and efficiency of five pre-germination treatments for overcoming dormancy of L. ferrea seeds. Seeds were

subjected to constant temperatures of 15, 20, 25, 30 and 35°C and to the following pre-germination treatments:

nicking with pincers; immersion in water for 24 hours at room temperature; scarification with sandpaper;

immersion in caustic soda for 60 minutes; and control (untreated seeds). Germination rate was assessed by

eficiência de cinco tratamentos pré-germinativos para a superação de dormência das sementes de L. ferrea,

sugeridos na literatura. As sementes foram submetidas a temperaturas constantes de 15, 20, 25, 30 e 35 ºC e

aos tratamentos pré-germinativos: corte com alicate no lado oposto ao hilo, imersão em água por 24 horas em

temperatura ambiente, escarificação com lixa d’água nº 4, imersão em soda cáustica por 60 minutos e a

mecânica por meio do desponte com alicate e o atrito em lixa.

Libidibia ferrea Mart. ex Tul., commonly known in Brazil

as pau-ferro or jucá, belongs to the family Caesalpiniaceae

and is a typical tree species found in the Caatinga. This tree

has high ornamental and medicinal potential (Silva et al.,

2015), and its high-density wood is used in the lumber

industry. Libidibia ferrea can be found from Piauí to Rio de

agents, and seedling setting (FERNANDES et al., 2012).

Temperature affects both germination percentage and

speed at which germination occurs (Ranzani et al., 2016)

owing to its direct impact on water uptake by seeds and on

biochemical reactions regulating metabolic processes during

germination. According to Carvalho; Nakagawa (2012), there

is an optimum temperature range for germination in which

responses each tree species can have as a function of

dormancy, viability and environmental conditions

(CARVALHO; NAKAGAWA, 2012).

In numerous forest tree species, seeds are dormant due

to an impermeable seed coat, as observed by Ataíde et al.

(2013).

Seed dormancy represents an effective survival

scarification is done by microorganisms, the digestive tract of

animals, soil acidity and fire. As for artificial scarification,

several methods are used, but one must not cross the

scarification limit of the seed coat to prevent damaging the

embryo.

Scarification can be chemical, such as using sulfuric acid

(Freire et al., 2016) and caustic soda (Cipriani et al., 2019);

mechanical, such as abrasion (Avelino et al., 2012); and

physical, such as dipping seeds into boiling water (ATAÍDE

et al., 2013). Among these, and according to the studies,

which germination is optimum.

Ripe fruits of L. ferrea were manually collected in April

2016, in different trees.

The seeds were manually removed from pods with the aid

of a hammer. After processing, seeds were selected and

placed in glass containers (amber), sealed up, and stored in a

refrigerator for 120 days.

digital caliper.

Eight replicates consisting of 100 seeds each were used to

determine the number of seeds in a kilogram. Seeds were

randomly picked and then weighed on an analytical scale.

Seed moisture content was measured by the oven drying

method, at 105 ± 3 ºC, during 24 hours, as standardized by

the Rules for Seed Analysis (Brasil, 2009). We used four

replicates and each replicate consisted of 50 seeds. Data are

expressed as percentage based on fresh weight of the sample.

The experiment was carried out in a completely

12-hour photoperiod using fluorescent bulbs (Phillips 15W)

in B.O.D. incubators (model 347 FANEN).

To overcome the coat-imposed seed dormancy, four pre-

germination methods were used: nicking with pincers on the

opposite side to the hilum; immersion in water for 24 hours

at room temperature; scarification with wet/dry sandpaper;

and immersion in caustic soda for 60 minutes. Before setting

up germination tests, seeds were immersed in a 5% sodium

hypochlorite for 5 minutes and then rinsed in distilled water.

soda at 20% (65g of caustic soda to 325 mL of water)

following recommendations of Garcia & Azevedo (1999).

First, seeds were placed in a beaker; then, 65 g of caustic soda

was added to the beaker containing the seeds; and, finally,

325 mL of distilled water was added to it, stirring the solution

with a glass rod and letting it rest for 60 minutes. After

removing seeds from the solution, caustic soda residues were

rinsed off them.

on the opposite side to the micropyle to rupture the coat

without damaging the embryo.

Seeds were sown in transparent gearbox-type boxes

measuring 10 x 10 x 4 cm (length, width, and depth,

respectively) containing vermiculite previously sterilized in

oven for 24 hours at 200°C and wetted with distilled water.

Moisture content in the substrate was maintained by watering

it every two days in accordance with the field capacity of it.

