Floriculture is a very dynamic industry, and besides being able to produce plants throughout the year, the development of new cultivars is one of the most important aims of this sector (Kuligowska et al., 2016; Noman et al., 2017). Control of flowering time is crucial to guarantee that the plants will flower at the same time, and thus fulfill the market demand, as well as for cross-pollination programs.
Plants from the Kalanchoë genus have been cultivated as ornamental plants in Europe since the beginning of the 20th century (van Voorst and Arends, 1982), and Kalanchoë is presently the second most economically important potted plant in Europe with a turnover of 67 million Euros in 2016 (Royal Flora Holland, 2016). The Kalanchoë genus comprises around 139 species (Descoings, 2005), with a great variety of morphological traits. However, mainly Kalanchoë blossfeldiana and its interspecific hybrids are popular ornamental plants of economic importance (Kuligowska et al., 2015). According to Currey and Erwin (2010, 2011), flower induction and the control of flowering time are difficult in several Kalanchoë species, and the lack of knowledge on the flower-inducing factors can limit the use of new plants by breeding companies.
Flowering is a complex process that assures successful plant reproduction. The flowering time needs to be tightly controlled by the environment to assure effective use of energy and available resources for the developing plant (Bratzel and Turck, 2015). In many plants, the flowering response is closely linked to endogenous hormonal levels, which is directly or indirectly associated with their developmental stage (Bratzel and Turck, 2015). Gibberellins are a class of hormones that play multiple roles in plant growth and development, such as seed germination, stem elongation, leaf expansion, shortening of juvenile phase and floral transitioning, and fruit patterning (Hedden, 2016). Gaskin et al. (1973) observed that the level of gibberellins increased considerably in Kalanchoë daigremontiana when flower formation was induced. Moreover, high concentration of GA3 in the leaves of K. daigremontiana was a prerequisite for the production of the floral stimulus (Gaskin et al., 1973). In general, Kalanchoë plants are responsive to SD or long SD (LSD) photoperiods, i.e., flowering will occur after a minimum number of SD cycles or when a period of long days (LDs) precedes the SDs (LSD plants) (Currey and Erwin, 2010, 2011; Zeevaart and Lang, 1962). However, other factors, combined with the photoperiodic requirement, such as cold night temperature can enhance flowering in Kalanchoë (Kroon et al., 1989; Sharma, 1970, 1973; Spear and Thimann, 1954).
Kalanchoë longiflora is a succulent shrub from South Africa, up to 40 cm tall with attractive light bluish-gray leaves and quadrangular stem. In nature, the flowers appear during autumn to winter (Notten, 2014). The color of the foliage, length and shape of the stem, and the resistance to drought are very desirable traits that could be introduced to new Kalanchoë cultivars. Kalanchoë pinnata is a perennial succulent naturalized in many tropical and subtropical parts of the world. It grows up to 2 m height and exhibits dark green leaves. The bell-like pendant flowers exhibit a reddish-purple color, which is the main ornamental trait of this species (Descoings, 2005). Furthermore, K. pinnata can also be explored for medical purpose as the leaf extract exhibits antimicrobial activity (Quazi et al., 2011).
The factors underlying flowering in K. longiflora and K. pinnata are not well understood. Therefore, this study aimed to evaluate the effect of GA3 on flowering in both species.
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