Tamarillo (Cyphomandra betacea (Cav.)) Origin, Cultivation, Breeding and Management

Abstract

Tamarillo has a unique flavor and rich history. South American fruit is popular in New Zealand. Tamarillo is commercially grown in New Zealand and South America. It grows best under sub-tropical areas. It matures in 18 months. It’s 2 m tall and has lifespan of about 7 years. For propagation, seeds or cuttings are employed, and plant trimming for effective output varies according to propagation method. Tamarillo plants are wind-sensitive and need cover or windbreaks. It’s a beautiful fruit with smooth, shining skin. Yellow, red, and purple fruits are available. This fruit contains vitamins, minerals, fiber, and antioxidants. It has a very low-calorie count. Breeding focuses on fruit quality through selection, hybridization, and biotechnological treatments for plantation and post-harvest management. Diseases, pests, viruses, and physiological abnormalities can be treated with plant protection techniques. Like other fruits, it’s edible after harvesting. Made into juices, concentrates, jams, gelatins, and sweets. If processing facilities and transport are available, it can be exported as pulp or concentrate. The tamarillo can diversify sub-tropical fruit production as a high-value cash crop, with excellent fruits commanding premium prices in Europe, North America, and Japan.

1. Introduction

The tree tomato (Solanum betaceum Cav., syn. Cyphomandra betacea (Cav. Sendt.)) is a lesser-known tiny shrub or semi-woody tree that grows at elevations of 500–2500 m. The tamarillo, sometimes known as a ‘tree tomato’ because of its flesh’s resemblance to that of a tomato, is a member of the solanaceae (nightshade) family [1]. The tree tomato is related to a group of taxa that used to be classified under the Cyphomandra genus. The species of the genus Cyphomandra were reassigned to the genus Solanum, subgenus Bassovia, based on morphological and genetic data [2, 3]. The scientific community now uses the Solanum designations to refer to tree tomatoes and wild cousins. In New Zealand, the term “Tamarillo” has become the usual commercial identification for the fruit [4]. It can be found in subtropical and mild temperate climates all over the world. Commercially, it is grown in New Zealand and a few parts of South America. Although some high-performing uniform lines have been produced, commercial plantings are of seed propagated populations. Although it is a largely unexploited species, it presents a wonderful chance to diversify fruit production as a high-value income crop in many subtropical and mild temperate production locations. It comes in two colors red and yellow, with the red being the more popular and prevalent. It’s a vivid red egg-shaped fruit with yellow-orange flesh and black seeds encased in purple gelatin. The red color comes from anthocyanin pigments, while the yellow-orange color comes from carotenoids. Tree tomatoes at the fruit-bearing stage require support to keep their branches from breaking off as they get packed with fruit. Because of its shallow root system, they are readily blown over by the wind. The plant is not affected by the duration of the day. Cyphomandra species such as C. hartwegii, C. sibundoyensis, and C. cajanumensis produce edible fruits in the wild. Other Cyphomandra species are employed as colors and in medical formulations. This category of plants is becoming more economically important, and it may have a lot of future promise.

2. Area and production

Tamarillo popularly known as arboreal tomato [5] is a fruit tree of Andean origin and is currently grown in California, Argentina, Colombia, Ecuador, Venezuela and New Zealand [6] for use in the fresh fruit market and for food processing industry. Tamarillo is also produced less widely in Zambia, Zimbabwe, Uganda, Sri Lanka and India [7, 8]. The fruit’s distinctive flavor and nutritional benefits are causing an uptick in interest today [9], which is keeping prices high. New Zealand and the United States have developed extensive plant breeding programmes to develop new cultivars that are more appealing to customers [10]. In Colombia, tamarillo orchards cover a total cultivated area of 7646 ha distributed in 18 provinces. However, Antioquia and Cundinamarca alone account for two-thirds of the total production (50 and 14%, respectively) [7]. In New Zealand about 2000 tons are produced on 200 ha of land and exported to the United States, Japan and Europe. New Zealand’s horticultural practices, handling, storage, and transportation methods have all been enhanced via research there. Some better cultivars and shipping containers and circumstances for overseas exports have resulted from these investigations. This crop is limited by factors such as a lack of clear differentiation among varieties, low fruit quality (heterogeneity and phytosanitary issues), the use of ineffective local and foreign variety substitutions, and the fact that the tree tomato is frequently a subsistence crop and not included in genetic conservation programmes.

3. Marketing and trade

New Zealand is one of only three countries to grow tamarillos commercially, the others being Colombia and Australia. New Zealand leads in the production and export followed by Colombia [11]. Tamarillos of New Zealand are exported to the United States, Japan and Europe (Table 1). For the export, the existing marketing channels developed for the kiwifruit are used [12] which have greatly benefited the farmers. Due to lack of international market and knowledge of the fruit, the export potential of this fruit crop has not been yet achieved to its level. There are relatively few barriers to trade and very few countries specifically refer to tamarillos in their tariff schedules. The United States of America continues to be the main export market for tamarillos. In Columbia majority of the produce is consumed locally, but some part is also exported to the Netherland, France, Canada, Germany and Spain. It is important to mention here that standards have been established among commercial growing country’s that market tamarillo fruits (New Zealand, Ecuador and Colombia) and in other countries, there is no such regulation and therefore no commercialization capacity [13, 14]. Fresh tree tomatoes are in high demand in foreign markets, particularly in the United Kingdom, the Netherlands and Spain, where they are especially popular if they are grown without the use of pesticides. Fair Trade accreditation also helps to open up new markets for the product. Imported fruit is processed into juices, syrups and other beverages as well as gelatins and other treats. It might also be exported in the form of fruit pulp or concentrate if processing facilities and suitable transportation were available.

Market	2014		2015		2016
	Volume	Value	Volume	Value	Volume	Value
United States of America	12	100,036	11	74,318	8	60,475
Pacific Islands	0.01	98	0	0	0.01	52
Australia	42	182,239	0	0	0	0
Japan	0.05	753	0	0	0	0
Fiji	0	0	0.01	80	0	0
New Caledonia	0	0	0.02	19	0	0
Thailand	4	12,392	0	0	0	0
Total	59	$295,518	11	$74,417	8	$60,527
% change (yr/yr)	173%	62%	−82%	−75%	−26%	−19%

Table 1.

Tamarillo export markets 2014–2016 (year ending June, tonnes and $NZ FOB).

Source: Statistics New Zealand.

