Propagation of Ornamental Plants Vol. 13, № 1, 2013: 40-45 DORMANCY LEVEL AND DORMANCY-BREAKING PRETREATMENTS IN SEEDS OF FRAXINUS ORNUS SUBSP. CILICICA, AN ENDEMIC TO TURKEY Mustafa Yilmaz* and Fatih Tonguç Kahramanmaraş Sütçü İmam University, Faculty of Forestry, Department of Silviculture, 46100 Kahramanmaraş, Turkey, *Fax: + 90 344 280 17 82, *E-mail: mustafayilmaz@ksu.edu.tr Abstract Fraxinus ornus subsp. cilicica is an ornamental tree endemic to southern Turkey. The present study was carried out to determine the level of dormancy and appropriate dormancy-breaking pretreatments and to investigate interpopulational variation in seed dormancy. The seeds were collected from seven populations (Menzelet, Boztoprak, Düziçi, Kozan, Pozantı, Gündoğmuş, Eğirdir). Average percentage of sound, insect-infected, and empty seeds was 74.0, 16.8, and 9.2, respectively. Germination percentages of populations varied signiicantly due mainly to different percentages of sound seed. The study suggests that seeds of this taxon have deep physiological dormancy, as they required about 18 weeks of prechilling treatment at 4°C for full dormancy removal, and depth of dormancy for seeds of all populations was relatively similar. Warm incubation at 20°C before the prechilling was not effective in decreasing the prechilling requirement for dormancy break. Key words: germination, prechilling, taurus lowering ash INTRODUCTION Fraxinus ornus L. subsp. cilicica (Lingel) Yatuk, Taurus Flowering Ash (TFA), is an endemic ornamental tree scattered on the Taurus Mountains in southern Turkey. The tree is mostly found on sunny southern slopes and grows on altitude from 350 m to 1500 m. Its height is usually 8-10 m but can reach up to 20 m (Yaltırık 1978, Browicz 1984). Research on seed physiology is needed to facilitate widespread seedling production and ex situ conservation of TFA. Fraxinus ornus (Oleaceae), also known as Manna ash (Fraxigen 2005), is an insect-pollinated tree (Verdú et al. 2006). The fruits are elongated, winged, singleseeded samaras that are borne in clusters (Bonner 2008). The species has male and hermaphrodite trees in a breeding population and only hermaphrodites produce fruits (Dommée et al. 1999, Verdú 2004, Verdú et al. 2007). Seed dormancy is a very prevalent characteristic of species in temperate regions of the world. Level of dormancy varies greatly depending on species, population location, and individuals within the populations (Bewley and Black 1994, Baskin and Baskin 1998). Depth of dormancy in the seeds of Fraxinus species varies greatly and seeds need 2 to 7 months cold stratiication at 4 ± 2°C for dormancy removal depending on the species Received: January 30, 2013 40 (ISTA 1996, Suszka et al. 1996, Bonner 2008). The main objectives of this study were to determine dormancy level and appropriate dormancy-breaking pretreatments in TFA seeds, and to investigate interpopulation variation of seed dormancy. MATERIALS AND METHODS Samaras were collected from seven populations in Turkey (Table 1) and dried to about 8% moisture content (MC) in the laboratory. MC of seeds was determined by low temperature oven method, 17 h at 104 ± 1°C (ISTA 1996). MC was expressed as the percentage of the fresh mass of the seed. Three replicates of 150 (3 × 50) seeds were cut lengthwise to determine the proportion of sound, insect-infected, and empty seed. Dormancy level and pretreatment requirements In preliminary test, seeds from three populations (Boztoprak, Düziçi, Pozantı) without pretreatments (control) and after 4 and 8 weeks prechilling at 4°C were taken to germination tests and none germinated. After preliminary results, therefore, longer prechilling durations