Effect of Temperature and Cold Storage Durations on Flower Induction in Bulbs of Two Iranian Onion Cultivars

Document Type : Full Paper

Authors

1 Department of Horticultural Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran

2 Department of Horticultural Science, Faculty of Agriculture, Bu-Ali Sina University. Hamedan, Iran

Abstract

In order to determine cold requirements for flower induction (vernalization), the adult bulbs of Ghermez Azarshahr and Sefid Qom onion cultivars were studied in four time periods (two, four, six and eight weeks) and three temperatures (5, 10 and 15 °C) in a factorial experiment based on a completely randomized design with three replicates. Scaning electron microscope (SEM) was used to determine swelling of reproductive meristem (meristem dome) after applying the treatments. Also, the temporal expression patterns of flowering integrator gene (AcFT2) were analyzed in cv; Ghermez Azarshahr, using Real-Time PCR. According to obtained results, the maximum meristem inflation of Sefid Ghom was observed in 10 and 15 °C, while in Ghermez Azarshahr at 5 °C. Bulbs showed the lowest meristem inflation (30.53%) after 2 weeks of cold storage, and with increasing vernalization time, up to 6 weeks, the meristem inflation (75.35%) increased. The highest relative expression of AcFT2 was observed in the Ghermez Azarshahr after 6 weeks of cold storage at 5 °C, which coincides with meristem inflation results. Ultimately, the best vernalization condition were determined as 6 weeks cold storage at 10 ° or 15 °C for Sefid Ghom and 5 °C for Ghermez Azarshahr.

Keywords

Main Subjects


Extended Abstract

Introduction

     Onion is a biennial plant that needs to be vernalized to produce flowering stalk and seeds in the second year. In most onion cultivars, the optimal conditions for vernalization is storage at 9 to 12 degrees Celsius for one month. By flower induction in the plant many physiological changes occur in the shoot apex, when the plant is in the vegetative stage the shoot apex is sunken. After transferring to the reproductive stage it becomes dome-shaped, which indicates flower induction phenomenon. Also, at this stage, the genes that stimulate flowering time are expressed in the terminal meristem causing to develop flowers. Three flowering time stimulating genes (FT, SOC1 and LFY) have been identified in many plants, including edible onion. It has been observed that AcFT2 gene expresses in high amounts in vernalized onions. Before vernalization, AcFT2 is not expressed in the plant, but with the beginning of cold treatments, AcFT2 is expressed at a high level in shoot apex, which means this gene is an important flowering time regulator in onion. Knowledge of controlling factors in initiation and development of inflorescences can be used in flowering inhibition or stimulation techniques for breeding and seed production programs. The present study was conducted with the aim of determining the duration and appropriate temperature of vernalization in two edible Iranian onion cultivars, and also investigating the expression pattern of AcFT2 gene.

 

Materials and methods

   This research was designed as a factorial experiment in the form of a completely randomized design with 3 replications. The first factor was the cultivar type (Sefide Qom and Ghermeze Azarshahr); the second, the storage temperature in three different levels (5, 10 and 15 degrees Celsius); and the third, the duration of cold treatment in four levels (two, four, six and eight weeks). After the required time for vernalization, 20 bulbs from each treatment were selected for microscopic studies of the shoot apex and comparison with the meristem of the control plants (kept at 25 degrees Celsius). In order to extract RNA, sampling was done from the terminal meristem of the red Azarshahr cultivar at two and six weeks after cold application. The relative expression level of the AcFT2 gene was investigated by the Real-Time PCR reaction method. The actin encoding gene was used as a reference gene.

 

Results and discussion

   The results obtained from the combination of all three factors (cultivar, time, and temperature) showed that the meristem swelling rate was low after two weeks. So, it can be concluded that two weeks of low temperature was not enough to induce flowering. Both cultivars showed completely different reactions after four weeks storage in cold. In this regard, the highest vernalization percentage was observed in Sefide Qom cultivar at 10 and 15 and in Germeze Azarshahr cultivar at 5 degrees Celsius, respectively. The difference between cultivars in the sixth and eighth weeks of storage was also quite obvious. So that, in Sefide Qom, the highest percentage of vernalization (90was observed in storage at 10 and 15 degrees Celsius without significant difference. However, in Ghermeze Azarshahr cultivar the highest percentage of vernalization (90%) occured at 5 degrees Celsius, while 10 and 15 degrees Celsius remarkably reduced the percentage of vernalized bulbs The significant amount of vernalized bulb of both onion cultivars after six weeks of storage in cold, indicates that a period of six weeks is sufficient for bulb vernalization of studied cultivars. The relative expression of AcFT2 gene in the shoot apex of Germeze Azarshahr cultivar, increased significantly compared to the control, six weeks after cold treatment. The highest relative expression was observed at 5 degrees Celsius (30.59 times in compare to the control) and the lowest at 15 degrees Celsius (7.48 times in compare to the control). Therefore, with increasing temperature, the amount of expression of AcFT2 gene decreased.

