Acta agriculturae Slovenica, 119/4, 1–10, Ljubljana 2023
doi:10.14720/aas.2023.119.4.2762 Original research article / izvirni znanstveni članek
Using pyrimidinecarboxylic acids as growth stimulants for Rhododen-
dron ledebourii Pojark and Rhododendron smirnowii Trautv.
Tatiana V . VOSTRIKOV A
 1, 2
, Andrey Yu. POTAPOV
 1
, Nadezhda V . STOLPOVSKAYA
 1
, Khidmet S. SHI-
KHALIEV
 1
Received July 05, 2022; accepted October 19, 2023.
Delo je prispelo 5. julija 2022, sprejeto 19. oktobra 2023
1 Voronezh State University, Voronezh, Russian Federation
2 Corresponding author, e-mail: tanyavostric@rambler.ru
Using pyrimidinecarboxylic acids as growth stimulants 
for Rhododendron ledebourii Pojark and Rhododendron 
smirnowii Trautv.
Abstract: Synthesised organic compounds of pyrimidi-
necarboxylic acids are characterised by high biological activ-
ity, even when their concentrations are low. These compounds, 
when applied to the seeds of Rhododendron, a genus of woody 
plants, with concentrations of 0.01, 0.05, and 0.1 %, stimulate 
the growth of the plants. The effect is more obvious 3 months af-
ter the start of the experiment, rather than 7 months after. Thus, 
Rhododendron ledebourii Pojark. seedlings grew by 13.3-33.5 %, 
and Rhododendron smirnowii Trautv. seedlings grew by 29.6-
48.1 %. Rhododendron ledebourii and Rhododendron smirnowii 
seedlings demonstrated similar direct correlations: when the 
concentration of 2-benzylamino-4-methyl-pyrimidine-5-car-
boxylic acid and 4-methyl-2-morpholin-4-pyrimidine-5-car-
boxylic acid (for Rhododendron ledebourii seeds only) rose from 
0.01 to 0.1 %, the height of the seedlings increased. It is suggest-
ed using 4-methyl-2-piperidin-1-yl-pyrimidine-5-carboxylic 
acid, 2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid, 
and 4-methyl-2-morpholin-4-pyrimidine-5-carboxylic acid at 
concentrations of 0.01, 0.05, and 0.1 % as growth stimulants for 
the species of Rhododendron genus.
Key words: growth stimulants, synthesized organic com-
pounds, pyrimidine carboxylic acids, Rhododendron
Uporaba pirimidin karboksilne kisline kot rastnega vzpod-
bujevalca za vrsti rododendrona, Rhododendron ledebourii 
Pojark in Rhododendron smirnowii Trautv.
Izvleček: Za sintetične organske spojine pirimidin kar-
boksilnih kislin je značilna velika biološka aktivnost, tudi pri 
majhnih koncentracijah. Tretiranje semen rododendrona s 
temi spojinami v koncentracijah 0,01; 0,05 in 0,1 %, stimulira 
rast rastlin. Ta učinek je jasnejši 3 mesece po začetku poskusa 
kot po 7 mesecih. Sejanke vrste Rhododendron ledebourii Po-
jark. so rastle pri koncentracijah 13,3-33,5 %, sejanke vrste 
Rhododendron smirnowii Trautv. pa pri koncentracijah 29,6-
48,1 % stimulanta. Sejanke obeh vrst so se na tretiranje odzvale 
podobno in sicer: kadar se je koncentracija 2-benzilamino-
4-metil-pirimidin-5-karboksilne kisline in 4-metil-2-morfolin-
4-pirimidin-5-karboksilne kisline (le za semena vrste Rhodo-
dendron ledebourii) dvignila iz 0,01 na 0,1 %, se je višina sejank 
povečala. Priporočamo uporabo 4-metil-2-piperidin-1-il-pi-
rimidin-5-karboksilne kisline, 2-benzilamino-4-metil-pirimi-
din-5-karboksilne kisline in 4-metil-2-morfolin-4-pirimidin-
5-karboksilne kisline v koncentracijah 0,01; 0,05 in 0,1 % kot 
rastne vzpodbujevalce za vrste iz rodu Rhododendron. 