4. Composition and uses

This fruit is found to be a good source of vitamin A, C, B6, E and antioxidants [15, 16, 17, 18]. Tamarillo has a relatively high content of vitamins A and C (Table 2). Levels of vitamin A are intermediate between those of tomato and carrot [19], while the ascorbic acid content is similar to that of citrus fruits. Tamarillo is rich in anthocyanins and carotenoids which are responsible for their color [20]. The presence of anthocyanins and carotenoids show its biological, therapeutic, and preventative properties [21]. Osorio et al. [22] using spectroscopic analyses revealed that tamarillo fruits are a rich source of natural pigments with potential antioxidant activity, giving them a remarkable added-value. Phenolics are the main antioxidants found in the tamarillo fruit pulp [23]. The seed of the fruit is consumed together with flesh [24]. Tamarillo seeds made up 1.0–1.5% wet basis of the fruit (50–80 g). The seeds of tamarillo were examined for their proximate components [25]. Protein content was discovered to be 22.63%, fat content to be 21.13%, and ash to be 3.15%, with a total carbohydrate content of 43.87%, in the seeds. Tamarillo seed oil’s fatty acid profile revealed that linoleic acid (70.47%), oleic acid (14.93%), palmitic acid (9.41%), stearic acid (2.23%) and linolenic acid were the most prevalent fatty acids (1.73%). Apart from these, the oil included arachidic acid (0.23%), phellonic acid (0.22%), and lignoceric acid (0.23%). The fruits are very low in calories (only about 40 calories per fruit). These fruits are available in both red and yellow varieties. However, the red varieties are more popular and more common [26]. Acosta-Quezada et al. [11] assessed fruits of purple and yellow/orange cultivars and did not find any relevant differences among them.

Constituents	Content per 100 g of edible portion
Moisture (g)	85.20
Ash (g)	1.30
Crude protein (g)	1.60
Crude fat (g)	0.00
Carbohydrate (g)	11.90
Total dietary fiber (g)	6.00
Calcium (mg)	11.20
Sodium (mg)	17.80
Magnesium (mg)	25.20
Potassium (mg)	410.60
Iron (mg)	0.30
Beta-carotene (vitamin A)	4.80 (mg/100 g DW)
Ascorbic acid (vitamin C)	55.90 (mg/100 g DW)

Table 2.

Nutritional composition of tamarillo fruits.

Tamarillo is grown mainly for their edible fruits and to a lesser extent as an outdoor ornamental. The tamarillo fruit has been described as “brazenly beautiful” and the aroma “unusual and attractive”. They have several culinary uses and can be eaten raw in salads or as dessert but preferably cooked [27]. The flesh can be eaten fresh or made into a range of sweet and savory dishes and condiments. Tamarillos are tangy and usually sweet with a bold and complex flavor that differs by variety. The fruit can be stewed to use on cereal or as a pie or crumble filling, added to stews or made into a delicious chutney, which is especially good with chillies. In Jamaica and the West Indies, the fruits are considered to have beneficial effects in relieving disorders of the liver [27]. 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. It is processed into jams, juices and jellies or canned in syrup or prepared in combination with milk products like yogurts, milk shakes and ice-creams. The fruit has high level of pectins, which makes it especially suited for jams and preserves [28]. It is also used for canning in syrup and for producing pulp, chutney, sauce, baby food and in combination with milk products like yogurt, milk shakes and ice creams [29]. The fruit can be used much as a regular tomato, but it has less moisture, so more water, stock or gravy is needed for most cooked dishes.

5. Origin and distribution

The tamarillo C. betacea (Cav.) is native to the Andean region of South America where most Cyphomandra species are found in cultivated state. It is also grown in New Zealand, Brazil, Argentina and Colombia. The area where C. betacea originated is not known, but some wild or naturalized populations have been reported in southern Bolivia and northeastern Argentina and may give an indication of its area of origin [30, 31]. It is found that S. betaceum is closely related to S. unilobum, S. roseum, and in particular to S. maternum, all of which are found in Bolivia in wild status [2, 3, 32, 33]. Little information is available on the domestication of the tree tomato, and at present it is unknown when and where this process took place. In New Zealand it is cultivated as a minor fruit crop. It was introduced to New Zealand as early as the late 1800s and there have been a number of further introductions [34]. It is cultivated and naturalized in Venezuela and grown in the highlands of Costa Rica, Guatemala, Jamaica, Puerto Rico and Haiti. Tamarillo was adopted on January 31, 1963 by the growers of New Zealand as the official common trade name for Cyphomandra betacea. The tree tomato was named as tamarillo in New Zealand in 1967 [35]. Tamarillo is a Maori word that indicates leadership, and “rillo” comes from the Spanish word for yellow, “amarillo” which was the original type of tamarillo to be grown and only in the 1920s was a new red variety developed [9]. It is possible to grow it successfully in areas with Mediterranean climates, where it has good prospects as a developing new fruit crop [36, 37, 38]. In India it is found growing in Sikkim, Darjeeling hills of West Bengal, Tamil Nadu, Meghalaya and in other north-eastern states. In Nepal during survey, it was found that it is grown in home gardens for vegetable purposes. It has been grown in Queensland and Australia in home gardens for many years and is a practical crop in the highlands of the Australian part of New Guinea. In USA it is grown in California and occasionally in Florida in pots and indoors. The plants fruit satisfactorily in greenhouses. In Malaysia C. betacea is cultivated in Cameron Highland (Peninsular Malaysia), and Kundasang (Sabah) and is locally known as “Pokok Tomato” or “Tamarillo” in Peninsular Malaysia and as “Buah Cinta,” “Moginiwang,” or “Tamarillo” in Sabah.