and warm incubation were applied in the current study. Seeds from seven different populations were subjected to six different pretreatments to ind out the dormancy level and pretreatment requirement Accepted: February 28, 2013 Mustafa Yilmaz and Fatih Tonguç. Dormancy level and pretreatments in seeds of Fraxinus ornus subsp. cilicica Table 1. Seed origins of Fraxinus ornus subsp. cilicica. Populations Menzelet (K.Maras) Boztoprak (K.Maras) Düziçi (Osmaniye) Kozan (Adana) Pozantı (Adana) Gündoğmuş (Antalya) Eğirdir (Isparta) Latitude Longtitude Altitude (m) Weight of 1000 seeds (g) 37°41’ 37°32’ 37°16’ 37°31’ 37°22’ 36°49’ 37°44’ 36°50’ 36°18’ 36°30’ 35°52’ 34°53’ 32°00’ 30°50’ 700 950 1400 380 1150 950 1450 35.5 31.9 36.2 27.0 32.6 27.0 23.6 Air dry weight, about 8% moisture content. of the taxon (Table 2). Pretreatments (warm incubation at 20°C and prechilling at 4°C) were applied without media in the plastic bottles covered with perforated aluminum folio under dark conditions. Seeds were hydrated to maximum moisture content (MC) (maximum MC of TFA seeds is about 50%) by daily water spraying for 3 days and then dried back to 40-42% MC. During the preatments, bottles were weighed weekly to check for altered moisture content of seeds and distilled water was added by spraying if needed. MC of seeds during the pretreatments without media should generally be about 8-10 point below the maximum MC of the seeds (Yilmaz 2006). Table 2. The pretreatments applied in the experiment. 4 weeks warm incubation + 10 weeks prechilling 4 weeks warm incubation + 14 weeks prechilling 4 weeks warm incubation + 18 weeks prechilling 10 weeks prechilling 14 weeks prechilling 18 weeks prechilling Germination test Germination tests were performed in 15-cm diameter Petri dishes on two sheets of ilter paper moistened with water, and three replicates of 50 seed were incubated at 5/15°C (16 h in light at 5°C, 8 h in dark at 15°C) alternating temperature, which is the appropriate germination temperature for the prechilled seeds of TFA (Yilmaz and Tonguç 2013). Seeds were rinsed with distilled sterile water for 5 min prior to the germination test. The seeds were considered to be germinated when their radicles protruded 3 mm and showed geotropism. The Petri dishes were examined every 2 days, at which time germinated seeds were counted and removed. Germination tests were terminated on day 28. Germination parameters Germination percentage (GP) and mean germination time (MGT) were calculated according to the following formulas (Bewley and Black 1994): GP G P (%) = ∑ n 100 , i N where GP is the germination percentage, ni is the number of germinated seeds at week i, and N is the total number of incubated seeds per test. MGT = ∑ (t .n ) , ∑n i i i where MGT is the mean germination time, ti is the number of weeks from the beginning of the test, and ni is the number of germinated seeds recorded on week t(i). Statistical analyses GP and MGT values of treatments were subjected to factorial ANOVA to detect the significance of population, germination temperature and pretreatment. Percentages of sound, insect-infected, and empty seeds also were subjected to factorial ANOVA to check for provenancial differences. Percent values (sound, insectinfected, and empty seed rate, GP) were transformed using arcsine square root (√P) to normalize error distribution prior to variance analyses. When a signiicant effect was detected, differences among the groups were identiied using Duncan’s New Multiple Range test. There was no germination after “4 weeks warm incubation + 10 weeks prechilling” and “10 wweeks prechilling” pretreatment and the results of these pretreatments were not included in