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Abstract

Two lettuce cultivars (Everglades and Virginia) were used to evaluate the performance of pelleted and bare seeds of lettuce under different germination temperatures. A completely randomized 2 x 2 x 5 factorial design was used. The factors consisted of two cultivars with pelleted and bare seeds, five intervals of germination temperatures (17 to 19ºC, 21 to 23°C, 25 to 28°C, 30 to 32°C, 34 to 38°C), with four replications. The first germination count, T50, germination, germination speed index, emergence, emergence speed index and dry mass of plants were evaluated. Sowing germination test was carried out on two sheets of blotting-paper, moistened with water at a ratio of 2.5 times the paper weight in 'gerbox' plastic boxes. The boxes with seeds were kept in a thermogradient table, with alternating light procedure: 12 hours of darkness and 12 hours of light. The temperature was regulated to a gradient according to each treatment. On the 4th day, first germination count and germination test were performed. On the 7th day, germination was evaluated with normal seedlings as a parameter. The cultivar Everglades showed a higher germination, especially with pelleted seeds. The germination performance of the cultivars is influenced by the use of bare or pelleted seeds and by temperature. Better seed quality and early growth of lettuce are observed in temperatures between 17 to 23°C.
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AJCS 11(03):338-342 (2017) ISSN:1835-2707
doi: 10.21475/ajcs.17.11.03.pne352
Quality of pelleted and bare lettuce seeds at different temperatures
Alan Mario Zuffo1*, Everton Vinicius Zambiazzi², Maria Laene Moreira de Carvalho², Natália
Trajano de Oliveira², Adriano Teodoro Bruzi², Igor Oliveri Soares², Jéssica Gentil Lima², Heloisa
Oliveira dos Santos²
1Department of Crop Production, State University of Mato Grosso do Sul, 79540-000, Cassilândia, Mato Grosso
do Sul, Brazil
²Department of Agriculture, Federal University of Lavras, 37200-000, Lavras, MG, Brazil
*Corresponding author: alan_zuffo@hotmail.com
Abstract
Two lettuce cultivars (Everglades and Virginia) were used to evaluate the performance of pelleted and bare seeds of lettuce under
different germination temperatures. A completely randomized 2 x 2 x 5 factorial design was used. The factors consisted of two
cultivars with pelleted and bare seeds, five intervals of germination temperatures (17 to 19ºC, 21 to 23°C, 25 to 28°C, 30 to 32°C, 34
to 38°C), with four replications. The first germination count, T50, germination, germination speed index, emergence, emergence
speed index and dry mass of plants were evaluated. Sowing germination test was carried out on two sheets of blotting-paper,
moistened with water at a ratio of 2.5 times the paper weight in gerbox plastic boxes. The boxes with seeds were kept in a
thermogradient table, with alternating light procedure: 12 hours of darkness and 12 hours of light. The temperature was regulated to a
gradient according to each treatment. On the 4th day, first germination count and germination test were performed. On the 7th day,
germination was evaluated with normal seedlings as a parameter. The cultivar Everglades showed a higher germination, especially
with pelleted seeds. The germination performance of the cultivars is influenced by the use of bare or pelleted seeds and by
temperature. Better seed quality and early growth of lettuce are observed in temperatures between 17 to 23°C.
Keywords: Everglades, Lactuca sativa L., Thermodormancy, Thermoinhibition, Virginia.
Abbreviations: FGC_first germination count; T50_time for 50% of the seeds to germinate; GER_germination rate; GSI_germination
speed index; ER_emergence rate; ESI_emergence speed index; PDM_plants dry mass.
Introduction
Lettuce (Lactuca sativa L.) is grown in all Brazilian regions
and stands out among the most leafy vegetables consumed in
Brazil due to its importance as a source of vitamins, minerals
and fiber (Santi et al., 2010; Teodoro et al., 2016). The main
obstacles in its cultivation are related to the sensitivity to
temperature changes in the germination environment
(Bertagnolli et al., 2003) and also to the size and shape of
seeds, which can hinder the sowing.
The germination process involves several metabolic
activities which occur during a scheduled sequence of
chemical reactions; each of these reactions has its own
temperature requirements (Marcos Filho, 2005). The
temperature also affects the speed, the rate and the uniformity
of germination, which results in poor quality and delay in
seedlings production (Menezes et al., 2000) and, therefore, a
direct damage to the producers (Nascimento and Cantliffe,
2001). For most lettuce cultivars, the ideal temperature for
seed germination is 20°C (Deng and Song, 2012).