 

Conclusion

   In general, it can be concluded that the optimal duration of vernalization is six weeks for both Ghermeze Azarshahr and Sefide Qom cultivars. Flower induction of the Ghermeze Azarshahr takes place at five and for Sefide Qom at 10 and 15 degrees Celsius. AcFT2 gene was expressed six weeks after cold application in the shoot apex of bulbs of Ghermeze Azarshahr cultivar. Two weeks of chilling did not show a significant difference in AcFT2 gene expression in this cultivar. The maximum amount of AcFT2 gene expression occurred at five degrees Celsius, which seems to be optimum temperature for vernalization of this cultivar. The results of AcFT2 gene expression in Ghermeze Azarshahr were in line with the results of meristem swelling.

Alemzadeh Ansari, N. (2010). Onion. Ahvaz: Shahid Chamran Ahvaz University. (In Persian). https://mybooket.com/books/646d34234b1a1d47/%D9%BE%DB%8C%D8%A7%D8%B2.
Bertaud, D.S. (1988). Effects of chilling duration, photoperiod and temperature on floral initiation and development in sprouted and un sprouted onion bulbs. Proceeding of the 4th Eucarpia Allium symposium, Welles Bourne, 254-261. https://worldveg.tind.io/record/15790/.
Brewster, J. L. (1987). The effect of temperature on the rate of sprout growth and development within stored onion bulbs. Annals of Applied Biology, 111, 463-467. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1744-7348.1987.tb01475.x.
Brito de Almeida, D. Barbosa, J. G. Saraiva Grossi, J. A. Finge, F. L. & Heidemann, J. C. (2017). Influence of vernalization and bulb size on the production of lily cut flowers and lily bulbs. Semina: Ciencias Agrarias, 38(4), 2399- 2408. https://www.locus.ufv.br/handle/123456789/16767.
Dennis, E. S. Finnegan, E. J. Bilodeau, P. Chaudhury, A. Genger, R. Helliwell, C. A. Sheldon, C. C. Bagnall, D. J. & Peacock, W. J. (1996). Vernalization and the initiation of flowering. Cell and Developmental Biology, 7, 441 - 448. https://www.sciencedirect.com/science/article/abs/pii/S1084952196900555.
Foster, T. Johnston, R. & Seleznyova, A. (2003). A morphological and quantitative characterization of early floral development in apple (Malus x domestica Borkh.). Annals of Botany, 92(2). https://academic.oup.com/aob/article/92/2/199/209246.
Ghaemizadeh, F. Dashti, F. & Shafeinia A. (2018). Expression analysis of gaLFY and AsFT during reproductive development in different organs of some Iranian garlic (Allium sativum L.) clones. Iranian Journal of Horticultural Science, 49(1), 269-278. (In Persian).  https://doi.org/10.22059/ijhs.2017.237091.1280.
Glover, B. (2007). Understanding of flowers and flowering: an integrated approach. Oxford University. https://academic.oup.com/book/5359.
Guimond, C. M. Andrews, P. K. & Lang, G. A. (1998). Scanning electron microscopy of floral initiation in sweet cherry. Journal of the American Society for Horticultural Science, 123(4), 509-512. https://journals.ashs.org/jashs/view/journals/jashs/123/4/article-p509.xml.
Haberman, A. Zelinger, E. & Samach, A. (2017). Scanning Electron Microscope (SEM) imaging to determine inflorescence initiation and development in olive. Bio-protocol, 7(19). https://bio-protocol.org/pdf/Bio-protocol2575.pdf.
Hsu, C.Y. Adams, J.P. Kim, H. No, K. Ma, C. Strauss S.H. & Yuceer C. (2011). FLOWERING LOCUS T duplication coordinates reproductive and vegetative growth in perennial poplar. Proceedings of the National Academy of Sciences, 10756-10761. https://www.pnas.org/doi/abs/10.1073/pnas.1104713108.
