ORIGINAL ARTICLE

Effects of scarification and storage on vigor expression of Albizia lebbeck (L.) Benth seeds

Efectos de la escarificación y el almacenamiento en la expresión del vigor de las semillas de Albizia lebbeck (L.) Benth

Marlén Navarro,^I G. Febles,^II Verena Torres,^II

ABSTRACT

An experiment was developed to estimate vigor of A. lebbeck seeds, related to the effect of scarification treatments (sulfuric acid, hot water, 24 h soak, cover cutting, puncture and control) and storage time (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 months after initiated the storage, mais) with vigor expression. According to the methodology, the analyzed variables were: days before the beginning of emergence (E), percentage of final emergence during test period (Emer), peak day (PD), peak emergence (PE), germination value (GV), germination energy (Ener) and emergence rate (ER). These variables were evaluated at the nursery. A general assessment of results shows the negative effects of acid and hot water methods on vigor expression of albizia seeds. It may be concluded that pre-sowing treatments, applied through dry and wet scarification, showed cut efficiency of cover and soak, respectively, as promoting methods of germination, emergence and efficiency of vigor. Except acid and hot water treatments, the rest of the treatments showed the best expression of variables related to vigor at 3 mais.

RESUMEN

Se desarrolló un experimento para estimar el vigor de las semillas de A. lebbeck, relacionando el efecto de los tratamientos de escarificación (ácido sulfúrico, agua caliente, remojo 24 h, corte de cubierta, pinchazo y control) y el tiempo de almacenaje (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 y 12 meses de iniciado el almacenamiento, mdia) con la expresión del vigor.  De acuerdo con la metodología, se evaluaron en vivero, las variables: días para el inicio de la emergencia (IE), porcentaje de emergencia final para el período de la prueba (Emer), día pico (DP), emergencia pico (EP), valor de la germinación (VG), energía de germinación (Ener) y tasa de emergencia (TE). Una valoración general de los resultados muestra la afectación que producen los métodos del ácido y el agua caliente en la expresión del vigor de las semillas de albizia. Se concluye que los tratamientos pre-siembra, aplicados mediante la escarificación seca y húmeda mostraron la eficacia del corte de cubierta y el remojo, respectivamente, como métodos propulsores de la germinación, la emergencia y la eficiencia del vigor. Con excepción de los tratamientos con ácido y agua caliente, el resto mostró la mejor expresión de las variables relacionadas con el vigor a los 3 mdia.

INTRODUCTION

The main challenge of researches on vigor tests is the identification of indicators related to seed deterioration, which precede the loss of germination ability and quality (Navarro et al. 2015).

 Vigor tests are based on concepts like stress resistance, germination speed, membrane integrity and plantlet development (Matthews et al. 2012). Detection of seed deterioration through vigor tests may be considered as an important component in the evaluation of elements related to quality and contributes to the particular characterization of seed industry and solution of problems, like storing. In addition, for dormant seeds, it is essential to decide which pre-sowing treatment should be used, resulting in a better security and success of planting with each seed lot.     

Navarro et al. (2012) stated the conceptual bases to establish the importance and efficiency of some biological variables during storing of seeds, in relation to vigor variability. Therefore, these authors adapted the statistical model of Torres et al. (2008) for measuring impact of innovation or technological transfer in agricultural and livestock field, and proposed an original and integral methodology for seed vigor estimation, as a quality indicator and later sowing success of plantation.

Previously, Febles et al. (2011a, b) used the method of Torres et al. (2008), to determine the influence of edaphoclimatic factors on the production of tree, forage legumes and grass seeds in different regions of Cuba.

In a general sense, although there are several methods available for testing vigor with established procedures and reliable results, there is always a chance for improvements or inclusion of more precise, objective and registered alternatives (Filho 2011). Therefore, the objective of this experiment was to estimate vigor of A. lebbeck seeds, related to the effect of treatments of scarification and storing time with vigor expression.

