Nativa, Sinop, v. 11, n. 2, p. 166-177, 2023.
Pesquisas Agrárias e Ambientais
DOI: https://doi.org/10.31413/nativa.v11i2.15580
ISSN: 2318-7670
Bertholletia excelsa
seeds in the Cerrado-Amazon transition region:
morphometry, colorimetry, viability and germination
Júlio Henrique Germano de SOUZA1, Daniela Roberta BORELLA2,
Kalisto Natan Carneiro SILVA1, Andréa Carvalho da SILVA1,3*
1Institute of Agricultural and Environmental Sciences, Federal University of Mato Grosso, Sinop, MT, Brazil.
2Postgraduate Program in Environmental Physics, Federal University of Mato Grosso, Cuiabá, MT, Brazil.
3Postgraduate Program in Agronomy, Federal University of Mato Grosso, Sinop, MT, Brazil.
*E-mail: andrea.silva@ufmt.br
Submission: 05/22/2023; Accepted on 06/25/2023; Published on 06/29/2023.
ABSTRACT: The objective of this study was to describe morphometric characteristics of fruits and seeds and
evaluate the viability and germination of seeds of Bertholletia excelsa stored on litterfall and under similar
microenvironmental conditions to those found in their natural habitat, in a Cerrado-Amazon transition area,
Brazil. The morphometric characterization consisted of measurements of diameters and latitudinal and
longitudinal circumferences of fruits, exocarp and mesocarp thickness, fruit and seed weights per fruit, number
of seeds per fruit, and seed thickness, width, and length. Seed moisture content was determined by the ratio
between the fresh and dry weights. Colorimetric characterization was performed for mesocarp, outer and inner
seed coats, and internal part of the seeds. Seed viability was evaluated using the tetrazolium test and germination
was evaluated using intact seeds without seed coat. Morphometric variability was found for fruits and seeds of
B. excelsa, regardless of the air humidity. Fruit color and seed outer coat color changed as the relative air humidity
decreased. Variations in relative air humidity during the storage period resulted in a significant decrease
(45.31%) in seed moisture content and compromised of the seed physiological quality, decreasing seed viability
and germination capacity. B. excelsa seeds are sensitive to variations in air humidity. Storing seeds inside the fruit
on litterfall and under similar microenvironmental conditions to their natural habitat for up to 96 days under
mean relative air humidity above 65% ensures the maintenance of seed moisture above the critical level (30%).
Viable seeds with germination potential present moisture contents above 45%.
Keywords: Amazon Rainforest; forest residues; recalcitrance; Brazil nut conservation; extractivism.
Sementes de
Bertholletia excelsa
na transição Cerrado-Amazônia: morfometria,
colorimetria, viabilidade e germinação
RESUMO: Este estudo objetivou descrever as características morfométricas dos frutos e sementes, e, avaliar
a viabilidade e germinação das sementes da B. excelsa armazenadas sob a serapilheira em condições
microambientais do seu habitat natural na transição Cerrado-Amazônia brasileira. A caracterização
morfométrica incluiu medidas de diâmetros e circunferências latitudinal e longitudinal dos frutos; espessura do
exocarpo e do mesocarpo, massa dos frutos e das sementes por fruto, número de sementes por fruto, espessura,
largura e comprimento das sementes. A umidade das sementes foi obtida pela razão entre massas. A
caracterização colorimétrica ocorreu no mesocarpo, tegumento externo e interno e na parte interna da semente.
A viabilidade das sementes foi avaliada pelo teste de tetrazólio e a germinação com sementes destegumentadas
e intactas. Observou-se variabilidade morfométrica dos frutos e sementes da B. excelsa independentemente da
umidade. A cor do fruto e do tegumento externo da semente mudaram de tonalidade com a redução da umidade
relativa do ar. As variações da umidade relativa do ar durante o período de armazenamento influenciaram na
redução expressiva de 45,31 % no teor de água das sementes e comprometeu a qualidade fisiológica, diminuindo
a viabilidade e capacidade de germinação das sementes. As sementes da B. excelsa são sensíveis as variações de
umidade. O armazenamento das sementes dentro do fruto sob a serapilheira em condições microambientais
do seu habitat natural por até 96 dias com umidade relativa do ar média acima de 65 %, garante a manutenção
da umidade das sementes acima da umidade crítica de 30 %. Sementes viáveis e com poder germinativo
apresentam teor de água acima de 45 %.
Palavras-chave: Floresta Amazônica; resíduos florestais; recalcitrância; conservação da castanha do Brasil;
extrativismo.
1. INTRODUCTION
Bertholletia excelsa Humb. & Bonpl., known as Brazil nut
tree, is an ombrophilous forest species of the Amazon region.
It has a wide geographical distribution, with the largest tree
populations in the Brazilian Amazon region and in border
countries, such as Bolivia, Peru, Venezuela, Colombia, and
Guianas (SALOMÃO, 2009). This species has a significant
social, economic, and ecological importance in the Amazon
Basin, as it is important for native populations and interacts
with several living organisms in the forest, mainly agoutis,
Souza et al.
Nativa, Sinop, v. 11, n. 2, p. 166-177, 2023.
167
which is a rodent animal that secondarily disperses its seeds
(ZUIDEMA, 2003; WADT et al., 2018; ANDRADE et al.,
2019).
These trees dominate the forest canopy; their lifespan
ranges from 361 (SCHONGART et al., 2015) to 1,000 years
(VIEIRA et al., 2005). Their cylindrical trunk is composed of
wood of moderate specific density (SILVA et al., 2017), with
the crown developing at the top, where the fruits are formed.
The fruit has a lignified indehiscent capsule (shell) that
contains a set of seeds; the seed consists of a triangular-
shaped lignified integument, with another integument
covering the nut (seed coats) (SANTOS et al., 2006). These
seeds are internationally traded as Brazil nuts and are
included in the human diet due to their desirable nutritional
and energetic characteristics (LIMA et al., 2021).