Ključne besede: rastni vzpodbujevalci, sintetične organ-
ske spojine, pirimidin karboksilne kisline, Rhododendron

Acta agriculturae Slovenica, 119/4 – 2023 2
T. V . VOSTRIKOV A et al.
1 INTRODUCTION
Over the past few years, the cultivation of plants has 
been facing a number of challenges, including a dramatic 
increase in temperatures, lack of soil water, and the need 
for more resistant and hardy plants, which grow even un-
der the harshest conditions. It is therefore vital to mini-
mise the time required for the growth of planting mate-
rial, which can be done using growth and germination 
stimulants, including synthesised chemical compounds 
Pentelkina, 2003; Vasin et al., 2008, 2009; Ostroshenko 
and Ostroshenko, 2011; Schuchka, 2006; Baranova, 
2013a; Khodaei-Joghan et al., 2018; Nesterkina et al., 
2019) and other original modes (Shibaeva et al., 2018). 
It has been noted high biological activity of pyridines 
and pyrimidines. For example, 1, 4-dihydropyridines 
have received large attention because of their fundamen-
tal role in different biological processes (Goldmann and 
Stoltefuss, 1991; Litvinov, 1998; Balalaie et al., 2008). It 
has been reported about the wide biological activity of 
dihydropyridine derivatives (Ghoneim and Assy, 2015). 
But a promising area of the study, related to the growing 
need for the development of effective and safe drugs, is 
the synthesis of new heterocyclic systems, containing a 
pyrimidine fragment. Pyrimidine fragments and pyrimi-
dine base are included in DNA. So pyrimidine deriva-
tives show different biological activity. There is another 
mode for applying chemical compounds, containing py-
rimidine fragments, for instance, as mutagens.
The composition of diethyleneimide-2-amidopy-
rimidyl phosphoric acid (phosphazine, phosphomid, syn. 
phosphemide - phospemidum) includes two ethylene 
imine groups connected to phosphorus and a pyrimidine 
base. Ethyleneimine causes mutations, the pyrimidine 
base is included in the chromosome during DNA syn-
thesis, determining the specificity of the effect (Weisfeld, 
2015). Laboratory seed germination and morphomet-
ric parameters of seedlings (length of roots and shoots, 
number of leaves) were studied after seed treatment with 
heterocyclic sulfur-containing compounds on the exam-
ple of woody plants (Vostrikova et al., 2020) and agricul-
tural crop (V ostrikova et al., 2021). As the composition of 
the phosphemide mutagen, pyrimidine-carboxylic acids 
contain a pyrimidine base. Sulfur (in the composition of 
alkylating compounds: diethyl- and dimethylsulfonate, 
ethylmethanesulfonate) enhances biological activity. It is 
known that mutagens in low concentration have stimu-
lating effect for plant objects. A necessary working step 
is the determination of concentration ranges (Bome et 
al., 2017).
Over the last years, attempts have been made to syn-
thesise new organic compounds, derivatives of pyrimi-
dines (Dlugosz and Dus, 1996; Elkholy and Morsy, 2006; 
El-Gazzar et al., 2009; Marjani et al., 2011; Tkachenko et 
al., 2013, 2018; Azizian et al., 2014), which can be used 
as growth regulators. Such compounds should be more 
effective than the existing commercial formulations be-
cause of their different concentrations that may have ei-
ther stimulating or inhibiting activity (Dlugosz and Dus, 
1996; Gavrilov et al., 1988; Litvinov, 1998; Brown et al., 
2004; Balalaie et al., 2008; Moiseeva et al., 2012a).
The effect of pyrimidine carboxylic acids on seed 
germination and plant height was studied using another 
annual flower – spreading marigold (Tagetes patula L.) 
(Vostrikova et al., 2012; Kalaev et al., 2013a). However, 
the effect of pyrimidinecarboxylic acids on the growth of 
other plants has not been studied yet. 
Up to the present time, there have also been no stud-
ies considering the results of application of synthesised 
chemical compounds of pyrimidinecarboxylic acids 
to the seeds of woody plants, which grow much slower 
than annual plants. It is therefore of great importance to 
conduct a longitudinal study and measure the height of 
ornamental woody plants over long time intervals (eg. 3 
and 7 months after the application of the growth regula-
tor) in order to determine, whether the growth stimulat-
ing effect lasts or deteriorates over time.
