0487-B4

Germination Characteristics of Autumn-Collected Pinus sylvestris L. Seeds

Fahrettin TİLKİ ¹

Abstract

This experiment was conducted to determine the effects of the date of cone collection and of cone storage on germination characteristics of Scots pine seeds. Cones were collected on five occasions between September 11 and November 26, 2000, from two altitudes in Bolu, Turkey, and stored at +5±1 °C for one month-1 year. The low level of cone moisture content (21-23 %) was found in late November. Seed moisture content ranged from 21 to 29 % during the month of September and October, and fell slowly to 14-15 % in December. Germination parameters were affected by the date of cone collection, and the cone and seed maturity improved up to 2nd November. If collection occurred as early as late September and stored at +5 °C for at least one month before extraction, cones gave seed with the same good properties as the seed from cones which had ripened under natural conditions on the trees. Following appropriate handling, germinability of autumn-harvested seed is not weakened, even after one-year storage. Germination percent and rate were also greatly affected by germination condition. The seeds collected in September and October germinated poorly in darkness at 10 and 20 °C. In conclusion, it seems that the seed is fully developed in late October and storage of the cones +5 °C during one month before the seed extraction seems to allow cone collection about one month earlier.

I. Introduction

Pinus sylvestris L. (Scots pine) is widely distributed in Turkey. It makes up about 5.5 % of total forest area as mixed and pure stands and occupies about 738000 ha in Turkey (OGM 1980). It grows in areas with an annual precipitation exceeding 2500 mm and in areas with an annual precipitation as little as 360 mm. Its altitudinal range is from sea level on the coastal belt of the Black Sea to about 2700 m in the northeastern Turkey. Most Scots pine forms more or less close stands between 1250-2000 m above sea level in Turkey (Kayacık 1963; Elicin 1972).

A seed's ability to germinate is determined largely by its degree of maturity. Anatomically or physiologically immature seeds germinate slowly even in favorable conditions. One way of improving the technical quality of seeds from seed stands is to artificial ripening, i.e., the cones are collected when the seeds are still immature and are then allowed to ripen under more favorable conditions than in nature. Several investigations on artificial ripening of Scots pine seeds have been made in Sweden and Finland (Asplund et al. 1973; Remrod and Alfjorden 1973; Sahlen and Bergstern 1993). Generally, storage of cones at low temperatures (0-10 °C) has been more beneficial than storage at high temperature. Sahlen and Bergstern (1993) stated that not only temperature but also light, cone moisture content and ripening time had an effect on seed quality after artificial ripening on Scots pine seeds. Light requirement for germination interact with cone collection date. As autumn proceeded, a greater proportion of seeds were able to germinate in darkness (Blomqvist 1972; Nygren 1987).

Scots pine has a rather important place in artificial regeneration in Turkey but there are many difficulties in cone collection from seed stands in late autumn and winter since most Scots pine seed stands is found between 1400-2000 m. It is of great importance to be able to start the cone collection early in the autumn so as to avoid the snow-hinder and to use the shortening working-days better.

The objective of this investigation was to analyze the germination characteristics of autumn-collected Scots pine seeds and to determine the effect of cone storage on ripening of Scots pine seeds collected at different stages of maturity.

II. Materials and Methods

Scots pine cones were collected during the period September-December 2000 from two natural stands in Bolu, a locality in the northwestern Turkey at 40° 36'N, 31° 35'E and 1370 and 1580 m above sea level. The collection dates were: September 11, 30, October 15, November 2, 22, and December 14. At each time of collection cones were sampled from 5 trees (average height 20 m and age 80-100 years). The collection was spread all over the crown as far as possible and for the cone collection the same trees were used every time. The cones were put into double plastic bags, well-sealed, the air having been sucked out of the inner one. The samples were immediately brought to the laboratory for analysis. On each collection, the sample material was divided into subplots. Each subplot was randomly allocated for germination test after the cones were stored in well-vantilated bags of nylonnet in a cold room (5±1 °C) for one month to 1year.

During the cone-analysis, Cone moisture content was determined using the oven-drying method (103 °C, 17 h) for 10 green cones at the time of collection, and 5 cones once a month during storing. A sample of 4*50 seeds was taken by the cutting of cones in order to determine seed-water content. Seeds were dried at 103 °C for 17 hours.

The cones were always manually cut into pieces and the seeds were extracted by hand. Germination parameters of filled seeds extracted directly after the cone collection from two elevations and after storage of cones for 1-12 months were determined in 4 replicates of 50 seeds at a constant 20±0.5 °C with a 24 h photoperiod and light intensity of 1000 lux. The germination percentage and rate were also found in freshly harvested seeds from 1580 m at 10 and 20 °C and different photoperiods (0, 8 and 24 h light).