MATERIALS AND METHODS

In order to evaluate vigor expression, a methodology proposed by  Navarro et al. (2012) was used, through the study of variables measured during the emergence of plantlets in each pre-sowing treatment at the greenhouse, under the sun. Six methods of scarification were evaluated in 13 storage times. For sowings, bags with a substratum composed by a mixture of red ferrallitic soil and organic matter were used, equally distributed (1:1). Before sowing, different methods of scarification (table 1) were applied, and there was a control, in which seeds received no pre-sowing treatment.

Evaluation frequency corresponded to storing times: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 mais. Irrigation was carried out until reaching field capacity of substratum.

According to the procedures described by Navarro et al. (2012), the analyzed variables were: days before the beginning of emergence (E), percentage of final emergence during test period (Emer), peak day (PD) peak emergence (PE), germination value (GV), germination energy (Ener) and emergence rate (ER). These variables were evaluated at the greenhouse, under the sun.

Later, and according to the proposed methodology, variables more related to vigor variability were defined. The relationship between biological variables and storing time was determined through the efficiency index (Ef), for establishing vigor groups, which will be composed by different storing times per each of the evaluated scarification treatments.

For processing the obtained information, the statistical model proposed by Torres et al. (2008) was used, and with data obtained from the evaluations at the greenhouse, a matrix of data was produced and premises of the application of multivariate methods were confirmed with the matrix of correlation. Statistical analysis allowed, first, to identify and select the order of importance of variables in the explanation of vigor variability and, second, classify the evaluations (storing times) according to pre-sowing scarification methods with support of efficiency index (Ef) and definition of groups with low and high vigor per each pre-sowing method. The statistical software SPSS, version 15 (StatPoint Technologies 2010) was used.

RESULTS AND DISCUSSION

Eingenvalues and explained variance (tables 2 and 3) evidenced that, in each evaluated pre-sowing method, variability was superior to 85 %, when most of them were grouped in the two first main components. According to Martín et al. (2008), this is interpreted as an accurate selection of variables that could be related to vigor.

Identification of importance order of variables related to vigor. Emergence, as the emergence rate, appear as the variables with higher preponderance values in all used treatments, even in the control (tables 2 and 3). This performance indicates that emergence rate is an indicator of considerable importance for vigor estimation, in agreement with Copeland and McDonald (2001) and Laskowski and Bautista (2002). This may be a negative factor from an agricultural point of view, because it does not allow to achieve, at the same time, a uniform plant population, regarding size and quality. On the other hand, emergence of plantlets is mainly related to time and speed of seed germination, which may be influenced by biotic and abiotic factors, as well as the election of sowing date (Gardarin et al. 2011).

When sulfuric acid was used as wet scarification method, variables emergence, energy and emergence rate were equally important in the main component 1(MC1). In the second component (MC2), variables beginning of emergence and peak day were also highlighted.

For hot water in MC1, the most important variables were emergence, peak emergence and emergence rate. In MC2, the essential ones were germination value and energy. For MC1 of soak method, emergence and emergence rate were the best variables and, in the second component, only the beginning of emergence was high.

For dry scarification and control, variables selected in MC1 were emergence, emergence peak, germination value, energy and rate of emergence, with similar values. In MC2, beginning of emergence and peak day were selected (table 2).

Because these mentioned variables vary the most, numerically, it may be stated that, through its analysis, seed vigor may be estimated.

Emergence rate is positively related to fast emergence in the field and to the development of many species of plantlets, while fast emergence is an obvious advantage for plantlet establishment. Filho (2005) defines germination speed as one of the first properties that are affected during seed deterioration process. Therefore, germination speed is an expression of seed vigor. According to Schmidt (2000), it is called “germination energy”.

Time of emergence, usually, determines whether a plant may successfully compete with its surroundings, it is consumed by herbivorous or flowers, reproduces and matures appropriately at the end of its growing stage (Forcella et al. 2000). Therefore, an emergence in short periods of time is also an indicator of high vigor in seeds.