Brazil is one of the main producers and exporters of fresh
or processed Brazil nuts, reaching 33,400 Mg, with a
production value of R$ (BRL) 142.4 million (IBGE, 2021).
Native local communities are at the base of this production
chain, as they are involved in the extraction and
commercialization of nuts from native Brazil nut trees, which
are activities that contribute to their income and are part of
their culture since pre-colonial times (ANDRADE et al.,
2019).
Besides the nuts, residues from seed processing can add
income to this extractivist activity. Studies have reported the
potential of the fruit and seed coat for producing activated
charcoal (SOUZA et al., 2021) and composing materials with
high mechanical strength (SONEGO et al., 2019; 2021). The
seed coat is nutrient-rich and has the potential to compose
agricultural substrates for crops (BOUVIE et al., 2016).
B. excelsa has been subjected to a domestication process
due to intense exploitation since the colonial period, which
resulted in migratory flows, territorial occupation, and
exploitation of resources by intentional and unintentional
forest management (ANDRADE et al., 2019). This
populational dynamic has caused impacts on the natural
regeneration of the species (ZUIDEMA, 2003), leading to
genetic erosion (BALDONI et al., 2020) and extinction
threats for this species (MMA, 2014).
Supporting and incentivizing commercial plantations of
B. excelsa is an alternative to maintaining the production
chain, generating employment opportunities and economic
returns. These initiatives can minimize anthropogenic
pressure on native Brazil nut groves and enable the
conservation of the genetic variability of the species,
management practices for existing trees, and natural forest
regeneration (TONINI; BALDONI, 2019).
Natural regeneration of this species is dependent not only
on fauna activity and management practices, such as opening
of canopy and trails, enrichment of native areas with
seedlings, and removal of lianas in trunks and crowns of
Brazil nut trees (SCOLES; GRIBEL, 2012), but also on
physiological quality of seeds, which is connected with
embryo maturity regulated by hormonal balance
(CAMARGO et al., 2000) and environmental humidity
conditions during dispersal (WADT et al., 2018; BORELLA
et al., 2020). Therefore, understanding seed
morphophysiological characteristics is important for the
propagation and conservation of this species.
The slow and uneven germination process is one of the
main challenges for propagating B. excelsa; it can vary from 6
to 18 months, as its oily seeds make the embryo hydration
slow (MÜLLER et al., 1980). Removing the woody seed coat
without damaging the embryo has been a practice to decrease
the germination time. However, other factors partly explain
the slow germination process of the species, such as the
existence of chemical dormancy (presence of inhibiting
compounds) and physiological dormancy (embryo
immaturity), i.e., seeds presenting no tissues at the advanced
stage of cell differentiation at the time at of maturation and
dispersal (CAMARGO, 1997; CAMARGO et al., 2000).
The tetrazolium test is applied to evaluate seed
physiological quality quickly and reliably; it is the most used
test, which classifies the quality of seeds of the same lot
through viability and vigor indexes. This test identifies seed
tissues that present respiratory activity based on the
reduction of the salt 2,3,5-triphenyl-tetrazolium chloride or
bromide by the activity of dehydrogenase enzymes that
catalyze respiratory reactions in the mitochondria during the
glycolyze and citric acid cycle, mainly, malate dehydrogenase
(FRANCE NETO; KRZYZANOWSKI, 2019). The
tetrazolium solution penetrates the seed, reacting with
hydrogen ions released by cell respiration, resulting in a
reduction of the salt, shown by a red, stable, non-diffusible
substance called triphenyl formazan or formazan (ABBADE;
TAKAKI, 2014).
In this context, the objective of this study was to describe
morphometric characteristics of fruits and seeds and evaluate
the viability and germination of seeds of B. excelsa stored on
litterfall and under similar microenvironmental conditions to
those found in their natural habitat, in a transition region
between the Cerrado and Amazon biomes, Brazil.
2. MATERIAL AND METHODS
2.1. Study area
The experiment was conducted in a Legal Reserve (RL)
not subjected to recent wood exploration or extractivism in
a Cerrado-Amazon transition area, in Claudia, MT, Brazil
11°34'19" S, 55°15'57'' W, and 391 m of altitude) (Figure 1).
The RL belonged to the Continental Farm, which hosts
Module 1 of the long-duration ecological research network
of the Biodiversity Research Program (PPBio), affiliated with
the Federal University of Mato Grosso (UFMT), Sinop
campus.
The climate of the region is Aw, tropical hot and humid,
according to the Köppen classification, with a rainy season
from October to April and a dry season from May to
September (SOUZA et al., 2013). The mean monthly
temperature varies from 24.9 to 27.7 °C; the mean monthly
relative air humidity varies from 52% to 86%; and the mean
annual rainfall depth is 1,945 mm, concentrating more than
1,700 mm in the spring and summer seasons. The soils in
northern Mato Grosso state under areas with the presence of
B. excelsa are deep and well-drained with a flat to undulating
topography and are classified as Typic Hapludult and Typic
Hapludox (SPERA et al., 2019; ALVES et al., 2022).
Micrometeorological conditions in the evaluation period
(rainfall depth and mean and minimum relative air humidity)
were obtained based on data from the Environment and
Plant Interaction Research Group
(www.gpambienteplanta.com). A mean air temperature of
25.66 °C was recorded in the study region during the
evaluation period. The mean relative air humidity varied from
84.77% to 61.35% from the rainy to the dry season; the
accumulated rainfall depth from January to April 2018 was
1,068.63 mm (Figure 2).
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Nativa, Sinop, v. 11, n. 2, p. 166-177, 2023.
