PLANT TISSUE CULTURE A simple, economical, and high efficient protocol to produce in vitro miniature rose Nguyen Hoai Nguyen 1 & Bui Van Le 2 Received: 31 March 2019 /Accepted: 9 December 2019 / Editor: Jianxin Chen # The Society for In Vitro Biology 2020 Abstract Due to its high commercial value, many studies on rose (Rosa hybrida L.) micropropagation have been published. However, there are a limited number of studies on rose in vitro flowering. These studies only focused on the roles of plant growth regulators in the formation and morphogenesis of flowers. In this protocol, cytokinin was confirmed to positively function in the induction of in vitro rose flowers. In fact, more than 40% of in vitro shoots were induced to flower when they were grown on a medium supplemented with benzylaminopurine (BA) (2 mg L -1 ) and IAA (0.1 mg L -1 ). In addition, this study showed that the growth medium supplemented with only coconut water (15 or 20% v/v) was very efficient to induce flowering of in vitro miniature rose plants (> 70%) after 60 d of subculture. In addition, the in vitro flowers were normal and almost similar to ex vitro flowers in terms of flower shape and color. Based on these results, a detailed procedure for in vitro miniature rose flower production is provided. Keywords Coconut water . In vitro flowering . Miniature rose Introduction The rose plant (Rosa hybrida L.) is the most common and valuable ornamental plant in the world. As one of the top cut flowers, roses are worth around US$11 billion per year (Zlesak 2006). They have been grown in many places with high diversity in the cultivar and color. People grow rose plants for many purposes including for cut flowers, ornamen- tal decoration, and extracting essential oils. In vitro flowering is considered as an efficient system to study flowering in plants including floral transition, morpho- genesis, and senescence. In addition, the in vitro flowers can be applied for in vitro breeding, especially in the cases of those plants that require a long growth period. Moreover, in vitro flowers could be commercialized and potentially used for interior decoration (Wang et al. 2002). In vitro flowering has been studied in different plants such as Panax ginseng, Cymbidium niveo-marginatum Mak, Fagopyrum esculentum L., Kniphofia leucocephala, Saposhnikovia divaricata, and Brachystelma glabrum Hook.f. (Chang and Hsing 1980; Kostenyuk et al. 1999; Kachonpadungkitti et al. 2001; Taylor et al. 2005; Qiao et al. 2009; Lakshmi et al. 2017). Despite its high commercial value, there are only a limited number of studies on in vitro flowering in several rose culti- vars (Wang et al. 2002; Vu et al. 2006; Zeng et al. 2013). These studies focused on the roles of plant growth regula- tors (auxin and cytokinin) and sucrose in the flowering of in vitro plants (Wang et al. 2002; Vu et al. 2006; Zeng et al . 2013). Zeng et al .(2013) found that 68.33% of in vitro shoots produced flowers when they were grown on Murashige and Skoog (MS) medium (Murashige and Skoog 1962), supplemented with 50 g L -1 of sucrose, 3.0 mg L - 1 of 6-Benzylaminopurine (BA), and 0.1 mg L -1 of 1-Naphthaleneacetic acid (NAA), even though some of the in vitro flowers appeared to be abnor- mal. In this study, the in vitro shoots of a miniature rose cultivar were successfully induced to produce normal flowers when they were grown on a basic growth medium supplemented only with coconut water. From these results, a simple and economical protocol is provided, which can be widely applied to produce in vitro mini-flowers. * Nguyen Hoai Nguyen nguyen.nhoai@ou.edu.vn 1 Faculty of Biotechnology, Ho Chi Minh City Open University, 97 Vo Van Tan Street, District 3, Ho Chi Minh City, Vietnam 2 Department of Plant Biotechnology and Biotransformation, Faculty of Biology-Biotechnology, University of Science, Vietnam National University Ho Chi Minh City, 227 Nguyen Van Cu Street, District 5, Ho Chi Minh City, Vietnam In Vitro Cellular & Developmental Biology - Plant https://doi.org/10.1007/s11627-019-10043-1