Temperatures above 25°C may negatively affect germination,
germination speed, water absorption and may also affect the
biochemical reactions, which are essential to the germination
process (Schwember and Bradfort, 2010).
Regarding size and shape, there are pelleted lettuce seeds in
the market in order to solve these problems. Caldeira et al.
(2016) reported that the commercial seeds are pelleted to
increase the size and facilitate sowing. This process consists
of coating the seeds with a dry, inert, fine-grained and
cementing (adhesive) material. However, the use of pelleted
seeds can affect gas exchange and radicle issuance, inhibiting
(Nascimento et al., 2009) or delaying germination when
compared to bare seeds (Franzin et al., 2004; Pires et al.,
2004). Another aspect that can affect seed’s response to
temperature during germination is the use of pelleted or bare
seeds. For Bertagnolli et al. (2003) pelleted seeds have
different hydrophilic and hydrophobic characteristics of the
materials used in the coating. Thereby, when compared to
bare seeds and exposed to different temperatures, they
promote different results. Reports presented by Nascimento
and Caliari (1989) show that pelleted seeds of lettuce are
more sensitive to high temperatures. However, those results
do not corroborate to the ones obtained by Salom et al.
(2008) who found a higher germination rate of pelleted and
bare seeds at 20 to 30°C and 15 to 25°C, respectively. The
discrepancy between the results may be related to the
thermotolerance of lettuce genotypes, considering that some
cultivars are more tolerant to high temperatures, as verified
by Catão et al. (2014). The authors observed that cultivar
Everglades can be considered thermotolerant due to the
germination rate at high temperature and with the increased
activity of endo-β-mannanase enzyme. Given the above, it is
necessary to determine the temperatures that promote
maximum germination efficiency of pelleted and bare seeds.
339
Besides, it is also necessary to obtain more tolerant lettuce
cultivars and with better physiological quality regarding the
germination for tropical and subtropical regions. The aim of
this study was to investigate the germination performance of
lettuce seeds in two cultivars, under different coatings and
temperatures.
Results and discussion
All the variables, except T50, were significantly influenced
(p<0,01) by the cultivars (Table 1). These results are similar
to the ones checked by Catão et al. (2014), who also showed
the effect of lettuce cultivars in the germination and
emergence variables. This fact is probably related to different
characteristics regarding genetic background.
For coating, temperatures, and the interaction cultivar x
coating, significant differences were observed in all the
characteristics under evaluation. Nascimento et al. (2012)
also observed the effect of temperature on physiological
quality of lettuce seeds. These findings are probably related
to the hydrophilic and hydrophobic characteristics of the
materials used in the coating (Bertagnolli et al., 2003), to
lettuce sensitivity to temperature gradients and to the intrinsic
characteristics of each cultivar.
In the interaction cultivar x temperature, there was a
significant effect on the emergence, emergence speed index
and dry mass of plants. The interaction coating x
temperatures significantly influenced (p<0.01) all the
variables, except the first germination counting and
emergence. For the interaction genotype x coating x
temperatures, significant differences for germination,
germination speed index, emergence speed index and
seedlings dry mass were observed. The cultivars differ from
each other since each genotype has different
morphophysiological and genetic characteristics. Thus, it was
not the objective of this study to unfold the interactions
between cultivars x coating and cultivars x temperatures.
Overall, it was observed that cultivar Everglades showed
better means in the tests related to germination in blotting
paper (Table 1). On the other hand, assessing the tests related
to emergence on commercial substrate, it was noted that
cultivar Virginia showed a better performance. These results
differ from those obtained by Catão et al. (2014), who
concluded that Everglades showed higher germination and
emergence rates in both substrates.
Pelleted seeds showed better results in all traits for coating
(Table 1). These results corroborate with those obtained by
Bertagnolli et al. (2003), who also verified a reduction in
physiological quality of bare seeds of lettuce subjected to
thermal stress, when compared to the pelleted seeds. The
authors reported that these findings are probably due to the
characteristics of the pellet material which helped to maintain
the performance of the seeds as the temperature is not the
most suitable.
In general, it was found that the two smallest temperature
gradients (17 to 19oC; 21 to 23oC) provided better
physiological performance in lettuce seeds (Table 1).