168
Figure 1. Location of Bertholletia excelsa mother trees in the Legal
Reserve. Claudia, MT, Brazil.
Figura 1. Localização das matrizes da Bertholletia excelsa na Reserva
Legal, em Cláudia-MT, Brasil.
Figure 2. Mean monthly and standard deviation of rainfall depths
and mean and minimum relative air humidity between January 01,
2018 and December 31, 2018 in Sinop, MT, Brazil.
Figura 2. Médias mensais e desvio-padrão da precipitação, umidade
relativa do ar média e mínima entre 01/01/2018 e 31/12/2018, em
Sinop-MT, Brasil.
2.2. Fruit sampling and harvesting
The dispersal of B. excelsa fruits in this region occurs
during the rainy season (October to March), enabling the
maintenance of seed moisture for some months. Thus, fruits
dispersed in January and February 2018, from 100 mother
trees in a radius of 1.5 km within the RL (Figure 1), were
placed at the base of some mother trees in the center of the
collection area and left in direct contact with the litterfall to
better maintain moisture under natural conditions (Figure 3).
Figure 3. Bertholletia excelsa fruits stored on the litterfall of a Brazil
nut grove in Claudia, MT, Brazil.
Figura 3. Frutos da Bertholletia excelsa armazenados sob a serapilheira
no castanhal, em Claúdia-MT, Brasil.
The morphometry and colorimetry of fruits and seeds
and moisture content, viability, and germination of seeds
were simultaneously analyzed. Ten evaluations (harvests)
were carried out for each analysis, with a mean interval of 21
days (0, 15, 44, 63, 96, 127, 142, 159, 178, and 192 days after
storage; DAS) from March 02 to September 10, 2018. The
fruits were processed with the aid of a hole saw coupled to a
drill and the seed coats were removed with a knife.
2.3. Fruit and seed morphometry
The B. excelsa fruit and seed morphometric
characterization was carried out following the methodology
proposed by Borella et al. (2017). The quantitative variables
obtained were: fruit diameter and latitudinal and longitudinal
circumferences (cm); exocarp and mesocarp thickness (mm);
fruit and seed weights per fruit (g); number of seeds per fruit;
and seed thickness, width, and length (mm) (Figure 4).
Morphometric measurements of fruits and seeds were
performed using a tape ruler, digital caliper, and semi-
analytical (centesimal) and analytical (millesimal) digital
balances. Visual qualitative descriptions of the fruit and seed
physical integrity were carried out between harvests.
Figure 4. Fruits and seeds of Bertholletia excelsa. Claudia, MT, Brazil.
Eq = latitudinal measure; Lo = longitudinal measure; Es = exocarp;
Mes = mesocarp; T = thickness; W = width; L = length; ExT =
outer seed coat; InT = inner seed coat.
Figura 4. Frutos e sementes da Bertholletia excelsa, Cláudia-MT, Brasil.
Em que: Eq: medida latitudinal; Lo: medida longitudinal; Es:
exocarpo; Mes: mesocarpo; T: espessura; W: largura; L:
comprimento; ExT: tegumento externo; InT: tegumento interno.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0
50
100
150
200
250
300
350
400
Precipitation
Mean
Minimum
Months
Precipitation (mm)
0
10
20
30
40
50
60
70
80
90
100
Rainy seasonRainy season
Air relative humidity (%)
Dry season
Souza et al.
Nativa, Sinop, v. 11, n. 2, p. 166-177, 2023.
169
2.4. Seed moisture
The B. excelsa seed moisture was determined immediately
after harvesting the fruits. The set of seeds was weighed to
obtain the fresh weight and, after drying the seeds in a forced
air circulation oven at 105 °C for four days or until constant
weight, they were weighed again in a digital analytical balance
to obtain the dry weight and moisture content (Eq. 1)
according to the Rules for Analysis of Seeds (RAS) (BRASIL,
2009).
M = ( )
 . 100 (01)
where: M is the moisture content (%); IW is the initial weight
(g); FW is the final weight (g).
2.5. Fruit and seed colorimetry
The colorimetric characterization of fruits and seeds of B.
excelsa was carried out on the external part of the fruits, outer
and inner seed coats, and inner part of the seeds (Figure 4).
The colorimetric standards were obtained through the
CIELAB system of the International Commission of
Illumination (Comission Internationale de l’Eclairage), using
the device Chroma Meter CR-400/410, calibrated with the
illuminant C (Y = 87.0; x = 0.3163; y = 0.3234), which
provides the colorimetric variables: L* - lightness in a scale
from 0 (black) to 100 (white), a* - hue in the red (+a) to green
(-a) axis, and b* - hue in the yellow (+b) to blue (-b) axis, both
scales from +60 to -60; and the variables C - chromaticity or
saturation in a scale from 0 to 60 and h - hue angle, both
derivatives from values of a* and b* (CAMARGOS;
GONÇALEZ, 2001).
2.6. Seed viability
The viability of B. excelsa seeds was tested using
tetrazolium, which is a colorless solution of 2,3,5-triphenyl-
tetrazolium chloride or bromide that acts in tissues with
respiratory activity. Seeds without seed coats were subjected
to asepsis using a 2% sodium hypochlorite solution (NaClO)
for three minutes.
A longitudinal cut between the poles of each seed was
made for imbibition in 200 mL of distilled water by direct
immersion inside Gerbox boxes placed in a BOD chamber
at 30 °C without photoperiod for 24 hours. The hydration of
seeds was carried out by imbibition in the tetrazolium
solution, at the concentration of 0.5% for 24 hours, in a dark
environment at 30 °C, as recommended by Borella et al.
(2020). After applying the treatments, the seeds were washed
in running water and kept on moistened paper towel until the
end of the evaluations.