6. Botany and taxonomy

The plant is a small shrub or half-woody, evergreen or partially deciduous, attractive fast growing, brittle tree, shallow-rooted reaching 3 m to 5.5 m in height rarely as much as 7.5 m. The dichasial branching is responsible for the shrubby habit of the tree, although seedling grown plants do go through a juvenile phase and the initial branching pattern may not occur until after 30 nodes growth [39]. The plant is not tolerant to drought stress, and can be damaged by strong winds because of shallow root system. The leaves are perennial, simple, 10–35 cm long and 4–12 cm broad, evergreen, alternate, more or less heart-shaped at the base, ovate and pointed at the apex, thin, softly hairy, with prominent veins and have musky smell and slightly tinged purple when the leaves are young. Flowers with fragrance are borne in small, loose clusters near the branch tips, 1.25–2 cm wide, have 5 pale-pink or lavender, pointed lobes with 5 prominent yellow stamens and green-purple calyx. The long-stalked, smooth, egg shaped are borne singly or in clusters of 3–12, pointed at both ends and capped with the persistent conical calyx. In length, it can be anywhere from 5 to 10 cm long, and in breadth, it can be anywhere from 4 to 5 cm wide. Red, orange, yellow, or red-and-yellow skin colors are all possible, as well as a variety of shades in between (Figure 1). Species-dependent variations in flesh color include shades of orange-red, yellow, and cream-yellow. In the two longitudinal compartments of dark-purple and red fruits, as well as yellow and orange fruits, a soft, juicy, subacid to sweet pulp surrounds the seeds. The exterior layer of flesh is luscious and bland, whereas the skin is rough and unpleasant to eat. In spite of their diminutive size, the seeds are tough and bitter. A weak or under-ripe tomato with a subtle resinous aftertaste has a resinous scent and flavor. The plant bears in first or second year after planting, but peak production is reached after 4 years and has a life expectancy of only 5–12 years. In general, it forms a large spreading crown at a height of 1.5–2 m from base of a single upright woody trunk.

Figure 1.

Tamarillo origin and general aspects (A) Andean region from where tamarillo is native; (B) tamarillo tree with red fruits; (C) Tamarillo’s flowers; (D) Tamarillo’s fruits range of colors. (http://funnelandspade.blogspot.pt/2010/06/tamarillos-also-known-as-treetomatoes.html;http://www.fancyplants.de/en/exotichome/nwhspec/tamarillo/).

7. Varieties and cultivars

There are apparently no named cultivars, but there are local preferences according to fruit color. Tamarillo have been described as three strains yellow, red (red skin, yellow-orange flesh), and purple (red-purple skin, light orange flesh), with the red being more popular and more common but no named varieties have been analyzed. In Europe and in the USA, the red and purple cultivars are the preferred by consumers due to its attractive color, flavor and nutritional properties. In Malaysia, the red variety of tamarillo can be easily grown at Cameron Highlands, Pahang. It is an egg-shaped bright red fruit with yellow-orange flesh and black seeds that are surrounded by purple seed coat. In Kenya the main varieties grown are the Gold-mine, Inca red, Rothamer, Solid gold and Ruby red. Red fruits are chosen for the fresh fruit markets because of their appealing color. Different selections have been developed in New Zealand from time to time. Commercial plantings of New Zealand’s current dominant “black” type were selected in the early 1920s as a variation on the yellow and purple variants that had been used in the past. A reselection process resulted in the creation of this massive, higher-quality red variety. New Black was chosen by William Bridge in 1927 for its huge fruit. Ruby Red has been a staple of the New Zealand economy for decades. Heart-shaped fruit with a deep crimson color and a savory flavor were selected in 1970. Inca Gold is a canning favorite because of its amber hue and oval shape. If you are looking for something a little more vibrant, Ecuadorian Orange is a great choice. In 1979, Kaitaia Yellow was chosen for its flavor and sweetness. New Zealand is testing a new cultivar named Goldmine. Rothemer is an 85-gram fruit from San Rafael, California, with a bright red exterior and a golden yellow pulp. Solid Gold is an orange, luscious fruit with a sweet flavor. Red Delight, Yellow, and Oratia Round are also made in New Zealand.

8. Breeding and crop improvement

Tamarillo’s chromosomes are diploid (2n = 2x = 24). However, spontaneous tetraploids, aneuploids, and triploids have all been documented. The flowers are autogamous and self-compatible but flowers need to be shaken for pollination. Traditional plant breeding has largely ignored the tamarillo, and few crop improvement techniques have been applied. Most attempts to transfer this crop into new areas have failed since they have relied on a single cultivar. As a result, the ability to use variety for local adaptation has been limited. On the other hand, the loss of genetic diversity in this crop and allied wild species is a major worry [40, 41]. Plantation management, fruit quality, and postharvest management are all improved through research and breeding. Breaking seed dormancy, improving fruit taste, and increasing yields are all key breeding goals. Little “stones” of sodium and calcium that occasionally form in the fruit skin offer a difficulty for industrial applications and must be eradicated through breeding. The following are the most important breeding procedures in this crop.

8.1 Selection

Although the tamarillo is essentially autogamous, there is some variation among plants of the same accession, particularly in traditional growing methods. This variance is caused by spontaneous mutations or by the inadvertent introduction of genetic material from different populations through genotype crossover [42]. This variation could be used to find a favorable variant that could be used in a future breeding effort for crop improvement. As a result, screening valuable genetic variety in traditional growing areas for conservation, selection, and crop improvement for this underutilized fruit crop is critical.

8.2 Hybridization

Pollen tubes pierce the ovary and set fruits in most interspecific matings with Cyphomandra, according to [30], but seeds do not mature. Pringle and Murray [43] experimented with interspecific hybridization of Cyphomandra with nine different Cyphomandra species and discovered that the majority of the crosses failed after fertilization. However, a species hybrid between the two Brazilian species C. corymbiflora and C. diploconos was obtained very easily. Most species’ combinations had reciprocal variances in compatibility. The results of these crosses indicate that the S locus is not involved in the regulation of interspecific incompatibility.

8.2.1 Intraspecific hybridization

There are no technical issues in crossing between different varieties of C. betacea. Tamarillo individuals have a high degree of homozygosity due to their autogamy, and crossing genetically dissimilar individuals produces homogeneous offspring. Commercial production of the hybrid tamarillo is simple because each fruit contains more than 300 seeds [44]. The agronomic behavior of F1 hybrids, on the other hand, is completely unknown. Most solanaceous horticulture crops have heterotic yield features [45], and the tamarillo is no exception. Obtaining segregant generations allows for recombination and segregation, allowing for the emergence of new superior genetic combinations. There are, however, a scarcity of investigations on the degree of diversity in segregant generations. Despite the fact that it takes several years to evaluate, tamarillo cannot be regarded a standard fruit crop, as individual genotype evaluation can take up to 20 years. Nonetheless, evaluating each individual takes 3–5 years, making yearly species breeding schemes impracticable, as it could take up to 10 generations before an improved cultivar is released. It will be impossible to determine the best effective breeding strategy for this crop until studies are conducted to determine the corresponding value of the additive and dominant components of genetic variation for each of the primary interest traits. Breeders are interested in developing pure lines or F1 hybrids that maximize heterozygosis’s. Vegetative propagation, on the other hand, allows for the propagation of the most valuable genotypes that may arise in segregant generations, such as an F2 produced by complimentary or transgressive crossings. Cloning permits the entire genotype to be preserved, which might be useful in the production of novel cultivars. Micropropagation for tamarillo [46] provides for vegetative propagation without the risk of viral transmission.

