Neem
(Azadirachta indica) Oil Affects
Morning Glory (Ipomoea purpurea)
Seedling Development
Inês Carolina Grenzel,
Marcelo da Silva Marinho and Eder Marques1*
1Department
of Agronomy, UPIS Faculdades Integradas,
Distrito Federal, Brazil
*For correspondence:
eder.marques.08@gmail.com
Received 14 October 2021;
Accepted 21 February 2022; Published 30 March 2022
Abstract
Keywords:
Allelopathy;
Alternative management; Phytotoxicity; Vegetable oils; Seed germination;
Seedling survival
Introduction
According to the broadest definition by the FAO
(2010), a pest is any species, race or biotype of plant, animal or pathogen
that is harmful to plants or plant products, and thus weeds are included as
important agricultural pests. Morning glory (Ipomoea purpurea L.) is a
weed belonging to the Convolvulaceae family. It is an annual plant with a
climbing habit and native to Mexico (Fang et al. 2013); that is, it is
an exotic pest. It was introduced in Brazilian
territory, where it is already widely distributed (CABI 2021). It is an
important invasive species for the country, as it has asynchronous germination,
remaining viable in soil seed banks for long periods (Jha et al. 2015)
and harms mechanized harvesting, becoming entangled in plants and jamming
machines (Piccinini et al. 2018). In addition,
some biotypes in Brazil have already developed herbicide tolerance (Pazuch et al. 2017) and they serve as a reservoir
for plant pathogens such as bacteria Xylella fastidiosa Wells (Wistrom and Purcell 2005) and insects (Simms and Rausher 1989). In soybeans, for example, losses of 27 to
45% have been reported (Piccinini et al.
2016). Such factors should be considered a warning for the future difficulty of
managing this weed plant in Brazil.
According
to the electronic platform for phytosanitary pesticides in Brazil (Agrofit 2021), there are approximately 258 products for the
chemical control of morning glory. As mentioned, glyphosate-tolerant biotypes
have already been reported in the country (Pazuch et
al. 2017), making it necessary to search for alternative sources of pest
management.
Neem (Azadirachta indica A. Juss)
is a tree species that belongs to the Meliaceae
family and has India as its center of origin (Alzohairy
2016). Neem oil, extracted from its seeds, has numerous uses and is widely used
to protect plants against insects (Campos et al. 2016), although its use
in weed management is not common. The product is natural, and it does not
affect mammals or the environment (Isman et al. 1990), although it has several
bioactive substances such as azadirachtin and meliantrol
(Campos et al. 2016). According to Kato-Noguchi et al. (2014) nimbolide B and nimbic acid are
the main substances with allelopathic properties present in this plant.
The
influence of neem leaf extract or its residues incorporated into the soil has
been studied in cultivated plants or in weeds (Xuan et al. 2004; Ashrafi
et al. 2008; Ogundare et al. 2016), as
well as the effect of neem oil on seed germination and plant development. Souza
Filho et al. (2009) evaluated the effect of this oil on plants such as
“touch-me-not” (Mimosa pudica Kunth.) and sicklepod (Senna obtusifolia L.). Some studies have also reported the
phytotoxic effect of the oil (Pinheiro et al. 2009). In addition to this
report, we have already evaluated the in vitro effect of neem oil on
morning glory seed germination (Andrade and Marques 2021). Given the above, the
aim of this study was to evaluate the allelopathic effect of neem oil on the
development of I. purpurea seedlings.
Materials and Methods
Test location
The work was carried out in Planaltina,
Brasília – DF, Brazil (15.58ºS, 47.73ºW), constituted by the Cerrado biome, during the month of July 2021. According to Köppen's classification, the municipality of Planaltina-DF has a seasonal tropical climate of megathermal savannah, with average annual precipitation of
1,400 mm, and the average temperature of the coldest month is above 18ºC.
Rainfall is concentrated between the months of October and March, with a dry
period from April to September, and an average minimum temperature of 15.9ºC,
maximum of 26.4ºC (Cardoso et al. 2014).
Obtaining neem oil and morning
glory seeds
The neem oil used was also
purchased from a commercial supplier, being a product of the insecticide /
fungicide class (Tetranortriterpenoid Chemical Group), in the formulation of Emulsifiable Concentrate (EC) and classified by the
Ministry of Agriculture of Brazil in Category 5 - product unlikely to cause
acute damage (Agrofit 2021). The seeds of Ipomoea
purpurea were also purchased from a commercial supplier, already chemically
treated, in order to avoid post-harvest fungi, and the batch was within the
expiry date.