The red carmine color hue of the seeds was evaluated
following the methodology of fruit and seed colorimetric
characterization described in item 2.5. The colorimetric
readings were carried out at positions A and C – apical and
basal parts, respectively, and B – middle part (embryo) of the
seed (Figure 5). The ∆E index was calculated (Eq. 2); it
consists of the initial and final color variation due to the
application of tetrazolium solution to the seeds.
∆𝐸 = √∆𝐿∗ + ∆𝑎∗+ ∆𝑏∗ (02)
where: ∆ is the variation between the initial and the final or
partial readings.
Figure 5. Reading position of colorimetric variables of Bertholletia
excelsa seeds.
Figura 5. Posição de leitura das variáveis colorimétricas das
sementes de Bertholletia excelsa.
The percentage of penetration was evaluated by
attributing scores of 1 (without penetration, visible only in
the cut region – 10% to 20% of the seed); 2 (surface
penetration – 20% to 40% of the seed); and 3 (partial
penetration – 40% to 60% of the seed) after a new
longitudinal cut in the other half of the seeds. Viable and
unviable seeds were then classified and counted.
2.7. Seed germination
B. excelsa seeds with apparently good phytosanitary status
were selected for sowing and evaluation of the germination
process per harvest. Seeds of this species present a lignified
tegument, with a high physical-mechanical strength that
hinders water absorption and consequently its germination,
requiring months to the occurrence of the process.
Therefore, intact seeds (without removal of the seed coat)
were used, as well as seeds subjected to a mechanical process
to overcome dormancy, with total removal of the seed coat
with the aid of pliers and knives.
Seeds without mechanical damage were sown to a depth
of 2.0 cm in washed sand on an above-ground bed made of
corrugated fiber-cement roofing tiles, with dimensions of
10.0 × 0.6 × 0.03 m (length, width, and depth), placed at 1.0
m above ground, and lined in the East-West direction. The
bed had upper, front, and side covers made of black
polyolefin screen with 80% shading. Irrigation was carried
out manually as needed to keep the seeds hydrated.
2.8. Statistical analysis
The results were subjected to descriptive statistics and
analysis of variance at 5% significance level. The number of
replications per analysis was as follows: i) morphometry = 20
fruits and 20 seeds (replications) per harvest; ii) seed moisture
= 5 fruits or 5 sets of seeds (replications) per harvest; iii)
colorimetry = 5 fruits and 5 seeds per fruit (replications) per
harvest; iv) viability = 22 seeds per replication and three
replications per harvest; and v) germination = 20 seeds
(replications) with and without seed coat per harvest. The
graphical representations were developed in the Origin® 6.0
program.
3. RESULTS
3.1. Fruit and seed morphometry
The B. excelsa fruits presented high variability in
morphometric characteristics, with latitudinal and
longitudinal diameters varying from 0.0749 to 0.1229 m and
from 0.0659 to 0.1285 m, and latitudinal and longitudinal
circumferences varying from 0.2370 to 0.4250 m and from
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170
0.2670 to 0.4130, respectively (Figure 6A-D). Mesocarp
thickness varied from 0.0039 to 0.0129 m, reaching a mean
of 0.0043±0.0011 m between 0 and 44 days after storage, the
period in which they were in the fruits (Figure 6E).
Fruit fresh weight varied from 0.2114 to 0.7301 kg, with
decreases from the beginning to the end of storage; the
number of seeds per fruit varied from 9 to 24; the fresh
weight of the set of seeds presented high variation during
storage: 0.0509 to 0.2430 kg (Fig 6F-H).
The B. excelsa seeds presented larger dimensions in length,
varying from 0.02 to 0.06 m, followed by width varying from
0.02 to 0.04 m and thickness varying from 0.01 to 0.03 m
(Figure 7A-C). In general, the ratios between the dry weights
of the set of seeds and the fruit were between 0.06 and 0.33
and this ratio decreased from the beginning to the end of
storage (Figure 7D).
Figure 6. Boxplot of linear measurements and weights of fruits and a number of seeds of Bertholletia excelsa harvested in a native forest after
0 to 192 days of storage under natural conditions. Claudia, MT, Brazil. I interquartile interval (amplitude between upper and lower quartile);
■ mean; – median.
Figura 6. Boxplot das medidas lineares e massas dos frutos e número de sementes da espécie Bertholletia excelsa colhidas em floresta nativa
entre 0 e 192 dias após armazenamento nas condições naturais, em Cláudia-MT, Brasil. Em que: I intervalo interquartil (amplitude entre o
quartil superior e inferior); ■ média; – mediana.
3.2. Seed moisture variation
The B. excelsa seed moisture at 0 days of storage on the
forest litterfall was 61.65%, with exponential decreases over
time. A significant decrease in seed moisture (25.01%) was
found after 127 days of storage, reaching 16.34% after 192
days, at the end of storage (Figure 8).
3.3. Fruit and seed colorimetry
The external part of fruits and outer and inner seed coats
of B. excelsa presented low lightness (L*), with values close to
0 (black). The parameters a* and b* showed the
predominance of red and yellow colors for fruit and outer
and inner seed coats over the storage period (Table 1).
The inner part of the seeds exhibited pigmentations close
to green and yellow and high lightness and hue angle,
denoting a lighter hue than the other seed parts; the color
saturation (C) was lower in the fruit and inner part of the seed
(Table 1).
3.4. Seed viability and germination
The seed positions A, B, and C (apical, middle, and basal
seed parts, respectively) presented no significant differences
(p>0.05) for colorimetric variables before or after applying
the tetrazolium test. Thus, colorimetric readings were
grouped by mean values and standard deviations in each
harvest to confirm the viability and vigor of seeds through
colorimetry and penetration of the tetrazolium solution.
Seed lightness (L*) after the tetrazolium test varied from
48.72 to 24.45, denoting low lightness, mainly after 96 DAS.
