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The Researches on Seed Characteristics of Silver Linden (Tilia tomentosa Moench.)
This study investigates seed maturation phases and collection time of Silver Linden (Tilia tomentosa), seed morphology and overcome of the seed dormancy or germination obstacles through a number of observations and experiments on seeds acquired from 5 different populations of natural stands in Marmara and Western Black Sea Regions.
Repetitive preliminary and main observations were performed in Istanbul-Belgrade Forest provenances in 2010 and 2011 under seed maturation process. Maturation phases model was developed based on the morphological transformations in seeds of Istanbul-Belgrade Forest provenances that were collected in 6 different periods at intervals of 10 days in 2012 pursuant to preliminary observations and determinations. As a result, it was determined that seeds of Silver Linden matured within 5.5 weeks as from the date of first collection (26 July 2012–T1) Significant changes were observed in pericarp colour and inner structure of seeds from the date of first collection (T1) until the last collection (T6). Thereby, it was ascertained that it would be appropriate to consider the pericarp colour, endosperm condition, seed coat colour, and embryo colour so as to ensure collection of Silver Linden seeds at the most suitable time.
The period when embryo is green with semi-solidified endosperm, snuff-coloured seed coat, and yellowish-green pericarp was defined as phase 1 (late August; semi-ripen) whereas the period when embryo is yellow, solidified endosperm, brown seed coat, and yellowish-dark brown pericarp was defined as phase 2 (early September; fully-ripen) and experiments as to seed physiology were performed with due regard for the 2 phases.
Given the fact that the seeds were collected in 6 different periods under seed morphology study, the moisture content of seeds which was 66.6% at the time of first collection was reduced to 21.9% at the time of last collection, implying that moisture content decreased in parallel with the ripening process. A number of differences were also observed in 1000-seed weights and seed sizes according to the collection time.
Morphological properties, vigor tests, dormancy condition, and overcome of dormancy were also analyzed in the seeds collected at 2 phases (semi-ripen; phase 1 and fully-ripen- phase 2) in 5 different provenances (Zonguldak-Kocaman, Karabük-Yenice, Bursa-Cumalıkızık, Düzce-Çilimli, Tekirdağ-Şarköy) representing the main spread of Silver Linden in Marmara and Western Black Sea regions.
1000-seed weights and seed sizes of seeds collected at 2 phases (phase 1 and phase 2) in 5 different provenances were determined in a manner to point out significant morphological differences in terms of both origins and phases. Accordingly, average 1000-seed weight was determined as 103.95 gr (max 118.79 gr – min. 95.52 gr) in phase 1 and 105.77 gr (max. 115.66 gr – min. 97.42 gr) in phase 2.
There is seed dormancy in Linden seed caused by physical and physiological dormancy. For this reason, cold stratification, warm+cold stratification, gibberellic acid (GA₃) + cold stratification, acid scarification + cold stratification, acid scarification + gibberellic acid (GA₃) + cold stratification were applied to seeds in order to overcome seed dormancy of the seeds collected from 5 different provenances in phase 1 and phase 2.
In that regard, the highest germination percentage for seeds collected in phase 1 turned out to be of Cumalıkızık provenance (% 35) germinated in 10/20 ºC left in cold stratification in sand medium for 240 days whereas the highest germination percentage for those collected in phase 2 was of Kocaman provenance (% 26) germinated in 10/20 ºC left in cold stratification in sand medium for 240 days.
Germinations had been occurred in long period for seeds at stratification in sand and perlite mediums in both phases. The highest germination percentage in stratification medium was of Kocaman provenance (phase 2 - % 70) at cold stratification with 20 minute (H₂SO₄) sulphuric acid as pre-treatment + 1000 ppm GA₃ + 224 days. Germination of all full seeds within long stratification period led to acquisition of low germination percentage in germination tests. Accordingly, high germination temperatures of 20 ºC and 10/20 ºC were resulted in secondary dormancy in Silver Linden seeds.
In general sense, it was revealed that perlite medium was more effective in removal of current dormancy than sand medium. 20 ºC fixed germination temperature proved to lower germination percentage than variable temperature of 10/20 ºC. Given the germination activities within stratification period, it occurred that Silver Linden seeds could be germinated in lower temperatures.
Cutting and tetrazolium tests were carried out under indirect methods used for determining seed viability in a short span of time. Cutting test proved to be efficient in determining empty-full rates of seeds whereas tetrazolium test reflected the viability of seeds to a certain extent.
As for field sowing, semi-ripe seeds fielded higher seedling percentage. Fully-ripen seeds, on the other hand, yielded lower seedling percentage and it was revealed that seeds continued for delaying to next year in seeding medium.