Experimental setup
From the original concentration of the product
(85%), dilutions were made to 65 and 45%. Then, in 200 mL disposable cups
containing commercial substrate, morning glory seeds were planted. Seven
treatments were evaluated, T1 (control, without oil), and to another three of
them were applied 1 mL of neem oil before germination (T2 to T4), immediately
after sowing, while for the remaining three (T5 to T7), 1 mL of oil was applied
on the seedlings that had already emerged, seven days after sowing. The
seedlings were kept on a bench in full sun and were watered three times a day.
The readings of the experiment were daily, where the number of seeds was noted
(only from treatments T1 to T4). At the end of the experiment (after 21 days),
the number of live seedlings and the fresh weight of all treatments were
measured. Before weighing, the seedling roots were rinsed under running tap
water.
Experimental design and statistical analysis
A Completely Randomized Design (CRD) was used with
five replications, consisting of one cup and six seeds each, totaling 30 seeds
in each. Based on the germination data, the average emergence time (Eq 1) and
the germination percentage (Eq 2) were calculated using the following equations
(Santana and Ranal 2004):
T = (∑(fi x
xi ))/(∑fi) (days) average germination time (Eq 1)
Germination index (%) = (germinated seeds)/(total number of seeds) ×100 (Eq 2)
Where fi= number of seeds germinated on
the i-th day; and xi = number
of days counted from sowing to the day of reading.
The test data were submitted to analysis of variance
(ANOVA) using the SISVAR 5.6 Program (Ferreira 2014). The average values of the
germinability parameters were compared by the Tukey test, at 5% probability.
Results
Germinability
Based on
the germinability data (Fig. 1), it was observed that the neem oil, applied
before germination, did not show a significant effect on the emergence time of
morning glory seeds, despite all treatments having delayed germination at 0.27
(45%), 1.4 (65%) and 0.93 days (0.85%). There was no interference in
germination, with 100% germination observed.
Fresh
weight of seedlings
Regarding
the fresh weight of seedlings, only application after emergence significantly
reduced this parameter (Fig. 2). Neem oil at concentrations of 45, 65 and 85%
caused evident phytotoxicity in the seedlings, leading to a symptom of leaf
blight of the morning glory's aerial parts, which did not recover; some plants
escaped this effect, although with reduced weight (Fig. 3).
Seedling
survival
Another
parameter evaluated was the survival rate of the morning glory seedlings
submitted to the application of neem oil (Fig. 4). The control and treatments
where oil was applied before germination showed survival of almost 100%, that
is, an average close to 6 plants per treatment/replicate. On the other hand,
for the treatments in which the oil was applied to morning glory seedlings,
after germination, there was a high mortality, varying between 51 and 62%, and
those that survived showed reduced weight.
Discussion
The concentrations
of neem oil at 45, 65 and 85% were tested in vivo, based on the results
of previous in vitro germination studies (Andrade and Marques 2021). These are not usual
Fig. 1: Average emergence
time, in days (y-axis), of morning glory (Ipomoea purpurea) seeds
treated with different concentrations of neem oil (x-axis) before germination.
Means followed by the same letter do not differ significantly by the Tukey test
(P < 0.05)
Fig. 2: Average fresh weight
of seedlings on the 21st day, in grams (y-axis), of morning glory
seedlings (Ipomoea purpurea) treated with different concentrations and
times (before or after germination) of neem oil (x axis). Means followed by the
same letter do not differ significantly by the Tukey test (P < 0.05)
concentrations
in practice, since the commercial product is recommended for use at
concentrations/doses that vary between 0.6 and 1.2%. At the concentrations used
here, high phytotoxicity was observed, inducing late blight symptoms of I.
purpurea seedlings. At these concentrations, weight and survival were
reduced, and germination was delayed.
However,
even at lower concentrations, phytotoxic effects of neem oil have been
reported. Pinheiro et al. (2009) report that the 5% concentration was
phytotoxic to common bean (Phaseolus vulgaris L.). Regarding weeds and
corroborating the present work, Souza Filho et al. (2009) described that
the oil, at a concentration of 3%, affected germination and development of
“touch-me-not” (Mimosa pudica Kunth.) and sicklepod (Senna obtusifolia L.) plants, reducing the hypocotyl and
roots of these plants.