Santorum et al. (2013), after evaluating vigor in soybean seeds, found that emergence rate, germination speed index and emergence speed were the tests of better correlation to emergence. Similar results were obtained in this study, after selecting variables with better relation in the expression of vigor variability.

Clasification of storing times for every pre-sowing scarification methods. Tables 4 and 5 show the efficiency of each variable for vigor estimation, after seeds are sown at different storing times. Navarro et al. (2012) stated that efficiency index depends on variables with the highest preponderance, and also expressed that the highest positive values indicate which have more influence on a particular storing time.

Wet scarification. For acid method, in the evaluation at 4 mais, there were better expressions of MC1 variables, without underestimating those values that appear at 9 and 11 mais, while at 6 and 7 mais, these variables had the worst expression.

In the hot water method, variables that typify MC1 showed the best positive effect, only at 9 mais, as well as at 0 and 4 mais for MC2, while the effect was negative for 9 mais in this same component. In this storing time, there was the worst expression of variables of MC2 (value of germination and energy). It is necessary to highlight that results of the experiment did not favor these two pre-sowing methods because, in the case of this study, these are aggressive pre-treatments that affect, probably, the embryo. This is consistent with the criteria of Navarro et al. (2010a, b).

In the case of soak, it did not occur in the same way. Storing times in which emergence and emergence rate (MC1) had the best expression were 1, 3 and 4 mais. The highest index was at 3 mais and the worst were found at 9 and 12 mais. According to efficiency index, the most negative value for the beginning of emergence (MC2) appeared at 3 mais, but this is biologically beneficial because if there is a high number of days, the delay for the beginning of emergence is lower.

Although the analysis of main components (AMC) only identified three variables in soak, this is not a deficiency of the method because these three are related to important measures in the development and growth of plantlets. Obviously, emergence is a manifestation of seed vigor and, together with emergence rate, it is supposed that plantlets emerge at a faster rate, which is maximized in those plantlets that emerge at a lower time. This coincides with reports from Salinas et al. (2001) y Valadez et al. (2007).

As previously stated, it is important to highlight that, in the control, all studied variables were distributed between both components. This may indicate that, due to the negative effect of acid and hot water, performance of peak emergence and germination value was affected for the acid method. For hot water, the affected variables were peak day and emergence rate. The fact that these variables had no influence on storing time may be an indication of deterioration of quality and, consequently, seed vigor. This idea was similar to that stated by Mandal et al. (2000) and Rajasekaran et al. (2005). These indicators are essential for the processes of germination, emergence and development so there should be a logic agreement to the performance of crops in the field.

Dry scarification and control. Regarding vigor manifestation, puncture and cut were less aggressive than acid and hot water. Previously, the way in which both methods may contribute to performance of germination and emergence was stated, which is confirmed with the values from table 5.    

According to this table, there was a positive performance for variables that typify MC1, sowing seeds that received a puncture at 3 mais. Likewise, there were positive results of sowings at 0, 5 and 9 mais, for selected indicators in MC2. At 2 and 4 mais, there were negative results.

In the case of cover cut, at 2 and 3 mais, there was a better expression of MC1 variables, and at 5 mais for MC2. The worst values were found at 8 mais (MC1) and at 3, 4 and 8 mais (MC2) for variables beginning of emergence and peak day.

In control treatment, the best values appeared at 3, 4 and 6 mais for the best represented variables in MC1. For MC2, the most positively related storing times were 5 and 9 mais, while the most negative were 2, 8 and 10 mais.

These results agree with reports of Navarro et al. (2010a, b), which refer that cut showed high efficiency in the surpassing of dormant states for A. lebbeck species.

Group formation. From the efficiency indexes in each pre-sowing method, there was an analysis of the existence of storing times with similar performances, so responses to pre-sowing methods were the most efficient as possible in the estimation of seed vigor.

