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«Andean roots and tubers: Ahipa, arracacha, maca and yacon M. Hermann and J. Heller, editors Promoting the conservation and use of underutilized and ...»

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Yacon. Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson 6 Geographical distribution and centres of diversity Yacon is being grown in many localities scattered throughout the Andes, from Ecuador to northwestern Argentina. In most cases just a few yacon plants are cultivated for family consumption (Fig. 7a). Less frequently yacon is grown as a cash crop to be marketed at the local level (Fig. 7b). Even in this situation, farmers rarely cultivate yacon as the main crop and seldom dedicate a high-proportion of their arable land to it.

Yacon is a rare crop in northwestern Argentina, present only in a few localities in the Salta and Jujuy provinces, where it was reported close to extinction by Zardini (1991). Cultivation was probably more widespread in the past, but at present the number of clones available in the area is reduced to two or three, and at risk of further losses.

While genetic erosion has probably also happened in Bolivia, cultivation of the species is still very common in most Andean departments of the country, Tarija, Chuquisaca, Cochabamba and La Paz. La Paz department, particularly the Camacho and Sud Yungas provinces, is most likely the one with the largest cultivated area and the largest germplasm diversity. However, Cochabamba, Chuquisaca and Tarija departments have been poorly researched up to now and may hold valuable material.

Fig. 7. The different scales of yacon cultivation: small home garden at 2700 m asl, Leon Cancha, Tarija department, Bolivia (a), medium size (large size for Andean standards) yacon parcel at 2000 m, Erquis, Tarija department, Bolivia (b), large size yacon farm at 600 m, Capão Bonito, São Paulo state, Brazil (c).

Promoting the conservation and use of underutilized and neglected crops. 21. 219 Yacon is grown in many localities throughout the Peruvian Sierra. The largest germplasm diversity is found in southeastern Peru, in the valleys around Cusco and east of Puno. Another region of diversity and widespread cultivation is located in northern Peru, particularly the province of Cajamarca and the area close to the Ecuadorian border.

Within Ecuador, yacon is predominantly grown in the southern provinces of Loja, Azuay and Cañar. The crop is also present in the central highland provinces, such as in Bolivar and Chimborazo and in the north of the country, namely in Pichincha, Imbabura and Carchi.

Cultivation of yacon in Venezuela and Colombia has been reported in the literature (National Research Council 1989; Zardini 1991; Rea 1992). In his monograph Wells (1965) indicates its presence in Cauca, Colombia, presumably because he studied specimens from that region. Three decades ago yacon traditional use appeared to be restricted to the eastern Colombian mountainous range (Patiño 1964, cited in Debouck and Libreros Ferla 1995). However, recent explorations have not confirmed the presence of yacon in Colombia, specifically in Boyaca, Cundinamarca, Huila, Nariño (Dr M. Hermann, 1997, pers. comm.).

A strip stretching along the eastern Andean slopes, from the Apurimac river basin (12ºS) in Peru to the La Paz river basin (17ºS) in Bolivia, encloses the area richest in yacon germplasm. This is also an area where at least three wild Smallanthus species, taxonomically very close to S. sonchifolius, occur spontaneously (S. macroscyphus, S. riparius and S. siegesbeckius). Thus, this area seems to be the most likely ‘origin centre’ of the species (Fig. 8).

In the last three decades yacon cultivation has extended to other continents. There are reports of cultivation in several states of the USA (National Research Council 1989), but not at a significant commercial level. An interesting experience is underway in the North Island of New Zealand, where the crop has reached the supermarkets as a specialty vegetable (Grau 1993). From New Zealand yacon has been introduced into Japan, where approximately 10 ha are being grown by several small farmers (Dr K. Ishiki, 1997, pers. comm.). From Japan it was distributed to Korea and Brazil. In Brazil the crop is being cultivated commercially in São Paulo state. The crop has apparently failed in the Czech Republic (Matejka 1994) and it is likely to fail in most of Central Europe because of the long winter period.

Provinces in Argentina and Ecuador are formally equivalent to departments in Bolivia and regions in Peru (where they replaced departments in 1987). They are the main political divisions of the state.

Departments in Bolivia and regions in Peru are subdivided into provinces.

Yacon. Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson

–  –  –

Fig. 8. Yacon distribution in the Andean region. Doubtful presence in Colombia at present is indicated by a question mark.