8.2.2 Interspecific hybridization

Interspecific hybridization could be effective for transferring desirable traits from wild species to cultivated forms, such as disease and worm resistance. Crossings between C. acuminata Rusby and C. uniloba Rusby have proven successful. These species are morphologically quite similar to C. betacea. Fertility is low in Tamarillo hybrids with C. acuminata. Those obtained using C. uniloba, on the other hand, are vigorous and prolific [30]. Other Cyphomandra species, such as C. hartwegii (Miers) Sendt. Ex Walp. and C. sibundoyensis Bohs, are edible as well, and may have some future potential as stand-alone plants or sources of genetic variety for tamarillo breeding. There is no publicly available enhanced breeding material for tree tomatoes. Nonetheless, numerous hybrids between S. betaceum and S. unilobum are being tested in Colombian fields as a result of breeding operations [47].

8.3 Polyploidy breeding

Triploid and tetraploid seedlings are found at low frequency among commercial plantings of the diploid tamarillo and may arise from the union of unreduced gametes. Further, [48] reported successful induction of tetraploids in the tamarillo (Cyphomandra,betacea (Cav.) Sendt.) by the application of colchicine to the germinating seed. Triploids and aneuploids are produced from interploidy crosses. Most aneuploids produce primary trisomics (2n = 2x + 1 = 25), but some possesses 26 chromosomes and few may be hyperpolyploids. Aneuploidy with 25 chromosomes, instead of 24 as the diploid types, show good fertility and give a similar or even higher yield and fruit size than their diploid counterparts. The pollen fertility of these plants can vary from 10 to 90%. The morphological traits of aneuploids and diploids were the same. For commercial use, aneuploids have fruit and seed sizes comparable to those of diploids. Tamarillo polyploids have been proven to have low fertility and poor agronomic properties, whether they are spontaneous or manufactured [12].

8.4 Biotechnological methods

Traditional techniques have revealed themselves inadequate for improving cultivars because of the low success of cross-pollination, the high incidence of incompatibility and phytosanitary issues [49]. A valid alternative for this plant’s breeding are biotechnological methods as in vitro cloning and genetic transformation [46].

8.4.1 In vitro regeneration systems

Tamarillo micropropagation methods have been described in various assays [49]. In vitro cloning can be achieved through (1) axillary shoot proliferation, which was the first method to be applied [10] (2) organogenesis, obtained on leaf explants [50] and (3) somatic embryogenesis, first obtained from mature zygotic embryos and hypocotyls cultures, and later from other explants [51, 52].

8.4.1.1 Somatic embryogenesis

Plant multiplication has the potential to be revolutionized by somatic embryogenesis, a powerful biotechnology tool. Auxin rich media is used to induce somatic embryogenesis in tamarillo, where embryogenic callus is first generated (induction phase) and subsequently developed into embryos after being switched to a medium free of auxin (development phase). Several explants of tamarillo have the potential to initiate embryogenic cultures including, mature zygotic embryos, young leaves, cotyledons and hypocotyls. Tamarillo mature zygotic embryos were one of the first explants tested for somatic embryogenesis. The formation of embryogenic tissue offers a great potential for large-scale production of plantlets [53] and is also useful in plant genetic transformation. Somatic embryos pass through different morphological phases similar to those occurring during zygotic embryogenesis [54]. The subculturing of somatic embryos, on auxin-free medium for a further 4–5-week period give rise to green normal plantlets.

8.4.2 Genetic transformation

A number of viral infections impact the health and vigor of tamarillo trees, as well as the appearance of the fruit. The tamarillo mosaic virus, the most important pathogenic virus, has no known resistance in Cyphomandra species (TaMV). There has been little success in using traditional breeding programmes to increase tamarillo’s virus resistance. Plants can now be genetically modified to be resistant to a variety of viruses, thanks to recent advances in molecular biology, including the tobacco mosaic virus. Agro bacterium mediated transformation of tamarillo has been successfully achieved and protocols for transformation are now available [55]. The use of genetic transformation offers the great opportunity for the improvement of many characters for which there is not enough genetic variation in the local germplasm. Genetic transformation is also being used as a functional genomics tool, helping to better understand the process of somatic embryogenesis [6]. The most successful strategy so far has involved constitutive expression in the host plant of the coat protein gene of the target virus. Recently, the coat protein gene for TaMV has been cloned and sequenced which may allow TaMV resistance to be engineered into tamarillo. The application of the Agro bacterium mediated transformation method to obtain genetically modified tamarillo plants regenerated via, organogenesis was used to introduce the pKIWI110 binary vector into leaf disks by using a virulent LBA4404 [56] and some of them also expressed the b-D-glucuronidase (gusA) reporter gene and chlorsulfuron resistance. Agrobacterium mediated transformation was also used to obtain tamarillo plants resistant to tamarillo mosaic virus (TaMV) that were regenerated by shoot proliferation [6]. The NEP25 gene has been silenced in tamarillo using Agrobacterium-mediated genetic transformation procedures [10]. After undergoing somatic embryogenesis, these plants have been regenerated and are currently being evaluated to see if they have the same capacity for somatic embryogenesis as untransformed plants.

8.5 Breeding for yield

At present, the tamarillo is being introduced as a promising crop in a variety of environments, e.g., regions with a Mediterranean climate [37, 57]. But most attempts to introduce tamarillo culture have been based on a single cultivar and this has restricted the opportunity to exploit variation for local adaptation. For this purpose, germplasm screening is essential in order to select the most adapted types in local environments. Several evaluations of tamarillo germplasm have shown a high degree of genetic variation for yield and fruit weight. Differences among different plant genetic materials can be as high as two-fold for fruit weight [37, 57]. The fruit yield is highly affected environmental components and exploitation of most adapted material could maximize the selection for yield.

