Short communication. Seed germination of different populations of wild (n = 9) Brassica montana and B. oleracea

The aim of this work was to evaluate seed germination characteristics of wild populations of Brassica montana (8 accessions) and B. oleracea (30 accessions). Seed germination at 25 C under a photoperiod of 16-h light/8-h darkness was variable in B. montana (0 to 86%) and more uniform in B. oleracea (73 to 100%). In both species, germination rate (as expressed by mean germination time) varied significantly among populations. A presowing treatment with gibberellic acid only significantly promoted germination in one of 14 populations tested from both species. The results of this study show high intraspecific variation in the germination pattern of seed from different B. montana populations and less variation in populations of B. oleracea. Additional key words: final germination percentage, gibberellic acid, interpopulation variation, intraspecific variation, mean germination time.

Brassica is the most important economic genus of the Brassicaceae.Several species of this genus have been cultivated from ancient times.Wild Brassica montana Pourret and B. oleracea L. are two species of the B.oleracea (n = 9) group which grow in Spain.These species are interfertile with each other and with cultivated B. oleracea.They can be an important source of genetic diversity for the breeding of cultivated B. oleracea.Both species are close related and grow in coastal habitats on vertical cliffs and on rocky slopes.In the Iberian Peninsula, B. oleracea grows on the Atlantic coast of North Spain and B. montana on the Mediterranean coast of Northeast Spain (Gómez-Campo et al., 1999).
Several papers have reported work on the phylogenetic relationships among wild Brassica species with the chromosome number 2n = 18 (Lannér, 1998;Gómez-Campo et al., 1999).However, we are not aware of any studies on the seed germination of wild populations of B. montana and B. oleracea.Seed germination is a major aspect of germplasm that needs to be understood when an increasing number of Spanish Journal of Agricultural Research (2005) 3(3), 331-334 samples of different origins are cultivated for experimental, breeding or commercial purposes (Bewley and Black, 1994) 1 and  2 show the collection site of each seed population.Seeds from all populations were equally ripe based on their colour and consistency.Seed was stored in a dry room at room temperature (ca.23°C) until the start of germination trials in the autumn of the year that the seed was collected.Four replicates of 25 seeds each were used in each trial.Seeds samples were placed in a 7-cm glass Petri dishes on two sheets of filter paper moistened with 3.5 ml of distilled water.The water was replaced regularly.Petri dishes were incubated at 25°C with a 16-h light/8-h dark photoperiod.Cool white fluorescent tubes provided lighting with an irradiance of 35 mmol m -2 s -1 .Seeds with an emerged radicle were counted daily and removed from the Petri dishes.The final germination percentage was scored after a 30-day incubation.
Application of gibberellic acid (GA3) was by soaking the seed in a GA3 water solution (1000 mg l -1 ) for 24 h prior to placing them in the germination cabinets.At the end of the germination period, the final germination percentage and the mean germination time (MGT, days) were calculated.The latter was determined according to the following formula (Bewley and Black, 1994): where Ti is the number of days from the date of sowing and Ni is the number of seeds germinated at each day.The MGT was not calculated when the final germination was equal to or less than 5%.For all the tests the final germination percentages (mean values ± standard error) were calculated and arcsine transformed values were subjected to analysis of variance.For each accession, a one-way factorial ANOVA was performed.The statistical analysis of MGT was also carried out using one-way ANOVA.
Table 1 shows the final germination percentage and the MGT for untreated seed and seed soaked in GA3 for all populations of B. montana.There were highly significant differences (P < 0.001) in the final germination among the different populations.The final germination of control seed ranged from 0 to 86%.The MGT also varied significantly (P < 0.01) among the different populations and ranged from 3.63 to 6.08 d.
Table 2 shows the final germination percentage and MGT for control and treated seeds from all B. oleracea populations.There were significant differences (P < 0.001) in final germination among the different populations.However, in all populations the final germination of control seed was > 70% and ranged from 73 to 100%.
Germination was ³ 90% in 23 of the 30 accessions.The MGT values also varied significantly (P < 0.001) from 1.35 to 3.70 days depending on the population.Soaking seed in GA3 did not significantly increase final germination (P > 0.05) over that of control seed in the six accessions that were assayed (Table 2).The MGT values of seed treated with GA 3 were significantly (P < 0.05 and P < 0.01) lower than in control seed in five of the six tested accessions.
Interpopulation differences in final germination were highly significant in B. montana.Populations from similar Germination of wild Brassica species 333 habitats may have different germination responses.These differences can arise from environmental variation during seed maturation and the effect of maternal genotype (Fenner, 1991;Wulff, 1995).Variability of germination response within populations of a species is frequent in wild Mediterranean species (Pérez-García et al., 2003).Indeed, interpopulation variability in seed germination may be interpreted as an important survival strategy of species growing under variable and unpredictable environmental conditions (Gutterman, 1994;Kigel, 1995;Baskin and Baskin, 1998;Cruz et al., 2003).
Less interpopulation difference was found in seed germination of B. oleracea.Also, the germination was high in all populations (> 70%).The germination of the different B. oleracea populations was much more uniform that of the B. montana populations.
Interpopulation variability in the germination of B. montana might have arisen as an adaptation strategy to the more unpredictable habitats where this species grow on Mediterranean coast.On the Atlantic coast of Spain there is frequent rain, even in summer, and temperatures are not extreme.On the Mediterranean coast the summer are usually very dry with high temperatures.The high variability in germination shown by the different B. montana populations could be explained by the stress conditions of high temperature and drought which are characteristics of a Mediterranean summer.
Gibberellic acid (GA3) only significantly enhanced germination in one of the eight accessions of B. montana and in none of the six accessions of B. oleracea which were tested.The MGT of GA3 treated seeds in both species was higher than in control seeds.Moreover, these differences were significant in five of the six B. oleracea accessions which were tested.These results suggest the presence of a low level of seed dormancy in both species.
In conclusion, the results of this study show high intraspecific variation in the germination pattern of seed from different B. montana populations (Mediterranean coast species) and less variation in populations of B. oleracea (Atlantic coast species).Therefore, future studies of the germination characteristics of B. montana should consider different populations.
. The objective of this work was to compare the germination responses (final germination percentage and mean germination time) of seeds from 8 populations of B. montana and 30 populations of wild B. oleracea under controlled germination conditions.Brassica montana seeds were collected from 8 locations on the Mediterranean coast of Northeast Spain in July 2003.Wild B. oleracea seeds were collected from 30 locations on the Atlantic coast of North Spain in July 2002 and July 2003.Tables

Table 1 .
Final germination percentage (mean value ± standard error) and mean germination time (MGT, days ± standard error) of eight Brassica montana accessions.All seed collection sites are on the Gerona coast (NE Spain).Seeds were collected in July 2003.Seeds were germinated at 25°C under a 16-h light photoperiod.When germination was £ 5%, MGT was not calculated (NC).

Table 2 .
Final germination percentage (mean value ± standard error) and mean germination time (MGT, days ± standard error) of 30 Brassica oleracea accessions.Seed of accessions 9801 to 9831 was collected in July 2002, seed of accession number 9887 was collected in July 2003.Seeds were germinated at 25°C under a 16-h light photoperiod.