Two ornamental woody plants, namely Rhododen-
dron ledebourii Pojark. and Rhododendron smirnowii 
Trautv. were used. The long history of studying these 
species (Moiseeva et al., 2012b; Baranova, 2013b) at the 
B.M. Kozo-Polyansky Botanical Garden of Voronezh 
State University has demonstrated, that Rhododendron 
ledebourii is a winter-hardy, drought-resistant, and fruit-
bearing shrub. Rhododendron smirnowii is also quite 
winter-hardy, though less drought-resistant. It also grows 
slower than Rhododendron ledebourii (Alexandrova, 
2003; Vostrikova, 2011). It has been reported about the 
antioxidant activity in Rhododendron leaves, connec-
tions between this characteristic in maternal plant and 
the cytogenetic structures in the seedlings of the Rho-
dodendron species (Vostrikova et al., 2022). Cytogenetic 
polymorphism of seed progeny of introduced plants has 
been studied on the example of Rhododendron ledebourii 
(Burmenko et al., 2018). It has been revealed the high 
seeds quality. So the representatives of the Rhododendron 
genus are valuable resource plant.
The aim of our research was to study the effect from 
pre-sowing seed treatment of the following woody plants: 
Rhododendron ledebourii and Rhododendron smirnowii 
by pyrimidine carboxylic acids. 
2 MATERIALS AND METHODS
The research was conducted at the B.M. Kozo-Pol-

Acta agriculturae Slovenica, 119/4 – 2023 3
Using pyrimidinecarboxylic acids as growth stimulants ...
yansky Botanical Garden of Voronezh State University 
(geographic coordinates: 39°22’ N, 51°40’ E; 168.2 metres 
above sea level). 
It has been focused on the effect of synthesised or-
ganic compounds of pyrimidinecarboxylic acids on the 
height of seedlings of Rh. ledebourii, and Rh. smirnowii. 
The following compounds were used: 4-methyl-2-pi-
peridin-1-yl-pyrimidine-5-carboxylic acid, 2-ben-
zylamino-4-methyl-pyrimidine-5-carboxylic acid, and 
4-methyl-2-morpholin-4-pyrimidine-5-carboxylic acid 
synthesised at the Department of Organic Chemistry of 
Voronezh State University.
Prior to the sprouting process, the seeds of Rh. lede-
bourii and Rh. smirnowii were soaked in a water suspen-
sion of the above listed compounds with concentrations 
of 0.01 %, 0.05 %, and 0.1 % for 18 hours. The control 
group consisted of the same type of seeds soaked in tap 
water solution of a commonly used growth stimulator, 
Epibrassinolide (commercial fraction Epin Extra pro-
duced by NNPP NEST M, Russia), with the concentra-
tion of 0.05 % (in accordance with the instruction). In 
case of each of the studied concentrations of the acids, as 
well as the control group, the experiment was conducted 
three times using a set of 100 seeds. After soaking, the 
rhododendron seeds were placed in Petri dishes contain-
ing blotting paper, and germinated in the laboratory con-
ditions at a constant temperature 22 
о
С. On the 21st day, 
the sprouts were planted in containers filled with high-
moor peat and then kept in a greenhouse. The height of 
the seedlings of Rhododendron ledebourii was measured 
with a ruler, 3 and 7 months after the start of the experi-
ment. Since Rhododendron smirnowii grows slower, the 
height of its seedlings was measured 7 months after the 
start of the experiment.
Sprouts are formed during the early stage of plant 
ontogenesis, which starts after the germination stage, i.e. 
when the seed coat develops, and finishes, when the first 
leaf of the hypocotyledonous stem (the shoot rising from 
the plumule) develops (Korovkin, 2007). After the first 
true leaves appear, young plants are considered seedlings 
(Korovkin, 2007). 