the statistical analyses. RESULTS The soundness of the seeds from different populations varied signiicantly (Table 3). The average percentage of sound, insect-infected, and empty seeds was 74.0, 16.8, and 9.2, respectively. Both pretreatment and population significantly affected the germination percentage of TFA seeds. The 41 Propagation of Ornamental Plants Vol. 13, № 1, 2013: 40-45 Table 3. The percentages of sound, insect-infected, and empty seeds from different populations. Populations Menzelet Boztoprak Düziçi Kozan Pozantı Gündoğmuş Eğirdir Average Sound (%) Insect infected (%) Empty (%) 89.3 ± 2.4 a 94.0 ± 2.0 a 81.3 ± 2.4 b 70.7 ± 3.5 c 72.7 ± 3.3 bc 73.3 ± 2.9 bc 36.7 ± 3.7 d 74.0 6.0 ± 1.2 a 4.7 ± 1.8 a 8.7 ± 1.8 a 24.0 ± 3.0 b 22.0 ± 2.3 b 18.0 ± 2.0 b 34.0 ± 2.3 c 16.8 4.7 ± 1.3 b 1.3 ± 0.7 a 10.0 ± 1.2 b 5.3 ± 1.8 b 5.3 ± 1.8 b 8.7 ± 1.3 b 29.3 ± 1.8 c 9.2 Means (± SE) within a column followed by the same letter are not signiicantly different according Duncan’s multiple range test at p < 0.05. Table 4. Effects of pretreatments and population on germination percentage (GP) and mean germination time (MGT) of F. ornus subsp. cilicica seeds, results of factorial ANOVA. Source Pretreatment (A) Population (B) A×B Error df 3 6 18 56 GP MGT MS F p-value MS F p-value 2729.1 1776.2 121.9 8.1 338.7 220.5 15.1 0.000 0.000 0.000 107.26 10.21 1.18 0.38 281.21 26.76 3.11 0.000 0.000 0.001 pretreatment × population interaction effect was also signiicant on GP and MGT (Table 4). Neither the “4 weeks warm incubation + 10 weeks prechilling” nor the “10 weeks prechilling” pretreatment resulted in any germination. There were signiicant differences between prechilling treatments (Table 5, Fig. 1) and the highest germination percentages were obtained for seeds receiving 18 weeks of prechilling. For the germination of the seeds, at least 14 weeks prechilling treatment was necessary. A 4 weeks warm incubation prior to 14 weeks and 18 weeks prechilling treatments did not affect the overall average GP (Table 5). However, Duziçi population demonstrated a higher germination percentage at “4 weeks warm incubation + 14 weeks prechilling” than “14 weeks prechilling” treatment. The 4 weeks warm incubation prior to prechilling decreased the germination percentage of Pozantı and Gündoğmuş populations which have more insect infected seeds and as a result signiicant amount of seeds from these populations either decayed or were dead after 4 weeks of incubation. The average GP after the “4 weeks warm incubation Table 5. Germination (%) of Fraxinus ornus subsp. cilicica seeds after different pretreatments. Germination (%) Populations Menzelet Boztoprak Düziçi Kozan Pozantı Gündoğmuş Eğirdir Average Warm incubation for 4 weeks + prechilling for 14 weeks Prechilling for 14 weeks Warm incubation for 4 weeks + prechilling for 18 weeks Prechilling for 18 weeks 56.7 ± 1.76 b 50.7 ± 2.91 c 54.7 ± 3.33 b 34.7 ± 2.40 b 24.7 ± 1.76 d 46.0 ± 2.31 c 6.0 ± 1.15 c 39.1 C2 47.3 ± 2.67 b 45.3 ± 2.40 c 19.3 ± 1.76 c 36.7 ± 2.40 b 41.3 ± 2.91 c 62.0 ± 2.31 b 7.3 ± 1.33 c 37.0 C 87.3 ± 2.40 a 77.3 ± 2.67 b 85.3 ± 3.53 a 65.3 ± 3.71 a 62.7 ± 2.40 b 59.3 ± 2.91 b 20.7 ± 1.76 a 65.4 B 90.0 ± 2.31 a 90.7 ± 3.53 a 79.3 ± 2.40 a 62.7 ± 2.91 a 74.0 ± 3.06 a 78.7 ± 3.33 a 25.3 ± 2.40 a 71.5 A Means (± SE) within a column followed by the same letter are not signiicantly different according Duncan’s multiple range test at p < 0.05. The values on the same row followed by the same capital letters are not signiicantly different at p < 0.05. 