Germination of Prunus mahaleb L. Seeds by Gibberellic Acid (GA) Treatments in Different Seed Age

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1 Europ.J.Hort.Sci., 77 (5). S. 1 23, 212, ISSN Verlag Eugen Ulmer KG, Stuttgart Germination of Prunus mahaleb L. Seeds by Gibberellic Acid (GA) Treatments in Different Seed Age V. Szabó, L. Magyar, A. Mándy and K. Hrotkó (Department of Floriculture and Dendrology, Faculty of Horticultural Science, Corvinus University of Budapest, Budapest, Hungary) Summary Prunus mahaleb L. is a commonly used cherry rootstock as seedling. Breaking the seed dormancy is essential for successful seedling production. Several authors report on successful application of gibberellins to break seed dormancy and improve germination. There are many molecular variations of gibberellic acid, the most widely used commercially and in experiment is GA 3. In this trial the efficiency of GA 3 and GA 4+7 was compared on Prunus mahaleb L. Korponay at different seed age. Germination percentage, mean germination time (MGT) and germination velocity were evaluated. The results show that GA 4+7 was more efficient than GA 3 in breaking dormancy of fresh harvested P. mahaleb L. seeds. The mean germination time of fresh harvested seed was decreased by both gibberellin treatments; though the application of GA 4+7 resulted in shorter MGT than that of GA 3. Korponay seeds when stored for a year, showed similar rates of germination compared to freshly harvested seeds. However, storing the seeds for a year did lead to slower germination speed. Application of gibberellins on seed stored for a year, did not have significant effect on the germination speed. Key words. seed dormancy breaking germination percentage germination rate germination speed mean germination time (MGT) seed ageing Introduction Seedlings of Prunus mahaleb L. are widely used as cherry rootstocks in large cherry producing countries like Turkey, Iran and USA (FAO 21). For the successful seedling production, efficient dormancy breaking, uniform germination, high germination rate and germination speed all are important. In practice, nurseries often use both fresh harvested and one year old seed, improving the germination rate and speed for both ages of the seed is essential (KRÜSSMANN 1978, HARTMANN et al. 17). Seed dormancy in Prunus species is caused mainly by abscisic acid in seed coat (testa) and the release of dormancy is associated with the capacity of gibberellin formation by the embryo, improved by cold treatment (HARTMANN et al. 17). CHEN et al. (27) showed that dormancy break in P. campanulata seeds is accompanied by a decrease in the ABA content of the covering layers; germination is associated by an increase of embryonic GA 4 content. Gibberellins can be applied successfully to break seed dormancy. There are several molecular variations of gibberellins but the most widely used, both commercially and in research, are gibberellic acid GA 3 and GA 4+7. Research on improving the seed germination of P. mahaleb L. has mostly focused on GA 3 (GERÇEKÇIOÐLU and CEKIÇ 19; AL ABSI 21; GHAYYAD et al. 21). Research determining the most efficient concentration of gibberellic acid has been inconclusive; suggested concentration amounts vary from 1 to 1 ppm. For P. avium seeds without endocarp ÇETINBAŞ and KOYUNCU (26) suggest a concentration level of 5 ppm, while YIN and SONG (28) found 1 ppm GA 3 as most efficient. In another case, P. serotina seeds were treated with 1 ppm GA 3 solution with good germination results (FARMER and HALL 1971). The combination of gibberellins and cold treatments on mahaleb seeds improved the germination rate and speed. GERÇEKÇIOÐLU and CEKIÇ (19) reported that the highest germination on P. mahaleb L. seeds was obtained by stratification for 12 weeks at 2 4 C with GA 3 solution in 1 ppm concentration. AL ABSI (21) recommended that P. mahaleb L. seeds should be stratified under cold conditions for 6 or 9 days with GA 3 at 1 ppm. Removing the endocarp from P. mahaleb seeds reduces the germination time (GHAYYAD et al. 21), but this method is hardly feasible in nursery practice. While the most efficient treatment method is thus still being debated, it is widely accepted that treatment of GA