Temperatures above 25oC reduced the physiological
potential, as evidenced by the germination test, first count of
germination, emergence speed index and dry mass of plants.
According to Catão et al. (2014), temperatures above 30°C
and especially at 35°C lead to thermoinhibition or
thermodormancy in lettuce seeds. These factors associated
with the negative potential make the germination unfeasible.
Additionally, high temperatures cause the weakening of the
seeds endosperm, which prevents the embryo growth and
restricts root protrusion (Sung et al., 2008).
In general, the higher means of T50 were at 34-38°C for the
coated and bare seeds. However, for coated seeds, it was
observed that there were no statistical differences between
the temperature gradients (Table 2). In temperature ranges of
30-32°C and 34-38°C, only the bare seeds had higher means
of T50. Therefore, it is evident that the coating protects the
seeds that are subjected to high temperatures, promoting a
more uniform germination under adverse temperature
conditions. Similar results were found by Bufalo et al.
(2012), who studied the germination of lettuce seeds under
different temperatures and stratification periods.
Cultivar Everglades showed higher germination rates in all
temperature gradients for pelleted seeds (Table 3). With
coating, Everglades germination was impaired only in higher
temperatures; for cultivar Virginia, there was a reduction in
germination at temperatures of 25 to 28°C. However, when
assessing the bare seeds, both cultivars showed unsatisfactory
germination, with average values below the minimum
standard of 80% that is required for the marketing of lettuce
seeds in Brazil, established by Normative Instruction No. 45
(BRASIL, 2013).
By analyzing the interaction between cultivars x
temperature within coating (Table 4) it was observed that
cultivar Everglades showed better germination rates when
pelleted seeds were used. However, there were no differences
in gradients of 25 to 28ºC and 30 to 32ºC for cultivar
Virginia. These results corroborate with the study that
characterizes the cultivar Everglades as thermotolerant
(Nascimento et al., 2004; Kozarewa et al., 2006; Catão et al.,
2014). Bertagnolli et al. (2003) which also verified a better
performance of pelleted lettuce seeds regarding the tolerance
to heat stress.
The higher germination rate in pelleted seeds of cultivar
Everglades is probably related to the ability that the coating
has to rapidly absorb and store water. Therefore, water is
readily available to the seed, which accelerates the
germination as reported by Manohar and Heydecker (1964).
In addition, water is also efficient in conducting heat energy.
Thus, lower temperatures can retard the germination of
pelleted seeds (Salum et al., 2008).
By analyzing the remaining seeds from the germination test
(Table 5), it was observed by the tetrazolium test that the
pelleted seeds of cultivar Virginia (in all temperature
gradients) and the bare seeds (in the smallest and the largest
temperature gradient) showed dormancy. Bertagnolli et al.
(2003) and Bufalo et al. (2012), analyzing the performance of
bare and pelleted seeds of lettuce subjected to heat stress, also
found that at 25°C or above 25°C, there was a reduction in
germination rate and speed, and at 35°C there was a cease of
seeds germination. This last fact has not been reported in the
present study, even for cultivar Virginia which showed a
lower tolerance to heat stress. For Valdes and Bradford
(1987), the thermodormancy is aggravated in pelleted seeds.
This fact was observed only in pelleted seeds of Virginia
(Table 5), probably due to the characteristics of this cultivar.
The germination speed was reduced when temperatures
between 34 and 38 ° C were used in pelleted seeds of
Everglades and in Virginias bare seeds (Table 3). On the
other hand, there was a reduction in vigor in pelleted seeds in
the gradients of 30 to 32°C and 34 to 38°C for bare seeds of
Everglades and pelleted seeds of Virginia. The pelleted seeds
of Everglades presented a greater germination speed index in
all temperature gradients (Table 4).
For emergence speed index, the pelleted seeds of Everglades
were not affected by temperature gradients. For cultivar
Virginia, there was a reduction in the emergence speed index
340
Table 1. Mean values for the first germination counting (FGC), time for 50% of the seeds to germinate (T50), germination rate
(GER), germination speed index (GSI), emergence rate (ER), emergence speed index (ESI) and plants dry mass (PDM) obtained in
the assay with bare and pelleted seed of lettuce cultivars exposed to different temperatures. Lavras, Minas Gerais, Brazil, 2014.
Source of variation
FGC
T50
GR
GSI
ER
ESI
PDM
%
unid.