8.6 Breeding for quality

Among fruit quality parameters fruit shape is of interest because it is directly related to consumer acceptance because it affects fruit attractiveness and is important in terms of packaging and presentation. The fruit shape varies from round to elongated, with a ratio length/width higher than two among accessions. Round to oval shapes appear to be preferred. Fruit color varies from yellow types to purple and it may have stripes or not. Differences among cultivars have been found organoleptic characters like soluble solids, titratable acidity, ascorbic acid and other characters [37, 58, 59, 60]. Cultivars with a higher sugar/acid ratio are probably more suited for processing industry. Sugar/acid ratio and sweetness were found to be higher in one of the seven accessions studied by [38] that had reduced acidity (between 15% and 23% and similar levels of soluble solids). Recently developed ‘Oratia Red’ and ‘Andys Sweet Red’ have a high sugar/acid ratio (Boyes and Strubi, 1997). Breeding for nutritive value is also possible as lot of variation for ascorbic acid content and vitamin A have been found among genotypes [19, 38, 58, 60]. Aromatic compounds of tamarillo have been identified [61, 62] and selection of high aromatic cultivars is of interest. However, aroma is a complex character, in which many interactions among different compounds are involved and in which environmental influence is considerable.

8.7 Breeding for disease resistance

Few studies have been devoted to tamarillo breeding for disease resistance. Most work has dealt with TaMV resistance. Resistance to TaMV has not been achieved yet, even in wild species belonging to the genus Cyphomandra. Genetic transformation is being used to develop tamarillo cultivars resistant to TaMV. Strategies used up to now have mostly involved the use of genetic constructs which include sequences of the coat protein of this virus. The use of mutagenic agents, such as nitrous acid for the production of defective TaMV strains, which could be used for cross protection has not been successful [56]. Resistance to anthracnose is also being attempted by in vitro selection of cells capable of growing in the presence of crude filtrate of the fungus [63]. However, there are no reports of the efficacy of this strategy in developing mature plants resistant to this disease.

8.8 Breeding for early harvesting

Early harvesting is of significance since different cultivars differ in how quickly their fruit ripens [64]. This could be exploited to select the earliest cultivars. There is also quantitative variation in the response to postharvest applications of ethylene in some cultivars so it is possible to achieve successful postharvest ripening [65]. Despite being considered a non-climacteric fruit [65], ethylene applications stimulate ripening [66, 67]. Fruit can be harvested during the turning stage and allowed to ripen after harvest in materials where ethylene induces ripening. Fruits that are turning may be stored in this way and matured as needed.

8.9 Breeding for parthenocarpy

Occasionally, parthenocarpic (seedless) fruit-producing trees can be discovered in orchards. These trees require vegetative propagation because they are the result of spontaneous mutations. Fruits from parthenocarpy are ovoid-shaped, red to orange in color, and have stripes that range from green to coffee in hue. Orange is the color of the flesh. Fruit weighs normally only 20 g and is smaller than other fruit. Due to their lack of seeds, parthenocarpic tamarillos would be very intriguing; nevertheless, before this form of fruit can become well-known, low weight and poor yield issues must be resolved.

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 longer-lived 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.

11. Layout and planting

The seedlings are transplanted in the field when they reach 5–7 cm in height, spaced 80 cm apart in rows and 2 m apart between rows. In New Zealand, the trees are kept 2.5–3 m apart in paired rows 2.5 m apart with 4.25 m between each pair. In mechanized production, single row planting distances of 1–1.5 m between plants and 4.5–5 m between rows is recommended. In unprotected areas where winds are strong closer planting is recommended by keeping 1.5–1.8 m between the plants and 2.5–3 m between the rows and the trees may be staked to prevent swaying and disturbing of roots. In India, the trees are planted in pits 1.2–1.5 m apart. On poorly drained soils, plants should be planted on ridges. In poor soils or soils where nematode infestations or virus infections are possible prevalent, replanting with clean stock will be necessary and is recommended after a period of 3 or 4 years.

12. Irrigation

To maximize and stabilize production, water and nutrient inputs should be provided when needed. The plants need continuous supply of water due to their shallow root system. Drought stress results in decrease of plant growth, fruit size and productivity. The tree tomato cannot tolerate prolonged drought and must have an ample water supply during extremely dry periods. A mulch may be very beneficial in conserving moisture at such times.

13. Nutrient management

The suggested fertilizer rates per hectare for intensive orchard production techniques are 170 kg of nitrogen, 45 kg of phosphorus, and 130–190 kg of potassium. While potassium and phosphorus are sprayed at the beginning of the growth season, nitrogen is applied all year round. It is recommended to apply 0.25–1.0 kg of NPK fertilizer per tree evenly between early spring and summertime. The producer should give the plants in their fifth or sixth year a special feeding of 2 parts superphosphate, 1 1/2 parts nitrate of soda, and 1 part sulfite of potash in late winter or early spring at a rate of 1–1.5 kg per plant or 100 kg per hectare.

14. Training and pruning

The plant should be trained by pruning back long shoots and pinching shoot tips to induce a compact growth and the production of the fruit clusters near the centre of the tree. Seedling trees are pruned back the first year after planting to a height of 0.9–1.2 m to encourage branching. Annual pruning thereafter is advisable to eliminate branches that have already fruited and induce ample new shoots close to the main branches since branches that have already carried fruits will produce smaller fruits with lower quality the next time. Annual pruning is also must otherwise, the tree will develop a broad top with fruits only on the outer fringe and wide-spreading branches are also subjected to wind damage. Pruning also facilitates harvesting and if done timely and appropriately can extend the total fruiting period. Light pruning facilitates the production of medium sized fruits and heavy pruning to large sized fruits. Under protected cultivation pruning can be helpful to prevent the excessive vegetative growth. Early spring pruning of in some trees brings about early maturity and fall pruning of other trees delays fruit maturity to the following fall. It is best to cut the roots on one side of the tree and lean it to the other when it is between one and one and half metres tall (in the direction of the midday sun at about 30–45 degrees). As a result, fruiting branches can develop along the entire trunk as opposed to simply at the top.

15. Intercropping and interculture

In plantations, tamarillo is frequently intercropped with citrus so that, for the first 4–6 years of its rapid growth to a productive size, it can be produced economically. Thereafter, the tamarillo plants are removed [72]. Mulching can aid in preserving soil moisture because plants are susceptible to drought stress. As traditional soil management techniques like plowing are impractical due to the thin and delicate root system, it can also be used as a tactic to control weeds. Because of the shallow root system, deep cultivation is not possible, but light cultivation is desirable to eliminate weeds until there is sufficient vegetative growth to shade them out. The plants have to be protected from wind. Their shallow root system does not provide enough stability and the lateral branches are fragile and break easily when carrying fruits. The tree has to be protected from the wind because its roots are weak and it can easily be blown over. It is also fragile, and strong winds can easily break its branches, especially when they are heavy with fruit. Before laying out the plantation, it is advised that windbreaks be built to protect the young plants for each 1/2 acre (1/5 hectare). In the New Zealand region of North Auckland, Albizia lophantha Benth. and Hakea saligna hedges are maintained clipped, narrow, and well-liked.