2 2 Szabó et al.: Germination of Prunus mahaleb L. Seeds does increase the germination rate of P. mahaleb L seeds. While most research has focused on GA 3, the aim of this trial was to compare the effect of GA 3 and GA 4+7 on the germination of both freshly-harvested and one-year-old P. mahaleb L. seed. Materials and Methods Trials were carried out on seeds of Prunus mahaleb L. Korponay, a self-fertile cultivar whose seedlings are quite uniform, vigorous in nursery and recommended for sour cherry cultivars (HROTKÓ 24). Seeds were harvested in July were stored in dry condition at room temperature (18 2 C) for 5 (freshly harvested) and 18 months (one-year stored). Prior to the cold stratification process, seeds were treated with 1 ppm GA 3 and GA 4+7 gibberellic acid solutions by soaking them for 24 hours. At the same time, control seed lot was soaked in tap water. In the first year the fresh harvested Korponay seeds were treated on 19 th December. In five repetitions, 5 pieces were counted in each treatment. Starting on the next day, seeds were stratified at 3.5 C for three months in moistened perlite, whose replicates were randomly arranged in the stratification chamber. The number of germinated seeds was counted eight times from 2 th March to 23 rd May in approximately in ten days intervals. Seeds with 2 mm or longer radicle were considered as germinated and removed from the seed lot. In the second year, GA treatments were on 2 th January and the three-month stratification began the following day. All other aspects were the same as the previous year. The results were expressed in percentage of germinated seeds and in mean germination time (MGT) per day using the formula MGT = (Σn i t i )/Σn, where n i is the number of seed germinated in t i days from beginning of the test and Σn is the total number of germinated seeds at the end of the test (NAYLOR 1981, HARTMANN et al. 17). MGT is a measure of the germination rate and the sharpness of the germination peak (CHEN et al. 28). The coefficient of germination speed was calculated for each day of seed counting as the reciprocal of mean germination time multiplied by 1 (HARTMANN et al. 17). All data were statistically analyzed by analysis of variance (ANOVA) using the statistical package SPSS (SPSS 14. for Windows). The means are separated by Duncan-test at level P =.5. The means of fresh and one-year stored seeds were compared by t-test of paired samples. Results Effects of different GA treatments on germination of freshly harvested seeds Significant differences in germination rate were found among treatments of freshly harvested Korponay seeds (Fig. 1). About 7 % of the control seed lot germinated on the day 153. At the same time, the seeds treated with GA 3 germinated about 81.6 %, while all the seeds treated with GA 4+7 germinated (1 %) (Table 1), showing significant differences between the treatments. On the 115 th day after the beginning of the test, seeds treated with GA 4+7 reached 1 % germination, while seeds on the same day treated with GA 3 (38 %) and control seeds (13 %) showed significant lower germination rates. The polynomial trend lines are shown in Fig. 1. GA 4+7 treated seeds show a faster raise than both GA 3 treated seeds and the control group. The germination speed of freshly harvested Korponay seeds is shown in Fig. 2. GA 4+7 -treated seeds showed significantly faster germination speed compared to the control group and the GA 3 treated seeds. We calculated considerable less MGT (Table 1) for GA 4+7 treatment (15 days) compared to the control group (124 days). Consequently, the GA 4+7 -treated seeds need shorter time to germinate. Table 1. Comparison of MGT and final germination rate (%) of freshly harvested and one-year stored Prunus mahaleb Korponay seeds treated by GA 3 and GA 4+7. Notes: Significant differences between treatments are marked with a, b and c, within columns. Significant differences between fresh and one-year-stored seed are marked with and y, between columns, separated by t-test of paired samples. Treatments MGT (days) Final germination rate (%) Fresh seed One-year-stored seed Fresh seed One-year-stored seed Control 131 c 113 a 69.2 a 72. a GA b 127 b 81.6 b 92. b GA a x b y 1. c 94. b

