Cynanchum bungei Decne (Baishouwu in China), a member of the Asclepiadaceae family, is a perennial climbing shrub distributed in China. Its root has been used as a tonic medicine or health food for centuries in traditional Chinese medicine. C. bungei has useful activities including antitumor and immune regulatory effect and is non-toxic (Gao et al., 2005). As a rare, endemic, and beneficial species, C. bungei is becoming more and more precious not only in China, but also in other countries such as Japan and Korea (Song et al., 2006).
C. bungei is grown mainly by cuttings and root propagation and seldom by seed propagation. With the increasing demand for this endangered wild resources (Zhang et al., 2010), seed propagation can be used to solve supply and demand, protect germplasm resource, and enrich genetic diversity of this species.
Environmental factors such as light and temperature are known to affect seed germination in Asclepiadaceae family. Seeds of Calotropis procera and Leptadenia pyrotechnica are quick germinating and do not have strict requirements for light and temperature conditions, whereas seeds of Cryptostegia grandiflora and Pergularia daemia are slow germinating and exhibit optimum germination in dark at ≈30 °C (Sen, 1968). Seeds of Asclepias tuberosa and Asclepias viridiflora germinate well at 21 °C and light is not an influencing factor (Norman, 1993). Seeds of Matelea maritima germinate at an optimum temperature of 25 °C in light, the process being optimized by alternating temperatures of 25/35 °C (Cuzzuol and Lucas, 1999). Also, light requirement for germination can vary with temperature (Smith, 1982).
Seed size is a factor that is associated with seed germination and seedling growth (Farhoudi and Motamedi, 2010). Studies of the relationship between seed size and seed germination and seedling performance have provided various results. A positive relationship between seed size and seed germination and seedling performance has been found within seed lots in a number of studies (Benard and Toft, 2007). In saline soils, smaller seeds of safflower and chickpea germinate faster and have better seedling performance compared with larger seeds (Farhoudi and Motamedi, 2010; Kaya et al., 2008). In different populations of the dimorphic Tragopogon pratensis subsp. pratensis, larger seeds yield higher germination percentage, yet no relationship has been found between seed size and seedling growth (Mölken et al., 2005).
Previous studies suggested that most of these factors show diverse effects on seed germination and seedling growth characteristics of different species. Information about C. bungei seed germination is lacking. The objectives of the study were to investigate seed germination and early seedling growth responses of C. bungei to photoperiod, temperature, and seed size to determine seed propagation requirements, develop standard germination procedures, and provide conservation strategies for C. bungei.
Baskin, C.C. & Baskin, J.M. 1998 Seeds: Ecology, biogeography, and evolution of dormancy and germination. Academic Press, San Diego, CA
Benard, R.B. & Toft, C.A. 2007 Effect of seed size on seedling performance in a long-lived desert perennial shrub (Ericameria nauseosa: Asteraceae) Intl. J. Plant Sci. 168 1027 1033
Bewley, J.D. & Black, M. 1994 Seeds: Physiology of development and germination. Plenum Press, New York, NY
Boyle, T.H. & Hladun, K. 2005 Influence of seed size, testa color, scarification method, and immersion in cool or hot water on germination of Baptisia australis (L.) R. Br. seeds HortScience 40 1846 1849
Bretagnolle, F., Thompson, J.D. & Lumaret, R. 1995 The influence of seed size variation on seed germination and seedling vigour in diploid and tetraploid Dactylis glomerata L Ann. Bot. (Lond.) 76 607 615
Farhoudi, R. & Motamedi, M. 2010 Effect of salt stress and seed size on germination and early seedling growth of safflower (Carthamus tinctorius L.) Seed Sci. & Technol. 38 73 78
Gao, L.J., Wang, J.H., Cui, J.H. & Wang, H.Z. 2005 Studies on immunoregulation of polysaccharides-1a from Radix Cynanchi Bungei China J. Chin. Mater. Med. 30 1352 1355
Hu, J., Zhu, Z.Y., Song, W.J., Wang, J.C. & Hu, W.M. 2005 Effects of sand priming on germination and field performance in direct-sown rice (Oryza sativa L.) Seed Sci. & Technol. 33 243 248
Kaya, M., Kaya, G., Kaya, M.D., Atak, M., Saglam, S., Khawar, K.M. & Ciftci, C.Y. 2008 Interaction between seed size and NaCl on germination and early seedling growth of some Turkish cultivars of chickpea (Cicer arietinum L.) J. Zhejiang Univ. Sci. B 5 371 377
Leishman, M.R. & Westoby, M. 1994 The role of seed size in seedling establishment in dry soil conditions—Experimental evidence from semi-arid species J. Ecol. 82 249 258
Mohsen, M.N., Mahdi, B. & Abolfazl, T. 2011 Effect of seed size and genotype on germination characteristic and seed nutrient content of wheat Sci. Res. Essay. 6 2019 2025
Mölken, T.V., Jorritsma-Wienk, L.D., Hoek, P.H.W.V. & Kroon, H.D. 2005 Only seed size matters for germination in different populations of the dimorphic Tragopogon pratensis subsp. Pratensis (Asteraceae) Amer. J. Bot. 3 432 437
Norman, C.D. 1993 Seed germination, theory and practice, 2nd ed; (1996) First supplement; (1998) Second supplement. Norman, C.D., State College, PA
Rebecca, W.D. 1984 The effect of seed size and maternal source on individual size in a population of Ludwigia leptocarpa (Onagraceae) Amer. J. Bot. 71 1302 1307
Sen, D.N. 1968 Ecology of desert plants and observations on their seedlings. II. Germination behaviour of seeds in Asclepiadaceae Österr. Bot. Z. 115 18 27
Song, Z.G., Wang, J.H., Wang, H.Z., Zhao, A.H., Liu, C.X. & Tian, J.C. 2006 Some properties of starch isolated from Radix Cynanchi bungei Starch-Stärke 58 243 248
Stebbins, G.L. 1971 Adaptive radiation of reproductive characteristics in angiosperms, II: Seeds and seedlings Annu. Rev. Ecol. Syst. 2 237 260
Susko, D.J. & Lovett-Doust, L. 2000 Patterns of seed mass variation and their effects on seedling traits in Alliaria petiolata (Brassicaceae) Amer. J. Bot. 87 56 66
Wulff, R.D. 1986 Seed size variation in Desmodium paniculatum. II. Effects on seedling growth and physiological performance J. Ecol. 74 99 114
Zhang, F., Yu, S.L. & Wang, J.H. 2010 Studies on the photosynthetic characteristics and its relationship to yield in Radix Cynanchum bungei Decne J. Nuclear Agr. Sci. 24 176 180