16. Flowering and fruit set

Tamarillo shows sympodial growth habit and each sympodial unit consists of 3–4 leaves and a terminal inflorescence. New season’s growth begins in October with shoots that originate in the axils of the previous season’s leaf scars. Before inflorescence commencement and branching, shoot extension advances up to 15 nodes at the start of the growth season. At the tip of the stalk, inflorescences develop, and later, continuation shoots develop, typically in the axils of the two most recent leaves. Monochasial and trichasial branches are also seen, despite dichasial branching being prominent. Although they begin at the shoot apex, inflorescences can eventually be found 30–40 mm above the branch fork. At maturity, the flowers and inflorescences hang pendulously, with the anthers and stigma facing downward. Typically, the inflorescence is a mono- or di-chasium with flowers arranged alternately along the rachises. Up to 15 flowers per rachis and 50 in total could be seen in each inflorescence. At 2–3-day intervals, flowers open in an acropetal succession. As a result, the same inflorescence may contain fruitlets, flowers, and flower buds. Particularly if a fruit had already set inside the inflorescence, apical flower buds on each rachis frequently abscise before flower opening. Inflorescences formed late in the season also lose their immature flower buds, and occasionally just one or two blooms fully opened.

In climates with little annual variation, tamarillo trees can flower and set fruit throughout the year. In climates with pronounced seasons (such as New Zealand), fruits ripen in autumn. The flower is pentamerous, radially symmetrical, stellate and hermaphrodite and 24 mm in diameter when the petals are fully reflexed. The petals have a variety of colors, ranging from white to pale pink to white with purple flecks, and are relatively lengthy and meaty. Each stamen is united to a petal and forms a cone around the style. The stamens have two anther sacs on either side of a wide, yellow connective tissue, as well as a short filament and an anther. The style extends 2–4 mm beyond the anther cone and is long and thin. Small, flat, and papillate describe the stigma. Pollen is formed in large quantities in anthers (800,000 pollen). Pollen grains in their desiccated state are oval and trilobed with a pitted exine bearing numerous fine spines. Individual flowers generally open before midday and the petals close around the anthers and style again in the evening. The following morning, each flower bloomed once more, and this pattern persisted for another 2–3 days before the petals fully closed. The number of days a flower is open has an impact on pollination. Nearly a day earlier than unpollinated blooms, pollinated flowers closed for the last time on average after 2.25 days (3.05 days). Either at flower opening or right before it, an anther opens. Pollen is not released spontaneously but anthers release a cloud of pollen via the apical pore if touched or squeezed. If the anthers are not disturbed the pollens remain in the anthers beyond final flower closure. All flowers bear stigmatic exudate on the day of flower opening and remain present on the stigma until Day 5, even though the petals had closed. On the stigma, pollen grains and tubes can be seen from days three to four, but their abundance is greatest on days zero and two. On Day 0, pollen grain germination is at its highest, and it gradually decreases over the following days. On any given day, there are observed to be comparable numbers of pollen tubes in the style and pollen grains on the stigma. After 24 h, pollen tubes are about two-thirds of the way down the style, and after 48 h, they are present surrounding the ovules, according to observations of the pollen tube growth rate.

It is self-compatible and usually autogamous, but the flowers need to be shaken by the wind or visited by insects for pollination to take place [30, 43]. If grown in conditions where flower vibration is limited, such as in a greenhouse, fruit set can be very low. Flowers pollinated on Days −3-1 had the highest probability of fruit set. Fruit set then decline sharply until no fruit set on flowers pollinated on Day 4. Fruit set is strongly influenced by treatments designed to modify the pollen source and the vector. On average, two fruit set in open pollinated inflorescences and 0.6 in inflorescences bagged to exclude external sources of pollen has been found. The flower pollination is carried out by honey bees (Apis melliferd) and bumblebees (Bombus terrestris or B. hortorum). Although fruit set is lower in both cases than in open-pollinated flowers, the quantity of fruits set per inflorescence is unaffected by the pollen source, whether “self” or “cross” (by hand pollination). Self-pollinated or cross-pollinated flowers produce between 0.7 and 0.9 fruit sets per inflorescence on average, as opposed to 2.0 from open-pollinated blooms (Figure 2).

Figure 2.

Floral phenology of the tamarillo flower based on observations from 20 flowers grown under glasshouse conditions (EPP—effective pollination period) [73].

17. Fruit growth development and ripening

Fruit growth and development involves changes in its morphology, anatomy and physiology whilst fruit ripening is associated with dramatic changes in rind texture, color, juice composition, increase in softness due to changes in the cell walls, the metabolism of organic acids and the development of compounds involved in flavor and taste. During development it follows a simple sigmoid growth curve and during ripening it behaves as a non-climacteric fruit. Fruit growth shows an increase of fresh weight (and volume) fast and linear between the sixth and sixteenth week after this period the growth ceases [65, 73]. However, the weight dryness of the fruit continues to increase until reach a maximum in the twentieth week after anthesis. Tamarillos are commercially mature at 21–24 weeks after anthesis. Maturity is indicated by color, firmness, juice content and soluble solids content. Heatherbell et al. [74] reported that tamarillo fruits grew rapidly and reached full size within 16 weeks after anthesis and maturity is attained 11 weeks later i.e., at about 27 weeks. Marked changes in the skin and pulp color occur during development. After 15 weeks the first purple coloration of the skin appears, and thereafter increase in intensity. The green chlorophyll underlay disappears from the fruits between 18 and 22 weeks. Tamarillo is a non-climacteric fruit; therefore, it does not exhibit adequate self-stimulated increase in ethylene production and a consequent respiratory increase as part of its ripening behavior [65]. Pratt and Reid [65] harvested red and yellow tamarillos from 5 to 23 weeks of age and they monitored their respiration rate, demonstrating that the respiratory rate decreases as the age of the fruit increases. The ripe fruits presented a relatively high respiratory rate immediately after harvest (35 mg CO₂ kg⁻¹ h⁻¹ at 20°C), which then decreased gently until the beginning of the senescence. In this study the ethylene production of the fruits harvested was measured and it was shown to be negligible length of fruit development (less than 0.10 μl kg⁻¹ h⁻¹ at 20°C) until the beginning of the senescence, when it increases abruptly together with the respiratory rate.