The results were statistically processed using the 
STADIA software package. The procedures of data 
grouping and processing were described by A. P. Kulai-
chev (2006). The mean values were compared using Stu-
dent’s t-test. Coefficient of variation (Cv) was counted 
according to G. F . Lakin (1990). If Cv was below 10 %, it 
meant that the degree of variation was low, with Cv be-
tween 10 and 25 % it was medium, and when Cv was over 
25 % - the degree of variation was high (Lakin, 1990). Av-
erage values of seedlings (plants) height were compared 
using Student’s t-test. The seed germination in control 
and experimental variants were compared using Z-test 
for equality of frequencies. To estimate the influence of 
various concentrations of the chemical compounds on 
the height of the plants, one-way analysis of variance was 
used. The power of influence was calculated according to 
Snedecor (in %).
3 RESULTS AND DISCUSSION
The standard growth stimulant hasn’t shown influ-
ence of the seed treatment on the height of Rhododen-
dron ledebourii seedlings. It hasn’t been revealed the 
significant difference between Сontrol group and Epin 
group. That means special stimulant impact for sowing 
qualities in Rhododendron seeds or specific seeds reac-
tion for the treatment. The seeds germination wasn’t 
strongly increased (Table 1-3). But there were significant 
differences between control and experimental groups in 
this parameter (Table 1-3).
Suspensions of 2-benzylamino-4-methyl-pyrimi-
dine-5-carboxylic acid at concentrations between 0.01 
and 0.1 % proved to be more effective than other growth 
stimulators (Table 1). When suspensions of 4-methyl-
2-morpholin-4-pyrimidine-5-carboxylic acid at con-
centrations of 0.05 and 0.1 % were used, the seedlings of 
Rhododendron ledebourii grew up to 55.6–116.7 % higher 
(Table 1).
Within 7 month after the start of the experiment all 
the studied compounds at any concentration proved to 
be effective for Rhododendron ledebourii (Table 2). 
Within 7 month after the start of the experiment, 
the height of the Rhododendron smirnowii seedlings also 
increased (Table 5). The parameter “height of the seed-
lings” varied greatly for the control group of Rhododen-
dron ledebourii 3 months after the start of the experiment. 
This is indicated by Cv = 44 %. For the experimental 
groups, Cv was medium (Table 1), which indicated that 
the reactions of individual seedlings to the compounds 
used were similar. 7 month after the start of the experi-
ment, the degree of variation was medium in the con-
trol group, and even low in the experimental group. This 
might mean that older seedlings adapt better to experi-
mental conditions. Changes of the seedlings growth are 
illustrated in Fig. 1-3. 
For the seedlings of Rhododendron smirnowii, a me-
dium coefficient of variation was observed (Table 3). Be-
cause of the slow growth and the small size, differences 
between experimental and control groups of Rhododen-
dron smirnowii are not significant 3 month after the start 
of the experiment. 

Acta agriculturae Slovenica, 119/4 – 2023 4
T. V . VOSTRIKOV A et al.
Table 1. The seedlings height of Rhododendron ledebourii seedlings 3 months after the seed were treated with the studied synthe-
sized organic compounds
Concentration, %
Average height 
of the plants, cm
Min - max, 
cm
Cv, 
%
The seeds  
germination, %
Increase in the height 
of the plants, %
Сontrol group
Epin group
1.8 ± 0.2
1.9 ± 0.1
1.0–3.0
1.5–2.5
44
15.8
72
75
–
–
4-methyl-2-piperidin-1-yl-pyrimidine-5-carboxylic acid
0,01 %
0,05 %
0,1 %
3.3 ± 0.1***
3
2.8 ± 0.1**
2
2.2 ± 0.1
1
3.0–3.5
2.5–3.0
2.0–2.5
9.1
 
10.7
13.6
 
78*
78*
79*
83.3
55.6
–
2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid
0,01 %
0,05 %
0,1 %
2.9 ± 0.2**
2
3.4 ± 0.2***
3
3.8 ± 0.2***
3
2.5–3.0
3.0–3.5
3.5–4.0
12.5
13.5
11.9
78*
80*
82**
61.1
88.9
111.1
4-methyl-2-morpholin-4-pyrimidine-5-carboxylic acid
0,01 %
0,05 %
0,1 %
2.3 ± 0.1
1
2.8 ± 0.1**
2
3.9 ± 0.2**
2
2.0–2.5
2.5–3.0
3.0–4.5
13.0
10.7
15.4
74
75
78*
–
55.6
116.7
Designations: 
Cv – variation coefficient 
* – differences with the control group are significant (p < 0.05) 
** – differences with the control group are significant (p < 0.01) 
*** – differences with the control group are significant (p < 0.001)
1
 – differences with the Epin group are significant (p < 0.05)
2
 – differences with the Epin group are significant (p < 0.01) 
3
 – differences with the Epin group are significant (p < 0.01)
Fig. 1: The height of the seedling of Rhododendron ledebourii (in mm) seedlings after the seed were treated with 4-methyl-2-pi-
peridin-1-yl-pyrimidine-5-carboxylic acid; 1 – seedlings (21 days), 2 – plants 3 months, 3 – plants 7 months 

Acta agriculturae Slovenica, 119/4 – 2023 5
Using pyrimidinecarboxylic acids as growth stimulants ...