The seed pigmentation a* and b* denoted red and yellow
colors varying from 42.37 to 34.46 and from 20.05 to 10.90,
respectively.
0 15 44 63 96 127 142 159 178 192
0.06
0.08
0.10
0.12
0.14
SM
mean
= 0.1419 0.0421
FM
mean
= 0.4363 0.0999
C. D.
Ld
mean
= 0.1024 0.0102
B.
Latitudinal diameter (m)
Ed
mean
= 0.0945 0.0090
0 15 44 63 96 127 142 159 178 192
0.06
0.08
0.10
0.12
0.14
Longitudinal diameter (m)
0 15 44 63 96 127 142 159 178 192
0.2
0.3
0.4
0.5
Lc
mean
= 0.3374 0.0318
Ec
mean
= 0.3230 0.0426
Latitudinal circunference (m)
0 15 44 63 96 127 142 159 178 192
0.2
0.3
0.4
0.5
Longitudinal circunference (m)
0 15 44 63 96 127 142 159 178 192
0.003
0.006
0.009
0.012
0.015
MT
mean
= 0.0080 0.0018
Mesocarp thickness(m)
0 15 44 63 96 127 142 159 178 192
0.2
0.4
0.6
0.8
1.0
F.
E.
Fruit mass (kg)
0 15 44 63 96 127 142 159 178 192
8
12
16
20
24
28
H.
G.
SN
mean
= 18.34 2.37
Days after storage
Seeds number per fruit
* Presence of esocarp only in the harvests 1, 2 and 3 with value mean of 0.0043
0.0011
0 15 44 63 96 127 142 159 178 192
0.05
0.10
0.15
0.20
0.25
0.30
Days after storage
Seeds mass (kg)
A.
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171
Seeds with light red hues were found between 0 and 63
DAS, and seeds with darker red hues were found after 96
DAS, which affected the seed color variation (∆E) (Table 2).
Color saturation (C) varied from 36.16 to 46.60; the hue
angles (h*) were low (17.28° to 26.32°), representing a more
intense and bright red color (Table 2). The penetration of the
tetrazolium solution into the B. excelsa seeds was not uniform.
Most seeds presented no penetration between 0 and 96 DAS,
i.e., showed visible color only in the region of disruption of
tissues; a higher percentage of seeds with surface penetration
was found at 159 and 178 DAS; and partial penetration in
most seeds were found at 142 and 192 DAS (Figure 9).
Viable seeds were those that presented light red carmine
color and vigorous tissues, which were characteristics found
in more than 50% of the seeds between 0 and 96 DAS;
unviable seeds were those that presented white milky and soft
tissues, which were characteristics found in most seeds after
127 DAS (Figure 9).
Figure 7. Boxplot of linear measures of seeds and seed dry weight ratio of Bertholletia excelsa fruits harvested in a native forest between 0 and
192 days after storage under natural conditions. Claudia, MT, Brazil. I interquartile interval (amplitude between the upper and lower
quartiles); ■ mean; – median.
Figura 7. Boxplot das medidas lineares das sementes e razão das massas secas de sementes por fruto da espécie Bertholletia excelsa colhidas
em floresta nativa entre 0 e 192 dias após armazenamento sob condições naturais, em Cláudia-MT, Brasil. Em que: I intervalo interquartil
(amplitude entre o quartil superior e inferior); ■ média; – mediana.
Table 1. Colorimetric characterization and color representation of Bertholletia excelsa fruits and seeds after different periods of storage
under natural conditions. Claudia, MT, Brazil.
Tabela 1. Caracterização e representação colorimétrica dos frutos e sementes da B. excelsa em diferentes períodos de armazenamento em
condições naturais, Cláudia-MT, Brasil.
Fruit (Mesocarp)
Outer seed coat
Harvest/DAS
L* a* b* C h
Color
representation
Harvest/DAS
L* a* b* C h
Color
representation
1/0 20.94
4.62
7.94 16.27
71.45
1/0 28.89
5.31
11.59
18.19
68.93
2/15 18.11
2.89
4.20 9.19
59.42
2/15 24.53
3.66
6.68
12.80
62.97
3/44 30.43
3.69
10.77 10.97
70.39
3/44 36.19
6.17
15.02
16.25
67.66
4/63 34.51
4.76
12.87 13.73
69.03
4/63 40.07
7.04
17.85
19.97
70.57
5/96 37.21
5.24
14.24 15.19
69.62
5/96 40.58
6.56
16.90
18.13
68.74
6/127 33.29
4.75
12.46 13.34
69.13
6/127 39.80
7.54
18.62
20.10
68.13
7/142 37.37
4.82
13.72 14.55
70.70
7/142 41.13
10.37
17.59
20.45
60.29
8/159 39.32
5.97
14.44 16.25
67.97
8/159 46.88
13.01
21.63
25.24
67.04
9/178 33.14
6.00
23.09 12.14
57.02
9/178 48.87
13.19
22.21
25.84
59.36
10/192 37.48
7.23
16.34 17.92
66.47
10/192 46.66
12.32
21.08
24.43
59.58
Mean 32.18
5.00
13.01 13.96
67.12
Mean 39.36
8.52
16.92
20.14
65.33
SD 8.24
1.88
8.41 4.06
9.38
SD 9.27
3.85
5.88
5.57
7.02
0 15 44 63 96 127 142 159 178 192
0.00
0.01
0.02
0.03
0.04
SW
mean
= 0.0252 0.0030
ST
mean
= 0.0152 0.0029
Seeds thickness (m)
0 15 44 63 96 127 142 159 178 192
0.01
0.02
0.03
0.04
0.05
Seeds width (m)
0 15 44 63 96 127 142 159 178 192
0.01
0.02
0.03
0.04
0.05
0.06
0.07
S/F
mean
= 0.1807 0.0750
SL
mean
= 0.0377 0.0049
Days after storage
Seeds length (m)
0 15 44 63 96 127 142 159 178 192
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
D.