3 Szabó et al.: Germination of Prunus mahaleb L. Seeds 21 germination (%) speed of germination ,9,8,7,6,5,4,3,2, Fig. 1. Cumulative curves of germination rate of freshly harvested Prunus mahaleb Korponay seeds treated by GA 3 ( and broken line) and GA 4+7 ( and simple line) and control ( and double broken line). Functions of germination trend: Control: y =.8x x x ; R 2 =.38. GA 3 : y=4e 5x 4.6x x x ; R 2 =.45. GA 4+7 : y= 1E 5x x 3.254x x ; R 2 = Fig. 2. Trends of germination speed of freshly harvested Prunus mahaleb Korponay seeds treated and control ( and double broken line). Functions of trend of germination speed: Control: y =.11x x x +.165; R 2 = GA 3 : y=9e 5x 4.36x x x +.143; R 2 = GA 4+7 : y= 4E 6x 5 + 4E 5x x 3.797x x.566; R 2 =.. Effects of different GA treatments on one-year stored Korponay seeds The germination potential of one-year stored Korponay seeds did not show any significant difference compared to the freshly harvested seeds in the various treatments. Germination rate curves showed rather similar patterns among treatments (Fig. 3). The final germination rate was 92 and 94 %, respectively for GA 3 and GA 4+7 treatments, while control treatment had a 74 % germination rate with no significant difference to fresh seed lots. Additionally, the total number of germinated seeds was not decreased by storage, but the germination speed showed difference compared to freshly harvested seeds. Both GA treatments gave linear growth of germination speed, which was 127 days MGT for GA 3 and 122 days MGT for GA 4+7 (Fig. 4). Surprisingly, control seeds showed the shortest MGT (113 days), which differed significantly from GA treated seeds (Table 1). Discussion Our results of the germination rate of freshly harvested Korponay agrees with the results reported by HROTKÓ and HOLCZBAUER (1988), who achieved similarly high germination potential with seed of the same cultivar. Our data show that GA 4+7 was better than GA 3 in improving the germination rate and speed. Our results confirm earlier reports (GERÇEKÇIOÐLU and CEKIÇ 19; AL ABSI 21; GHAYYAD et al. 21) on the improvement of the germination rate of fresh mahaleb seeds by GA 3 treat-

4 22 Szabó et al.: Germination of Prunus mahaleb L. Seeds 1 speed of germination germination rate (%) ,2 1,8,6,4, Fig. 3. Cumulative germination curves of Prunus mahaleb Korponay oneyear stored seeds treated and control ( and double broken line). Functions of germination trend: Control: y = Ln(x) ; R 2 = GA 3 : y =.2x x x x ; R 2 =.79. GA 4+7 : y= 3E 5x x 3.525x x ; R 2 = Fig. 4. Trends of germination speed of one-year stored Prunus mahaleb Korponay seeds treated and control ( and double broken line). Functions of trend of germination speed: Control: y=2e 6x 4.2x x 2 +.9x +.434; R 2 = GA 3 : y =.175x.417; R 2 = GA 4+7 : y =,13x ; R 2 = ments, although GA 4+7 proved to be more efficient. The applied gibberellin concentration (1 ppm) provided efficient germination, which is in agreement with results provided by YIN and SONG (28) on cherry seed, rendering the application of higher concentration of gibberellin unnecessary. The one-year stored Korponay seeds did not loose their germination potential. This result is confirmed by literature (KRÜSSMANN 1978, KÜPPERS 1978) and practical experiences. However, the response to gibberellins treatment slowed down. We can conclude that the one-year-long storage at room temperature did not decrease the germination potential of P. mahaleb L. Korponay seeds and that after one year storage, the time required to reach the maximum germination rate is extended (Fig. 3 and Table 1). Gibberellin treatments (1 ppm GA 3 and GA 4+7 ) slightly increased the germination rate of one-year stored seeds, but still reached the germination peak later compared to the control group. This means that neither the GA 3 nor the GA 4+7 treatments could overcome the slowing of germination by ageing of P. mahaleb seeds. Significant differences between seed lots of different age were found only for MGT for GA 4+7 treatments, which suggests that the sensitivity of seeds to GA 4+7 treatments may decrease by ageing.