Tamarillos of red cultivars remain green until the fruit growth around the sixteenth week after anthesis. From that moment, it begins to appear a violet color at the apical end subsequently, it will spread over the whole fruit. Around the nineteenth week after anthesis, the green base color begins to turn yellow and the apparent color purple reveals to be red. Violaceous coloring of the tissue surrounding the seeds is evident around the 12th week after anthesis, and intensifies until the Twenty-first week, when it begins decrease in intensity again. The fruits of yellow cultivars present a pattern of similar color change, except that the red coloration is very slight, resulting finally in a light orange color, and without that red pigmentation appears around the seeds. Changes in skin color are due to the degradation of chlorophyll and increase in the concentration of anthocyanins and carotenes. However, the increase in concentration of anthocyanins in the skin is very small in the 4–6 weeks before the commercial maturity. The concentration of anthocyanins, carotenes and chlorophylls from the tissue that surrounds the seeds is maximum when the fruit is in the violet state and then decreases.

The immature fruits have a high Starch content (14% of fresh weight) that, before the end of the stage of active growth, begins to decrease until reach less than 1% in ripe fruits. The decrease in starch content is accompanied by an increase in concentration of soluble solids and sugars. The sucrose is the predominant sugar in tamarillos. The citric and the malic are the organic acids predominant in tamarillo throughout the fruit development. The concentration of citric acid increases rapidly during the period of active fruit growth, reaching more than 2% of the fresh weight; the decreases up to 1.4% in mature fruits. Malic acid concentration is relatively low during the entire period of fruit development (0.2% of fresh weight in mature fruits). The pectin content decreases throughout the fruit development. The lysis of unions between pectin’s and hemicelluloses results in increase in the solubilization of pectin’s during ripening. Tamarillo’s soluble solid content appears to rise to 10–12°B during ripening (normally, the values range between 10.0 and 13.5°B), while the titratable acidity gradually declines (typically, the values range between 1.0 and 2.4%), increasing the SSC/TA ratio and, as a result, the sensory flavor rating. The stems also undergo changes when the fruit ripens, turning yellow instead of green as a result of increased water loss and chlorophyll degradation [75]. Further, according to [76] an SSC value over 12% can qualify tamarillo either for raw consumption or industrial processing.

18. Fruit retention and fruit drop

Self-pollination occurs naturally in tree tomato blossoms. Unless there are bees to transmit the pollen, pollination may suffer if wind is fully stopped so as not to move the branches. Flowers that have not been pollinated will wilt quickly.

19. Harvesting and yield

The tree typically starts bearing when it is 1 1/2 to 2 years old and keeps producing for another 5 or 6 years. It may continue to bear fruit for 11–12 years if given appropriate nutrition. The crop does not ripen simultaneously and several pickings are necessary. Tamarillos are picked when fully colored. The optimum time to harvest the tamarillos of red cultivars is when they are violet color. Other recommended indices to determine the maturity of the fruit with greater accuracy are the firmness, the content of juice and the content of soluble solids [66]. The color of the pedicel in combination with the skin color was also suggested as Maturity index. Fruit can also be picked when they are at the turning stage (when the green color of the skin begins to change and the characteristic skin color begins to show) and then treated with ethylene to stimulate ripening [66, 69]. This early picking and subsequent postharvest ripening reduce the risk of crop failure, increases earliness and concentrates harvesting as it allows harvesting to be advanced by up to 1 month [66]. The fruits are clipped, leaving about 12.5 cm of stem attached. They are collected in bags worn by the harvesters. A single tree can produce more than 30 kg fruits per year. A regular orchard yields 15–17 tons per hectare.

20. Protected/high tech cultivation

Tamarillos are suitable for growing as indoor container plants, though their swift growth, their light, water and humidity requirements and their large leaves can pose a challenge within a limited space. Plants grown in the greenhouse are heavily pruned to prevent excessive vegetative growth. Greenhouse tamarillo production can be somewhat inconvenient due to its long life and extended growing cycle [77]. If grown in conditions where flower vibration is limited, such as in a greenhouse, fruit set can be very low [78].

21. Disease, pest and physiological disorders

21.1 Diseases

21.1.1 Powdery mildew and leaf spot

If left unchecked, this fungus can produce a significant amount of defoliation. It is possible to remove powdery mildew by using commercial pesticide washes and neem oil sprays (Oidium sp.).

21.1.2 Bacterial blast

It is caused by Pseudomonas syringae and P. solanacearum. It affects the shoot and leaves. Anthracnose (Colletotrichum gloeosporioides).

21.1.3 Anthracnose (Colletotrichum gloeosporioides)

The damage it inflicts is immense. Good orchard management can help lower the risk of pest and disease control in markets that demand immaculate fruit. As long as the nursery is kept clean, predator insects can reduce the need for chemical pesticides.

21.2 Viral diseases

21.2.1 Tamarillo mosaic virus (TaMV)

TaMV symptoms include a mosaic mottling on the leaf and ugly irregular spots on the fruit skin that are a darker red than the cultivar’s typical skin color. Inside the fruit, there are no visible symptoms, and the eating quality is unaffected. Due to the milder background color typical of this variety of fruit, the darker red splotch on golden tamarillos is particularly ugly. The plants grow stunted as a result. TaMV can only be controlled after symptoms occur by removing trees that are seriously infested [79].

21.2.2 Cucumber mosaic virus and potato virus Y

These not only diminish the plant’s strength and health but also distort the leaves, produce skin blemishes, and lower the plant’s marketability. They result in fruit mottling and yield loss. The severity of the symptoms will be greater if multiple viruses have simultaneously attacked the plant and will be worse on young or sickly plants. In the valleys of Ecuador’s Pichincha region, PLRV, ToRSV, PVY, and AMV were the most often discovered viruses linked to symptoms of viral diseases [80]. Alfalfa mosaic virus (AIMV), tomato spotted wilt virus (TSWV), arabis mosaic virus (ArMV), tobacco streak virus (TSV), and tomato aspermy virus (TAV) are other viruses that have affected the tamarillo, albeit the losses they cause are not as severe as those produced by TaMV [56]. The Colombian tamarillo crop’s declining yield is caused by a virus complex [81]. Phytosanitary problem, among which anthracnose (Colletotrichum acutatum) and viruses (PLCR, CMV, Potyvirus and ToMV) and others, apparently less influential (AMV, ToRSV and TSWV) has major effect on expansion plans of the tamarillo cultivation in Colombia [82]. Good orchard hygiene, pruning and burring infected plants and a good pest management programme will help to reduce pests and diseases in crop. A suitable spraying schedule can also be helpful. However, there is no cure for a virus once it has infected a plant; the only option is prevention. Since aphids are the primary transmitters of viruses, it is crucial to have effective control over them. Since there is no proof that viruses affecting the tamarillo may be propagated by seed, seed-based reproduction is a strategy for restricting their spread.

