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Agrociencia

versão On-line ISSN 2521-9766versão impressa ISSN 1405-3195

Agrociencia vol.52 no.8 México Nov./Dez. 2018

 

Natural Renewable Resources

Variation in germination and vigor of Pinus cembroides and Pinus orizabensis seeds

Leticia A. Hernández-Anguiano1 

Javier López-Upton1  * 

Carlos Ramírez-Herrera1 

Angélica Romero-Manzanares2 

1Forestal. Campus Montecillo. Colegio de Postgraduados. 56230. Montecillo, Estado de México.

2Botánica. Campus Montecillo. Colegio de Postgraduados. 56230. Montecillo, Estado de México.

Abstract

Pinus cembroides and P. orizabensis produce edible seeds, which are sold at different prices depending on the color of their seed coat or testa. Germinative quality of the seeds was evaluated considering their color and three provenances per species: Colón and Cadereyta, Querétaro, and Santiago de Anaya, Hidalgo, for P. cembroides; Tepeyahualco, Puebla, and El Carmen and Altzayanca, Tlaxcala, for P. orizabensis. The combination of the factors color, provenance and species allowed us to form 18 lots. Testa thickness and germination were determined with four replications of 25 seeds and 15 replications for the imbibition test per lot. Analyses of variance were performed to test differences between species and among provenances and seed coat colors. Testa thickness, germinative capacity, peak value, and rates of imbibition and germination were different between species. The P. cembroides testa was 0.1 mm thicker and germination capacity was 4% higher than P. orizabensis. The peak value was higher and germination faster in P. cembroides (12.7 vs. 13.4 d to reach 50 % germination). Provenance was significant for germinative capacity, days to 50 % germination, peak value, and days to reach peak value. P. cembroides from Cadereyta had the highest germination (95 %); seed from Colón germinated faster. Lower vigor and germination (4.4 and 87.5 %) were found in seeds from Santiago de Anaya. The P. orizabensis seeds from El Carmen had higher germination (87.1 %) and those from Tepeyahualco and Altzayanca higher germination rate. Brown seeds of both species had thicker testa and higher germination capacity. Black P. cembroides seeds have thinner testa and germinated at a faster rate than those with brown seed coat. Brown P. orizabensis seeds were more vigorous.

Keywords: germination; seed testa color; Pinus cembroides; Pinus orizabensis; peak value

Introduction

Pinus cembroides Zuccarini and P. orizabensis (D.K. Bailey) D.K. Bailey & F.G. Hawksworth are pines of the Parrya section of the sub-genus Strobus (Gernandt et al., 2003). They are medium stature, low-branching and slow-growing trees. Its wood is used mainly as fuel (Wolf, 1985; Bailey and Hawksworth, 1992; Romero et al. 1996). Pinus cembroides is distributed in Arizona, Texas and New Mexico in the USA and in 14 states of central and northern Mexico above 20º N, including the states of Querétaro and Hidalgo, as southern locations (Farjon and Styles, 1997). Pinus orizabensis, endemic to Mexico, is found in Puebla, Tlaxcala and central Veracruz, below 20° N (Perry, 1991; Farjon and Styles 1997). The importance of these species is ecological, economic and cultural. Its adaptive potential is high, growing in places with little precipitation. Both species are useful for reforestation in degraded ecosystems in arid and semi-arid areas at altitudes from 800 to 2800 m (Mohedano-Caballero et al., 1999), but birds and rodents eat the seeds (Romero et al., 1996). The seed (pine nut) is collected for selling and for home consumption. It is a source of income for the owners of these forests who supply pine nuts for typical dishes and candies (Fonseca, 2003; Hernández et al., 2011).

Germinative capacity and vigor are the main variables that define the quality of the seeds for plant production (Bonner et al., 1994; Trujillo, 1996). Germinative capacity is the percentage of seeds that germinate in a period and defines the amount of seed required to produce seedlings (Kolotelo et al., 2001). Vigor refers to germination rate and is defined by the number of days needed to reach 50% of the seed germinative capacity, or when determining the peak value (PV) of accumulated germination divided by the number of days to reach the peak value (Kolotelo et al., 2001). The more rapid and even the germination, the higher the seed vigor and uniformity of plant production (Bonner et al., 1994; Trujillo, 1996).