Kamenetsky, R & Fritsch,R.M. (2002). Florogenesis. In Allium crop sciences, Recent Advances. Edited by Rabinowitch, H.D & Currah. L. New York: CABI International, Wallingford. 101–117. https://www.cabi.org/VetMedResource/ebook/20023117383.
Kamenetsky, R. & Rabinowitch, H.D. (2002). Ornamental Alliums. In Allium Crop Science. Recent Advances. Edited by Rabinowitch, H. D. & Currah, L. New York: CABI Publishing, Wallingford. 459-488. https://www.cabi.org/VetMedResource/ebook/20023117383.
Khokhar, K.M. (2008). Effect of temperature and photoperiod on the incidence of bulbing and bolting in seedlings of onion cultivars of diverse origin. Journal of Horticultural Science and Biotechnology, 83: 488-496. https://www.tandfonline.com/doi/abs/10.1080/14620316.2008.11512412.
Khokhar, K.M. Hadley, P. & Pearson, S. (2007). Effect of cold temperature durations of onion sets in store on the incidence of bolting, bulbing and seed yield. Scientia Horticulturae, 112, 16-22. https://www.sciencedirect.com/science/article/abs/pii/S0304423806004900.
Lee, R. Baldwin, S. Kenel, F. McCallum, J. & Macknight, R. (2013). FLOWERING LOCUS T genes control onion bulb formation and flowering. Nature Communications, 4, 2884. https://www.nature.com/articles/ncomms 3884.
Noy-Porat, T. Flaishman, M. A. Eshel, A. Sandler-Ziv, D. & Kamenetsky, R. (2009). Florogenesis of the Mediterranean geophyte Narcissus tazetta and temperature requirements for flower initiation and differentiation. Scientia Horticulturae, 120(1), 138-142. https://www.sciencedirect.com/science/article/abs/pii/S0304423808004020.
Peters, R. (1990). Seed Production in onions and some other Allium species. In: Onions and Allied crops. Botany, Physiology and Genetics. Edited by Rabinowitch, H.D. & Brewster, J.L. Vol. 1, Boca Raton, Florida: CRC Press. 161-176. https://www.taylorfrancis.com/chapters/edit/10.1201/9781351075169-8/seed-production-onions-allium-species-ross-peters.
Reghin, M.Y. Otto, R.F. Olinik, J.R. Jacoby, C.F.S. & de Oliveira, R.P. (2005). Vernalization of bulbs and the effect on yield and physiological potential of onion seeds. Horticultura Brasileira, 23, 294-298. https://www.scielo.br/j/hb/a/LmgVrZ5CJN5YG56LDVn9zrb/abstract/?lang=en&format=html.
Shishido, Y. & Saito, T. (1975). Studies on the flower bud formation in onion plants. 1. Effects of temperature, photoperiod and light intensity on the low temperature induction of flower buds. Journal of Japanese Society for Horticultural Science, 44, 122-130. https://www.jstage.jst.go.jp/article/jjshs1925/44/2/44_2_122/_article/-char/ja/.
Sinnadurai, S. (1970). A note on the bulbing and flowering habit of the bawku onion. Tropical Agriculture, 47, 77-79. https://www.cabdirect.org/cabdirect/abstract/19700306414.
Song, J. Angel, A. Howard, M. & Dean, C. (2012). Vernalization a cold-induced epigenetic switch. Journal of Cell Science, 125, 3723–3731. https://journals.biologists.com/jcs/article/125/16/3723/32471/Vernalization-a-cold-induced-epigenetic-switch.
Streck, N.A. (2003). A vernalization model in onion (Allium cepa L.). Revista Brasileira de Agrometeorologia Santa Maria, 9(2), 99-105. https://periodicos.ufpel.edu.br/index.php/CAST/article/view/520.
Wien, H. C. & Stutzel H. (2020). The physiology of vegetable crop. 2nd edition. New York. CABI. Press, Wallingford. 497. https://worldveg.tind.io/record/23718/.
Woodbury, G.W. (1950). A study of factors influencing floral initiation and seed stalk development in the onion, Allium cepa L. Idaho Agricultural Experiment Station Research Bulletin, 18- 27. https://www.cabdirect.org/cabdirect/abstract/19511603065