Physiological Quality of Soybean Seeds Subjected to Industrial Treatment Before and After Storage

This research work aimed to evaluate the physiological quality of soybean seeds subjected to different chemical treatments, before and after seed treatment, throughout conventional storage. A completely randomized design was adopted, with 4 replications, in which the treatments were arranged in a 2 × 7 × 6 factorial scheme (time of treatment (before and after) × industrial seed treatment (IST) × storage period (0, 15, 30, 45, 60 and 90 days). For each IST, the specific volume of slurry was 0, 700, 900, 1400, 900, 1100 and 1600 100 kg -1 of seeds, respectively. A total of 2.5 kg of seeds, cultivar BMX Alvo RR, were used. After being treated, the seeds were placed in kraft paper bags and stored at controlled temperature and humidity in a cold chamber. Their physiological quality was evaluated after each storage period using standard germination test, first germination count, emergence speed index, final emergence in sand substrate, accelerated aging, radicle length, shoot length, and whole seedling length. Their physiological quality was reduced in treatments with higher volumes of slurry. Deleterious effects on vigor were observed with increasing storage period, both before and after IST. After seed treatment, the mean of the analyzed variables was considered higher, compared to the time prior to seed treatment.


Introduction
The physiological potential of seeds is considered one of the main factors with regard to the use of high quality ones, as physical, physiological, sanitary and genetic quality is essential to achieve high agronomic performance in the field (Krzyzanowski et al., 2018).Given this scenario, it is imperative to highlight that seed treatment has a favorable cost for soybean producers, since the use of fungicides and insecticides makes it possible to guarantee adequate plant populations, especially in adverse edaphoclimatic conditions.In this context, industrial seed treatment (IST) has become essential, as pathogens transmitted via seeds, as well as soil pests, are responsible for reducing plant stands (Abati et al., 2014).
The ambient temperature and storage time are the main factors reducing physiological quality of soybean seeds (Coradi et al., 2020).Vigor in soybean seeds is considered as the expression of their maximum physiological potential, so high-vigor seeds result in a high initial growth rate, culminating in superior productive yield (Scheeren et al., 2010).
Although the deterioration process is an inevitable, continuous and irreversible event, it is determined by the vigor, physiological maturity and quality of seeds, particularly when the storage period begins (Deluche & Baskin, 1973).Under these conditions, a reduction in the germination rate is observed, as well as the occurrence of abnormal seedlings.However, it is paramount to stress that storage plays an essential role in maintaining physiological quality; nonetheless, authors such as Santos et al. (2018) point out that the composition and quantity of chemicals used in IST are harmful to maintaining vigor, especially during storage.

Material and Methods
The experiment was conducted at the Seed Technology Laboratory of the Center for Agriculture-Applied Research (Nupagri), belonging to the Center for Agricultural Sciences of the State University of Maringá.
A total of 2.5 kg of seeds, cultivar BMX Alvo RR, were used.For the industrial seed treatment (IST), a continuous seed coating device was used; subsequently, the seeds were placed in kraft paper bags and kept under controlled temperature and relative humidity conditions in a cold chamber.The experimental design used was completely randomized, with 4 replications, in a factorial arrangement (2 × 7 × 6) consisting of two times of treatment (before and after chemical treatment), seven industrial treatments and six storage periods (0, 15, 30, 45, 60 and 90 days).
For each IST, the specific volume of slurry was 0, 700, 900, 1400, 900, 1100 and 1600 mL 100 kg -1 of seeds, respectively.The drying powder was added to the slurry, since this product has the characteristic of quickly drying the seeds.
Statistical analysis: data were analyzed using the R software, version 4.0.2(R Core Team, 2020).The hypothesis of normality and homogeneity of variances referring to the variables was verified using the Shapiro-Wilk and Bartlett's tests.The F test of the analysis of variance was applied in order to identify differences between the industrial treatments, time of treatment and storage periods.When significance was observed in the F test of the analysis of variance, Tukey's test was employed to compare the means of the chemical treatments.In all analyses, a significance level of 5% was considered.The analyzed factors were unfolded in order for statistically significant differences to be detected.