In the grouping process of each pre-sowing method, it was decided to perform the cut for a certain dissimilarity coefficient (table 6), which favored the classification of storing period (evaluations) and the formation of groups. Space representation of dissimilarity coefficient in known as dendrogram. According to Hair et al. (1999), this is a quantitative estimator that describes the degree of association of similarity among compared elements.

Definition of vigor groups. For the selection of groups, where vigor was more efficiently expressed, those selected had the best global performance in variables with the best preponderance in the MC1 for each scarification method.

Acid. In the evaluation at 4 mais (group IV), the highest means appeared for variables germination value, emergence, energy and rate of emergence (table 7). In addition, according to results of table 3, the highest positive value of efficiency index was registered at 4 mais.

It is important to state that the analysis allowed to determine that the highest value of vigor is expressed after the application of H₂SO₄ as a pre-sowing treatment in seeds with 4 mais. Nevertheless, this criteria could be too rigid and, probably, it should be convenient to flexibilize this concept and evaluate another or other groups close to the best, according to the performance of variables that appear in MC and MC2, and with efficiency index. According to these assumptions, group I may be evaluated, which includes 0, 9, 10, 11 and 12 mais storing times. Likewise, variables selected in the AMC (table 2) in groups 1 and 4 (78 %), have a relatively superior expression in the months that appear in both groups (tables 2, 5 and 6). This interpretation is supported by the analysis of storing times included in both groups and efficiency index. The best expression of variables was at 4 mais and in the 80% of storing times from MC1 and/or MC2.

Hot water. In group III, the highest means for emergence, peak emergence and emergence rate were observed. It means that seeds from this group emerged in a higher percentage, more regular and at a higher rate (table 7). These same variables were identified by the AMC as those that varied the most when seeds received pre-sowing treatment with hot water (table 2).   

Results lead to state that the highest vigor corresponded to those seeds that were sown at 9 mais (group III), after remaining three minutes under water at 80 °C.

Group II included the evaluations that, together, showed the lowest values of beginning of emergence, peak day and emergence rate. This performance indicates that seeds from this group had a faster beginning of emergence and, at the same time, maximum daily emergences were registered earlier. However, they showed the worst percentage of plantlets at the end of the test (21 d) and the lowest percentage of plantlets during the same day. These last variables, besides the emergence rate, were the ones represented in the MC1 (table 2).  At the same time, evaluations comprising group II showed negative values of efficiency index (table 4). Therefore, unfavorable performance in group II identifies it as the worst expression of vigor.

The highest values for beginning of emergence and peak day were found in group I. This agrees with the results of group I with H₂SO₄ treatment. The effect represented by both values was previously explained. However, these two variables were not considered in the extracted main components (table 2). Group I had the highest means for germination value and energy (variables of MC2), and these variables showed efficiency in the evaluations 0 and 4 mais (group I). All this reasoning allows to state that group I shows seeds with mean vigor expression.

In order to assess other groups, close to that with the highest vigor, group II was analyzed, which owns storing times 1 and 3 mais. In this group, the two variables selected in MC1 (table 2) showed values relatively close to those of group III (high vigor). Variables of MC1 (EfMC1) had the best expression at 1 and 3 mais.

 In group IV (9 md), the emergence began faster, but the percentage of emerged plantlets was lower for the soaking method and, in turn, occurred the worst mean values for peak emergence and emergence rate. Added to this, the efficiency index was the highest negative value at 9 mais (table 5), which was manifested in the variables expressed in MC1 showed the worst performance in this evaluation. This analysis showed that group IV had the worst performance for seed vigor expression in the soaking method.

Puncture. In the puncture, it was deduced that seeds showed the highest vigor at 3 mais (group III). The highest values of the variables, chosen in the MC1 (tables 3 and 7), and the highest positive value of the efficiency index (table 5) appeared at 3 mais.