%
-
%
-
mg-1
Cultivar¹
Everglades
60 a
1.55 a
77 a
30.22 a
63 b
20.24 b
6.24 b
Virginia
53 b
1.67 a
70 b
26.32 b
72 a
22.13 a
7.61 a
Coating¹
Pelleted
60 a
1.32 b
85 a
32.62 a
87 a
25.83 a
8.17 a
Bare
51 b
1.90 a
62 b
23.92 b
47 b
16.64 b
5.67 b
Temperatures²
17 19ºC
65 a
1.31 b
85 a
33.76 a
70 a
23.49 a
8.48 a
21 23ºC
61 a
1.31 b
83 a
32.72 a
71 a
23.19 a
8.08 a
25 28ºC
57 b
1.31 b
78 b
31.09 a
71 a
21.01 b
6.27 b
30 32ºC
53 b
1.68 b
70 c
26.00 b
67 a
19.90 b
6.36 b
34 38ºC
46 c
2.43 a
49 d
17.79 c
57 b
18.60 b
5.41 c
Mean
56.00
1.61
73.06
28.27
67.31
21.24
6.92
CV (%)
13.82
21.93
11.32
13.93
9.68
13.62
15.80
¹Means followed by the same letter do not differ by F test. ² Means fo llowed by the same letter in the column do not differ statistically by Scott and Knott test at 5%
probability. CV - coefficient of variation.
Table 2. Mean values of the time for 50% of the seeds to germinate regarding the interaction between coating vs. temperature
obtained in the test with bare and pelleted seeds of lettuce cultivars exposed to different temperatures. Lavras, Minas Gerais, Brazil,
in 2014.
Temperature
Pelleted
Bare
17 19 ºC
1.0 Aa
1.0 Ba
21 23 ºC
1.0 Aa
1.0 Ba
25 28 ºC
1.0 Aa
1.0 Ba
30 32 ºC
1.0 Ab
2.0 Aa
34 38 ºC
2.0 Ab
3.0 Aa
Means followed by the same capital letter in t he column and. lowercase in line. They belong to the same group. by Scott test Knott (1974). at 5% of probab ility.
Table 3. Mean values of germination (GER), germination speed index (GSI), emergence speed index (IVE) e seedling dry mass of
lettuce regarding the interaction between cultivars vs coating within the temperatures. Lavras, MG, Brasil, 2014.
Coating
Temperature
GER (%) GSI ESI SDM (mg-1)
Ever.
Virg.
Ever.
Virg.
Ever.
Virg.
Ever.
Virg.
Pelleted
17 19ºC
100 Aa
90 Aa
41.8 Aa
32.6 Ab
33.6 Aa
26.8 Ab
11.0 Ab
13.1 Aa
21 23ºC
100 Aa
89 Ab
40.9 Aa
31.5 Ab
31.1 Aa
21.6 Bb
9.2 Bb
12.5 Aa
25 28ºC
100 Aa
73 Bb
41.7 Aa
26.8 Ab
29.1 Aa
17.6 Cb
3.4 Cb
9.3 Ba
30 32ºC
98 Aa
63 Cb
39.0 Aa
19.6 Bb
28.7 Aa
16.9 Cb
6.6 Ba
7.4 Ca
34 38ºC
76 Ba
59 Cb
33.5 Ba
18.3 Bb
28.9 Aa
23.5 Bb
4.3 Ca
4.7 Da
Bare
17 19ºC
75 Aa
76 Aa
27.0 Ab
33.5 Aa
15.0 Ab
28.4 Aa
4.8 Aa
4.9 Aa
21 23ºC
70 Aa
75 Aa
26.9 Aa
31.4 Aa
13.2 Ab
26.6 Aa
5.5 Aa
5.1 Aa
25 28ºC
68 Aa
70 Aa
25.5 Aa
30.3 Aa
14.0 Ab
23.1 Ba
6.3 Aa
6.1 Aa
30 32ºC
54 Bb
68 Aa
16.3 Bb
28.8 Aa
11.8 Ab
22.1 Ba
4.7 Ab
6.5 Aa
34 38ºC
26 Ca
34 Ba
9.2 Ca
10.0 Ba
7.6 Bb
14.2 Ca
6.4 Aa
6.5 Aa
Means followed by the same capital letter in the co lumn and. lowercase in line. They belong to t he same group. by Scott test Knott (1974). at 5% of probability. Ever -
Everglades, Virg - Virginia.
