A Novel Regeneration System for Tamarillo (Cyphomandra betacea) via Organogenesis from Hypocotyl, Leaf, and Root Explants

Cyphomandra betacea (Cav.) is commonly known as Tamarillo or tree tomato. This species is mainly used for its edible fruits which have a high nutritional value and contain relatively high amounts of proteins, vitamins B6, C, E, and provitamin A. The cultivation of Tamarillo in Rwanda is facing major challenges caused mainly by viral diseases such as Tamarillo mosaic virus (TaMV). These diseases are difficult to control and are transferred through vegetative propagation, often resulting in heavy productivity losses and poor-quality fruits. Thus, this study was conducted to evaluate the possibility of using tissue culture as an alternative propagation method. Tamarillo seeds were sterilized using a commercial bleach and germinated in vitro to get clean starting explants. Explants (hypocotyls, leaves, and roots) were cultured on semisolid Murashige and Skoog (MS) media supplemented with 6-benzylaminopurine (BA), N6-2-isopentyl adenine (2iP), 6-furfurylaminopurine (kinetin) evaluated at 5, 10, 20, 40 mM, and thidiazuron (TDZ), evaluated at 0.1, 0.5. 1.0 1.5 mM in separate experiments. Data were collected on the number of microshoots and roots 2 months after culture and analyzed using the Statistical Software for Social Sciences (SPSS) Software version 8. The results showed that the growth regulators evaluated had a significant (P £ 0.05) effect on plantlet regeneration from leaf and hypocotyl explants. The media supplemented with BA 40mM was the most effective in inducing multiple shoots from leaf explants producing 4.67 ± 0.15 shoots per explant. Root explants showed the least morphogenic responses for all the parameters evaluated. The regenerated plantlets were transplanted to the greenhouse and a survival rate of 90% was recorded. During this study, a simple, reproducible, single-step protocol was developed. These results would be useful formass propagation of Tamarillo. Cyphomandra betacea is a woody plant belonging to the Solanaceae family. It is commonly known as Tamarillo or tree tomato (Correia et al., 2009). The name ‘‘Tamarillo’’ was adopted in New Zealand and has become the standard commercial designation for the fruit (Morton, 1987). Tamarillo is grown mainly for their edible fruits and, to a lesser extent, as an outdoor ornamental. They have several culinary uses and can be eaten raw in salads or as dessert but preferably cooked (Guimar~aes et al., 1996). In Jamaica and the West Indies, the fruits are considered to have beneficial effects in relieving disorders of the liver (Guimar~aes et al., 1996). Tamarillo is an important component in Rwanda’s exotic fruit industry and consumption of the fruit is traditionally recommended for people suffering from stomach ailments. In this country, it is mainly used for making jams and juices but unfortunately in low quantities because of low productivity, mainly due to viral diseases. Tamarillo is considered an interesting crop from the nutritional viewpoint as it is comparatively high in protein (1.5–2 g/100 g of food), vitamin C (30–45 mg/100 g), and E (1.85 mg/100 g), provitamin A,mineral elements (K, P), low in carbohydrates (4.7 g/100 g), and in calories (about 28Kcal/100g) (McCane andWiddowson, 1992). The plant is propagated mainly through seeds, cuttings, or by grafting (Fouque, 1973; Prohens et al., 2001). Propagation through seeds is not recommended as this method is known to produce high degree of genetic variability that negatively affects fruit color resulting in rejection of fruits on the international market. On the other hand, vegetative propagation by cuttings has been found to transmit deadly viral diseases. Therefore, there is a compelling need to develop alternative methods to propagate the plant in Rwanda. Tissue culture offers a feasible solution to produce large numbers of diseasefree planting materials. It is also known that in vitro propagated Tamarillo plants produce higher yields and shorter gestation period compared with traditional methods (The Indian Agriculture Information Wing, 2009). Another advantage offered by tissue culture methods is the large scale availability of planting materials at any time of the year irrespective of the season. This study aimed to developing an efficient and rapid propagation protocol for C. betacea plant through tissue culture techniques. An increasing number of studies describing in vitro propagation of Tamarillo using axillary buds have been reported (Barghchi, 1998; Obando et al., 1992; Waweru et al., 2011). Somatic embryogenesis has also been reported by Espinosa et al. (2005), Obando and Jordan (2001), Correia et al. (2009), Guimar~aes et al. (1996), and Correia et al. (2011). However, there are no documented studies on the direct organogenesis in Tamarillo. An important advantage of direct organogenesis is the potential formaintaining genomic stability of regenerated plants, whereas regeneration via an intermediate callus phase increases the possibility of somaclonal variations (Kahia, 1999). Furthermore, a highly efficient and reproducible in vitro regeneration system is an absolute prerequisite for producing transgenic plants. Materials and Methods The study was conducted at the plant tissue culture laboratory ofRwandaAgriculture Board (RAB) located in Rubona, Southern Received for publication 8May 2015. Accepted for publication 19 June 2015. Corresponding author. E-mail: j.kahia@cgiar.org. HORTSCIENCE VOL. 50(9) SEPTEMBER 2015 1375 PROPAGATION AND TISSUE CULTURE