C.
B.
Days after storage
Seeds/Fruit mass
A.
Seeds of Bertholletia excelsa in the transition Cerrado-Amazon...
Nativa, Sinop, v. 11, n. 2, p. 166-177, 2023.
172
Inner seed coat
Seed
Harvest/DAS
L* a* b* C h
Color
representation
Harvest/DAS
L* a* b* C h
Color
representation
1/0 47.96
13.62
26.05 29.76
60.13
1/0 87.24
-1.18
14.34
14.07
94.59
2/15 41.01
11.14
15.91 29.43
62.11
2/15 85.60
-0.93
15.85
15.87
93.59
3/44 49.99
13.69
26.28 29.73
61.66
3/44 85.71
-0.90
13.48
13.52
94.31
4/63 47.40
13.21
23.70 27.24
61.42
4/63 87.59
-1.19
13.64
13.70
95.08
5/96 46.81
14.55
26.00 29.81
60.61
5/96 87.83
-0.96
12.60
12.64
94.31
6/127 47.22
14.34
23.47 27.56
58.26
6/127 87.79
-0.56
13.58
13.62
94.51
7/142 49.15
15.21
25.47 29.72
59.15
7/142 88.56
-1.00
12.56
12.60
94.52
8/159 48.99
15.08
25.98 30.05
59.79
8/159 87.92
-1.26
13.56
13.62
95.33
9/178 46.65
14.37
23.29 27.41
57.94
9/178 87.02
-0.87
14.37
14.41
93.33
10/192 47.49
14.60
24.14 28.26
58.54
10/192 87.67
-0.91
12.58
12.61
94.08
Mean 47.27
13.98
24.03 28.90
59.96
Mean 87.25
-0.97
13.65
13.66
94.36
SD 4.40
1.93
4.59 3.52
3.63
SD 2.63
0.54
2.19
2.20
1.52
DAS = days after storage; SD = standard deviation. Source: https://www.nixsensor.com/free-color-converter/
DAS é dias após armazenamento; SD é desvio padrão. Fonte: https://www.nixsensor.com/free-color-converter/
Table 2. Colorimetric characterization and representation of Bertholletia excelsa seeds subjected to the tetrazolium test after different periods
of storage under natural conditions. Claudia, MT, Brazil.
Tabela 2. Caracterização e representação colorimétrica de sementes de Bertholletia excelsa submetidas ao teste de tetrazólio em diferentes
períodos de armazenamento em condições naturais, Cláudia-MT, Brasil.
Harvest/DAS L* a* b* ∆E C h
Color
representation
1/0 44.92 40.38 20.05 2.96 45.03 26.32
2/15 47.11 38.13 18.74 2.69 42.52 26.30
3/44 48.72 38.54 17.93 2.72 42.52 24.71
4/63 48.68 37.61 18.58 2.47 41.92 26.28
5/96 25.23 38.55 13.94 4.24 41.04 19.54
6/127 24.64 35.43 11.79 5.74 37.41 17.88
7/142 24.45 34.46 10.90 5.49 36.16 17.28
8/159 30.73 42.37 19.10 2.80 46.60 23.95
9/178 28.93 40.45 17.39 3.03 44.05 23.14
10/192 26.93 38.43 15.07 4.00 41.31 21.14
Mean 34.68 38.42 16.27 3.61 41.81 22.56
SD 11.05 4.79 4.43 1.49 5.94 4.18
Source: https://www.nixsensor.com/free-color-converter/
Fonte: https://www.nixsensor.com/free-color-converter/
B. excelsa seed germination was monitored for 266 days
after sowing seeds from the first harvest, at 0 DAS. The mean
time for germination was 4 months (116.62 days), varying
from 3 to 6 months, showing high germination percentages
at 44, 63, and 96 DAS for seeds without seed coats. There
was a low germination percentage of seeds with seed coat,
which totaled 3 seeds (Table 3).
Table 3. Germination percentage of Bertholletia excelsa seeds subjected to mechanical scarification after different periods of storage under
natural conditions. Claudia, MT, Brazil.
Tabela 3. Porcentagem de germinação das sementes de Bertholletia excelsa submetidas a escarificação mecânica e em diferentes períodos de
armazenamento em condições naturais, Cláudia-MT, Brasil.
Harvest/DAS
Without seed coat
(%)
With seed coat
(%)
Total
germination
(%)
Mean time
for germination (day)
1/0 5 0 2 103.0
2/15 10 0 3 112.5
3/44 45 0 15 117.1
4/63 25 5 10 80.0
5/96 45 5 17 172.0
6/127 20 5 8 118.7
7/142 5 0 2 113.0
8/159 0 0 0 0
9/178 0 0 0 0
10/192 0 0 0 0
Total of seeds 31* 3*
34*
116.62 ± 16.56
* number of germinated seeds.
* número de sementes germinadas.
Souza et al.
Nativa, Sinop, v. 11, n. 2, p. 166-177, 2023.
173
Figure 8. Exponential regression between seed moisture and days
after storage in a native forest under natural conditions. Claudia,
MT, Brazil.
Figura 8. Regressão exponencial entre umidade das sementes e dias
após armazenamento em floresta nativa sob condições naturais, em
Cláudia-MT, Brasil.
Figure 9. Percentage of penetration of the tetrazolium solution into
the seeds (A); and percentage of viable and unviable seeds of
Bertholletia excelsa harvested in a native forest between 0 and 192 days
after storage under natural conditions. Claudia, MT, Brazil.
