec: 2 May 2016, publ: 2 May 2016
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Table 2. Results of nested ANONA tests and mean values for the growth and reproductive traits measured on the native and invasive Senecio
vulgaris plants grown in the greenhouse.
F value of source of variation Mean value for each
parameter
Range Population (in range) Mother Plant (in population) Invasive Native
Height (cm) 1.98 ns 4.44*** 1.33 ns 28.38 27.02
Branches 23.48*** 5.03*** 1.37 ns 10.17 6.81
Number of Leaves 24.09*** 5.44*** 0.72 ns 39.20 28.52
Capitula 14.81*** 6.55*** 1.11 ns 44.37 33.13
Capitula 13.55*** 2.41* 0.97 ns 1.20 0.84
Fresh weight Shoot 26.07*** 3.14** 0.56 ns 7.66 5.38
(g) Root 37.75*** 4.11*** 1.03 ns 1.81 1.16
Whole plant 28.70*** 3.46*** 0.59 ns 10.67 7.38
Capitula 17.01*** 2.67** 1.13 ns 0.20 0.13
Dry weight Shoot 36.86*** 4.07*** 0.81 ns 0.70 0.46
(g) Root 43.15*** 4.60*** 0.94 ns 0.13 0.08
Whole plant 34.76*** 3.93*** 0.80 ns 1.03 0.68
Proportion Fresh weight: Capitula/ whole plant 0.53 ns 1.82ns 2.28** 0.11 0.11
Dry weight: Capitula/whole plant 1.46 ns 3.26** 1.75* 0.19 0.18
Ratio Fresh weight: Root/shoot 1.75 ns 1.27 ns 1.14 ns 0.24 0.22
Dry weight: Root/shoot 5.51* 1.44 ns 1.89* 0.19 0.17
Percentage
(%)
Shoot dry weight /shoot fresh weight 0.67 ns 1.69 ns 1.13 ns 9.35 8.96
Root dry weight/root fresh weight 0.01 ns 0.2 ns 0.3 ns 8.16 10.43
Level of significance: *p < 0.05. **p < 0.01. ***p < 0.001; ns: not significant
Degree freedom of source of variation (Df): Range: 1; Population (in range): 10; Mother Plant in population): 24.
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Table 3. Results of nested ANONA tests and mean values for the growth and reproductive parameters of the native and invasive Senecio vulgaris
plants grown in the common garden.
F value of source of variation Mean value for each
parameter
Range Population (in range) Mother Plant (in population) Invasive Native
Height (cm) 0.28 ns 1.94 ns 1.74* 26.11 26.65
Branches 0.32 ns 2.43* 1.06 ns 8.72 9.06
Number of Leaves 3.12 ns 1.67 ns 1.13 ns 28.91 25.93
Capitula 1.24 ns 1.67 ns 1.20 ns 32.35 29.98
Capitula 8.60** 1.75 ns 1.27 ns 1.66 1.34
Fresh weight Shoot 14.16*** 1.52 ns 1.98* 5.45 4.56
(g) Root 31.79*** 3.81*** 1.47 ns 3.06 2.13
Whole plant 22.04*** 2.43* 1.67* 10.17 8.02
Capitula 9.64** 2.28* 1.44 ns 0.34 0.28
Dry weight Shoot 23.34*** 1.69 ns 1.76* 0.89 0.71
(g) Root 57.61*** 3.83*** 1.52 ns 0.33 0.22
Whole plant 26.59*** 2.58** 1.84* 1.54 1.20
Proportion Fresh weight: Capitula/Whole plant 0.09 ns 0.95 ns 1.57 ns 0.16 0.16
Dry weight: Capitula/Whole plant 0.05 ns 1.80 ns 1.42 ns 0.22 0.22
Ratio Fresh weight: Root/shoot 13.06*** 3.21** 1.43 ns 0.57 0.47
Dry weight: Root/shoot 12.82*** 1.95 ns 1.40 ns 0.38 0.31
Percentage
(%)
Shoot dry weight/shoot fresh weight 0.31 ns 1.11 ns 1.14 ns 15.99 15.77
Root dry weight/root fresh weight 0.00006 ns 0.003 ns 0.012 ns 10.92 10.77
Level of significance: *p < 0.05. **p < 0.01. ***p < 0.001; ns: not significant
Degree freedom of source of variation (Df): Range: 1; Population (in range): 10; Mother Plant (in population): 24.
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Figure 1. The scoring and loading plots of the Principle component analysis (PCA) of all variables measured from Senecio vulgaris plants
grown in a greenhouse and common garden. a: Scoring plot with PC1 and PC2; b: loading plot. Empty dots: plants grown in the greenhouse; solid
dots: plants grown in the common garden. red dots: invasive plants; black dots: native plants. Propotion1: biomass of capitula in whole plant by
fresh weight; Propotion2: biomass of capitula in whole plant by dry weight. Ratio1: root/shoot ratio in fresh weight; Ratio2: root/shoot ratio in dry
weight.
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Supplementary Materials
Figure S1. Seedlings prepared for the study
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(A)
(B)
Figure S2. Senecio vulgaris grown in the two different conditions
A: group treated with a solution of liquid pesticide in a greenhouse
B: group grown outside the greenhouse
PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2012v1 | CC-BY 4.0 Open Access | rec: 2 May 2016, publ: 2 May 2016