Results and Discussion
Initially, the Shapiro-Wilk and Bartlett's tests showed that the hypotheses of normality and homogeneity of variances were accepted (p-value < 0.05).Table 1 displays the results for the F test of the analysis of variance; it is possible to notice that there was significance (p-value < 0.05) for the main effects, as well as double interactions and triple interaction.With regard to the standard germination test (SGT), Table 2 shows that, in a comparison between seed treatments, considering each of the storage periods, as to before seed treatment, there are significant differences between the treatments, with ISTs 6 and 7 presenting, in most periods, the lowest means for the observed variable.Such results corroborate with Castro et al. (2008); for these authors, using insecticides in association with biostimulants has a deleterious effect on soybean seeds, since they favor the growth of fine roots, indicating phytotoxicity.However, contrary results indicate that seeds coated with fungicides, insecticides and biostimulants promote superior results when it comes to soybean germination, vigor and productivity (Pereira et al., 2018).From the same perspective, Segalin et al. (2013) found that slurry volumes below 1400 mL per 100 kg of seeds do not affect the physiological potential of the latter.
Concerning the period after seed treatment, significant differences can be observed between treatments, with ISTs 5 and 6 representing, in most periods, the lowest means for the SGT response variable.In this scenario, it is essential to point out that studies by Taylor and Salanenka (2012), Dias et al. (2014), Yang et al. (2018), andPereira et al. (2020) showed that the deterioration process is intensified by the translocation of chemical products, especially by the use of insecticides, since the high permeability of the tegument facilitates the entry of such agrochemicals.Under these circumstances, the volume of slurry significantly contributes to maximizing the contact of these products with the tegument, leading to the death of the embryo.
As for the comparison between times of treatment, considering the industrial seed treatments (ISTs), in each storage period, it is possible to observe, with the exception of the IST 1 treatment, significant differences in the treatments employed.It is also noted that the longer the storage period, the lower the mean of the variable under analysis, both before and after seed treatment, and that, after IST, the mean of the FC variable under analysis increases, compared to the time prior to seed treatment.
As for the first count variable, in a comparison between seed treatments, after 15 days of storage, before and after chemical treatment, Table 2 shows that, in general, there are significant differences between treatments; treatments ISTs 6 and 7 present, in most periods, the lowest means for the FC variable, indicating a behavior similar to that observed with the SGT.
Regarding the comparison between times of treatment, considering the industrial seed treatments, after 30 days of storage period, with the exception of IST 1, significant differences can be seen in the treatments employed.It is possible to observe that, as the storage period increases, the mean of the FC variable becomes smaller, both before and after seed treatment.In this study, after seed treatment, the mean of the variable under analysis increases, in comparison with the time prior to seed treatment.Results from Matera et al. (2018) indicated that, after 45 days of storage, adding a biostimulating fertilizer to the industrial treatment ensured superior results in the germination of soybean seeds.
With regard to the ESI variable, it is possible to infer from the results contained in Table 2 that, in a comparison between seed treatments, considering each of the storage periods, before and after chemical treatment, that there are significant differences between treatments, with ISTs 6 and 7 presenting, in most periods, the lowest means for the observed variable.
When it comes to the comparison between times of treatment, considering the industrial seed treatments, in each storage period, statistically significant differences are verified, with the exception of the IST 1 treatment.Finally, as in the other comparisons between periods, it can be noted that, as the storage period increases, the means of the variables under analysis become smaller, both before and after IST, since, after the chemical treatment, the mean of the variable under analysis (ESI) increases in comparison with the time prior to seed treatment.Therefore, it is recommended that seed treatment be carried out close to the time of sowing.Under these circumstances, Zambon (2013) and Strieder et al. (2014) emphasize that seed treatment performed shortly before sowing minimizes possible toxic effects on germination and on adequate seedling development.Observing the FE variable, Table 3 shows that, in a comparison between seed treatments, considering each of the storage periods, with regard to the time prior the seed treatment, the results indicated significant differences between the treatments, with ISTs 5 and 7 presenting, in most periods, the lowest means for the variable under analysis.
With regard to time after seed treatment, it is noted that there are significant differences between treatments, with ISTs 4 and 7 showing, in a large portion of the periods, the lowest means for the FE variable.Based on results from Suzukawa et al. (2019), this behavior is due to the fact that the volume of slurry used is higher than that in the other treatments, since seeds treated with agrochemicals present a reduction in seedling vigor and emergence, respectively.
Concerning the comparison between times of treatment, considering the IST, in each storage period, it is verified, with the exception of the IST 1 treatment, that there were significant differences in the treatments used, in which a behavior similar to that of other analyzed variables is observed, with longer storage periods having the lowest means, both before and after seed treatment.Moreover, after IST, the mean of the FE variable increases, compared to the time prior to seed treatment.
Table 3 shows the results pertaining to the AA variable; it is worth noting that, when compared between the industrial treatments, considering each of the storage periods, before seed treatment, in general, there are significant differences between treatments, with ISTs 4 and 7 presenting once again, in a large portion of the periods, the lowest means for the aforementioned response variable.
As for AA, Abati et al. (2020a) found similar results showing that high slurry volumes associated with drying powder reduce the physiological quality of the seeds, since the moisture and composition of the mixture favors deterioration, resulting in low percentages of germination and emergence in soybeans.Referring to the period after seed treatment, it is observed, in general, that there are significant differences between treatments, with IST 7 (slurry volume of 1600 mL 100 kg -1 of seeds) presenting the lowest means for the aforementioned variable.
As for the comparison between times of treatment, considering the industrial seed treatments, in each storage period, it is noted, with the exception of the IST 1 treatment, that there are significant differences between treatments.It is also possible to see that, the longer the period of conventional storage, the lower the mean of the variable under analysis, both before and after seed treatment, and that, after chemical treatment, the mean of the AA variable was higher, in comparison with the time prior to seed treatment.Table 4 shows that significant differences between treatments were observed through the F test of the analysis of variance (p-value < 0.05), both in the main effects and in the double and triple interactions, that is, it was necessary to unfold the analyzed factors in order to identify where the statistically significant differences were found.The results contained in Table 5, referring to the RL variable, considering each of the storage periods, before and after seed treatment, allow inferring that there are significant differences between the industrial treatments, with the IST 7 treatment presenting, in a large portion of the periods, the lowest means for the variable considered.Such results corroborate with Ludwig et al. (2011), andAbati et al. (2020b), as well as with other authors mentioned above; the observed results are associated with the increase in moisture content in the seeds, since, as the slurry volume increases, the physiological potential is negatively affected, especially if the seeds remain stored for long periods.
With regard to the comparison between times of treatment, considering the industrial seed treatments, in each storage period, it is possible to see, with the exception of the IST 1 treatment, that there are significant differences in the treatments addressed.Observing RL, over the storage periods, it is noticed that, the longer the period, the lower the mean of the variable under analysis, both before and after chemical treatment.Results by Binsfeld et al. (2014) indicate that seed storage promotes irreparable damage to seed quality and vigor, since harmful effects are observed during the deterioration process.
When it comes to the result after seed treatment, the mean of the variable under analysis is higher compared to the time prior to IST.
It is possible to see, from the results contained in Table 5, that the SL variable, when compared between seed treatments, considering each of the storage periods, showed significant differences between treatments, with IST 6 presenting, in the majority of the periods, the lowest means for the variable under analysis.
With respect to the comparison between times of treatment, in each storage period, it is verified, with the exception of treatment 1, that there are significant differences in the treatments.This behavior repeats in relation to the period, indicating that longer storage periods lead to lower means in the response variable, before and after seed treatment; after IST, the mean of the variable increases, compared to the time prior seed treatment.
Based on the WSL variable, the results contained in Table 5 show that, when compared between seed treatments, considering each of the storage periods, significant differences between treatments were observed, with IST 7 (slurry volume of 1600 mL 100 kg -1 of seeds) showing, in most periods, the lowest means.For Abati et al. (2020a), seedling length, as well as other variables, is directly affected by slurry volume; however, such effects are mitigated by adequate temperature and storage.Referring to the comparison between times of treatment, considering the IST, it is noted, with the exception of treatment 1, that there are significant differences in the treatments adopted.It is possible to observe that the longer the storage period, the lower the mean of the variable; this condition is found before and after seed treatment, since, after IST, the mean of the variable under analysis increases, compared to the time prior to seed treatment.