Figura 9. Percentual de penetração da solução de tetrazólio nas
sementes (A); e percentual de sementes viáveis e inviável de
Bertholletia excelsa colhidas em floresta nativa entre 0 e 192 dias após
armazenamento nas condições naturais, em Cláudia-MT, Brasil.
4. DISCUSSION
Despite the Brazil nut tree is represented by a single
species (Bertholletia excelsa), studies have reported genetic
diversity between populations (BALDONI et al., 2020) and
between individuals of the same population (CAMARGO et
al., 2010; COELHO et al., 2017), and consequently a high
phenotypic variability, shown by yield indexes (KAINER et
al., 2007; TONINI; PEDROZO, 2014; ROCKWELL et al.,
2015), dispersal rates (WADT et al., 2018), morphology (size
and shape), fruit weight, and number of seeds
(CARMARGO, 2010; BORGES et al., 2016; BORELLA et
al., 2017).
In general, most fruits exhibit an elongated shape
(60.53%), meaning that they have a larger diameter and
longitudinal circumference than the latitudinal
circumference. However, Borella et al. (2017) found different
results: more flattened (47.75%) or rounded (40.30%) fruits.
Contrastingly, the mean exocarp and mesocarp thickness, as
well as the size and number of seeds were similar to those
found in the present study.
The absence of exocarp found after 63 days after storage
was due to seed deterioration by action of microorganisms
(Figure 10). Intensification of attack of microorganisms is
associated with high relative air humidity and direct contact
of fruits with the soil and litterfall microbiota, which make
the decomposition faster, as observed by Borella et al. (2017).
Borges et al. (2016) found fruit weights varying from
0.2288 to 0.9257 kg, mean seed weight per fruit of 0.1054 kg,
and a mean number of 17 seeds per fruit. Borella et al. (2017)
found lower fruit weights (from 0.0490 to 0.2770 kg), mean
seed weight per fruit of 0.1160 kg, and 17.5 seeds per fruit,
whereas 18.34 seeds per fruit were found in the present study.
Both studies were carried out in the same region of the
present study.
Variations in fresh fruit weight and seed weight were due
to relative air humidity conditions during the harvest period,
as well as due to exocarp deterioration. In addition, the
presence of fungi in fruits and seeds may have affected seed
weight loss and quality from the beginning to the end of
storage.
Figure 10. Exocarp deterioration in Bertholletia excelsa fruits under
natural conditions of relative air humidity. Claudia, MT, Brazil.
Figura 10. Deterioração do exocarpo nos frutos de Bertholletia excelsa
em condições ambientais de umidade relativa do ar, Cláudia-MT,
Brasil.
B. excelsa seeds exhibit a triserial triangular-angular shape,
and an angular base, margin, and apex (SANTOS et al., 2006)
requiring measurements of length, width, and thickness. The
seed dimensions presented variability, as also found by
Muller et al. (1995), who reported seed lengths of
approximately 0.04 to 0.07 m. Peres; Baider (1997) found a
mean seed length of and width of 0.047 and 0.021 m,
respectively.
These morphological variations in fruits and seeds (size,
weight, and number of seeds) in native species of the region
are common, as they are strongly affected by species genetic
diversity, geographical distribution, and edaphoclimatic
conditions (CAMARGO et al., 2010; BALDONI et al.,
2020).
0 20 40 60 80 100 120 140 160 180 200
10
20
30
40
50
60
70
Y = 342.3815 + e
-0,2443x
R
2
= 0.9497
Seeds humidity (%)
Days after storage
Seeds of Bertholletia excelsa in the transition Cerrado-Amazon...
Nativa, Sinop, v. 11, n. 2, p. 166-177, 2023.
174
The dry weight ratios between the set of seeds and fruit
decreased from the beginning to the end of storage, mainly
after 96 DAS, denoting a direct relation between fruit weight
loss and seed weight loss. Decreases in fruit and seed dry
weights are connected to the action of microorganisms,
mainly on seeds, as their nutrient, protein, oil, and enzyme
composition are attractive to fungi and bacteria, resulting in
weight loss.
The seeds consisted, on average, of 18% dry fruit and
approximately 32% moisture, but, different results were
reported by Muller et al. (1995), who found approximately
25%. Zuidema (2003) found approximately 35% and Borella
et al. (2017) found approximately 32% on wet basis. The
remaining percentage is forest residues that can be used as
substrate for crops, such as the case of seed exocarp and
tegument, which have important macronutrients (N, K, Ca,
S, Mg, and P) and micronutrients (Mn, B, Zn, and Cu), as
well as adequate physical attributes, such as density, pH, and
C to N ratio for manufacturing agricultural substrates
(BOUVIE et al., 2016).
The mesocarp is composed of two types of lignified
thick-wall cells (~56%), forming fibers that create a tangled
structure, which provides it with high mechanical strength
and potential for composing resistant materials (SONEGO
et al., 2019;2021). The seed mesocarp and tegument have
high C to N ratios (BOUVIE et al., 2016) and can be used
for producing activated charcoal for energy production
(SOUZA; SILVA, 2021), whereas the exocarp has nutrients
and adequate physical attributes (density, pH, and C to N
ratio) for manufacturing agricultural substrates (BOUVIE et
al., 2016).
The B. excelsa fruits and seeds exhibit a color, hue, and
lightness pattern that is probably connected to its chemical
composition. The hue of the fruit and outer seed coat varied
as the relative air humidity decreased. Burtin et al. (1998)
explained that wood color varies due to air humidity and
temperature, as well as to degradation of the material by
photochemical reactions of chemical components in its
structure. These variations in brown hues in fruits are also
connected to the deterioration of the exocarp and the
presence of fungi.
