«Andean roots and tubers: Ahipa, arracacha, maca and yacon M. Hermann and J. Heller, editors Promoting the conservation and use of underutilized and ...»
(1997), in that region field preparation begins with tree-cutting and land-clearing (roce), usually in June-July. The material is left to dry, then placed in rows and burned in during August. The material not burned (branches, stems) is taken out of the field (manq’opeo). From the beginning of September until the end of November, depending on rainfall, the yacon offsets are planted manually. Planting distance varies: 70cm between rows and 60-80 cm between plants.
In northern Bolivia traditional cultivation begins with the preparation of ploughed maize or potato fields, where the offsets are planted in furrows (Rea 1992).
Rows are cultivated and earthed-up during the growing season. Where irrigation is available, planting can be done throughout the year.
In São Paulo, Brazil, yacon offsets are placed in furrows, 1 m wide and 30-40 cm high, at a depth of 15 cm, 90-140 cm apart (Kakihara et al. 1996). Soil pH, normally around 4.0 in these lateritic soils, is modified to 6.0 with the addition of dolomite.
Management includes fertilization with N-P-K plus Zn (4-14-8 at 2000 kg/ha) and ammonium sulphate (200 kg/ha), and irrigation by aspersion.
11.3 Pests and diseases In cloud forest areas, like the Cusco region, Peru, yacon crops are affected by a wide range of insects. However, natural control agents are present and effective (Lizárraga et al. 1997). Pest pressure is much lower in the dry intermontane valleys. In any case, control measures are not commonly used in the Andes. Table 5 lists some of the species associated with yacon.
A few bacteria and fungi have been cited affecting the underground organs and stems of yacon. Fusarium in Peru (Lizárraga et al. 1997) and Erwinia chrysanthemi in Japan (Mizuno et al. 1993) have been identified as causal factors of wilting, while an unidentified rot affects the xylem of stems in Bolivia. Sclerotinia causes soft rot of the tuberous roots in Peru (Lizárraga et al. 1997). Alternaria has been found producing marginal necrosis of the leaves in Ayacucho, Peru (Barrantes 1988).
Promoting the conservation and use of underutilized and neglected crops, 21. 233 Table 5. Yacon pests
Few studies are available on viruses affecting yacon. There is a report indicating that yacon is free of several common tuber viruses, including those affecting potato (potato leaf-roll, X, Y, S, M; National Research Council 1989). However, clonal decline (cansancio = fatigue) and the need to ‘rejuvenate’ the ‘seed’ have been reported by farmers in the La Paz region, a phenomenon that strongly suggests viral infection.
Kuroda and Ishihara (1993) indicated that cucumber mosaic cucumovirus infected yacon under field conditions, yielding less vigorous plantlets in vitro.
Agoutis, rodents of the genus Dasiprocta, have been mentioned attacking yacon tuberous roots in the La Paz region, Bolivia.
Yacon, being a perennial plant, has been suggested as a crop adequate to reduce soil erosion in steep slope areas of the Andes. Yacon leaves tolerate partial shading, a trait that could be used with advantage in agroforestry systems. These two traits warrant a more detailed study, as they can be critical in many regions of the Andes.
Yacon may have been associated with slash-and-burn agriculture since prehistoric times. In modern times, however, population pressure and land scarcity make this strategy unsustainable in many areas. Therefore, it would be critical to develop sound agroforestry systems where yacon could fit as a stabilizing component.
11.4 Harvesting and post-harvest handling Roots reach maturity in 6-7 months in the medium-altitude sites and up to a year in high sites. Storage roots are very brittle when turgid and the plant must be dug carefully to prevent breaking them. Tuberous roots are usually dug and separated Yacon. Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson manually from the crown. Mechanical potato harvesters have been successfully employed in Brazil (Kakihara et al. 1996).
For consumption the roots are exposed to sunlight for a few days to increase their sweetness. This procedure leads to the partial hydrolysis of oligofructans, yielding larger amounts of reducing sugars (fructose, glucose and sucrose). Table 6 shows the changes in reducing sugars and non-reducing sugars.
For long-term storage the roots are placed in a dark, dry, cool room. Under these conditions yacon roots can be kept for several months. Virtually no changes have been observed in the relative amounts of sugars in yacon tuberous roots stored at 4°C (Table 7).
Metabolic activity of harvested yacon tuberous roots is low, similar to potatoes and lower than oca (Oxalis tuberosa) and mashua (Tropaeolum tuberosum) (Table 8).