Although
this is not the focus of the work, the allelopathy of extracts from this plant
has also been studied. Xuan et al. (2004) reported that neem bark and
leaf extract (dried, powdered and at 5% concentration) inhibited germination
and growth of cultivated plants, such as alfalfa (Medicago sativa L.),
Adzuki bean (Vigna angularis (Willd.) Ohwi and H. Ohashi), carrot (Daucus carota L.),
radish (Raphanus sativus L.), rice
(Oryza sativa L.) and sesame (Sesamum indicum L.), as well as
weeds such as Indian goosegrass (Eleusine Indica (L.) Gaertn (Elein)), pickerel weed (Monochoria vaginalis (Burm.f.)
C. Presl.) and Indian jointvetch
(Aeschynomene indica L).
Neem oil
delayed the germination of morning glory seeds by up to 1.4 days, even when applied to the soil, as
demonstrated in vitro (Andrade and Marques 2021), although
without significant difference. Regarding the germination index, the present
results agree with the reports by Ferreira and Áquila
(2000), in which allelopathy did not exhibit an (significant) effect on
germination, being more efficient in delaying it. On the other hand, studies by
this same research group report that the aqueous extract of guaco (Mikania
glomerata Spreng) (Castro et al. 2021),
the alcoholic extract of eucalyptus-lemon (Corymbia
citriodora (Hook.) K.D. Hill and L.A.S. Johnson) (Fonseca and Marques 2021)
and castor oil (Ricinus comunnis L.) significantly reduced morning glory germination (Oliveira et
al. 2021).
Fig. 3: Neem oil allelopathy
bioassay using morning glory seed seedlings, where: A) seedlings gathered on
the day of the test reading (T1 = controls, T2 to T4 = oil applied after
sowing, T2 = 45% oil, T3 = 65% oil and T4 = 85% oil; T5 to T7 = oil applied
after emergence, T5 = 45% oil, T6 = 65% oil and T7 = 85% oil); B) treatment
with 65% neem oil applied after emergence, where an escaped seedling is
observed and the others show late blight and C) treatment with 85% neem oil
(pure) applied after emergence, where the complete burning of the seedlings is
seen
Fig. 4: Surviving seedlings
(%) of morning glory (Ipomoea purpurea) when treated with different
concentrations of neem oil and times (before or after germination) (x-axis).
Means followed by the same letter do not differ significantly by the Tukey test
(P < 0.05)
Conclusion
Neem oil
has a phytotoxic effect on I. purpurea seedlings, reducing their
survival and fresh weight when applied after germination, in addition to
influencing (delaying) seed germination when applied to the soil. The effect of
lower concentrations that are close to economically viable and practiced in the
field should be studied in the future.
Author Contributions
ICG, MSM and EM planned the experiments and
interpreted the results, ICG and EM made the write up and statistically
analyzed
Conflicts of Interest
All authors declare no conflict of interest
Data Availability
Data presented in this study will be available on a
fair request to the corresponding author
Ethics Approval
Not applicable to this paper
References
Agrofit
(2021). System of Phytosanitary Pesticides in Brazil. Available at:
https://agrofit.agricultura.gov.br/agrofit_cons/principal_agrofit_cons
(Accessed 09 September 2021)
Alzohairy
MA (2016). Therapeutics role of Azadirachta
indica (Neem) and their active constituents in diseases prevention and
treatment. Evid Based Complement Alternat Med 2016:7382506
Andrade MJS, E Marques
(2021). Neem oil influences morning glory seed germination. J Res Weed Sci 4:264–269
Ashrafi ZY, Y Ashrafi, A Rahnavard, S Sadeghi, M Alizade,
HR Mashhadi (2008). Study of the allelopathic
potential of extracts of Azadirachta indica
(Neem). J Biol Sci
8:57–61
CABI – Centre for
Agriculture and Bioscience International (2021). Invasive Species
Compendium: Ipomoea purpurea (tall morning glory). Available at:
https://www.cabi.org/isc/datasheet/40052 (Accessed: 02 February 2022)
Campos EVR, JL Oliveira, M Pacoli, R Lima, LF
Fraceto (2016). Nim
oil and crop protection: From now to the future. Front
Plant Sci 7:1–8
Cardoso MRD, FFN Marcuzzo, JR Barros (2014).
