Introduction

Seed growth needs proper nutrition from plant during the reproduction process. Seed reserves sufficient nutrition  and food for plant development at germination stage (HELENURM, SCHAAL 1996, CORBET, 1998). The study of  seed germination is important to determine the management information of the plant species for conservation and  economical value (MELO et al., 1998). Also, photoperiod influences the dormancy, flowering, tuberization and  abscission of the plant growth in semi-dry season. The tropical plants may not influence always due to heavy rainfall  for growth of plant (STUBBLEBINE et al., 1978). However, photoperiod is important factor for flowering and sexual  reproduction of the plants through cross pollination (THOMAS; VINCE PRUE, 1997). The study of photoperiod in  controlled light shows that length of day may affect the plant growth (KLEIN et al., 1996; ZAIDAN; FELIPPE 1994). 

The genus Bauhinia (Fabaceae-Caesalpinoideae), consists of 250 species found in America, Africa, Asia and  Oceania. It is widely known as pata-de-vaca. Bauhinia holophylla Steud is found in Brazil. Its height is 0.4 meters to 4 meters in semi deciduous seasonal forest. The roots are long and hard with xylopodium to  survive in hot and dry condition.

The objective of this study was to investigate the reproduction of B. holophylla using seed and xylopod and to determine the role of photoperiod in influencing the formation of xylopodium in controlled greenhouse and soil conditions.

Materials and Methods

Seeds of fruit were collected at the Mogi Guaçu Biological Reservation center. The study was conducted in (RBEE) (Martin Prado Júnior, São Paulo) (MANTOVANI; MARTINS, 1983). To evaluate the germination and photoperiod effect, 30 seeds were placed in six petri dishes (9.0 cm in diameter), containing filter paper moistened with distilled water. Petri dishes with seeds were placed into the germination chamber (BOD) with light conditions (160 W), relative humidity (± 80) and continuous temperatures (20°C, 25°C, 30°C, 35°C ) under the white and dark light. Germination were observed every day. The growth of roots is considered as the germination of seed.

The germination (G) was calculated by the method described by Labouriau (1983), the rate of germination (GSI) by Ferreira Borghetti (2004) for the study with 30 days. After 3 months, the germinated seeds were placed in a container with grassy soil (2.5 L) and treated with different photoperiod for 8, 12, 16 and 20h. After that the seeds were placed separately in bright light and fluorescent light chamber with 3.5 mol photons m^-2 s^-1 (RUGGIERO, ZAIDAN 1997, RONDON, 2006; ZAIDAN; CARREIRA, 2008). The height, diameter, number of stem leaves were considered as the growth of plant at each month. The plants were collected after 10 months according to stem, leaves and root and placed in a plastic bag to dry with 60°C. After 4 months, the plants were weighed to determine the weight. 

Statistical analysis

All data were analyzed using one way ANOVA.

Results

Figure 1 shows the data of temperature, humidity and rainfall in the RBEE of Moji Guaçu from June to November 2017, when experiments and field observations were made.

Figure 1. Climatic data obtained from Moji Guaçu Biological Reservation center and experimental meteorological place, Moji Guaçu, SP, during the study period.

The rain is started in August and September, and the heavy rainfall was observed in December and January. This period considered as the beginning of plant growth time. The dry season was considered as low temperatures and low rainfall in May, June and July in RBEE in Moji Guaçu.

After 10 months of daily photoperiod treatments, it was observed that the stem length and the number of leaves of plants were 16 to 20 hours long in compared to the plants treated with 8 and 12 hours (Table 1).

Table 1. Growth of Bauhinia holophylla seedlings behavior at different photoperiod treatments for 10 months.  The degree of results are shown with capital and small letters.

Plants were grown with photoperiod of 16 and 20 hours which showed high values of 0.26 and 0.38 mm of diameter, respectively. The diameter and number of leaves of plant were not significantly different at 8 and 12 h photoperiod time (Table 1). Plants exposed to 16 and 20 h photoperiod treatments showed 4 times more leaves than in plants exposed to 8 and 12 hour photoperiods (Table 1).

The dry weight of different parts of the plant was higher in the plants kept in the photoperiod of 20 h, which values of dry mass (stem + root) were 700 g and 1600 g, respectively (Figure 2). The dry mass ratio of shoot and ground was higher in 16 and 20 h photoperiod treatments (Figure 2).

Figure 2. weight of underground and aerial part of Bauhinia holophylla with different photoperiodic treatments after a period of 10 months. Letters compare the dry mass of different treatments (Tukey 5%).

The results showed the significant difference (Tukey 5%) among the number of healthy seeds (66.9%), predated (13.7%) and aborted (19.4%) seeds.