Table 4. Mean values of germination (GER), germination speed index (GSI), emergence speed index (ESI) e seedling dry mass of
lettuce regarding the interaction between cultivars vs temperature within coating. Lavras, MG, Brazil, 2014.
Temperature
Coating
GER (%) GSI ESI SDM (mg-1)
Ever.
Virg.
Ever.
Virg.
Ever.
Virg.
Ever.
Virg.
17 19ºC
Pelleted
100 A
90 A
41.8 A
32.6 A
33.6 A
26.8 A
11.0 A
13.1 A
Bare
75 B
76 B
27.0 B
33.5 A
5.0 B
28.4 A
4.8 B
4.9 B
21 23ºC
Pelleted
100 A
89 A
40.9 A
31.5 A
31.1 A
21.6 B
9.2 A
12.5 A
Bare
70 B
75 B
26.9 B
31.4 A
13.2 B
26.6 A
5.5 B
5.1 B
25 28ºC
Pelleted
100 A
73 A
41.7 A
26.8 A
29.1 A
17.6 B
3.4 B
9.3 A
Bare
68 B
70 A
25.5 B
30.3 A
14.0 B
23.1 A
6.3 A
6.1 B
30 32ºC
Pelleted
98 A
63 A
39.0 A
19.6 B
28.7 A
16.9 B
6.6 A
7.4 A
Bare
54 B
68 A
16.3 B
28.8 A
11.8 B
22.1 A
4.7 B
6.5 A
34 38ºC
Pelleted
76 A
59 A
33.5 A
18.3 A
28.9 A
23.5 A
4.3 B
4.7 A
Bare
26 B
34 B
9.2 B
10.0 B
7.6 B
14.2 B
6.4 A
6.1 A
Means followed by the same capital letter in the co lumn and. lowercase in line. They belong to t he same group. by Scott test Knott (1974). at 5% of probability. Ever -
Everglades, Virg - Virginia.
341
Table 5. Number of remaining seeds (N) and viability (%) of lettuce seeds subjected to the tetrazolium test performed 7 days after
sowing, obtained at the test of pelleted and bare seeds of cultivars exposed to different temperatures. Lavras, Minas Gerais, Brazil,
2014.
Temperature
Everglades
Pelleted
Bare
Viable (%)
Dead (%)
Viable (%)
Dead (%)
17 19ºC
0
0
0
20
0
100
21 23ºC
0
0
0
24
0
100
25 28ºC
0
0
0
26
4
96
30 32ºC
2
0
100
37
0
100
34 38ºC
19
0
100
59
36
54
Surface
Virginia
Pelleted
Bare
Viable (%)
Dead (%)
Viable (%)
Dead (%)
17 19ºC
8
88
12
19
32
68
21 23ºC
9
44
56
20
0
100
25 28ºC
22
18
82
24
0
100
30 32ºC
30
10
90
26
0
100
34 38ºC
33
6
94
53
30
70
¹ seeds do not germinate in the germination test in a total of 80 seeds.
from the temperature gradient above 21 to 23°C (Table 3).
The pelleted seeds of Everglades showed higher emergence
and germination speed index in all temperature gradients
(Table 4). These results are similar to those observed by
Catão et al. (2014), who verified that the germination and the
emergence speed index reduced when the temperature
increased from 20°C to 35°C. Regarding the dry mass (Table
3), the pelleted seeds of Everglades showed higher value in
the lowest temperature gradient. For the seeds of Virginia, the
dry mass was affected at the gradient of 25 to 28°C. On the
other hand, the bare seeds of both cultivars did not differ
statistically among the temperature gradients. By comparing
the interaction between cultivars vs temperature within
coating (Table 4), the pelleted seeds of Everglades showed
higher means in all the temperature gradients. This fact is
probably related to the seedlings that emerge first, as
evidenced by the emergence speed index (Table 4). The
seedlings certainly grow more and present more dry mass due
to the photosynthesis in the early growth stages.
Materials and methods
Experiment establishment and management
The experiment was performed in a completely randomized
2 x 2 x 5 factorial design. The factors consisted of two lettuce
cultivars (Everglades and Virginia), with pelleted and bare
seed and five gradients of germination temperatures (17 to
19ºC, 21 to 23°C, 25 to 28°C, 30 to 32°C, 34 to 38°C), with
four replications. Cultivar Everglades can be considered
thermotolerant. The tests were conducted with a sample of 20
seeds per replication, in a total of 80 seeds per treatment.