Germination counts were recorded every day for 21 days and a seed was considered to have germinated when the length of the radicle reached at least the length of the seed itself. Germination occurred in glass petri dishes on filter paper in germination cabinets. After 21 test days, the percentage of empty and viable seeds among those ungerminated was determined by a cutting test. Seeds displaying abnormal radicles were excluded from germination counts. The number of empty seeds was calculated at the end of each germination trial and the results were expressed in terms of percentage of full seeds.

In the present study, The germination data were calculated and expressed as germination capacity (GP), the percentage of seeds that had germinated normally at the end of the test and peak value (PV), an index of germination speed (Czabator 1962); and germination value (GV), which combines germination speed and capacity into a single value (Djavanshir and Pourbeik 1976).

Percentages were transformed to arc sin p ^1/2 for statistical analysis. Results were analyzed by factorial analysis, and the means were compared with Duncan tests.

III. Results

The water content was almost above 50 % in September 11 (Figure 1). Up to the 15th October the values fell slowly in cones collected from 1580 m, and thereafter very rapidly. In cones collected from 1370 m, the values fell rapidly in October. The low level of cone moisture content (21-23 %) was reached after late November. Seed moisture content ranged between 21 and 29 % during the month of September and October, and fell slowly to 14-15 % in December (Figure 2).

Analysis of variance showed significant differences among two localities and dates of cone collection (P<0.01) (Table 1). The germination percent (GP) were significantly affected at seeds collected September 30 and were the lowest for seeds collected in September 11. Later, the GP increased to more than 90 % by November 2 in two localities.

PV and GV of seeds were also significantly affected at September 30. They reached to highest value in November and there were not significant differences among the dates of cone collection in November and December.

The GP, GV and PV were slightly higher for seeds collected from 1370 m than seeds from 1570 m in September. For seeds from later collections, there were no significant differences.

The GP, GV and PV of filled seeds extracted directly after the cone collection and after storage of the cones for 1-4 months are shown in Table 2. Storing seeds for 1-4 months enhanced the germination percentage and germination rate of seeds from two collections in September 11. For longer durations of storing, the GP and PV were increased to more than 80% and 9.0, respectively. For seeds from later collections (September 30-December 14), the GP and PV increased considerably during even one-month storage. And GP and PV were not changed after 2-3 months cone storage. Storing the cones eliminates the differences between two elevations with regards to germination parameters. After storing the cones for 1 year collected from September 11 to December 14, GP and PV of seeds from two elevations were still high (Table 2). The lowest GP and PV at the end of one year were found in seeds collected in September 11.

The seeds collected in September from the elevation of 1580 m didn't germinate in darkness at 10 °C (Table 3). The seeds collected in September and October germinated poorly in darkness at both temperatures. In the late-November and December collections, germination percentages of seeds in darkness were >30 % at 10 °C, and >80 % at 20 °C. For 8-h photoperiods, The GP ranged from 0 to approximately 65 % at 10 °C and 18.5 to 91.0 % at 20 °C. For 24-h photoperiods, GP ranged from 7.5 to 95.5 %, depending on temperature regime. In all collections, PV was also affected by photoperiods and found the lowest in darkness at both temperature regimes.

Table 1. Effects of cone collection dates and altitudes on germination of Scots pine seeds collected in 11 September-14 December 2000.

Figure 1. Changes in Scots pine cone moisture content     Figure 2. Changes in Scots pine seed moisture content

Table 2. Germination percentage (GP) and peak value (PV) of seeds stored in the cones at 5 °C for several months.

Table 3. Germination percentage of seeds collected at 1570 m and incubated at different temperatures and photoperiods.

IV. Discussion

Concerning the handling of harvested cones and seeds, the process of ripening and changes in cone and seed moisture content is of basic importance. According to Remrod and Alfjorden (1973), the seed of Scots pine seems to be ripe at a water content of the cones of 40-45%, which is higher than the results reported in this study. The moisture content of Scots pine cones decreases only slightly until October and falls suddenly from 80 to 20-30 % by the end of December (Matyas 1973). Parallel to this, changes in moisture content in seeds show the same tendency and the low level of cone moisture content (20-25 %) is reached during the month of December. In the present study, cone moisture content was below 30 % in November and December and the low level of seed moisture content (15-23 %) is reached during the months of late November and December.

The effect of incubation temperature was obvious; seeds germinated more slowly at 10 °C than at 20 °C. The GP and PV was low in darkness but was enhanced at both 8-hour and 24-hour photoperiods. The GP and PV were, however, gradually enhanced during autumn so that seeds collected in November and December were able to germinate readily even at +10 °C. Light requirement for germination interacted with cone-collection date. As autumn proceeded, a greater proportion of seeds were able to germinate in darkness. This finding is in agreement with earlier observations of Scots pine seed light requirement (Nygren 1987).