Germinated seeds were counted daily when the radicle is

emerged and seedlings were 2 cm long or more. Tests were

brought to an end on the 50th day when there were no

germination events for three consecutive days. Maguire

(1962), developed the following formula for the GSI

(Equation 1):

Labouriau; Valadars (1976) cited the formula used to

calculate the germination time as follows (Equation 2):

Seeds treated by nicking and rubbing against sandpaper

had higher germination percentages in comparison with the

remaining treatments at every temperature tested but 25 °C

at which nicking and caustic soda treatments were more

efficient. At 20 °C and 30 °C, germination percentage of

seeds immersed in caustic soda was not significantly different

The interaction between the evaluated treatments

indicated that the highest germination speed index (0.26) was

obtained by using mechanical chiseling by topping, at a

temperature of 25 ºC, followed by immersion treatment, with

an index of 0.22, at temperature maximum of 23 ºC. In the

water immersion treatment, there was a higher germination

speed index (0.15), at a temperature of 19 ºC, after which

there was a decrease up to 30 ºC, with an index of 0.03. It

was also observed that without the use of efficient pre-

scarification treatments, low rates of germination speed of

immersion in water, respectively.

As for the number of days to germination as a function

of temperature, regressions were significant only for the

treatments control and immersion in water. Germination

events of these treatments were delayed compared to the

remaining treatments (Figure 4). Maximum mean time to

start germination of untreated seeds was 13 days at 27 °C

whereas for immersion in water at room temperature, the

higher the temperature, the longer seeds take to germinate.

The number of days to finish germination as a function

of temperatures yielded a significant regression for

immersion in water, caustic soda and control (Figure 4).

Caustic soda reduced the number of days to finish

germination up to 26 °C, and from there on, number of days

rose up again, while control treatment had an inverse

behavior. NFG increases in the control group up to 27 °C,

and from there on, it decreases. Immersing seeds in water at

room temperature shortened number of days to finish

germination between 15 and 20 °C. From the latter

contents of 7.46% and 6.9% in their studies with seeds of the

same species evaluated in our study. This low seed moisture

content lengthens viability of seeds (MATOS, 2015).

Seed metrics is fundamental for characterization of a seed

lot by providing information about different sizes and storage

content of seeds. According to Silva et al. (2012), these

differences might be linked to strategies of using nutrients

and available water resources, to local environmental

variations, and to the own genotypic diversity of populations

that might result in different phenotype characteristics for the

species.

Untreated seeds and seeds immersed in water at different

temperatures had low germination percentage, which

indicates that in the absence of a scarification pretreatment,

germination events are slow, uneven and, therefore,

unsuitable for seedling production, due to the presence of a

coat-imposed dormancy (COELHO et al., 2013).

Conversely, the use of efficient pre-germination treatments,

such as chemical scarification with caustic soda, and

mechanical scarification by either nicking or rubbing against

sandpaper, can result in high germination rates.

the species and the species’ regions of origin.

Temperature influences biochemical reactions of

germination, which may affect both capacity and speed of

seed germination. Seeds germinate most readily when they

are in the characteristic temperature range of the species;

however, the time taken to obtain the maximum germination

percentage is dependent on the temperature. Increasing

temperature makes water more fluid and with more kinetic

energy, facilitating its movement from the outer to the inner

side of the seed and, in consequence, water uptake is

range of 20 to 30 °C. The optimum temperature for

germination is a physiological adaptation of seeds to local

environmental conditions where the species occurs or is

grown; thus, this temperature may have a direct relationship

with the biome in which the seeds were produced. Species

with different ecological and geographical distributions

produce seeds varying as to temperature requirements for

germination (BRANCALION et al., 2010).

Mechanical scarification of the seed coat was efficient

when breaking the dormancy of seeds of various species of

speed and decreased labor requirements. Mechanical

scarification is more laborious and takes longer when done

manually; though, mechanical methods do not use chemical

products, thereby avoiding accidents with these products.

Oliveira et al. (2017) pointed out that manual techniques,

such as mechanical scarification by nicking, either on the

opposite side to the hilum or at the tip where the seed

attached to the pod, is more desirable since both have equal

efficiency to overcome dormancy of L. ferrea seeds.

Generally, depending on the site where seeds are

Brancalion et al. (2010) who affirm that Brazilian arboreal

species have a maximum potential for germination next to

the 25 to 30°C range. Oliveira et al. (2014) evaluated the seed

germination of four native Caatinga tree species (Sideroxylon

obtusifolium (Roem & Schult.), Myracrodruon urundeuva (All.),

Amburana cearensis (All.) and Schinopsis brasiliensis (Engel.),

verified that the seeds of different species from the same

ecological and climatic conditions present different

germinative behavior as to the ideal germination temperature,

but the optimum temperature range was on average from 20

Chemical and mechanical scarification treatments started

and ended germination in a smaller number of days,

compared to water immersion and control treatments.

Scarification ruptures the integument through which larger

amounts of water enter the seed in a shorter period of time,

leading to turgidity and in consequence, hydrolytic enzymes

are activated and the germination process begins.

By comparing scarification methods (nicking by pincers,

rubbing against sandpaper and immersion in caustic soda),

Zucareli et al. (2010) highlighted nicking as the most

Metrics of L. ferrea seeds is more variable as to length and

width, and less variable as to thickness. Chemical scarification

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