Discussion

In the present study, it was observed that the photosynthesis of the plants showed a greater influence in plant growth for photoperiod (RONDON et al., 2006). The effect of photosynthesis was also observed in B. holophylla plants with 20 h photoperiod treatment which showed high dry mass in compared to the other parts with different photoperiod. B. holophylla of 60 and 210 days of age were placed in continuous light showed high number of leaves and dry mass than B. holophylla treated with shadow.

Diplosodon virgatus Pohl. (Lythraceae), a sub-forest species grown in the savanna, showed that the growth and flowering behavior with 12 and 16 h treatments were significantly different from short photoperiods. This result showed a long-day flowering behavior of the plant (CESARINO et al., 1998), which supports the results of B. holophylla. The growth of xylopodium was observed in one-month old B. holophylla with long photoperiods. However, similar results were observed for young B. holophylla with controlled photoperiod conditions which could be comparable to D. virgatus with long day photoperiod. B. variegata L., an exotic species, grown in four photoperiodic treatments showed higher growth in long-day photoperiodic treatments than B. holophylla (RONDON, 2006). Despite photoperiodic treatment, the leaves were usually better length in long days. Number of leaves are increased due to long photoperiod and is useful for the plant growth as better photosynthesis. Thus, photosynthesis is important to increase the number of leaves and thereby increasing the dry mass.

The seedling behavior of B. holophylla did not show any significant difference for germination due to photoperiod and temperature. However, the germination rate was higher at 25°C in dark and constant light conditions. Therefore, the light and temperature (25°C and 30°C) have no effect for the germination of seed in savanna due to less interaction between seed and soil and this is dependent on only on temperature. Felippe and Silva, (1984) analyzed the germination of several species of Savanna and found that the most of plant species can germinate at the temperature of 25°C and 30°C. Although the number of seeds of B. holophylla is high, the damaged seeds shows low production in savanna. This result may be due to absence of cotyledon seedlings B. holophylla.

Furthermore, B. holophylla seeds treated with chemicals for 12 minutes shows that the germination is high and constant at 27°C. In addition, this showed no difference due to light. So, chemical treatment can be standardize method to improve the germination process.

However, B. holophylla seeds have no dormancy behavior which is a common feature of legume species (POPINIGIS, 1977; LOPES MATHEUS, 2008).

The B. holophylla seed is kind of food for the Coleoptera Gibbobruchus cavillator (Fahraeus). So, partially eaten or damaged seeds and cotyledons do not conatin starch, sugars and other nutrition such as galactose, glucose and arabinose constituents of the endosperm which is important for germination. These sugars are the energy sources for the germination and development of the seedling. The endosperm cell wall swells after interaction with water. The cell wall of B. holophylla seeds also can swell and release galactomannan, polysaccharide, to enhance the access of water in the seed for growth and germination (BUCKERIDGE et al. ., 1995).

B. holophylla seeds shows a considerable amount of starch in the cotyledonary parts In biochemical studies of B. holophylla seeds at different stages of imbibition observed throughout the pre-embedding process followed by germination, for up to 168 hours at 30°C in constant light. In our preliminary study, seeds of B. holophylla was considered to store for one year at room temperature (N = 250) but it is shown that(30% of pre-dried seeds with perforation due to predatory insects (RONDON, 2006). The larva of insects were found inside the seed at the time of flowering. This seed has lateral perforations due to oxypopods in the floral hipantum in savanna.

The presence of xylopodium was also observed in Terminalia argentea L. (Ferreira et al., 1998) and B. holophylla (VAZ; MARQUETE, 1993) and other savanna species. According to Barroso et al., (1984). This part works as a reservoir through an effective adaptive activity, because it allows plants to prevent unfavorable edaphic and climatic conditions (RIZZINI, HERINGER, 1962, LABOURIAU et al. 1964). The presence of this organ favors the regrowth of the aerial part when it is damaged because of fire.  Thus the growth of the aerial part of the savanna species can be able to grow again (EITEN, 1990; VAZ; MARQUETE, 1993).

B. holophylla can be grown in rough condition due to presence of starch stored in the root as a reserve source. Plant roots of B. holophylla shows 30% starch at three months of age.

Vegetative propagation may be considered as main factors of the growth of plant because some studies shows that some plants are grown in Roupala Montana and Itirapina Savanna, which is damaged due to fire of 18 years ago with low growth rate (MIRANDA-MELO, 2004).

Conclusion

In conclusion, B. holophylla young plants can grow from xylopodium in the savanna.  xylopodium provides energy and water during the dry season, which facilitates seedlings. This mechanism in juvenile plants is not only promoted by photoperiod, but also by temperature and rainfall. Although the preaching of B. holophylla seeds is the main cause of the absence of seedlings, the natural regeneration of this species is due to xylopodium. In adult plants, this part ease the vegetative reproduction and survival at different photoperiod and rainfall in the savanna.

Acknowledgements

The authors are thankful to CNPq and Biota FAPESP to support this study.

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