Conclusion
The physiological quality of soybean seeds reduces as the volume of slurry used increases.The damage caused is intensified with the storage period, both before and after seed treatment.
The observed results indicate that sowing should be carried out soon after seed treatment, since, regardless of the chemical products used, the decrease in seed vigor is notable.
Note. * Means followed by distinct letters, lowercase in columns and uppercase in rows, differ from each other by Tukey's test (p-value < 0.05).
Note. * Means followed by distinct letters, lowercase in columns and uppercase in rows, differ from each other by Tukey's test (p-value < 0.05).

Table 1 .
Summary of the analysis of variance for the following variables: standard germination test (SGT), first count (FC), emergence speed index (ESI), final emergence in sand (FE) and accelerated aging (AA)

Table 2 .
Means obtained in the standard germination test (SGT), first count (FC) and emergence speed index (ESI) of soybean seeds, as a function of times of treatment, unfolded within the storage periods (SP) and industrial seed treatment (IST) Note. * Means followed by distinct letters, lowercase in columns and uppercase in rows, differ from each other by Tukey's test (p-value < 0.05).

Table 3 .
Means obtained in the tests referring to final emergence (FE) in sand substrate and accelerated aging (AA) of soybean seeds, as a function of times of treatment, unfolded within the storage periods (SP) and industrial seed treatments (IST)

Table 4 .
Summary of the variance analysis for the following variables: radicle length (RL), shoot length (SL) and whole seedling length (WSL) Note.*** Considered significant if p-value < 0.05 by F-test; SP: Storage Period; TT: Time of Treatment; IST: Industrial Seed Treatment; DF: Degrees of Freedom; CV: Coefficient of Variation (%); RL: Root Length; SL: Shoot Length, and WSL: Whole Seedling Length (WSL).

Table 5 .
Means obtained in the evaluations referring to radicle length (RL), shoot length (SL) and Whole Seedling Length (WSL) as a function of the times of treatment unfolded within the storage periods (SP) and industrial seed treatments (IST)