Group IV showed the lowest mean values for percentage of emergence, peak emergence, germination value and energy, which are four out of five variables identified in the component 1 (table 3). In the evaluations of group IV, there were negative efficiency indexes (EfMC1), which allowed to decide that this group showed the worst performance of seed vigor expression.

Cover cut. After conducting a cut on the seminal cover at 3 mais, seed vigor was higher. In group III, as in the best group of puncture (3 mais), the best mean values of emergence, peak emergence, germination value, energy and emergence rate (table 7) were found, which were the same variables that represented MC1 (table 3). Table 4 shows that, at 3 mais, the highest positive efficiency index was found for EfMC2, and one of the highest negative EfMC2. In the latter, this performance is advantageous, in which, as explained above, variables beginning of emergence and peak day were more favorable as their values were lower. However, deciding that 3 mais was the evaluation of the highest vigor is a rigid assertion. Group II (2 mais) contained the second best values for the variables identified in the MC1 (56%), and its expression in the efficiency index was similar to that exhibited at 3 mais.

Group IV showed the lowest values of emergence: peak day, peak emergence, germination value, energy and emergence rate. According to Table 5, in this evaluation, the highest negative value of the efficiency index was recorded, indicating the negative performance of MC1 variables (Table 3) in this storing time, so group IV is considered as the group with the worst vigor.

Control. In group III, there were evaluations in which seeds expressed the highest vigor. This group contained the highest means for the percentage of plantlet emergence, peak emergency, germination value, energy and emergence rate, as well as the lowest value for the beginning of emergence (table 7), which is a very positive aspect. In general, it can be stated that the seven variables related to vigor in group III (2 and 3 mais), distributed between MC1 and MC2 (table 3), showed the best performance, which is also demonstrated in table 4. It should be noted that 3 mais corresponded to the evaluation that recorded one of the highest positive values of the efficiency index (EfMC1) and, simultaneously, a considerably high negative value (close to 1) for EfMC2. A similar performance for efficiency indexes was observed at 2 mais.

Nevertheless, storage times 1, 4, 6 and 7 mais, contained in group II, should not be discarded, because results pointed this group as the closest performance to group III, due to the means of selected variables by the MCA, but also by the efficiency with which variables were expressed at storing time. Group II can be considered of medium vigor.

Group IV (table 5) had the minimum evaluations (table 7) for percentage of emerged plantlets, germination value, energy and emergence rate, as well as the highest mean value of beginning of emergence and peak day. As it has been repeatedly explained, these values are adverse for the plantation. Added to this, table 4 shows that evaluations of group IV presented high negative values for the efficiency index in the MC1 (EfMC1) and high positive values in the MC2 (EfMC2). Seeds evaluated in storing times (5, 9, 11 and 12 mais), contained in this group, showed the lowest vigor for control method.

A general assessment of the results of different scarification treatments demonstrated the effect that produce acid and hot water methods on vigor expression of albizia seeds. Navarro et al. (2012), in a study on the germination performance of albizia seeds, ratified the aggressiveness of both pre-sowing methods for the embryo. As for the storing time, results are consistent with Corbineau (2012), who stated that seed vigor affects the sensitivity of plantlets to external factors and storing capacity of seed lots.

CONCLUSIONS

With the use of appropriate methods, aspects of seed quality were evaluated through the study of germination viability, dormancy and aging. Pre-sowing treatments, through wet and dry scarification, showed the efficiency of cover cut and soaking, respectively, as propellant methods of germination, emergence and vigor efficiency. Except for the treatments with acid and hot water, the rest showed the best expression of variables related to vigor at 3 mais.

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Received: 28/09/2015
Accepted: 01/08/2016

Marlén Navarro, Estación Experimental “Indio Hatuey”. Universidad de Matanzas “Camilo Cienfuegos”. Central España Republicana. CP44280. Matanzas, Cuba. Email: boulandier@ihatuey.cu