5 Szabó et al.: Germination of Prunus mahaleb L. Seeds 23 References AL ABSI, K.M. 21: The effects of different pre-sowing seed treatments on breaking the dormancy of mahaleb cherries, Prunus mahaleb L. seeds. Seed Sci. Technol. 38, ÇETINBAŞ, M. and F. KOYUNCU 26: Improving germination of Prunus avium L. seeds by gibberelic acid, potassium nitrate and thiourea. Hort. Sci. (Prague) 33,119. CHEN, D.S.Y., C.T. CHIEN, J.D. CHUNG, Y.S. YANG and S.R. KUO 27: Dormancy-break and germination in seeds of Prunus campanulata (Rosaceae): role of covering layers and changes in concentration of abscisic acid and gibberellins. Seed Sci. Res. 17, CHEN, S., S. KUO and C. CHIEN 28: Roles of gibberellins and abscisic acid in dormancy and germination of red bayberry (Myrica rubra) seeds. Tree Physiol. 28, FAO 21: Faostat statistical information about cherries ( FARMER, R.E. JR. and G.C. HALL 1971: Gibberellic acid induces germination and growth of dormant black cherry seed. Tree Planters' Notes 22, 1 3. GERÇEKÇIOÐLU, R. and C. CEKIÇ 19: The effects of some treatments on germination of mahaleb (Prunus mahaleb L.) seeds. Turkish J. of Agric. and Forestry 23, GHAYYAD, M., M. KURBYSA and G. NAPOLSY 21: Effect of endocarp removal, gibberelline, stratification and sulfuric acid on germination of mahaleb (Prunus mahaleb L.) seeds. American-Eurasian J. Agric. & Environ. Sci. 9, HARTMANN, H.T., D.E. KESTER, F.T. DAVIES and R.L. GENEVE 17: Plant propagation. Principles and practices. Prentice-Hall, Inc. Englewood Cliffs, New Jersey. HROTKÓ, K. and Z.S. HOLCZBAUER 1988: Germination and seedling s quality of Prunus mahaleb cultivars. (Lang. Hungarian; Sajmeggy fajták magvainak kelése és a csemete minősége.) (Kertészeti- és Élelmiszeripari Egyetem Közleményei) Publ. Univ. Hort. 51, HROTKÓ, K. 24: Cherry rootstock breeding at the department of Fruit Science. Budapest. Acta Hort. 658, KRÜSSMANN, G. 1978: Die Baumschule. Verlag Paul Parey, Berlin, Hamburg. KÜPPERS, H. 1978: Die Problematik der Veredlungsunterlagen von Sauer- und Süsskirschen im Spiegel von 25 Jahren. Dt. Baumsch. 11, NAYLOR, R.E.L. 1981: An evaluation of various germination indices for predicting differences in seed vigor in Italian ryegrass. Seed Sci. Technol. 9, YIN, Z.W. and J.W. SONG 28: The effect of different concentration gibberelin treatment on the germinate of cherry seeds. Northern Horticulture 12, xx xx. Received 5/21/212 / Accepted 9/2/212 Addresses of authors: Veronika Szabó, Lajos Magyar, Andrea Mándy, and Károly Hrotkó (corresponding author), Department of Floriculture and Dendrology, Faculty of Horticultural Science, Corvinus University of Budapest, 1518, Budapest, Pf.:53., (corresponding author): karoly.hrotko@uni-corvinus.hu.