42 20 0 0 4 8 12 16 20 24 28 (day) Mustafa Yilmaz and Fatih Tonguç. Dormancy level and pretreatments in seedsTime of Fraxinus ornus subsp. cilicica 100 4w+14w 14 w 80 4w+18w 18 w 60 40 20 Germination percentage (%) Germination percentage (%) Germination Germinationpercentage percentage (%)(%) 100 Menzelet Boztoprak 80 Düziçi Kozan 60 Pozantı Gündoğmuş 40 Eğirdir 20 0 0 0 4 8 12 16 20 24 0 28 4 8 12 16 20 24 28 Time (day)(day) Time Time (day) Time (day) Fig 1. Average germination of Fraxinus ornus subsp. cilicica seeds (%) from seven populations after four different pretreatments, at 5/15°C. Fig. 2. Germination of seven populations (%) after 18 weeks prechilling, at 5/15°C. 100 Germination percentage (%) Menzelet Boztoprak + 18 weeks prechilling”, and “18 weeks prechilling” Düziçi treatments were 65.4% and 71.5% and did not differ Kozan 60 signiicantly. The GP of Menzelet and Boztoprak popuPozantı lations reached 90.0 and 90.7 while the maximumGündoğmuş GP 40 of Eğirdir population was 25.3 at 18 weeks prechilling Eğirdir treatment. 20 There was very distinct difference between GP of “14 0weeks prechilling” and “18 weeks prechilling” treatments (Fig. 1).8 The part of16ungerminated 0 4 12 20 24 seeds 28 after the “4 weeks warm incubation Time (day) + 14 weeks prechilling” and “14 weeks prechilling” pretreatments were found to be sound while the ungerminated seeds after the “4 weeks warm incubation + 18 weeks prechilling”, and “18 weeks prechilling” pretreatments were either decayed or infected. There was distinctive difference between the average GP of populations. Menzelet and Boztoprak populations demonstrated the highest average GP while the overall GP of Eğirdir population was 14.8%, evidently lower than those of other populations due to a lower germination potential (Fig. 2). 80 The period of prechilling also affected the germination speed. The longer the prechilling period, the faster germination occurred. While the average MGT was 16.4 day after 14 weeks prechilling, it was 12.4 day after 18 weeks of prechilling (Table 6). The 4 weeks warm incubation before the prechilling treatment didn’t affect the average germination speed. Population factor was not generally effective on the MGT at different pretreatments (Table 4). Only Eğirdir population with the lowest percentage of sound seed germinated slower than other populations. DISCUSSION This study suggests that the seeds of TFA have deep physiological dormancy and about 18 weeks prechilling duration was needed for full elimination of the seed dormancy. Four weeks of warm incubation at 20°C were not effective in breaking dormancy. Depth of dormancy generally varies according to species, species locations, or individuals in the same Table 6. Mean germination times of Fraxinus ornus subsp. cilicica seeds after different pretreatments. Mean germination time (day) Population Menzelet Boztoprak Düziçi Kozan Pozantı Gündoğmuş Eğirdir Average Warm incubation for 4 weeks + prechilling for 14 weeks Prechilling for 14 weeks Warm incubation for 4 weeks + prechilling for 18 weeks Prechilling for 18 weeks 15.2 ± 0.2 b 16.0 ± 0.4 c 15.9 ± 0.5 c 16.3 ± 0.6 b 16.1 ± 0.2 c 16.4 ± 0.3 c 18.6 ± 0.8 b 16.3 b 15.5 ± 0.4 b 16.2 ± 0.5 c 17.6 ± 0.8 b 16.6 ± 0.3 b 16.0 ± 0.4 c 15.0 ± 0.4 b 18.1 ± 0.3 b 16.4 b 12.0 ± 0.3 a 11.5 ± 0.3 b 11.7 ± 0.2 a 12.3 ± 0.3 a 12.9 ± 0.2 b 12.2 ± 0.2 a 14.5 ± 0.2 a 12.4 a 12.1 ± 0.2 a 12.8 ± 0.1 a 12.2 ± 0.1 a 12.7 ± 0.3 a 11.4 ± 0.2 a 11.8 ± 0.4 a 14.1 ± 0.6 a 12.4 a Means (± SE) within a row followed by the same letter are not signiicantly different according Duncan’s multiple range test at p < 0.01. 