These two pine nut pines are allopatric and P. orizabensis is distributed in more southern conditions and at higher elevations than P. cembroides. They differ by the number of needles per fascicle, the amount of wax on the needles and the position of stomata (Bailey and Hawksworth, 1992). This presupposes differences in adaptation between these taxa, and so reforestation with the wrong pine nut tree would alter the natural distribution of the species and may affect the development and survival of the plants.

Producers use seed coat color (black, bi-color and brown, or “parraleño” as they call it in Tlaxcala) as the criterion for quality and price of the seeds because seeds with a bi-color or brown testa are more highly demanded by the food industry, their price is higher (Hernández et al., 2011), and each tree produces testa of only one color. Martínez et al. (1987) document significant differences in seed quality based on the color of the testa of P. johannis M.-F. Robert seeds: 36.5 % of seeds with brown testa were viable and 35 % germinated, while 99 % of those that were light colored or black (dark) were viable with 84 and 79 % germinative capacity, respectively.

Water is a determining factor in seed storage and germination and depends on seed chemical composition. Thus, in managing forest nurseries it is important to document seed imbibition behavior when it initiates metabolic processes (Bonner et al., 1994). The objective of this study was to determine differences in germinative characteristics of P. cembroides and P. orizabensis seeds from several provenances, and to evaluate differences in germination among seeds of different color testa. The hypothesis was that there are differences in germinative capacity and energy of seeds of both pines and of those from the provenances tested, and that seed germination is different depending on the color of the testa.

Materials and methods

Seeds were collected in natural populations of P. cembroides and P. orizabensis in 2014 and 2015 (Table 1). In the case of P. cembroides, the trees were selected because they are geographically close to the other species and at high elevation and thus could be compared. In each provenance, 15 healthy trees with good crown conformation were chosen; the trees were at least 50 m apart. The number of cones collected varied from 10 to 15 per individual tree. The cones from each tree were packed in paper bags labeled with the name of the species, provenance and date. The strobili were transported to the laboratory of the graduate program in Forest Sciences of the Colegio de Postgraduados in Texcoco, state of Mexico, to be processed and the seed analyzed.

Table 1 Location of the populations of Pinus cembroides and P. orizabensis included in this study. 

Población nombre, municipio, estado Latitud N Longitud O Altitud (m)
Pinus cembroides
El Carrizal, Colón, Querétaro 20° 52’ 40.23” 100° 05’ 07.23” 2159
La Laja, Cadereyta, Querétaro 20° 48’ 44.32” 99° 38’ 18.72” 2831
La Florida, Santiago de Anaya, Hidalgo 20° 28’ 36.06” 98° 59’ 01.50” 2002
Pinus orizabensis
Tepeyahualco, Tepeyahualco, Puebla 19° 30’ 25.60” 97° 30’ 26.27” 2417
Rancho Domínguez, El Carmen, Tlaxcala 19° 24’ 01.28’’ 97° 42’ 44.39’’ 2671
Las Cuevas, Altzayanca, Tlaxcala 19° 22’ 44.30” 97° 43’ 02.10” 2479

Data obtained with a geographic positioner Garmin® Etrex 10 Datum WGS84

Because we observed that each tree produces seed with seed coat of only one color and that producers obtain higher prices with seeds that are not black, we decided to test this factor as well as the species and their geographic origin. The number of seeds of some species-provenance-testa color combinations was small, and for this reason, in the tests a smaller sample size than suggested by the ISTA (International Seed Testing Association, 1999) was used. For the same reason and because we did not find trees that produced certain colors of testa in some provenances, we formed 18 lots of seed depending on the amount available per species, provenance and testa color on two collection dates (Table 2). Each lot is a group of seeds composed of several trees that had seed of a certain test color in each location of a certain year. Differences in germinative capacity (CG), viability, peak value (VP), days to peak value (DVP), days to reach 50 % of the germinative capacity (GERM50), testa thickness and imbibition were determined. In both species three colors were identified (black, brown and bi-color). Only for P. cembroides there were not sufficient bi-color seeds for the tests, and we considered only the other two colors for tests with this species.

Table 2 Lots formed for analysis of germination, viability, vigor, imbibition and testa thickness of Pinus cembroides and P. orizabensis seed, established to determine differences between species and among provenances and seed coat colors. 

