Introduction

Picloram is an important herbicidal molecule, marketed under various commercial products worldwide and registered for several crops (^{Batistão et al., 2018}). This molecule is characterized by being extremely active in dicotyledonous plants, and it is commonly used in mixtures with other herbicides, such as 2,4-D (^{Rodrigues and Almeida, 2005}; ^{Franceschi et al., 2017}). Picloram can persist in the environment for up to 360 days, causing intoxication in sensitive species grown in succession (^{Santos et al., 2006}; ^{Batistão et al., 2018}). In addition, due to the high leaching potential, it can cause contamination in groundwater (^{Assis et al., 2010}).

These herbicides have long periods of residual activity, preventing, in the short and medium term, the cultivation of other agricultural species in environments that previously received treatment with these products (^{Santos et al., 2006}), which can make unfeasible the use of areas where the farmer wants to carry out crop-livestock integration (^{Assis et al., 2010}).

The intoxication symptoms produced in the leaves of several dicotyledons by auxinic herbicides are easily characterized and, therefore, are used to detect residues of these herbicides (^{Thill, 2003}). one of the best known symptoms is the disorganized growth and epinasty of the leaves and stem twisting (^{Nascimento and Yamashita, 2009}). In this sense, bioassays are carried out to evaluate residues of picloram + 2,4-D, using indicator plants with sensitivity to these compounds, such as cucumber (Cucumis sativus) (^{Barros et al., 2014}). In this context, there is a need to seek methods that reduce the impacts caused by these pesticides. The use of agroecological practices has become an indispensable tool for family farmers, as it allows them to be autonomous in the field, reducing their dependence on external inputs.

According to ^{Trebbi et al. (2016}) and ^{Bonato et al. (2009)}, from a sustainability point of view, the application of homeopathy in agriculture can offer potential benefits due to its high dilution, low cost and having few or no ecological side effects. To explain the effectiveness of homeopathy, alternative models have been proposed which, although outside the conventional scope, show strong theoretical coherence (^{Trebbi et al., 2016}). According to ^{Yinnon and Elia (2013}), the hypothesis is that, as the dynamization process introduces mechanical energy and turbulence into the system, the preparation procedure (dilution and sucussion) can generate long-term changes in high dilutions.

When carrying out research with homeopathy, it is of great importance to choose the appropriate homeopathic preparations and to pay attention to the purpose of the study. According to ^{Casali et al. (2002)} and ^{Felito et al. (2019a)}, the choice of homeopathic preparation to be used in the plant should be punctuated by the possibilities of analogy with human and animal materia medica. In this sense, the objective of the present study was to investigate the potential use of homeopathic preparations in reducing the harmful effects caused by residues of auxinic herbicide (picloram+2,4-D - Artys™) in the cucumber crop, which could be proposed to practical use in a context of sustainable agriculture.

Material and methods

Results and discussion

For the germination percentage was not verified effect of the isolated factors nor the interaction between them. For the variables: phytointoxication scores, air length, root length and total dry mass, there was only effect of the isolated factors (p< 0.05). Only for the variable percentage of dead plants did the effect of isolated factors and their interaction occur (p< 0.05) (Table 2). Despite the contamination of cucumber seeds with the herbicide, the germination process was not affected, with high germination (above 90%), regardless of treatment.

However, it is noteworthy that during the experiment, clear symptoms were observed in inhibiting the development of seedlings exposed to herbicide contamination, causing root base atrophy, abnormal air growth and premature exhaustion of seed reserves. According to ^{Oliveira (2011)}, the growth of plants exposed to the solution with the herbicide is negatively affected due to its hormonal action, acting similar to the natural but more persistent and active auxin. This behavior is considered the main mechanism of action of this herbicide, stimulating the production of 1-carboxylic acid-1-aminocyclopropane (ACC) synthase, the enzyme responsible for the biosynthesis of the hormone ethylene (^{Queiroz and Vidal, 2014}), explaining the symptoms observed in this study.