43 Propagation of Ornamental Plants Vol. 13, № 1, 2013: 40-45 site (Bewley and Black 1994, Copeland and McDonald 1999). Prechilling durations up to 14 weeks was clearly insuficient for the complete elimination of dormancy while the seeds exhibited their full germination potential after 18 weeks prechilling. After the full elimination of dormancy with 18 weeks prechilling, the seeds collected from the highest (Eğirdir, 1450 m) and the lowest altitudes (Kozan, 380 m) demonstrated relatively lower germination. Eğirdir population clearly had the lowest germination percentage than seeds from the other populations after all the pretreatments, likely because of a low germination ability arising from its highest altitudinal and furthest western and northern location. Insect infection was the main reason in relatively lower germination percentages of Pozanti (74.0 %) and Gündoğmuş (78.7 %) populations. The general dormancy requirement of TFA seeds is 2 to 8 weeks warm incubation and 8 to 15 weeks prechilling (Piotto 1994, Piotto and Di Noi 2003). In this study, the warm incubation was not effective on the seeds (Table 5). Further, 10 weeks and 14 weeks prechilling clearly were insuficient to completely eliminate dormancy, while 18 weeks prechilling treatment totally eliminated the dormancy. Seeds of some ash species (F. excelsior, F. americana, F. nigra, and F. pennsylvanica) have morphophysiological dormancy (Villiers and Wareing 1965, Suszka et al. 1996, Bonner 2008) and warm incubation + prechilling can break some levels of this dormancy (Baskin and Baskin 2004). However, warm incubation is not recommended for F. ornus (Drăghici and Abrudan 2011). Similarly, 4 weeks incubation at 20°C before the 10, 14, and 18 weeks prechilling treatments did not signiicantly affect germination. Since TFA has fully developed embryo after the mid October (Yilmaz and Tonguç 2009), we suggest that TFA seeds have deep physiological dormancy and do not have morphological dormancy. The cold-wet strafication method in dormancy elimination of seeds is applied in a material such as sand or peat at 4°C. In this method, the pretreatment is usually stopped when the seeds start to germinate and the pretreatment durations become insuficient for some part of the seeds due to the heterogenity of dormancy level of seed lot (Suszka et al. 1996). In the current study, both warm incubation and prechilling treatments were applied without medium. When the level of MC of some seeds during the prechilling is controlled at 8-10 point lower than maximum level, the prechilling duration could be extended without any germination until the elimination of dormancy from all the seeds (Muller et al. 1999, Yilmaz 2005). Our study demonstrated that the level of moisture content can be effectively controlled at 40-42%, 8-10 point lower than maximum level for the prechilling treatments in TFA seeds. The prechilling without medium has been 44 also successfully used in F. excelsior seeds (Tylkowski 1990, Suszka et al. 1996). Seed dormancy is closely related to the natural distribution of plant species (Schmidt 2000, AlvarezAquino and Williams-Linera 2002, Fenner and Thompson 2005). In a study on F. angustifolia seeds, it was found that seeds originating from southern Italy had lower level of dormancy than the northern populations (Piotto and Piccioni 1998). In the current study, the depth of dormancy was relatively similar in all the populations (Table 5). There were signiicant differences among the populations in terms of GPs due mainly to different proportions of sound seeds. At the end of the 18 week prechilling, overall average of 96.6% sound seeds germinated. The high percentage of F. ornus (Arrillaga et al. 1992), F. excelsior and F. angustifolia (Raquin et al. 2002, Dancheva et al. 2010) embryos germinate in in vitro conditions without applying prechilling treatments. 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