Lote Especie Procedencia Color de testa Cosecha
1 P. cembroides Colón Negro 2015
2 P. cembroides Cadereyta Negro 2015
3 P. cembroides Cadereyta Pardo 2015
4 P. cembroides Santiago de Anaya Negro 2015
5 P. cembroides Santiago de Anaya Pardo 2015
6 P. orizabensis Tepeyahualco Negro 2015
7 P. orizabensis Tepeyahualco Bicolor 2015
8 P. orizabensis Altzayanca Negro 2015
9 P. orizabensis Altzayanca Bicolor 2015
10 P. orizabensis Altzayanca Negro 2014
11 P. orizabensis Altzayanca Pardo 2014
12 P. orizabensis Altzayanca Bicolor 2014
13 P. orizabensis Tepeyahualco Negro 2014
14 P. orizabensis Tepeyahualco Pardo 2014
15 P. orizabensis Tepeyahualco Bicolor 2014
16 P. orizabensis El Carmen Negro 2014
17 P. orizabensis El Carmen Pardo 2014
18 P. orizabensis El Carmen Bicolor 2014

The physiological tests were conducted with seed collected in two consecutive years. The 2014 seed was stored at humidity below 8 % in a cold chamber at -6 °C. No significant differences between the collection years were detected in germination tests, and thus, this factor was not considered in later analyses.

Seed moisture content

Moisture content was determined in two seed samples that had initial weight of 3 to 4 g. These samples were placed in aluminum boxes with covers and put into a drying oven Riossa® at 130 °C for 1 h (ISTA, 1999). The seed was weighed on an analytical balance Edam® PW124, with a precision of 0.1 mg. Moisture content (MC) was calculated with the following formula (Kolotelo et al., 2001; Bonner et al., 1994):

MC = (seed fresh weight - seed dry weight)*100 / seed fresh weight.

Testa thickness

Testa thickness was measured in four replications of 25 seeds per lot. The seeds were broken with a die press C-Clamp (Truper, model 17666 PTR-2). Each seed was placed vertically in the press with the micropyle pointing downward and moderate pressure was exerted until the testa fractured longitudinally. The larger piece of the testa was measured. Measurement of thickness was done at the opposite ends of the testa at a distance of 5 mm above the micropyle near the middle of the testa with a digital vernier (Mitutoyo, model CD-6CS). The value reported was the average thickness for the lot.

Seed imbibition

The seed imbibition curve of the 18 lots was constructed by monitoring seed weight gain. Four replications of 15 seeds per lot were placed in 100 mL distilled water at room temperature in precipitation beakers. Init ial weight was recorded and monitored every 2 h for 24 h and later every 4 h for additional 20h. Weight was quantified on an Edam® PW124 analytical balance. The water used for each sample was changed every 12 h. The percentage of absorption obtained was accumulated seed weight per unit of time, relative to initial seed weight.

Seed viability

Four replications of 25 seeds from each lot were used. The testa was eliminated, and the embryos and megagametophytes were soaked for 12 h in distilled water. The megagametophyte was cut longitudinally with a #4 scalpel to saturate the embryo in a 1 % solution of 2, 3, 5 tetrazolium chloride (TZ) in glass Petri dishes. The Petri dishes with the samples were placed for 24 h at room temperature in darkness in aluminized bags that did not allow passage of light. The seeds were classified as viable when the megagametophyte and embryo dyed intense red (Kolotelo et al., 2001).

Germination

Before the germination test, the seeds were disinfected in a solution (0.25 %) of commercial sodium hypochlorite (Cloralex®) by immersion for 5 min plus washing with abundant running water. The testa was scarified with 3 % hydrogen peroxide (v:v) for 2 min and the seed was soaked in distilled water for 12 h before the germination test. The seeds were placed on a cotton cloth in 20 x 27 x 12 cm transparent rigid plastic boxes with hermetic covers. Plastic separators were installed between treatments and 75 mL distilled water was added. They were then sprayed with a fungicide solution of 0.2 % Captán. The boxes with seeds were placed in a chamber with daytime temperature of 24 to 26 °C and night temperature of 22 to 24 °C.

