Strawberry ‘Tokun’ (2n = 10x = 70) is an interspecific hybrid (Fragaria ×ananassa and Fragaria nilgerrensis) with pale yellowish orange fruit and the fruit has aroma components of caramel, coconuts, and peach (Noguchi, 2011), which attracts a lot of consumers. A major drawback of this cultivar is its late maturity, which hampers its extension. Noguchi and Yamada (2015) reported that the harvest of this variety started in February in Japan. We also found a late-harvest start of this variety in the middle of January when cultivated in Central Yunnan, China (lat. 23°19′–27°03′N; elevation, 1700–2300 m). Studies of the unique cultivar Tokun are needed to find practical ways to advance flowering and fruit harvest, which will benefit both growers and consumers.
Intense studies have been done regarding the effects of temperature and photoperiod on flower induction of octoploid strawberries, and SD and night-chilling treatments have been used to induce flowering and promote early fruit production in autumn (Durner, 2015, 2016; Heide and Sønsteby, 2007; Ruan et al., 2011; Serçe and Hancock, 2005; Sønsteby et al., 2009). For ‘Tokun’, SD combined with night-chilling treatments are also found to be effective at inducing flower buds and promoting early fruit production in Japan (Noguchi and Yamada, 2015). Aside from Japan, however, no reports were found regarding regimes to promote ‘Tokun’ flowering and fruiting. Practical techniques to advance flowering and fruiting of ‘Tokun’ should be developed according to the local climate and production systems.
Plant nutrient status, especially N status, is another factor that influences flower bud induction (Guttridge, 1985). In general, less N can promote flower bud induction (Seo et al., 2014), especially for vigorous cultivars. However, SD treatment and timing of N fertilization have strong interactive effects on flower bud induction. The right timing of N fertilization can promote flower bud initiation for some octoploid strawberries such as ‘Korona’ (Sønsteby et al., 2009, 2013). For the decaploid strawberry ‘Tokun’, the effects of timing of N fertilization relative to start of SD treatments on flower induction need to be studied.
The Central Yunnan area, with its high elevation and low latitude, has the mildest climates in China (Wu et al., 2017). The perpetual spring-like weather provides ideal growth conditions for strawberries (Wang et al., 2018). In this area, 4 weeks of SD treatments in natural summer temperatures is enough for octoploid strawberries ‘Akihime’ and ‘Seolhyang’ to induce flower budding and to harvest in autumn (Ruan et al., 2015). There are no reports of flower bud induction of ‘Tokun’ in the Central Yunnan area regarding SD treatment and N fertilization. Thus, in our study, we investigated the parameters of flowering and fruiting, as well as some morphological traits, of ‘Tokun’ plants conditioned with 5, 6, and 7 weeks of SD treatment supplemented by different timing of N fertilization. A practical regime was developed and recommended to advance flowering and fruiting for decaploid strawberry ‘Tokun’ in the Central Yunnan area.
Durner, E.F. 2015 Photoperiod affects floral ontogeny in strawberry (Fragaria × ananassa Duch.) plug plants Scientia Hort. 194 154 159
Durner, E.F. 2016 Photoperiod and temperature conditioning of ‘Sweet Charlie’ strawberry (Fragaria × ananassa Duch.) plugs enhances off-season production Scientia Hort. 201 184 189
Guttridge, C.G. 1985 Fragaria × ananassa, p. 16–33. In: A.H. Halevy (ed.). CRC handbook of flowering. CRC Press, Inc., Boca Raton, FL
Heide, O.M. & Sønsteby, A. 2007 Interactions of temperature and photoperiod in the control of flowering of latitudinal and altitudinal populations of wild strawberry (Fragaria vesca) Physiol. Plant. 130 2 30 34
Heide, O.M., Stavang, J.A. & Sønsteby, A. 2013 Physiology and genetics of glowering in cultivated and wild strawberries: A review J. Hort. Sci. Biotechnol. 88 1 30 34
Konsin, M., Voipio, I. & Palonen, P. 2001 Influence of photoperiod and duration of short-day treatment on vegetative growth and flowering of strawberry (Fragaria × ananassa Duch.) J. Hort. Sci. Biotechnol. 76 1 30 34
Noguchi, Y. 2011 ‘Tokun’: A new decaploid interspecific hybrid strawberry having the aroma of the wild strawberry Journal of Japan Association on Odor Environment 42 2 30 34
Noguchi, Y. & Yamada, T. 2015 Flower bud initiation of a decaploid strawberry ‘Tokun’ by night chilling and short day treatment Acta Hort. 1049 907 910
Ruan, J.W., Lee, Y.H., Yeoung, Y.R. & Larson, K.D. 2011 Influence of short day treatment on autumn fruit production of June-bearing strawberry cultivars Hort. Environ. Biotechnol. 52 3 30 34
Ruan, J.W., Yang, C.M., Cao, H., Li, J.Z., Shan, Q.L., Wang, G.X., Wu, L.F., Li, H. & Xu, F. 2015 A method to induce flower bud for June-bearing strawberry in Central Yunnan. Chinese patent ZL201410363186.7. (in Chinese)
Ruan, J.W., Yang, C.M., Wang, G.X., Wu, L.F., Li, S.C., Tao, P., Liao, C.F., Yeoung, Y.R. & Wang, J.H. 2017 Segregation ratio in selfed and crossed progenies demonstrates single dominant gene inheritance of day-neutrality in strawberry Hort. Environ. Biotechnol. 58 6 30 34
Seo, J.B., Shin, G.H. & Jeong, H.J. 2014 Effect of a water-soluble complex fertilizer on growth and development of strawberry runner plants Acta Hort. 1049 541 544
Serçe, S. & Hancock, J.F. 2005 The temperature and photoperiod regulation of flowering and runnering in the strawberries, Fragaria chiloensis, F. virginiana, and F. × ananassa Scientia Hort. 103 2 30 34
Sønsteby, A. & Nes, A. 1998 Short days and temperature effects on growth and flowering in strawberry (Fragaria × ananassa Duch.) J. Hort. Sci. Biotechnol. 73 6 30 34
Sønsteby, A., . Opstad, N & Heide, O.M. 2013 Environmental manipulation for establishing high yield potential of strawberry forcing plants Scientia Hort. 157 65 73
Sønsteby, A., Opstad, N., Myrheim, U. & Heide, O.M. 2009 Interaction of short day and timing of nitrogen fertilization on growth and flowering of ‘Korona’ strawberry (Fragaria × ananassa Duch.) Scientia Hort. 123 2 30 34
Verheul, M.J., Sønsteby, A. & Grimstad, S.O. 2006 Interactions of photoperiod, temperature, duration of short-day treatment and plant age on flowering of Fragaria × ananassa Duch. cv. Korona Scientia Hort. 107 2 30 34
Wang, G.X., Sun, J.L., Jiang, H.Y., Yang, C.M., Wu, L.F., Shan, Q.L., Yu, R.P. & Ruan, J.W. 2018 Determination and analysis of major economic traits of day-neutral strawberry cultivars Southwest China Journal of Agricultural Sciences 31 10 30 34 (in Chinese with English abstract)
Wu, L., Dong, C., Pang, L. & Zeng, S. 2017 Effect of climate changing on landscape environment in Kunming in recent 65 years and sponge city technical analysis Construction Technol. 46 6 30 34 (in Chinese with English abstract)