Determined variables
The physiological quality of seeds was evaluated by the
following determinations:
Germination test
Sowing was carried out on two sheets of blotting-paper,
moistened with water at a ratio of 2.5 times the paper weight
in gerbox plastic boxes. The boxes with seeds were kept in a
thermogradient table, with alternating light procedure: 12
hours of darkness and 12 hours of light. The temperature was
regulated for a gradient according to each treatment. On the
4th day, first germination count and germination test were
performed. On the 7th day, germination was evaluated, with
normal seedlings as parameter, according to the Rules for
Seed Analysis (2009). The results were expressed as
percentage of normal seedlings at the germination test. The
time required for 50% of the seedlings to germinate (T50)
was calculated (Côme, 1970).
Tetrazolium test
It was performed with the remaining seeds from the
germination test (seeds that did not germinate), removing the
seed coats and embryos submitted to the tetrazolium test. A
solution of 2,3,5-triphenyl tetrazolium chloride was used in a
concentration of 1% during 3 hours in the dark at 30°C. The
percentage of viable seeds was determined according to the
Rules for Seed Analysis (2009).
Emergence test
The seeds were sown in gerbox plastic boxes containing
commercial substrate Tropstrato HA Hortaliças®, with water
retention capacity adjusted to 60%. The boxes with seeds
were kept in thermogradient table under the same conditions
of the germination test. Daily evaluations were performed
from the beginning of the emergence, computing the number
of emerged seedlings until stabilization.
Germination and emergence speed
They were performed simultaneously with germination and
emergence tests. It was computed, daily and at the same time,
the number of seedlings which presented two fully open
leaflets. The indices calculation was performed with formula
proposed by Maguire (1962).
Seedlings dry mass
On the 7th day after test sowing, the seedlings were washed
and 5 uniform seedlings (shoot and root) were collected from
each gerbox. Later, they were placed in paper bags model
'Kraft' to be dried at 60°C for 72 hours. The dry mass was
composed by the average weight of seedlings expressed as
mg-1.
342
Statistical analysis
Analysis of variance was performed by the adoption of a
statistical model and a similar analysis procedure provided by
Ramalho et al. (2012). The means were grouped by the Scott-
Knott test (1974). Statistical analysis was performed with the
aid of SISVAR® statistical package (Ferreira 2011).
Conclusions
Cultivar Everglades showed higher germination, especially
when pelleted seeds were used. The germination performance
of cultivars is influenced by temperature and by the use of
bare or pelleted seeds. From 17 to 23ºC, it is observed a
higher quality seed and an early growth of lettuce.
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... A ação da temperatura sobre o processo germinativo tem sido reportada por pesquisadores em diferentes espécies de hortaliças (AMARO et al., 2014;CATÃO et al., 2014;NASCIMENTO et al., 2016;SOARES et al., 2017). Em sementes de alface, observa-se que temperaturas acima de 25 °C causam diminuição do potencial fisiológico, reduzindo a germinação, a velocidade de germinação, a absorção de água, bem como reações bioquímicas chaves ao processo germinativo dessa espécie CANTLIFFE, 2002;ZUFFO et al., 2017). Mas para espécies como o jambu, apesar de sua crescente relevância no Brasil, informações em relação ao seu processo germinativo e desenvolvimento, frente a variações ambientais, ainda não estão devidamente esclarecidas, o que impede a aplicação de métodos confiáveis de análises físicas e fisiológicas de sementes, limitando assim a expansão na produção da espécie. ...
... The action of temperature on the germination process has been reported by researchers for a great variety of species of vegetables (AMARO et al., 2014;CATÃO et al., 2014;NASCIMENTO et al.,2016;SOARES et al., 2017). In lettuce seeds, for example, temperatures above 25 °C are known to cause decrease in physiological potential, reducing germination, germination speed, and water absorption, as well as biochemical reactions central to the successful germination of this species CANTLIFFE, 2002;ZUFFO et al., 2017). However, for species such as jambu, despise of growing relevance in Brazil, information concerning the effect of environmental variation on the germination process and development of A. oleracea, have yet to be properly elucidated, which impedes the use of reliable methods of physical and physiological analysis for the species, as well as limiting expansion of commercial production of the species. ...