For aerial length, no difference was verified between the homeopathic preparations and the control composed only of seeds contaminated by the herbicide (TH). However, a difference was observed in relation to the control composed of seeds without contamination (T0). There was a difference in the response to the dynamizations used, with the lowest values of aerial growth being found in 24CH and 12CH, while the highest averages were verified in Control 0 (Table 3).

The plant’s response to the application of homeopathic preparations can be negative; however, in other situations they may have a positive effect, depending on the similarity between the product and the plant. In this regard, ^{Kolisko and Kolisko (1978)} state that among homeopathic medicines, depending on their similarity with the plant, stimulating, inhibitory effects or even no effect on the metabolism of living beings can be observed. Thus, this variation in response to homeopathic treatment, causing positive or negative changes, which has already been portrayed in other studies (^{Castro, 2002}; ^{Armond, 2003}; ^{Duarte, 2003}; ^{Andrade, 2004}; ^{Felito et al., 2019a}), is called of pathogenesis (^{Bonato, 2004}; ^{Lisboa et al., 2005}).

Another factor related to plant response to the tested homeopathic preparations may be due to the level of stress to which the plants were exposed (soaking in herbicide solution), which may have caused them irreversible damage in the normal resumption of seed germination. Homeopathy contributes as a detoxification treatment, but the response time of living organisms to homeopathic medicines occurs according to the degree of intoxication to which they are submitted (^{Lisboa et al., 2005}).

^{Felito et al. (2019b)} found that homeopathic preparations of Nux vomica, Carbo vegetabilis and Arsenicum album reduced the toxicity of 2,4-D + picloram in cattle manure, but there was no complete neutralization of the herbicide action in the early development of cucumber plants. Thus, plant responses to stress depend on duration, severity, number of exposures and combination of stressors (^{Bonato, 2007b}), which may explain the results found in the present study.

Root development was also impaired by the action of the product, as the plants showed characteristic symptoms of intoxication caused by auxinic herbicides, with the formation of tumors and thickening at the base of the stem and root being verified during the experiment. These symptoms are common and are considered the most obvious alterations caused by auxinic herbicides (^{Silva et al. 2005}). Among the studied homeopathic treatments and dynamizations, only Witness 0 presented higher values for the root length variable, statistically different from the others. The 24CH dynamization promoted lower averages than the other treatments, even when compared with Control H (Table 3), with no positive effect of homeopathic treatments on decontamination.

This harmful result of some dynamizations, observed in the present work, is commonly found in experiments with homeopathic preparations, being described by ^{Espinoza (2001)} as a ‘zigzag’ effect, which occurs when a substance in different dynamizations manages to revert its effect to certain characteristics.

In homeopathy, the same medicine often causes different effects depending on the dynamization applied. In certain dynamizations an increase may occur, while in other inhibitions may be reported within a specific physiological variable (^{Bonato, 2007a)}. Thus, this possible inversion of dynamization results may have been the cause and effect verified in the evaluations of this variable. The homeopathic preparation Arsenicum album had lower scores, demonstrating better results regarding the symptoms caused by the herbicide, followed by Nux vomica and Carbo vegetabilis, which did not differ from each other. However, it is worth noting that, despite the significant difference, the average scores were not as expressive.

The dynamizations also influenced the intensity of symptoms, with 6CH, 30CH and 12CH promoting better plant development (Table 3). Alterations in the phytointoxication analysis were differentiated according to the homeopathic preparations and dynamizations used. These results highlight the principle of specificity of action of homeopathic medicines, that is, each ultradilution manifests different characteristics (^{Figueiredo, 2009}).

For the homeopathic medicine Nux vomica, the dynamizations that provided lower mortality were 6CH and 12CH; Carbo vegetabilis had a better response in 30CH and Arsenicum album had the lowest mortality rate among all treatments and dynamizations, with only 6% mortality in 6CH (Table 4).