Designations:  
Cv – variation coefficient 
* – differences with the control group are significant (p < 0.05) 
** – differences with the control group are significant (p < 0.01) 
*** – differences with the control group are significant (p < 0.001)
1
 – differences with the Epin group are significant (p < 0.05)
2
 – differences with the Epin group are significant (p < 0.01) 
3
 – differences with the Epin group are significant (p < 0.01)
Table 2: The height of Rh. ledebourii seedlings 7 months after the seed were treated with the studied synthesized organic com-
pounds
Concentration, %
Average height 
of the plants, cm
Min - max, 
cm
Cv, 
%
The seeds 
germination, %
Increase in the height 
of the plants, %
Сontrol group
Epin group
5.6 ± 0.2
5.7 ± 0.2
4.5–6.5
5.0–6.5
11.5
9.3
72
75
–
–
4-methyl-2-piperidin-1-yl-pyrimidine-5-carboxylic acid
0,01%
0,05%
0,1%
7.7 ± 0.2***
3
7.6 ± 0.2***
3
6.8 ± 0.2***
3
7.0–8.5
6.5–8.5
6.0–7.5
7.6
 
8.7
7.9
 
78*
78*
79*
22.9
27.5
33.5
2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid
0,01%
0,05%
0,1%
7.2 ± 0.2***
3
7.7 ± 0.2***
3
8.4 ± 0.2***
3
6.5–8.0
7.0–8.5
7.5–9.0
7.5
7.5
6.9
78*
80*
82**
22.9
27.0
17.8
4-methyl-2-morpholin-4-pyrimidine-5-carboxylic acid
0,01%
0,05%
0,1%
6.4 ± 0.2*
1
6.5 ± 0.2**
2
6.9 ± 0.2***
3
5.5–7.5
5.5–7.5
6.0–7.5
11.5
11.5
6.9
74
75
78*
13.3
14.6
19.0
Fig. 2: The height of the seedling of Rhododendron ledebourii (in mm) seedlings after the seed were treated with 4-methyl-2-mor-
pholin-4-pyrimidine-5-carboxylic acid, 1 – seedlings (21 days), 2 – plants 3 months, 3 – plants 7 months

Acta agriculturae Slovenica, 119/4 – 2023 6
T. V . VOSTRIKOV A et al.
The growth ratio of Rhododendron ledebourii seed-
lings (in the experimental group as compared to the 
control group) after the seeds were treated with organic 
compounds of pyrimidinecarboxylic acids, demonstrates 
that the stimulating effect is most obvious 3 month after 
the start of the experiment. However, some treatment do 
not effect growth (Table 1). 7 month after the start of the 
experiment, the stimulating effect deteriorates, but all the 
compounds at any concentration studied in this paper 
still have a positive effect (Table 2). 
It was shown significant influence of the treatment 
of seeds with the synthesised organic compounds (as a 
factor) on the height of the Rhododendron seedlings. The 
power of influence of the treatment of seeds with the syn-
thesised organic compounds on the height of the seed-
lings was evaluated using the one-way analysis of vari-
ance (Table 4-6).