Color variation is used to identify the different fruit
maturation stages and evaluate fruit quality without removing
fruit samples or using other materials. This information,
combined with morphometric characteristics, contributes to
the development of classification and selection protocols for
fruits and seeds during harvesting and processing. However,
seed physiological evaluations through viability and/or
germination tests are needed for understanding the
propagation of species.
Considering that B. excelsa seeds are recalcitrant, i.e.,
sensitive to long storage periods and decrease in humidity
(MÜLLER et al., 1980; BARBEDO, 2018), the seed viability
and vigor were affected by the gradual decreases in relative
air humidity, which decreased seed water content to critical
levels (<30%) after 127 DAS (Figures 8 and 9). This was
evidenced in the tetrazolium test after 96 DAS when the
seeds started to present tissues with darker carmine red hues,
as well as after 142 DAS when seeds presented flaccid tissues
with a milky appearance (Figure 11) and significant decreases
in germination percentage (Table 3).
A water content below 30% in recalcitrant seeds induces
the deterioration processes, such as denaturation of proteins,
changes in peroxidase activities, and damage to the
membrane system, which may result in viability losses and
low germination rates. Recalcitrant seeds should be stored
under high relative humidity to maintain seed moisture above
30% and between 50% and 70% moisture to reach
physiological maturity; however, seed contamination by
microorganisms should be considered under storage
conditions (PAMMENTER; BERJAK, 2014).
Seed recalcitrance is associated with the immature stage;
some species present strategies to elongate and anticipate
their maturation cycle and, depending on the environmental
conditions, the seed dispersal can occur before maturation,
producing seeds with levels of different recalcitrance
(BARBEDO, 2018). This may be one of the possible reasons
for the high levels of recalcitrance of B. excelsa seeds, besides
genetics and edaphoclimatic conditions.
Figure 11. Red carmine color pattern of Bertholletia excelsa seeds
subjected to the tetrazolium test. Claudia, MT, Brazil.
Figura 11. Padrão de coloração vermelho carmim nas sementes da
Bertholletia excelsa submetidas ao teste de tetrazólio, Cláudia, MT.
The color and penetration of tetrazolium solution into
seed tissues indicate the presence of respiratory activity. The
red carmine color was exhibited in all seeds evaluated from 0
to 192 DAS, however, with differences in hue (Table 2),
penetration (Figure 9), and coverage region (Figure 11) of the
solution. Thus, the tetrazolium test used was adequate to
identify viable seeds.
Vigorous seeds with a light red carmine color were found
in the first harvest; however, there was the penetration of
tetrazolium solution only into the tissue cut region and a low
germination (Tables 2 and 3). Thus, the recently dispersed
seeds were probably immature, with low respiratory activity,
and reached maturity over time, as indicated by the increases
in germination percentage from 44 to 96 DAS and partial
penetration of the solution.
Mature seeds started to present dark carmine hues, a
distinction of flaccid tissues, and no respiratory activity (dead
tissues) after 127 DAS (Figure 11), as confirmed by the high
percentage of unviable seeds and low germination (Table 3).
The decrease in air humidity was a determining factor for the
loss of physiological quality and degrees of salt penetration in
these seeds.
Despite the germination peak from 44 and 96 DAS
(45%), the percentage was still low. The B. excelsa seeds
present minerals, proteins, and high lipid contents in their
composition (LIMA et al., 2021), which makes water
absorption slow, thus resulting in dehydration. A large
Souza et al.
Nativa, Sinop, v. 11, n. 2, p. 166-177, 2023.
175
amount of embryo reserves and/or the internal hormonal
balance can slow the imbibition process, enzymatic
activation, and differentiation of the seed's meristematic
tissues of seeds, consequently affecting germination
(CAMARGO et al., 2000).
Müller et al. (1980) explain that the dispersal of premature
fruits of B. excelsa may occur, which may be related to the
hormonal balance. In addition, the seeds present no tissues
at advanced stage of differentiation at the time of seed
maturation and dispersal, such as other common seeds that
form plumule, radicles, and cotyledons. These may be some
of the possible reasons for the challenging assessment of the
physiological quality and germination of these seeds
(CAMARGO et al., 2000).
B. excelsa seeds are sensitive to variations in air humidity
and there is no efficient protocol to keep them stored for a
long time. These seeds can be stored for short periods inside
the fruit on litterfall and under similar microenvironmental
conditions to their natural habitat for up to 96 days under
mean relative air humidity above 65%; these conditions may
ensure the maintenance of seed moisture above the critical
level (30%), as viable seeds with germination potential
present water contents above 45%.
5. CONCLUSIONS
The viability loss of Bertholletia excelsa seeds is connected
to decreases in air humidity levels during the storage period.
The germination does not depend only on the seed moisture,
but also on the seed maturity.
Under adequate conditions of seed physiological maturity
and moisture, the propagation of B. excelsa through seeds
should be carried out using seeds without seed coat to
decrease the time for germination.
Morphometric characteristics of B. excelsa fruits and seeds
present high phenotypic variability, denoting that these
variations may originate from genetic and microclimate
diversities.
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Acknowledgments:
The authors thank the Brazilian National Council for Scientific
and Technological Development (CNPq) and the Brazilian
Coordination for the Improvement of Higher Education Personnel
(CAPES).
Author Contributions:
J.H.G.S; D.R.B.; and K.N.C.S - methodology, research or data
collection, statistical analysis, writing (proofreading and editing).
A.C.S. - conceptualization, funding acquisition, methodology,
research or data collection, statistical analysis, administration,
supervision, and writing (original draft); All authors read and agreed
with the published version of the manuscript.
Funding:
Brazilian Coordination for the Improvement of Higher Education
Personnel (CAPES; Financing Code 001).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Date Availability Statement: Data of this study can be obtained
upon request to the corresponding author or the first author,
through e-mail (andrea.silva@ufmt.br).
Conflicts of Interest:
The authors declare no conflict of interest.