**9. Soil and climate**

Tamarillo plants grow best in light, deep, fertile and rich in organic matter soils. However, soils must be well drained, since the plants are not tolerant to water-logging. They grow naturally on soils with a pH of 5–8.5. The tamarillo requires full sun and freedom from competition with roots or shade from other plants. The tamarillo prefers subtropical climate, they grow in many parts of world with rainfall between 600 and 4000 millimeters and annual temperatures between 15°C and 20°C. Although species can also thrive in colder climates, in areas with temperatures not lower than 10°C and where extreme freezing does not occur [49], but it is intolerant to frost (below −2°C) and drought stress. Even though extreme cold could severely damage tamarillo plants, often the plant has the capacity of recovering. During first year of planting the cuttings and seedlings should be protected from frost as plants are highly susceptible to frost and can readily be killed. Frost kills the small branches and foliage of mature trees but not the largest branches and main stem. It is assumed that fruit set is affected by night temperatures. Areas where citrus is cultivated provide good conditions for tamarillos. Tree tomatoes cannot survive in areas with prolonged drought. They must have ample water during the dry season. The best way to retain moisture in a tree tomato plantation is to apply mulch, which also reduces weed growth. Branches of Tamarillo's are fragile, brittle and break easily when laden with fruit so wind breaks should be established before actual planting of the fruit plants in an area where wind may be a problem. Further these plants have a shallow root system and can be blown over by strong winds if not protected sufficiently. Hailstones can also damage the leaves and break the brittle branches. However, damage to fruit is not so severe as in other fruit crops due to their thick skin and strong attachment to the plant.

## **10. Propagation and rootstock**

The plant is mostly multiplied through seeds, cuttings, or grafting [12] as well as more contemporary methods of in vitro clonal propagation, which include axillary branch proliferation, organogenesis, and somatic embryogenesis and are commonly referred to as micropropagation. Seed propagation is simple and best done in protected areas. Seeds produce a high-branched, erect tree, ideal for sheltered locations. Seeds for planting are first washed, dried in the shade and then placed in a freezer for 24 h to accelerate germination. They are then planted in boxes of rich soil by keeping 30 cm distance between seeds and 60 cm between rows and virtually 100% will germinate in 4–6 days. Seedlings should be kept in the nursery until they reach a height of 1–1.5 m for efficient growth. Cuttings should be taken from healthy plants that are free from pathogenic viruses from the basal or aerial suckers should be of 1- to 2-year-old wood with thickness ranging from 10 to 25 mm and length 45–75 cm. They are planted directly in the field until they reach a height of 1–1.5 m. Cuttings develop into a shorter, bushy plant with low-lying branches, suitable for exposed, windy sites. Tamarillo can be grafted on several closely-related rootstock species. In Java, *Cyphomandra costaricensis* is sometimes used as a rootstock to attain a longerlived plant. The cuttings can also be grafted on wild tobacco trees (*Solanum mauritianum*). The Solanaceae family, which includes many tamarillo cousins, has strong and frequently undesirable alkaloids that can transmit to scions and into fruits grafted on such roots. This is important to remember. It is not advisable to integrate tamarillo on an unknown or untested rootstock.

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 in the international market. Thus, methods of vegetative propagation are usually used to obtain uniform plants [49]. Vegetative propagation by cuttings has been found to transmit deadly viral diseases. Tissue culture offers a feasible solution to produce large numbers of disease-free planting materials. It is also known that *in vitro* propagated Tamarillo plants produce higher yields and shorter gestation period compared with traditional methods [68]. 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.

Nodal explants are surface sterilized, added to Murashige and Skoog media containing Benzyl amino purine (BAP), and then incubated in a growth environment with a temperature of 25°C and a 16-h photoperiod. Rooting occurs without the use of an exogenous source of auxin 2 weeks after micro shoot development, and they grow to a height of 40 mm in 4 weeks. After that, the rooted plantlets are brought to the greenhouse to begin weaning. *In vitro* propagation of Tamarillo using axillary buds have been reported [69]. Somatic embryogenesis and direct organogenesis have also been reported by [49, 70]. Direct organogenesis has the potential to keep regenerated

plants' genomes stable, whereas regeneration through an intermediary callus phase raises the probability of somaclonal changes [71]. A very effective and repeatable in vitro regeneration technique is moreover an absolute requirement for creating transgenic plants.