Promoting the conservation and use of underutilized and neglected crops. 21.

7 Properties and uses of the species

7.1 Chemical composition Several carbohydrates are stored in the roots of yacon: fructose, glucose, sucrose, low polymerization degree (DP) oligosaccharides (DP 3 to 10 fructans), and traces of starch and inulin (Asami et al. 1989; Ohyama et al. 1990). Inulin, a high-DP oligofructan with DP of about 35, is a main storage compound in many plants of the Compositae family, such as Helianthus tuberosus and Dahlia sp. However, in yacon inulin appears to be only a minor component. On the contrary, oligofructans with a lower DP (average 4.3) may account for up to 67% of the dry matter content at harvest (Asami et al. 1991). Oligosaccharides purified from yacon have been identified as beta-(2 1)-fructooligosaccharides with terminal sucrose (inulin type oligofructans; Goto et al. 1995). The relative proportions of oligofructans and monosaccharides fluctuate significantly during the growing cycle and after harvesting (Asami et al. 1991; Fukai et al. 1995), leading to apparently contradictory results. For example a detailed analysis of yacon root carbohydrates has been published by Ohyama et al. (1990) (Table 2) indicating that oligofructans account for just 20%, instead of 67% as reported by Asami et al. (1991). However it is important to note that Ohyama and coworkers used material after more than 3 months in cold storage, while Asami’s team utilized roots immediately after harvest. Unfortunately, a significant amount of information concerning storage sugars in yacon has been published only in Japanese, and it is not intelligible to most readers.





Table 2. Content of soluble carbohydrates in yacon tuberous roots, 96 days after harvest, maintained under cold conditions (Ohyama et al.

1990)

–  –  –

GFn= fructosylsucrose; n indicates depolymerization degree.

Yacon. Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson Besides storage carbohydrates, the tuberous roots contain small amounts of fiber, vitamins and minerals (Table 3). Interesting protein levels have been reported for stems (11% DW) and leaves (17% DW) (Calvino 1940).

Table 3. Chemical composition of yacon roots (summarized from Lizárraga et al.

(1997), a compilation from different sources)

–  –  –

7.2 Uses In the local markets of the Andes yacon is classified as a fruit and sold together with chirimoyas, apples, avocados, pineapples, etc. and not with potatoes, oca, ulluco or mashua (Tropaeolum tuberosum), as a foreign observer would expect.

Yacon tuberous roots possess an agreeable sweet flavour, an attractive crunchiness and are commonly eaten raw, usually after a period of exposure to the sun. The drying time varies from site to site, being shorter in the dry inter-Andean valley than in the cloud forest region. This procedure, called ckochascca (Herrera 1943), increases the sweetness of the roots, and they are considered ready for consumption when the skin is slightly wrinkled. They are eaten peeled, as the skin has a somewhat resinous taste, and they are particularly tasty chopped up in fruit salads mixed with bananas, oranges, pawpaws, etc. Tuberous roots also can be stewed, retaining in part their crispiness, or grated and squeezed through a cloth to obtain a sweet refreshing drink.

In an extended area from Peru to northwestern Argentina yacon is consumed particularly during the ‘Corpus Christi’ festival, which displaced the K’apac Raymi Promoting the conservation and use of underutilized and neglected crops. 21. 223 feast of Inca times (Cárdenas 1969). In Ecuador, yacon roots are especially consumed during the ‘Todos los Santos’ and ‘Day of the Dead’ festivals (National Research Council 1989). These current practices may indicate old religious values, modified after the advent of the Catholic religion.

In Bolivia yacon is commonly consumed by diabetics and persons suffering from digestive problems. Properties to treat kidney problems and skin-rejuvenating activity also have been mentioned. Medicinal (antidiabetic) properties have been attributed to yacon leaves (Kakihara et al. 1996) in Brazil, where the dried leaves are used to prepare a medicinal tea. Dried yacon leaves are used in Japan, mixed with common tea leaves. Hypoglycemic activity has been demonstrated in the water extract of dried yacon leaves, feeding rats with induced diabetes (Volpato et al. 1997).

