Mechanical Scarification, Seed Origin, and Substrate Influence on Germination of Samanea Tubulosa
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bioRxiv preprint doi: https://doi.org/10.1101/2020.02.10.940759; this version posted March 26, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. Mechanical scarification, seed origin, and substrate influence on germination of Samanea tubulosa Leonardo L. P. Regnier1* 1 Departamento de botânica -Instituto de Biociências- Universidade de São Paulo - R. do Matão, 187 - Butantã, São Paulo - SP, 05508- 09036036-900, Brazil *Corresponding author: [email protected] ABSTRACT Samanea tubulosa is an important species mainly to its uses in reforestation projects and as a wood and fruit resource. This species seed dormancy and other scarce germination information have been limiting the adequate seedling production process. Thus, this study tried to understand how seed origin, mechanical scarification, and substrate could influence the seedling production process. The population affected the time required for germination and germination speed, probably due to high genetic variability. Whereas mechanical scarification did not present statistical differences in the control treatment, with seeds in the natural condition, indicating that seed dormancy could be variable. Substrate promoted significant differences in germination rate. The population seems to affect, but not preclude seedling production. Mechanical scarification did not provide a relevant enhancement of germination. Vermiculite presented a significantly higher germination rate than the organic-based substrate. Keywords: Forestry seeds, Fabaceae, Seedling production, Sete-cascas, Saman afforestation and reforestation programs, especially in disturbed areas 1. Introduction [2]–[5]. Samanea tubulosa (Benth.) Fruits are the main source of this Barneby & J. W. Grimes, popularly species. They are usually employed as known in Brazil as Sete-cascas, and cattle food and when empowered are Saman in Spanish America, is an applied to goat and chicken feeding arboreous and deciduous tree. This because of their high protein and sugar species is native to South America and content [1]. Fruits can be eaten by presents high tolerance to sunlight and humans and are usually utilized in the natural occurrence fires of Cerrado, cachaça production, resulting in the Brazilian savannah. It is “Aguardente-de-saman”. The wood characterized as a pioneer species, from this species is widely exploited, colonizing glades and open fields [1]. especially in the furniture industry and This species is commonly used in urban bioRxiv preprint doi: https://doi.org/10.1101/2020.02.10.940759; this version posted March 26, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. fences [6]. Alcohol production, timber, However, this seed dormancy and paper production are other recent overcoming procedure is very expensive uses of this species [1]. and imposes some practical obstacles. Seed dormancy is characterized by In general, these compounds are very seeds that even when exposed to difficult to manage when a large favorable environmental conditions, number of seeds are submitted to this such as light exposure, moisture, process, present the risk of accidents oxygen, and temperature, they do not [9], [11], or even generate wounds to germinate [7], [8]. Seed dormancy is a seed embryonic tissues [7], promoting common problem in the seedling abnormalities in seedlings [14]. production of arborous trees, and Alternative methods, such as hot water especially frequent in the Fabaceae treatment, are mentioned as not family [7], [9]–[11], being nocuous to the adequate to overcome S. tubulosa seed seedling production process because dormancy [10], [11]. fast and uniform germinations are Mechanical scarification is required [10]. recommended by some authors [4], [7], Understanding seed behavior [11], [15] as a viable alternative to from seeding until seedling chemical scarification. However, these establishment is also important for the authors recommend manual successful application of wild species in scarification techniques with sandpaper reforestation programs [12], [13]. Thus, and discourage the use of the rotary recognizing techniques that could drum because of the great damage that improve the seedling production this last technique could provide to the process is important [10], [11]. embryo. Oliveira et al. [10] also Especially of S. tubulosa since it is one of measured the impact of mechanical the most indicated species to use in this scarification of S. tubulosa with scissors. kind of project and urban afforestation. In addition, these mentioned The S. tubulosa high-level mechanical methods are infeasible in dormancy is already recognized as a the seedling production context, which result of its impermeable tegument [1], requires the processing of an extensive [6], [7]. In general, in the natural number of seeds without taking too environment, temperature variations, much time. acid soil, microorganism metabolism, In general, to forestry seeds, the and animal consumption of fruits are parent plants seem to influence the main methods to overcome seedling quality [16]–[18]. Affecting dormancy [11]. Chemical scarification some germination parameters, such as using acid compounds is the most the total germination rate [19], the time common pre-germinative procedure to required for germination, or even both overcome S. tubulosa seed dormancy. [18]. This aspect is very important to be bioRxiv preprint doi: https://doi.org/10.1101/2020.02.10.940759; this version posted March 26, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. analyzed because, in the seedling Plant material was collected in production context, the choice of a the city of São Paulo between progenitor population used as seed September and October of 2018 from sources could affect seedling two different populations about 125 km production [16], [17]. away from each other. The harvesting The substrate is essential for method consisted of mature fruits seedling germination [11]. Conflicting gathered directly from the ground. The information could also be found about material was kept in open plastic bags at the best germination substrate, while room temperature for 15 days to some authors point out that to S. recognize the emergence of insects tubulosa better germination indexes and/or pathogens [17]. After this period, were obtained when sowed in the fruits were opened and seeds were organic-based substrate [20], others removed, as indicated by Carvalho [1], affirm that vermiculite is the best using a rubber hammer. substrate for S. tubulosa production Population influence on [11]. However, proper comparison germination was measured using 630 between germination on inert seeds from population I and 126 from substrates such as sand or vermiculite population II. These seeds, without and in the organic-based substrate has treatment, were planted in 280 cm³ not been extensively explored. greenhouse tube, with an organic-based Thus, this study focused on substrate composed by 2 liters of local understanding how mechanical horizon B soil, 8 liters of rice husk, 5 scarification, seed origin, and substrate liters of Basaplant® forestry substrate, could influence Samanea tubulosa 46.5g of Yoorin K® potassium germination. thermosetting fertilizer, and 46.5 g of gradual release fertilizer Osmocote 2. MATERIAL & METHODS Plus®. Evaluation of the seed processing method involved a sample of 252 This study was conducted at the scarified seeds and 630 seeds in a Harry Blossfeld plant nursery of São natural condition, planted in the Paulo, situated in the city of Cotia previously mentioned organic-base (23°36'30.0"S 46°50'48.9"W). According substrate and greenhouse tubes. The to Köppen’s climate classification, the mechanical scarification procedure study area presents Cwa, an altitude consisted of the use of electronic emery tropical climate [21]. Featuring until conspicuous seed tegument moderate and concentrated rains rupture of the opposite side of the during summer, dry winter [21], and the mycropile. highest mean temperature above 22°C. bioRxiv preprint doi: https://doi.org/10.1101/2020.02.10.940759; this version posted March 26, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. Seeking to test substrate tubulosa seed germination (Figure 1) influence, 252 scarified seeds were since we observed only differences sowed in the same previously between the mean germination rate mentioned organic-based substrate and (Figure 1B), mean germination time the greenhouse tubes. While 1452 (Figure 1C), and Germination speed scarified seeds were seeded in white (Figure 1D). Germination rate (Figure 1A) polypropylene trays containing was not affected by seed origin during vermiculite as the substrate. the analyzed period. These same After all the mentioned indexes were also affected when treatments, the material was kept in a comparing the population influence to greenhouse with white plastic covering Pterocarpus rohrii, another species of and a fogging watering system with the Fabaceae family [18]. periodic activation every 35 min. Plant Mean germination time (MGT) emergence was recorded about 20 days represents the mean time