4-methyl-2-piperidin-1-yl-pyrimidine-5-car-
boxylic acid, 2-benzylamino-4-methyl-pyrimidine-
5-carboxylic acid, and 4-methyl-2-morpholin-4-py-
rimidine-5-carboxylic acid with concentrations of 0.01, 
0.05, and 0.1 % resulted in the increase in the height of 
Fig. 3: The height of the seedling of Rhododendron ledebourii (in mm) seedlings after the seed were treated with 2-benzylamino-
4-methyl-pyrimidine-5-carboxylic acid1, 1 – seedlings (21 days), 2 – plants 3 months, 3 – plants 7 months
Designations: 
Cv – variation coefficient 
* – differences with the control group are significant (p < 0.05) 
** – differences with the control group are significant (p < 0.01) 
*** – differences with the control group are significant (p < 0.001)
1
 – differences with the Epin group are significant (p < 0.05)
2
 – differences with the Epin group are significant (p < 0.01) 
3
 – differences with the Epin group are significant (p < 0.01)
Table 3: The height of Rh. smirnowii seedlings 7 months after the seed were treated with the studied synthesized organic com-
pounds
Concentration, %
Average height 
of the plants, cm
Min - max, 
cm
Cv, 
%
The seeds 
germination, %
Increase in the height 
of the plants, %
Сontrol group
Epin group
1.4 ± 0.1
1.4 ± 0.1
1.0–2.0
1.0–2.0
24.1
28.1
58
60
–
–
2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid
0,01 %
0,05 %
0,1 %
1.8 ± 0.1*
1
1.9 ± 0.1**
1
2.0 ± 0.1**
2
1.5–2.0
1.5–2.0
1.5–2.5
14.7
12.7
20.4
64*
68*
72**
29.6
37.0
48.1

Acta agriculturae Slovenica, 119/4 – 2023 7
Using pyrimidinecarboxylic acids as growth stimulants ...
Rhododendron ledebourii seedlings. A direct correla-
tion can be observed: the higher the concentration of 
2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid 
(within the range between 0.01 and 0.1 %), the higher 
the seedlings of Rhododendron ledebourii and Rhodo-
dendron smirnowii are. The same correlation is observed 
for Rhododendron ledebourii seedlings, when 4-methyl-
2-morpholin-4-pyrimidine-5-carboxylic acid is applied. 
When Rhododendron ledebourii seeds were treated with 
4-methyl-2-piperidin-1-yl-pyrimidine-5-carboxylic acid 
at the concentration between 0.01 and 0.1 %, a negative 
correlation was observed: the lower the concentration, 
the higher the seedlings.
W e can thus say, that the studied synthesised organic 
compounds of pyrimidinecarboxylic acids are character-
ised by high biological activity and stimulate the growth 
of ornamental woody plants when their concentrations 
are low. The stimulating effect is most obvious 3 months 
after the seed treatment (the seedlings are 55.6–116.7 % 
higher than the seedlings in the control group). 7 month 
after the start of the experiment the stimulating effect 
starts deteriorating. Compounds of pyrimidinecarbox-
ylic acids increase the height of Rhododendron ledebourii 
seedlings by 13.3-33.5 %, and the height of Rhododen-
dron smirnowii seedlings by 29.6-48.1 %. Apparently, 
pyrimidinecarboxylic acids are more biologically active 
than other chemical substances, as their chemical struc-
ture is similar to the structure of a natural growth stimu-
lator - indole acetic acid (heteroauxin). It can be assumed 
that auxin activity was kept better within 3 month, than 
during 7 month after the start of the experiment. 
Earlier research studied the stimulating effect of 
0.01–0.05 % 4-methyl-2-piperidin-1-yl-pyrimidine-
5-carboxylic acid on the germination and growth of the 
seedlings of spreading marigold: with the concentration 
of 0.03-0.05 %, the height of the plants increased (dif-
ferences with the control group are reliable, p < 0.001). 
However, other compounds of pyrimidine-5-carboxylic 
acids at the studied concentrations demonstrated strong-
er stimulating effects (Vostrikova et al., 2012; Kalaev et 
al., 2013 a).