Classificação climática de Köppen-Geiger para o Estado de Goiás e o Distrito
Federal. Acta Geogr 8:40–55
Castro LA, DO Beltrão, PGA Santos, YB Carvalho, NR
Nogueira Filho, JPL Costa, E Marques (2021). Allelopathic
effect of crude plant extract on Ipomoea purpurea L. J Res Weed Sci
4:188–199
Fang Z, AM Gonzales, ML
Durbin, KKT Meyer, BH Miller, KM Volz, MT Clegg, PL Morrell (2013). Tracing the
geographic origins of weedy Ipomoea purpurea in the Southeastern United
States. J Heredit 104:666–677
FAO – Food and Agriculture
Organization of the United Nations (2010). Online Version of the Glossary of
Phytosanitary Terms – All Languages. Available at: https://www.ippc.int/en/publications/621/
(Accessed: 25 September 2021)
Ferreira AG, MEA Áquila (2000). Alelopatia: Uma área
emergente da ecofisiologia. Rev Bras Fisiol
Veg 12:175–204
Ferreira DF (2014). Sisvar: A guide for its Bootstrap procedures in multiple
comparisons. Ciênc Agrotec
38:109–112
Fonseca JGC, E Marques (2021). Lemon-scented gum
extracts influence the germination of morning glory seeds. J Res Weed Sci
4:236–241
Isman
MB, O Koul, A Luczynski, J
Kaminski (1990). Insecticidal and antifeedant bioactivities of neem oils and
their relationship to azadirachtin content. J Agric. Food Chem 38:1406–1411
Jha P, JK Norsworth, V Kumar, N Reichard (2015). Annual changes in
temperature and light requirements for Ipomoea purpurea seed germination
with after-ripening in the field following dispersal. Crop
Prot 67:84–90
Kato-Noguchi H, MA Salm, O Ohno, K Suenaa (2014). Nimbolide
B and Nimbic acid B, phytotoxic substances in neem
leaves with allelopathic activity. Molecules 19:6929–6940
Ogundare
SK, AS Hinmikaiye, TO Oladitan,
AI Agbona (2016). Effect of neem residues and weed
control methods on soil properties, weed infestation, growth and yield of
eggplant (Solanum melongena L.) in Kabba,
Nigeria. J Trop Agric 21:73–82
Oliveira JPP, MS Marinho, E Marques (2021). Effect
of castor oil (Ricinus comunnis L.) on morning
glory (Ipomoea purpurea L.) seed germination. J Res Weed Sci
4:280–285
Pazuch
D, MM Trezzi, ACD Guimarães,
MVJ Barancelli, R Pasin, RA
Vidal (2017). Evolution of natural resistance to glyphosate in morning glory
populations. Planta Daninha 35:e017159430
Piccinini F, SLO Machado, TN Martin, ND Kruse, A
Balbinot, A Guareschi (2018). Interference of morning
glory in soybean yield. Planta Daninha 36:e018150988
Piccinini F, TN Martin, SLO Machado, ND
Kruse, R Schmatz (2016). Soybeans competitiveness
with morning glory. Planta Daninha 36:25–33
Pinheiro PV, ED Quintela, JP Oliveira, JC Seraphin
(2009). Toxicidade do óleo de nim para ninfas de Bemisia tabaci biótipo
B criadas em feijão seco. Pesq Agropec Bras 44:354–360
Santana DG, MA Ranal (2004) Análise da
germinação, um enfoque estatístico, p:248. Brasília:
Universidade de Brasília
Simms EL, MD Rausher (1989). The evolution of resistance to herbivory in
Ipomoea purpurea. II. Natural selection by insects and costs of
resistance. Evolution
43:573–585
Souza Filho APS, RL Cunha, MAM Vasconcelos (2009).
Efeito inibitório do óleo de Azadirachta indica A. Juss. sobre plantas
daninhas. Rev Ciênc
Agrar
52:79–86
Wistrom C, AH Purcell (2005).
The fate of Xylella fastidiosa in vineyard weeds and other alternate
hosts in California. Plant Dis 89:994–999
Xuan TD, E Tsuzuji, T
Hiroyuki, M Mitsuhiro, TD Khanh, I-M Chung (2004).
Evaluation on phytotoxicity of neem (Azadirachta
indica A. Juss) to crops and weeds. Crop Prot 23:335–345