Miracle berry (S. dulcificum), also called miracle fruit or red berry, is an indigenous tropical plant growing in West Africa. It is a very promising species but a poorly studied resource. S. dulcificum is an evergreen shrub reaching 4 m tall. Leaves are entire, alternate, symmetrical, and obovate–lanceolate to broadly lanceolate and pointed at apex with 4.3–7.5 cm long and 3.1–3.8 cm wide. Flowers are bisexual, white, small, solitary, or in small clusters. The calyx consists of four to five sepals, the corolla with four to five petals, and the androecium with five stamens. Within the gynoecium, the style is simple, erect with an inconspicuous stigma. The ovary is superior with the outer wall heavily covered with hairs. Fruit is an ovoid to oblong berry 2–2.5 cm long, 1 cm wide, finely pubescent, with a persistent protruding style, green turning to bright red when ripe. It has a large seed surrounded by a thin layer of berry flesh with a faint cherry-like flavor (Achigan-Dako et al., 2015; Chen et al., 2012; Du et al., 2014).
Miracle fruit is a rare fruit crop with high economical value in the medical and food industry.
The fleshy pulp of the miracle fruit contains miraculin, which is a glycoprotein with taste-modifying activity. Miraculin exerts an extraordinary effect on the taste buds of the tongue where it makes every sour or acidic food eaten or drunk to taste sweet (Kant, 2005; Temussi, 2006). Miraculin could possibly help diabetics to eat sweet food without taking in sugar and has been investigated as a possible source for a natural food sweetener (Kant, 2005).
Scientific literature on the type of pollination for S. dulcificum is scarce. However, flowers are hermaphrodite and the species is certainly autogamous. Crosspollination is also possible as well. Knowledge on floral biology and pollination is of paramount importance for breeding; and for S. dulcificum more data are needed. S. dulcificum is an evergreen species which flowers and fruits throughout the year. However, the phenological phases (e.g., growth duration, flowering time, fruiting time, and maturation time) need further investigation to complete previous investigation by Oumorou et al. (2010) who reported that flowering and fruiting occur two to three times per year. According to that report, in Benin, the species flowers from April to May, July to August, and from November to December and fruits are available in May, August, October, and from December to February (Oumorou et al., 2010). When there is no disturbance (e.g., wind, birds, and overexploitation by human), stands bear mature fruit for 30–60 d.
The study of the flower initiation and development of high economical value crop provide further informative insights of the mechanisms in manipulating flowering process and fruit loading (Teeri et al., 2006; Tromp, 2000; Valiente and Albrigo, 2004). Such study has economical and scientific importance especially in botany and agricultural investigations (Dennis et al., 2006; Esumi et al., 2007; Teeri et al., 2006). Floral initiation is an important process in plant development where the plant undergoes physiological and structural changes from the vegetative stage to reproductive stage involving the changes in the apex geometry and inception of the flower primordial (Albrechtova et al., 2004; Jaeger et al., 2006; Kwiatkowska, 2006). With the aid of microscopic techniques, the transition of vegetative primordial to reproductive stage can be detected (Foster et al., 2003; Kurokura et al., 2005; Kwiatkowska, 2006) and scanning electron microscope (SEM) has been used for observation at higher definition in the floral structure and development of fruit crops (Esumi et al., 2007; Foster et al., 2003).
Despite the importance of miracle fruit in the horticultural and food industry, many studies had been conducted focusing on the miraculin (Kant, 2005; Temussi, 2006). The study on flower morphology of miracle fruit which been done by Ayensu (1972) and the existence of petaloid staminodes had been reported. However, the study of the flower ontogeny and development of miracle fruit is still lacking. In this study, an observation on the flower morphology and flower development of miracle fruit has been conducted with the aid of microscopic techniques and description of flower and fruit developmental stages. Our results could improve understanding of pollination ecology and methods to manipulate flowering and fruit development.
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