The germinated seeds were recorded every day for 35 d. When the root was as long as the seed, the seed was considered germinated. The variables were germinative capacity (CG), peak value (VP), days to reach peak value (DVP) and time to reach 50 % total germination (GERM50), calculated with the following formulas:

CG (%) = (germinated seeds/total seeds)*100

VP = MAX Σ germination/days (Kolotelo et al., 2001)

DVP (day) = test day on which accumulated germination divided by the number of days lapsed was the highest (Kolotelo et al., 2001).

GERM50 (days) = number of days to reach 50 % of the germinative capacity.

Experimental design and statistical analysis

In the germination test, we used a completely randomized design with 20 replications of 10 seeds per treatment (Table 2). Prior to the statistical analyses, the data on germinative capacity and viability were standardized because it is information expressed in percentage. The percentage data were transformed with the arcsine function of the square root of p (θ =arcoseno √p, where θ is the value of germinative capacity or viability). This transformation is applied to data between 0 and 1 to improve their normal distribution (Sokal and Rohlf, 1981). All the statistical analyses were performed with the MIXED procedure (SAS Institute, 2003). None of the variables were different between years, and this factor was not considered in the statistical models used. Thus, some combinations color-species or provenancespecies had more repetitions.

The models used for the analysis to test differences between species and provenances were:

Yijkl =μ+Ri+Ej+REij+Pk(j)+RPijk+Eijkl

where Yijkl is the observed value of the lth lot of a certain testa color of the kth provenance of the jth species in the ith replication, µ is the general mean, Ri is the random effect of the ith replication, Ej is the fixed effect of the jth species, REij is the random effect of the interaction of the ith replication with the jth species, Pk(j) is the fixed effect of the kth provenance within the jth species, RPijk is the random effect of the interaction of the ith replication with the kth provenance within the jth species, and Eijkl is the experimental error.

To test differences among testa colors, the analysis was performed for each species with the model:

Yijkl =μ+Ri+Cj+RCij+Eijk

where Yijk is the observed value of the kth lot of a certain provenance of the jth seed testa color in the ith replication, µ is the general mean, Cj is the fixed effect of the jth seed testa color, RCij is the random effect of the interaction of the ith replication with the jth testa color, and Eijk is the experimental error.

Results and discussion

Moisture content and testa thickness

There were no significant differences between species or among provenances or testa colors. The moisture content of P. cembroides was 0.33 % higher than in P. orizabensis (Table 3). The mean values of seed moisture content with different testa colors varied from 7.24 % to 9.64 %. Seeds of the genus Pinus are orthodox, since they tolerate low moisture content (5-8 %) and remain viable over long periods of storage in controlled temperature with suitable packaging (Bonner et al., 1994).

Table 3 Mean values and standard error (e.e.) of testa thickness, initial moisture content based on fresh weight, moisture content at 44 h of imbibition and percentage of absorption of Pinus cembroides and P. orizabensis seeds in general and by testa color of each species. 

Especie /
color de testa
Grosor testa (mm)
media ± e.e.
C.H. inicial (%)
media ± e.e.
C.H. 44 h (%)
media ± e.e.
Absorción (%)
media ± e.e.
P. cembroides 0.87 ± 0.007 aՓ 7.73 ± 0.21 a 24.64 ± 0.82 b 32.97 ± 1.69 b
P. orizabensis 0.78 ± 0.004 b 7.40 ± 0.13 a 27.49 ± 0.50 a 38.27 ± 1.02 a
Pinus cembroides
Negro 0.87 ± 0.009 b 7.94 ± 0.30 a 24.43 ± 1.26 a 32.70 ± 2.32 a
Pardo 0.91 ± 0.011 a 7.52 ± 0.36 a 24.05 ± 1.39 a 31.73 ± 2.54 a
Pinus orizabensis
Bicolor 0.77 ± 0.006 b 7.24 ± 0.24 a 27.13 ± 0.80 b 37.38 ± 1.68 b
Negro 0.75 ± 0.006 c 7.38 ± 0.19 a 28.90 ± 0.80 a 41.33 ± 1.68 a
Pardo 0.84 ± 0.008 a 7.58 ± 0.19 a 26.13 ± 1.03 b 35.50 ± 2.17 b

Moisture content. Percentage weight gain of seed at the end of the test, relative to its initial weight. Different letters in each section indicate differences, p=0.05.