Scots pine seed in Sweden seems to be anatomically fully developed in the end of August or in the beginning of September. The physiological maturity occurs about one month later (Nygren 1987). Ripening is not influenced by temperature in the range of +5 °C to +10 °C constant and maximum seed vigor is achieved of the ripening time is at least nine weeks (Sahlen and Abbing 1995). It was also stated that the GP of Scots pine seeds collected in August was not enhanced by artificial ripening. For seeds collected as from September 3 to October 15, however, the germination percent and germination rate increased considerably during artificial ripening.

In the present study, the GP were significantly affected at seeds collected September 30 and were the lowest for seeds collected in September 11. Later, the GP increased to more than 90 % by November in two altitudes. PV and GV of seeds were also significantly affected by the date of cone collection and were significantly affected at September 30 in two altitudes. They reached to highest value in November and there were no significant differences among the dates of cone collection in November and December.

Cones collected on late September and stored at +5 °C for at least one month before seed extraction, gave seed with the same good properties as the seed from cones which had ripened under natural conditions on the trees in the present study. Sahlen and Wiklund (1995) stated that physiological maturity was attained around the middle of October for seeds from different localities, which corresponds with the results reported here.

The elevational difference of 200 m has an influence on the seed germination percent and rate at the samples of September but this effect had disappeared in October. Also storage of seeds collected in September at least one month eliminates this difference. According to Boydak (1984), the elevational difference of 350 m has an influence on the seed germination percentages of Scots pine if cones were collected during August and September.

In the present study, autumn harvested Scots pine seeds kept their high germination percent and rate for one year when they stored at 5 °C. According to Boydak (1984) Scots pine seeds collected after 15 ^th September kept their higher germination capacity and rate at the end of 11 years cold storage. However, 3 years storage of early harvested Scots pine seeds was not recommended in the study done by Matyas (1973).

On the basis of the germination percent, germination rate, germination value, cone moisture content and seed moisture content studied in this investigation, the seed seems to be fully developed in late October. The specific gravity at this time had fallen to 1.0, which means that the cones floated in water. Storage of the cones at +5 °C during at least one month before the seed extraction, seems to allow cone collection about one month earlier. The seeds of Scots pine collected in mid-September could be stored for one year without any risk for low germination percent and germination rate.

V. Acknowledgements

This study was supported by the Research Fund of The University of Istanbul (project number: T-865/17072000).

VI. References

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Blomqvist, S., 1972. Seed maturity in seed orchards of pine in central Sweden. Inst. Skogsf. Uppsala Grafiska AB, Uppsala. pp: 87-119.

Boydak, M., 1984. Sarıcam ve Karaçam tohumlarinda olgunlasma zamani ile saklama sureleri arasindaki iliskiler. I.U. Orman Fak. Derg. Seri A, Cilt 34, Sayi 2, pp: 104-125, Istanbul.

Czabator, F.J., 1962. Germination value: An index combining speed and completeness of pine seed germination. Forest Science 8: 386-396.

Djavanshir, K. and H. Pourbeik, 1976. Germination value- A new formula. Silvae Genetica 25: 79-83.

Elicin, G., 1972. Turkiye Sarıçam (Pinus sylvestris L.)'larında Morfogenetik Arastirmalar. I.U. Orman Fak. Yayinlari No 1662/80. Istanbul.

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Kayacik, F. 1963. Turkiye camlari ve bunlarin cografi yayilislari uzerine arastirmalar. I.U. Orman Fak. Derg. Seri A, Sayi 1, pp: 1-7, Istanbul.

Matyas, C. 1973: Handling of Autumn Harvested Cones in Scots Pine Seed Orchards. International Symposium on Seed Processing, 11 p. Bergen, Norway.

Nygren, M., 1987. Germination characteristics of autumn collected Pinus sylvestris seeds. Acta Forestalia Fennica 201. Helsinki. 39 p.

OGM. 1980. Turkiye Orman Envanteri. OGM Yayin No: 13, Ankara.

Remrod, J. and G. Alfjorden, 1973. Time for cone collection in seed orchards of Scots pine (Pinus sylvestris L.). International Symp. on Seed Processing, Bergen, Norway. 15 p.

Sahlen, K. U. and Bergsten, 1993. Artificial ripening of early collected Scots pine cones and cones attached to branches. In: Dormancy and barriers to germination (Edwards, D.G. ed.). Pacific Forestry Centre, Victoria, B.C., pp: 113-120.

Sahlen, K. and K. Abbing, 1995. Effects of artificial conditions on anatomical and physiological ripening of Pinus sylvestris L. seeds. New Forests 9: 205-224.

Sahlen, K. and K. Wiklund, 1995. Anatomical and physiological effects of osmotic priming on Pinus sylvestris seeds of different maturity. Seed Science and Technology 23: 725-737.

¹ Faculty of Forestry, University of Kafkas, Artvin-08000, TURKEY
E-mail: [email protected]