Obtained results are consistent with earlier studies 
by R. G. Gafurov and co-workers on carbon N- and O-
benzyl-containing compounds that have bright auxin ac-
tivity, which is ensured by the presence of a benzyl group 
at the nitrogen or oxygen atom (Gafurov and Makhmu-
Table 4: The power of influence (in %) of the seed treatment on the height of Rhododendron ledebourii seedlings on the 3 month 
after the start of the experiment
Stimulator
as compared to 
the control group
as compared to 
the Epin group as is
4-methyl-2-piperidin-1-yl-pyrimidine-5-carboxylic acid 5.0*** 8.8*** 8***
2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid 7.4*** 7.9*** 8.3***
4-methyl-2-morpholin-4-pyrimidine-5-carboxylic acid 7.2*** 8.9*** 8.2***
Designations: *** - the influence of the factor is significant (p < 0.001)
Table 5: The power of influence (in %) of the seed treatment on the height of Rhododendron ledebourii seedlings on the 7 month 
after the start of the experiment
Stimulator
as compared to 
the control group
as compared to 
the Epin group as is
4-methyl-2-piperidin-1-yl-pyrimidine-5-carboxylic acid 6.7*** 7.5*** 6.7***
2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid 8.4*** 8.9*** 8.5***
4-methyl-2-morpholin-4-pyrimidine-5-carboxylic acid 4.9*** 3.3** 5.6**
Designations: *** - the influence of the factor is significant (p < 0.001)  
*** - the influence of the factor is significant (p < 0.001)
Table 6: The power of influence (in %) of the seed treatment on the height of Rh. smirnowii seedlings on the 7 month after the 
start of the experiment
Stimulator
as compared to the con-
trol group
as compared to the Epin 
group as is
2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid 4.3*** 4.2*** 6.2***
Designations: *** - the influence of the factor is significant (p < 0.001) 

Acta agriculturae Slovenica, 119/4 – 2023 8
T. V . VOSTRIKOV A et al.
tova, 2003, 2005). These compounds contain effector 
fragments that together determine the stress protective 
activity, namely, the quaternary ammonium and benzyl 
groups and the hydroxyethyl group - an analog of the 
benzoxyethyl group (Budykina et al., 2005; Timeyko et 
al., 2005). Tested substance (2-benzylamino-4-methyl-
pyrimidine-5-carboxylic acid) contains similar frag-
ments, so it also shows bright auxin activity. Based on 
the literature data (Budykina et al., 2005; Timeyko et al., 
2005) and the results of our research, it can be assumed 
that used compound has the stress-protective activity for 
valuable ornamental plants of Rhododendron species.
4 CONCLUSIONS 
In this paper, it has been demonstrated that the ef-
fect of the same concentrations of synthesised organic 
compounds of pyrimidine carboxylic acids on the seed-
lings of woody plants after the pre-sowing seed treatment 
doesn’t differ. Rhododendron ledebourii and Rhododen-
dron smirnowii seedlings demonstrated similar direct 
correlations: when the concentration of 2-benzylamino-
4-methyl-pyrimidine-5-carboxylic acid and 4-methyl-
2-morpholin-4-pyrimidine-5-carboxylic acid (for Rho-
dodendron ledebourii seeds only) rose from 0.01 to 0.1 %, 
the height of the seedlings increased. Therefore, 4-me-
thyl-2-piperidin-1-yl-pyrimidine-5-carboxylic acid, 
2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid, 
and 4-methyl-2-morpholin-4-pyrimidine-5-carboxylic 
acid at concentrations of 0.01, 0.05, and 0.1 % can be 
used as growth stimulators for species of Rhododendron 
genus. 2-benzylamino-4-methyl-pyrimidine-5-carboxyl-
ic acid proved to be more effective at the initial develop-
ment stages of Rhododendron seedlings. Within 3 month 
after the seeds of Rhododendron ledebourii were soaked 
in water suspensions of 2-benzylamino-4-methyl-pyrim-
idine-5-carboxylic acid at concentrations of 0.01-0.1 %, 
the height of the seedlings increased by 61.1-111.1 %. 
Thus, investigated pyrimidine carboxylic acids at con-
centrations of 0.01-0.1 % can be recommended as effec-
tive growth stimulants for Rhododendron.
5 ACKNOWLEDGEMENTS
The study received financial support from the Min-
istry of Science and Higher Education of the Russian 
Federation within the framework of State Contract with 
universities regarding scientific research in 2023–2025, 
project No. FZGU-2023-0009.
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