The differences in seed testa thickness between species and among provenances and testa colors were significant (p≤0.01). The testa of P. cembroides seeds was thicker, and this may have influenced the lower absorption of water by making imbibition difficult (Table 3). Testa of black seeds of both species was thinner, and so they probably absorbed water more easily. Farjon and Styles (1997) report a greater range of testa thickness for P. orizabensis, 0.7 to 1.1 mm, than for P. cembroides, 0.6 to 1.0 mm.

Seed imbibition

The seeds rapidly absorbed water. After only two hours, P. cembroides seed absorption percentage was 10 % and 12.7 % for P. orizabensis seeds. Later, the rate of absorption decreased but was higher in P. orizabensis seeds. Water absorption of P. cembroides seeds was 25 % at 24 h and at 16 h for P. orizabensis. At the end of the test (44 h), P. cembroides and P. orizabensis had absorbed 32.4 % and 37.6 %, respectively (Figure 1). The highest absorption at the highest rate of the P. orizabensis seeds may be due to the thickness of its testa, which was 0.1 mm thinner than that of P. cembroides.

Figure 1 Accumulated imbibition of Pinus cembroides and P. orizabensis seeds. 

Initial moisture content may have an influence in the seed’s imbibition period (Mápula et al., 2008). In our study, it was 7.8 % for P. cembroides and 7.4 % for P. orizabensis; therefore, absorption was greater in P. orizabensis whose seed was less moist. Soaking in running water for 24 to 48 h is adequate to promote total imbibition of the seeds, and this period varies among conifer species. Seeds of some species can undergo damage if soaking is prolonged (Landis et al., 2014). In Mexican nurseries, the seeds are submerged for 12 or up to 18 h before sowing. Our results indicate that the period of immersion should increase for these seeds, and care was taken so that overexposure to immersion did not have adverse effects on the seeds, such as appearance of pathogens and the lack of oxygenation (Landis et al., 2014). Germination of P. edulis Engelman seeds improved when they were soaked in running water for 48 h (Ronco, 1990).

Black P. cembroides seeds absorbed water faster: 25 % in 22 h, contrasting with 28 h for brown seeds (Figure 2). Black P. orizabensis seeds reached 25 % in 14 h, while brown and bi-colored seeds took 16 and 20 h, respectively (Figure 3).

Figure 2 Accumulated imbibition of Pinus cembroides seeds with testa of different colors. 

Figure 3 Accumulated imbibition of Pinus orizabensis seeds with testa of different colors. 

Seed viability

Differences in seed viability were not significant (p>0.05) between species or among provenances and testa colors. Viability was high in seeds of both species: 93.5 % in P. cembroides and 90.8 % in P. orizabensis (Table 4). The highest values of viability were recorded for P. cembroides collected in Cadereyta (98 %) and the lowest for seeds collected in Colón (89 %). Viability was high for recently collected seeds and for those stored in refrigeration for one year.

Table 4 Percentage of viability of Pinus cembroides and P. orizabensis seeds, by species, provenance and testa color. 

Especie Procedencia Color de testa Viabilidad (%)
P. cembroides --- --- 93.50 ± 1.45
P. orizabensis --- --- 90.82 ± 1.88
Cadereyta --- 98.00 ± 3.18
P. cembroides Colón --- 89.00 ± 3.08
Santiago de Anaya --- 93.50 ± 2.18
Altzayanca --- 90.80 ± 1.38
P. orizabensis El Carmen --- 91.67 ± 1.78
Tepeyahualco --- 90.00 ± 1. 38
Negro 94.00 ± 1.29
P. cembroides Pardo 95.00 ± 1.58
Bicolor 90.20 ± 1.55
P. orizabensis Pardo 92.33 ± 1.99
Negro 90.21 ± 1.55

Seed germination and vigor

The two species differed significantly in germinative capacity (CG), peak value (VP) and in days to reach 50 % germination (GERM50) but not in days needed to reach peak value (DVP). However, the differences were significant among provenances for the four variables (Table 5).

Table 5 Analysis of variance for germinative capacity (CG), days to 50 % CG (GERM50), peak value (VP) and day on which peak value appears (DVP) between species and provenances of Pinus cembroides and P. orizabensis

Efecto CG GERM50 VP DVP
Valor F Pr>F Valor F Pr>F Valor F Pr>F Valor F Pr>F
Especie 4.39 0.0497 5.93 0.0249 6.73 0.0178 0.46 0.5068
Procedencias 7.96 0.0001 12.9 0.0001 6.06 0.0003 11.17 0.0001

Degrees of freedom of the numerator 1 and 4, of the denominator 19 and 76 for species and provenance, respectively.