For 6CH and 12CH of Nux vomica treatment tested in this research, it was found that these low dynamizations provided reduction in mortality of contaminated plants, being an indication of the possible degradation of herbicide compounds that became toxic to seedlings. This consequence demonstrates the action and efficacy of homeopathy for the studied treatment and, according to ^{Andrade and Casali (2011)}, low dynamizations are efficient in the degradation of intoxicating compounds to the organism and provide efficacy in the reestablishment of the organism caused by several imbalances, causing the self-regulation of metabolic processes vital to the body.

It can be inferred that these results are consistent with the Law of Similitude, in which the toxic dose substance that generates several symptoms in the healthy living being, when given to the patient with the same symptoms, causes the state of balance (^{Moreno, 2000}). that is, when receiving similar information, the environment is stimulated to the reaction (^{Casali et al., 2006}). As observed in this study, ^{Bonato (2007a)} argues that when the homeopathic preparation that would be capable of producing the same symptoms in the plant is applied, the result was the minimization of the harmful effects caused by the biotic and abiotic factors, which in this case was the action of the herbicide.

The application of homeopathy may have triggered the secondary metabolism of seeds, establishing their defense mechanism, which reacted to external factors (herbicidal action of the chemical compound) seeking their survival by self-regulation. These results, as argued by ^{Queiroz (2015)}, confirm that homeopathic preparations, governed by immateriality, when administered by similitude, access and strengthen the vitality of all living beings. The percentages obtained for seedling mortality observed throughout the evaluations show the beneficial effects of the application of homeopathic preparations to the seedlings, since low values were accounted for Arsenicum album treatments at 6CH dynamization with average of 6% followed by Nux vomica in the same dynamization with only 10% mortality.

It is worth mentioning the high mortality rate of Nux vomica and Arsenicum album, verified from 18CH and 12CH, respectively. Such results may be due to the pathogenesis reaction, that is, the antagonistic effect in similarity studies with plant homeopathy. This antagonism implies the opposition of incompatible systems, causing actions and reactions in the opposite direction, even if temporarily (^{Castro, 2002}; ^{Bonato, 2004}; ^{Lisboa, 2006}). In the same way that homeopathic treatment can result in plant healing symptoms, the final result of this antagonism can be converted into negative effects, through physiological modifications that act on the vital force of the plant, changing its state and physiologically impairing its metabolism (^{Bastide, 1998}). According to studies by ^{Arruda et al. (2005)} and ^{Lisboa et al. (2005)}, this alteration, called pathogenesis, portrays the resonance between the opposite energies involved.

Thus, the ultradilutions used in this study with different homeopathic preparations (Nux vomica and Arsenicum album) provoked weak signals, but which caused great responses in the physical systems, as is the case of the mortality rate of the plants, due to the amplification mechanisms triggered by stochastic systems or ion channels (^{Galvanovskis et al., 1996}). According to ^{Casali et al. (2006)}, in several situations, the effect over time tends to come into balance, with oscillation within a certain range of dilution, due to the greater or lesser plasticity (morphological and physiological) of the plant species, when adapting to new conditions. energy and informational properties acquired by ultradilutions, generating the plant’s capacity for self-regulation.

No significant difference was found for the determination of the total dry mass accumulation among homeopathic drugs, except for Witness 0, whose treatment promoted the production of higher values of this variable; however, there was no difference between the witnesses. Among the dynamizations, 18CH and 6CH were the ones that provided the largest dry mass accumulation, but not differing from the W control. Therefore, according to the dynamization used, the effect in response to stress caused by the herbicide can be opposite to the expected and may harm the body more than provide benefits (Table 4). This is another response that can be considered pathogenesis, as seen in the seedling mortality rate reported earlier.