Yacon can be processed in different ways. The juice obtained from pressing the tuberous roots can be boiled and concentrated to produce solid dark-brown blocks called chancaca (National Research Council 1989), similar to the product obtained from concentrating sugarcane juice. The juice also can be concentrated at low pressure, with the addition of sodium bisulphate to inhibit enzymatic darkening.

The final product is a dense syrup similar to sugarcane syrup but with significantly lower energy value for humans (Chaquilla 1997). Another promising processing technique is the production of dry chips. In this case yacon tuberous roots are peeled and cut in thin slices. The slices are first dried in a plastic tunnel, then oven-dried at 60°C (Kakihara et al. 1996). Dried yacon chips can be stored indefinitely.

Yacon pulp can be preserved after heating at 89°C for 10 minutes and washing with sodium bisulphate (0.5%) for 5 minutes, by adding potassium sulfate (0.l%), ascorbic acid (0.3%) and adjusting the pH to 4.5. The heated and washed material can also be added to sugar syrup and made into ‘glacé’ fruit. Yacon pickles are produced and marketed in Japan (Dr K. Ishiki, 1997, pers. comm.).

All yacon carbohydrates including oligofructans can be rapidly metabolized by ruminants, so tuberous roots can be used to feed cattle or sheep. The foliage, with a protein content of 11-17% (dry weight basis) has been suggested as forage (National Research Council 1989). However, there is no experimental information on the subject. Terpenoid lactones produced by epidermal glands may affect the palatability of the foliage.

224 Yacon. Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson 8 Genetic resources

8.1 Genetic variation Although yacon is a clonal crop, there is some morphological and physiological variation. However, this variation may reflect to some extent the phenotypic plasticity expressed in the contrasting environments where it is grown rather than genetic variation. Dr M. Hermann (1997, pers. comm.) found it very difficult to differentiate yacon clones from a wide geographical range, from Ecuador to Argentina, when they were grown in the same environment.

Even if the traits available can be exploited, yacon could gain significant variation by incorporation of genes from its wild relatives. Thicker root bark, looser storage root arrangement (which would reduce deforming pressures), reduced sweetness (which may indicate higher oligofructans level) and tuberous roots with sprouting capacity that could be used as propagules are some of the traits that could be incorporated from wild relatives.

A number of morphological descriptors have been proposed by Seminario (1995a). The variation of characters of potential breeding value is presented below.

Morphological characteristics: erect and semi-erect plant type; internode length (8-25 cm); stem colour (purple, green, pale green); stem and leaf pubescence (dense, medium); number of flowerheads (0-70); colour (pale yellow, yellow, orange); shape and teeth number (2-3) of the corolla; root grouping (compact, lax); root shape; root skin colour (white, cream, pink, purple, brown); root flesh colour (white, cream, white with purple striation, purple, pink and yellow); number of tuberous roots per plant (5-40); root size (6-25 cm length).

Physiological characteristics: flowering habit and duration (6-9 months until flowering); tuberous root yield (1-15 kg/plant) and quality; dry matter content (10-30%); oligofructan content; reducing sugar content; changes in sugar patterns during post-harvest period.

8.2 Geographical distribution of important traits Considerable variability for tuberous roots yield has been found by Castillo et al.

(1988) in Ecuador (30-73 t/ha), Seminario (1995b) in northern Peru (1.5-9.5 kg/plant) and Lizárraga et al. (1997) in southern Peru (l.7 to 3.3 kg/plant).

Variability for flesh colour is higher in southern Peru (Meza 1995; Lizárraga et al. 1997) and northern Bolivia, where clones with white, cream, yellow and purple flesh can be found, than in Ecuador or southern Bolivia and northwestern Argentina, where only white and yellow clones have been reported.

8.3 Importance of wild relatives as a source of diversity The possibility that some of the wild relatives may have contributed to the yacon genome makes them good candidates for future breeding attempts, as part of introgression programmes. However, wild Smallanthus species are still poorly Promoting the conservation and use of underutilized and neglected crops. 21. 225 known and only a few potential useful traits that could be introduced into yacon have been mentioned in Section 8.1.

8.4 Institutions holding germplasm Systematic collecting of yacon germplasm began in the 1980s, sponsored by the IBPGR.

It focused mainly on crops of global importance such as potato. However, some work was diverted to secondary crops such as the other Andean tubers and yacon. The collecting effort lasted about 5 years and concentrated on Ecuador and Peru.



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