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... This technology improves lettuce seedling mechanization, and reduces the manual work input and the number of seeds necessary for plant growing (Kang, 2004). Studies comparing the characteristics of pelleted and non-pelleted lettuce seeds have been conducted by many researchers worldwide (Wurr & Fellows, 1985;Silva et al., 2002;Zdravković et al., 2006;Contreras et al., 2008;Silva et al., 2015;San Martin et al., 2016;Zuffo et al., 2017, Kadilok et al., 2019. ...
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... A resposta ao tratamento de sementes pode ser influenciada pelo genótipo da cultivar. Zuffo et al. (2017) verificaram diferenças na germinação de sementes de cultivares de alface em função de tratamentos de peletização. No caso da pesquisa em questão, a cultivar Batavia Cacimba é do grupo classificado como alface-crespa roxa, diferente das demais, que são do grupo alface-crespa verde. ...
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... Everglades were used to evaluate the performance of pelleted and bare seeds of lettuce under different germination temperatures at 17 to 19ºC, 21 to 23ºC, 25 to 28ºC, 30 to 32ºC, 34 to 38ºC. The cultivar Everglades showed a higher germination, especially with pelleted seeds (ZUFFO et al., 2017). ...
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Lettuce seeds have a high sensitivity to variations in humidity and temperature of the environment where they germinate, therefore, studies with the aim of improve the germination and physiological performance of these have been conducted. Thus, the study aimed to evaluate the efficiency of pre-germination treatment stratification (5 °C) for different periods, and increase the uniformity of germination of lettuce seeds submitted to different conditions of light and germination temperatures. In the pre-germinative treatment, the seeds of lettuce (Lactuca sativa L.) var. American Great Lakes were placed in plastic boxes dark of the type “gerbox” and subjected to temperature stratification of 5 °C and the dark for 4, 8, 12 and 16 hours. After periods of stratification the seeds were submitted to germination tests which were transferred to plastic boxes type “gerbox” transparent (constant light) and dark (no light) and were maintained in a germination chamber B.O.D with light constant at temperatures of 20, 25, 30 and 35°C. The design used was the entirely randomized with four repetitions, in a factorial outline 5x4x2, five pre-germinative treatments, four germination temperatures and two light conditions. Stratification for 16 hours and temperatures of 20 and 25 °C stimulated the germination of lettuce seeds, providing a higher germination percentage, germination speed index and minor mean germination time. The presence of light resulted in increased germination at 0, 4, 8 and 12 hours of stratification.As sementes de alface apresentam grande sensibilidade às variações na umidade e temperatura do meio onde germinam e, por isso, estudos com o intuito de melhorar a porcentagem de germinação e o desempenho fisiológico dessas têm sido realizados. Dessa maneira, o trabalho teve como objetivo avaliar a eficiência do tratamento pré-germinativo de estratificação (5°C) por diferentes períodos, na uniformização e incremento da germinação de sementes de alface submetidas à diferentes condições de luz e temperaturas de germinação. Para a realização do tratamento pré-germinativo, as sementes de alface (Lactuca sativa L.) var. Grandes Lagos Americana foram acondicionadas em caixas plásticas escuras do tipo ‘gerbox’ e submetidas a estratificação à temperatura de 5°C, na ausência de luz, por 4, 8, 12 e 16 horas. Após as sementes foram submetidas ao teste de germinação, em caixas plásticas tipo ‘gerbox’ transparente (luz constante) e escura (ausência de luz), mantidas em câmara de germinação do tipo B.O.D com luz constante nas temperaturas de 20, 25, 30 e 35°C. O delineamento foi inteiramente casualizado, com quatro repetições em esquema fatorial 5x4x2, cinco períodos de estratificação, quatro temperaturas de germinação e duas condições de luz. A estratificação por 16 horas e as temperaturas de 20°C e 25°C estimularam a germinação das sementes de alface, propiciando maior porcentagem de germinação, índice de velocidade de germinação e menor tempo médio de germinação. A presença da luz resultou em maior germinação nos períodos de 0, 4, 8 e 12 horas de estratificação.
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Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive 'Dark Green Boston' (DGB) and thermotolerant 'Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1- carboxylic acid at 10 mM increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.
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It is sometimes useful in an analysis of variance to split the treatments into reasonably homogeneous groups. Multiple comparison procedures are often used for this purpose, but a more direct method is to use the techniques of cluster analysis. This approach is illustrated for several sets of data, and a likelihood ratio test is developed for judging the significance of differences among the resulting groups.