Despite the dynamization behavior acting at random, better results were found in lower dynamizations for this variable (Table 3). Positive responses found due to lower dynamizations are also reported by other authors, such as ^{Felito et al. (2019a)}, studying Nux vomica homeopathic preparations at 6CH, 12CH, 18CH, 24CH and 30CH, which provided increased dry mass in cucumber. ^{Queiroz (2015)} also observed that treatments with Nux vomica in the 3CH and 6CH dynamizations stimulated the production of lettuce dry mass when planted in soil without previous cultivation. This behavior may be due to low dynamization homeopathic preparations being denser and more molecular and may act on the physical body due to the resonance frequencies (^{Vithoulkas, 1980}).

^{Krainer and Cuéllar (2009)} reported that the dry mass of lettuce shoots treated with Carbo vegetabilis 12CH homeopathic preparation provided increase compared to other treatments. ^{Bonato et al. (2009)} report that 24CH and 30CH dynamizations of Arsenicum album promoted increase of Mentha arvensis fresh biomass when compared to the control and other analysis dynamics, however the dry biomass of the shoot and root system did not increase. was affected by Arsenicum album.

In homeopathic science these described behaviors occur frequently, since the same medicine can cause different effects on living beings, depending on the dynamization applied (^{Castro, 2002}; ^{Bonato and Silva, 2003}). In some dynamizations promote stimulation and in other situations, an inhibition is verified (^{Armond, 2007}). The wave event is common in nature and in living beings (^{Kent, 1996}). ^{Casali et al. (2006)} describe those plants, in their immobility (autotrophic beings), respond with great intensity through their self-regulation. This regulation will move the secondary metabolism of the plant, seeking return to the balance of its physiological functions, vital for its survival in the midst and subsequent perpetuation of the species.

However, the modes of action by which the life force keeps the organic constituents in life and promotes the integrity of the living organism has still been studied aiming at the elucidation and understanding of the whole process (^{Bonato, 2004}). The behavior observed in this study, as well as similar results in several other studies with the use of plant-applied homeopathy, demonstrates a different behavior from those described in Organon (^{Lisboa et al., 2005}), in which increased dynamization does not elicit progressive physiological responses (^{Bonato, 2004}). Each homeopathic preparation produces in the healthy plant peculiar symptoms according to its own wave frequency (^{Armond, 2007}).

The action of homeopathic solutions under different study conditions, as was the case of this research, has been studied by ^{Zacharias (2006)} states that these effects are based on three models. Structural structures in which dynamization alters the molecular structure of the solvent and acts as a drug agent, the informational models in which the molecular structure is replaced by the informational structure the homeopathic medicine acting as a controlling element of the organism dynamics and finally the phenomenological models which after the dynamization process the agent becomes the organism’s own response to some stimulus.

Moreover, another hypothesis, presented by ^{Bonamin (2007)} to explain the activity of homeopathic medicines, is that attributed to the ‘side effect’, that is, in a given substance, when in ultra diluted doses, it would be devoid of its primary effects on the sensitive organism but would retain its side effects. In this sense, the results observed in the different dynamizations in cucumber seedlings can be attributed to this side effect, whose symptoms occurred due to their overlap with the primary effects in this species and the studied dilutions.

The finding of specific properties of dynamized systems and the difficulty in designing experimental models and explanatory theories that can clarify these properties indicate the need to retreat expectations and, instead of seeking explanation for a probable mechanism of action of ultradilutions, from an even more fundamental basis: the description of their properties (^{Bonamin, 2007}).

Conclusions

Homeopathic treatment of cucumber seeds contaminated with picloram + 2,4-D herbicide causes positive changes, causing interesting effects in herbicide neutralization. However, for some variables, the results are inconclusive with the preparations (Nux vomica, Carbo vegetabilis and Arsenicum album), and their ultradilutions (6CH, 12CH, 18CH, 24CH and 30CH), requiring further research in order to evaluate and describe the complexity of properties inherent to homeopathic treatment.