21.3 Nematodes

The plant is also harmed by Pseudomonas solanacearum wilt, root knot (Meloidogyne sp.), root rot, crown rot, and other diseases. Good cultural norms ought to help prevent these issues.

21.4 Physiological disorders

21.4.1 Abnormality

In order to make jam, small, hard, irregular, semi-transparent stones that are present in the flesh of tree tomatoes must be strained out. If these resemble the two grit-filled bumps in the fruit’s wall, that is unknown. Probably in the form of silicates, borates, aluminum-magnesium-oxygen complexes, aluminates, or magnesium oxides, these stones are highly concentrated sources of sodium and calcium.

21.4.2 Fruit scarring

Tamarillo fruit scarring is a cosmetic condition that costs New Zealand’s tamarillo growers significantly lost revenue [83]. According to estimates, the condition affects 10–20% of the fruit, which will result in considerable economic losses. When the scars are about 3 cm long, they first appear as little, dark lines on the skin of young fruit. As the fruit grows, the scars turn into corky lesions. Phillips et al. [84] reported that a physical injury caused the scarring. A dark, uneven, and crazy corky scar was routinely produced when the epidermal layer was scratched with a toothbrush. Physical injury such as wind rub has been reported to cause corky scarring in other fruits also, such as avocado [72]. Wounding fruitlets by scratching or removing a patch of epidermis resulted in the characteristic scarring, which suggests that any type of physical epidermal damage incurred early in fruit development may result in scarring.

22. Package and transport

Fruits are sorted by size as small, medium, large and packed in paper-lined wooden boxes for marketing. Polythene films can also be used to reduce water loss and maintain fruit quality [85]. Packaging usually consists of wooden or cardboard boxes containing one tray of tamarillos or preformed plastic trays with 3–8 fruits. Because of its firm flesh and tough skin, the fruit can be transported to long distances without bruising. However, it deteriorates rather rapidly under ordinary storage conditions.

23. Postharvest handling and storage

Different studies carried out to improve post harvesting ripeness showed that application of ethylene or ethephon is helpful to decrease the risk of crop failure and an earlier delivery to the consumer, thereby enhancing the marketability of tamarillo [67]. The fragile lateral branches can break easily when loaded with fruits, so premature harvest helps to reduce this risk and allows storage of fruits up to 20 days at room temperature. Tamarillos can be stored for about 12–14 weeks at 3.5–4.5°C. A cold water dipping process, developed by the New Zealand Department of Scientific and Industrial Research also allows further storage of 6–10 weeks. At higher temperatures, postharvest diseases multiply rapidly. One of the main causes of postharvest loss is bitter rot caused by a Colletotrichum sp. Applications of postharvest fungicides greatly reduce the number of fruits affected. Another alternative for postharvest disease control is to dip the fruit in water at 5°C for 10 min [86]. Temperatures below 7°C will reduce softening, weight loss, TA reduction, and color change, among other postharvest handling characteristics that might impact quality. On the other hand, extremely low temperatures (between 0 and 2°C) raise the danger of chilling injury and worsen stem and calyx discolouration.

24. Processing and value addition

Pomegranate can be used in both savory and sweet dishes, and it can even be eaten raw. Fruits can be used to make preserves because of their high pectin content. However, if they are left untreated, they will oxidize and eventually fade. Yellow fruit is preferred for industrial production. As it turns out, it can be utilized in the same way as tomatoes are used in many other cuisines. Simply slice the tomatoes in half, sprinkle them with sugar, then consume the pulp and flesh by scooping it out. Chopped bacon and cream cheese go on top of sandwiches. Diced fruits, bread crumbs, butter, and seasonings are used as a stuffing for roast lamb. Dessert in the form of a pie sliced tree tomatoes, either on their own or accompanied by an apple, are available. They may be filled with water or sugar syrup, then packed into plastic containers with 50% sugar syrup and quickly frozen for later use as pie fillings or puddings. In a blender or on the stove, puree the peeled fruits, remove the seeds, and freeze in containers. Before blending, add some lemon juice into the purée to enhance the flavor even further. Several slices of fresh tree tomato are placed on top of the gelatin, milk, sugar, and lemon juice-cooked fruits. Cooking tree tomatoes with sugar, lemon zest, and juice results in a jam or chutney; the tomatoes can also be cooked with onions and apples for chutney, depending on the desired consistency. Chutney for the commercial market is made in an Auckland, New Zealand, facility. Pectin in the fruit makes it simple to turn into jelly, but the fruit quickly oxidizes and discolors if not treated further. Using whole, peeled fruits and sugar, a thick sauce is cooked to serve with ice cream. The peeled fruits can be used for tomatoes in tomato sauce. Tamarillo jelly can be made from tomatoes with a 50°C Brix sugar concentration, sucrose, and 2% pectin.

25. Conclusions

Tamarillo is a very unique fruit with not only a distinct flavor but also a fascinating history. This fruit is immensely popular in New Zealand, despite the fact that it is native to South America. Tamarillo grows best in a subtropical climate, although it can also be grown in areas where citrus crops are grown. Although it is currently grown in many countries, it is only commercially farmed in New Zealand and a few parts of South America. It rarely bears fruit in low-lying tropical places. It grows quickly and bears fruit in about 18 months. It reaches a height of around two meters and has a lifespan of about 7 years. Seeds or cuttings are commonly used for propagation, with plant trimming for efficient production varying according on the propagation method. Tamarillo plants are wind-sensitive and should be planted in naturally sheltered regions or protected by windbreaks. It is a really attractive fruit with a smooth and shiny skin on the outside. Vitamins, minerals, fiber, and antioxidants abound in this fruit. It has a very low-calorie count. It can be eaten after harvesting, much like most fruits. Juices, concentrates, jams, gelatins, and desserts are all made from it. It could be exported as fruit pulp or concentrate if processing facilities and suitable transportation are available. The tamarillo provides a chance to diversify fruit production in many subtropical fruit production locations as a high-value cash crop, with fine fruits fetching premium prices in niche markets in Europe, North America, and Japan.

Conflict of interest

The authors declare no conflict of interest.