Germinative capacity of P. cembroides seeds was higher than that of P. orizabensis (Figure 4, Table 6), and germination of P. cembroides seeds was faster, as seen with the fewer number of days required to reach 50 % germination. The peak value shows that P. cembroides seeds are more vigorous, but the days to reach peak value indicate similar germination rate (Table 6).

Figure 4 Germination of Pinus cembroides and P. orizabensis seeds. 

Table 6 Mean values and standard error (e.e.) of the germinative capacity (CG), days to 50 % germinative capacity (GERM50), peak value, and days to reach peak value (DVP) of Pinus cembroides and P. orizabensis seeds and their respective provenances. 

Especie /
procedencia
CG (%)
media ± e.e.
GERM50 (días)
media ± e.e.
Valor pico (%/d)
media ± e.e.
DVP (días) )
media ± e.e.
P. cembroides 88.17 ± 1.38 a 12.74 ± 0.28 b 5.02 ± 0.12 a 16.29 ± 0.36 a
P. orizabensis 84.22 ± 0.86 b 13.38 ± 0.21 a 4.70 ± 0.08 b 16.53 ± 0.26 a
Pinus cembroides
Cadereyta 95.00 ± 2.03 a 12.55 ± 0.38 b 5.34 ± 0.17 a 16.08 ± 0.50 b
Colón 82.00 ± 2.85 c 11.13 ± 0.51 c 5.37 ± 0.23 a 14.20 ± 0.67 c
Santiago de Anaya 87.50 ± 2.03 b 14.55 ± 0.38 a 4.35 ± 0.17 b 18.60 ± 0.50 a
Pinus orizabensis
Altzayanca 83.40 ± 1.31 b 13.11 ± 0.27 b 4.74 ± 0.12 a 16.35 ± 0.35 b
El Carmen 87.13 ± 1.46 a 14.08 ± 0.29 a 4.63 ± 0.13 a 17.38 ± 0.38 a
Tepeyahualco 82.13 ± 1.46 b 12.95 ± 0.29 b 4.72 ± 0.13 a 15.88 ± 0.38 b

Lower values indicate higher rate. Different letters indicate differences (p=0.05).

Between 8 and 13 % more of the P. cembroides seed collected in Cadereyta germinated than that collected in Santiago de Anaya and Colón (Figure 5). However, germination rate was higher in seeds collected in Colón, 1.4 d and 3.4 d fewer to reach 50 % germination, compared with seed collected in the other two sites. The peak value shows that seeds from Colón and Cadereyta is more vigorous and seed from Santiago de Anaya is less vigorous.

Figure 5 Germination of Pinus cembroides seed from different provenances. 

P. orizabensis seed germination was more homogeneous and the differences between the extreme values of CG was 5%. Germination of seed from El Carmen was higher (Figure 6) but slower to germinate and with less vigor, around 1 d of difference in reaching 50% of total germination. Altzayanca seed exhibited greater vigor, based on peak value, but Tepeyahualco seed reach peak value more rapidly.

Figure 6 Germination of Pinus orizabensis seed from different provenances. 

The germinative capacity of P. cembroides seed was higher in our study than the value reported for seed of the same species collected in the Ejido La Amapola in San Luis Potosí, where it was 81% (Sandoval et al., 2000). The germinative capacity of P. orizabensis seed in our study was also superior to the same species (48 %) collected in Altzayanca, Tlaxcala (Sánchez et al., 2005); these authors report that germination initiated 30 d after the experiment was set up in agrolite in a greenhouse, unlike our study where it began on the sixth day.

In both pines there were significant differences in germinative capacity among the different testa colors (Table 7). Brown P. cembroides seeds had 5.5% more germination than black seeds, and 8.4% more with brown P. orizabensis seeds. In this species, germination of bicolor and black testa seeds was similar (Table 8; Figure 7). However, only with P. cembroides seed were there differences in days to reach 50 % germination and in number of days to peak value (Table 7). More seeds with brown testa germinated, but P. cembroides seeds with black testa germinated more rapidly, with fewer days to 50 % germination and to peak value. This did not occur with P. orizabensis (Table 8; Figure 8).

