Germination Responses of Araribá (Centrolobium tomentosum - Guillem. ex-Bentham - Fabaceae) when Subjected to Different types of Betterments

Introduction

Ecological restoration and forest restoration actions are increasingly urgent to combat several current environmental problems. To make forest restoration viable, there is a need for fundamental raw material, which are the seeds.

It is known that seeds of different species have different germination potentials and vary in relation to the time they take to germinate. Technicians and researchers have acquired technical and scientific experiences to increase the germination potential of seeds and/or shorten the germination time.

Associated with the germination potential of seeds, we have the phenomenon of dormancy, which constitutes a physiological state or condition, for viable seeds, characterized by temporary inactivity. There are several modalities of seed dormancy, such as physiological, physical, combinational, morphological, and morphophysiological [1, 2]. The inactivity of the embryo occurs due to the absence of some external stimulus (for example, low humidity, inadequate temperature or light, or chemical conditions), or even immaturity of the embryo. This condition usually prevents the plant against adverse environmental situations and befriends germination (only) when environmental conditions are minimally adequate [3, 4].

However, both germination potential and dormancy are ecophysiological processes of the plants that influence the logistics, costs and success of activities such as agriculture and forest restoration and can be obstacles in these activities. In the context of forest restoration, which is an activity that normally demands rapid actions and results, breaking the dormancy may be a strategy to accelerate seedling production in greenhouses or even at the final planting site. There are several methods for breaking dormancy, some mechanical and others chemical [5].

For this study we tested dormancy-breaking methods for the species regionally known as Araribá (scientific name: Centrolobium tomentosum - Guillem. ex Bentham - Fabaceae). The biological and ecological aspects that justified the choice of this species for the present study are described as follows.

Results

Of the total of 54 seeds sowed, considering the six experimental conditions, 40.7% germinated. The treatment that showed the highest germination rate was the “dry with cutting” (Table 1). No germination was recorded of the seeds that were burnt to try to break dormancy.The overall average time for germination was 32.3 days. Of the total number of germinated seeds, 20 (90.9%) had their germination time between 30 and 38 days.

Two outliers of 24 days occurred, one in control condition and the other in condition H2O no cutting. The Kruskal-Wallis test showed no significant difference at p=5% between the experimental conditions where germinated seeds were recorded. The seeds that had a part of tegument cut, both immersed in water and kept dried, presented the lowest variation coefficients of time of germination. This can bring implications in works developed in seedling production nurseries, as explained ahead.

Discussion

Studies have shown that keeping the seed immersed in water for 24-48 hours at 25oC helps to overcome dormancy. The process that occurs is the rupture of the outer tegument [11]. However, the present study demonstrated that even in dry seeds, if the tegument is ruptured with the help of pruning shears, the result can be the same or better, and it is faster, since the process of cutting is rapid. Comparing the results and their respective methods, it is possible to infer that the type of dormancy we are dealing with is mechanical and that the use of the water immersion technique can soften the tegument and somehow facilitate the emergence of the embryo (facilitate, but not necessarily stimulate). For the cutting method, the fact that it causes a rupture in the tegument facilitates the emergence of the embryo, especially the root system. Perhaps the process of sanding the seed could result in a similar outcome, but because the outer part of the seed is thorny, handling the seed can become difficult, and cutting it, as explained and tested in this study, can bring advantages.

Although, as previously reported, Araribá seeds have little or no dormancy, the present study showed that the germination potential of the seeds can fall by half if no treatment is implemented, while if a slight cut is made on the side of the seed the germination potential increases. The treatments that had cutting as an intervention action showed lower coefficient of variation values for germination time. For work involving seedling production nurseries, this information may be important, since greater uniformity of germination and growth means optimization and facilitation of the logistics of seedling management work [12, 13].

The fact that there were no survivors for the seed lots that were subjected to the burning process (dry or immersed in water) suggests that, in areas of Cerrado that experience the occurrence of fire events and have C. tomentosum seeds on the soil surface, such seeds will have little or no chance of surviving, possibly compromising the seed bank of this species. In this context, it seems more likely that individuals of the species survive fires and can resprout than that their seeds survive and germinate after fire events [14].

Final Remarks

This study showed that the seed burning procedure was not successful in germinating and breaking dormancy in the species studied.

The procedure of keeping the seeds immersed in water, which is the most common according to the literature, presented identical results in terms of germination for the seeds that were not cut.

It was demonstrated that the procedure of only cutting the seed (without immersion in water) provided the best results in terms of germination when compared to the control condition, and the seeds in the control condition (which did not undergo any type of intervention) presented a shorter germination time.

The results obtained in this study raise a question: is there a distorted concept about the techniques for breaking dormancy in Araribá (previously immersion in water, now evolving to small cuts in the epicarp) or are we studying a species that presents a dormancy pattern known as complex or combined dormancy? To adequately answer this question, new, more detailed studies need to be conducted. Perhaps other dormancy-breaking methods may be even more efficient.

Declaration of Competing Interest and Declaration of Use of Artificial Intelligence

The author declares that he has no known competing monetary interests that could have appeared to influence or manipulate the work reported in this manuscript.

The author also declares that the manuscript was elaborated manually (hard work!!!) and AI was used to improve English grammatical elements of the text.

Acknowledgements

To the Campus of the Sorocaba Institute of Science and Technology - Unesp, for providing the space to carry out the study.

Availability of Data and Material

The data is available upon request to the authors.