Table 7 Analysis of variance of germinative capacity, days to 50 % germinative capacity (GERM50), peak value, and days to peak value of Pinus cembroides and P. orizabensis seeds with different testa colors. 

Variable Color de testa en P. cembroides Color de testa en P. orizabensis
G.L. núm G. L. den. Valor de F Pr > F G.L. núm. G. L. den. . Valor de F Pr > F
Capacidad germinativa 1 19 9.09 0.0071 2 38 6.80 0.0030
GERM50 1 19 8.12 0.0102 2 38 2.45 0.1000
Valor pico 1 19 2.85 0.1079 2 38 7.38 0.0020
Días al valor pico 1 19 10.51 0.0043 2 38 2.18 0.1271

G.L. = Degrees of freedom of the numerator and denominator.

Table 8 Mean values and standard error (e.e.) of the germinative capacity, days to 50 % of germinative capacity (GERM50), peak value, and days to peak value of Pinus cembroides and P. orizabensis seed with different testa colors. 

Color Capacidad germinativa (%)
media ± e.e.
GERM50 (días)
media ± e.e.
Valor Pico (%/d)
media ± e.e.
Días al valor pico (días)
media ± e.e.
Pinus cembroides
Negro 87.17 ± 1.27 b 12.47 ± 0.33 b 4.74 ± 0.16 a 15.80 ± 0.44 b
Pardo 92.75 ± 1.55 a 13.95 ± 0.40 a 5.09 ± 0.14 a 18.08 ± 0.54 a
Pinus orizabensis
Bicolor 83.20 ± 1.43 b 13.61 ± 0.27 a 4.58 ± 0.12 b 16.73 ± 0.35 a
Negro 81.60 ± 1.43 b 13.24 ± 0.29 a 4.55 ± 0.12 b 16.44 ± 0.35 a
Pardo 90.00 ± 1.81 a 12.97 ± 0.32 a 5.16 ± 0.15 a 15.97 ± 0.41 a

Lower values indicate higher rate. Different letters indicate differences (p=0.05).

Figure 7 Germination curve of Pinus cembroides seeds with different testa color. 

Figure 8 Germination curve of Pinus orizabensis seeds of different testa color. 

Martínez et al. (1987) observed that P. johannis seeds with different testa color were not significantly different in viability, but germination of mottled seed was 36.5 %. This value is a third of that obtained with brown or mottled P. cembroides and P. orizabensis seeds (more than 90 % in both species). The same authors indicate that the seed with lightcolored or black testa had a germination of 84 and 79 %. For the study of P. cembroides and P. orizabensis seed, that with black test had the lowest germinative capacity, 87 and 81 %, respectively. No differences in germination among the different testa colors were reported with P. sylvestris L., and each tree produces testa of different colors (Kaliniewicz et al., 2013).

P. cembroides seed testa is thicker and has a lower rate of water absorption, and contrary to what was expected, more seeds germinated and at a faster rate than P. orizabensis seeds. A prediction could be that the seeds that absorb water at a faster rate, such as those of P. orizabensis, germinate at a faster rate, but it is possible that some physiological mechanism is involved in rapid germination of P. cembroides, and this physiological response could be an adaptive opportunist trait, confirming the existence of morphological and adaptive differences that deserve distinction and management as different taxa, particularly in repopulation that is carried out in the country.

The results of viability and germination indicate the absence of latency in the seed of both species despite the thick testa, which is composed mainly of dead cells and acts as a protective covering for the live inner tissues (Kolotelo et al., 2001). The seeds presented only quiescence and germinate when the environmental conditions are suitable (Baskin and Baskin, 2004).

Conclusions

Pinus cembroides seeds have thicker testa, lower rate of water absorption, but a higher germinative capacity than the seeds of P. orizabensis, which confirms morphological and potentially adaptive differences.

Provenance of the seed had significant effects on seed quality; P. cembroides seed from Cadereyta and P. orizabensis seed from El Carmen were outstanding.

Seed testa color had influence in germination variables. Brown seeds, the most valuable, have greater germinative capacity than black seeds, but the latter is more vigorous and germinate more rapidly.

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Received: January 2017; Accepted: November 2018

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