11.5 Yields A very interesting trait of yacon is its high productivity. Table 9 summarizes some data available on yacon fresh matter yield. Dry matter varies from 15 to 30% of fresh weight. More detailed information concerning dry matter productivity is required to assess accurately its potential for processing and industrial purposes.
Table 9. Maximum yacon productivity obtained in different environments
12 Limitations While in some situations they can affect yields in the Andean region, none of the pests and diseases mentioned in Section 11.3 appears to be decisive in limiting yacon production. Yacon’s progressive disappearance from many areas seems to be more dependent on its intrinsic characteristics, cultural change and market factors. As a limited source of energy, yacon does not play a vital role in subsistence agriculture, and priority is probably given to crops that are essential in the diet. As a rather unusual sort of ‘fruit’, yacon is always in danger of being displaced by conventional fruits, especially when they are associated with ‘westernizing’ cultural changes.
Local Andean markets are not organized adequately to promote yacon qualities and to present it in a stimulating form to the customers. Unlike other, colourful Andean tubers (e.g. oca, ulluco), yacon’s comparatively dull aspect may be a deterrent to anyone who does not have a strong cultural attachment to it.
If yacon were to increase its importance as a crop, several agronomic aspects may pose limitations.
• Viral infections are the likely cause of ‘seed decline’, an issue that may require the development of virus-free propagation material schemes.
• Fungal and bacterial rot and wilt problems under field conditions.
• Splitting and cracking of the tuberous roots before harvest is a problem under certain environmental conditions. Irrigation management is a critical aspect to be addressed to avoid this problem.
• Tuberous roots are easily affected by physical damage during harvest and postharvest handling, and the wounds can easily lead to fungal or bacterial rot during storage.
Promoting the conservation and use of underutilized and neglected crops. 21. 237 13 Prospects
13.1 Advantages of yacon Yacon possesses an attractive set of features advantageous to producers, processors, consumers and the environment.
• High fresh weight productivity
• Adaptability to a wide range of climates and soils
• Potential good fit in agroforestry systems
• Erosion control
• Potential use as a forage for both underground and aerial parts
• Wide range of processing alternatives
• Good post-harvest life, if managed properly
• Exceptional qualities for low-calorie diets
• Medicinal properties.
13.2 Development objectives Yacon has been suggested as an industrial crop, particularly as a source of sugar syrup (National Research Council 1989). Yacon productivity is much higher than that of topinambur, an older source of inulin and a potential competitor. It is tempting to speculate about yacon being transformed into a modern industrial crop with the application of modern agronomic technology, fertilization, genetic engineering, etc.
However it is yet to be seen if yacon could compete with other established starch and sugar crops, which are being subjected to enormous breeding efforts, in an age when many of them are still heavily subsidized. Even if a strategy like this succeeds, it is unlikely that the Andean region would benefit much from it. In general, Andean ecosystems pose severe limitations to large-scale industrial crops.
Less spectacular but more attractive may be the further development of yacon as what it already is, a specialty and health food. Urban populations are increasing in the Andean countries and urban inhabitants are the ones who could require the sort of food properties that yacon can provide. Small- or medium-scale Andean systems that emphasize low input, environmentally friendly and organic production of yacon could compete advantageously with large-scale and probably higheryielding crops in other regions.
238 Yacon. Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson 14 Research needs Compared with most other Andean root and tubers, yacon knowledge is rather limited and many fundamental aspects of its biology and agronomy are virtually
unknown. As a first approach, several specific courses of action can be proposed:
Field collecting, conservation and evaluation of local clones should continue.
Field collecting of wild Smallanthus species/wild yacon.
Chromosomic and molecular analysis of the different yacon accessions/morphotypes in order to clarify their relationships.
Taxonomic and phylogenetic studies of the genus Smallanthus in South America using conventional morphological, numerical systematic, chromosomic and molecular analysis in order to clarify the relationships between the different wild species and yacon.
Artificial crossing between different clones of yacon and different species of Smallanthus.
Breeding interspecific hybrids to increase variation.
Physiological analysis of tuberous root formation and development, propagation material and dormancy.
Physiological analysis of pollen viability and longevity.
Physiological analysis of seed viability, germination, dormancy and longevity.
Evaluation of pests and diseases and the resistance/tolerance present in different clones.
Development of IPM and organic management systems for yacon. While pest pressure appears to be low at present, this may rapidly change if there is an increase in the cultivated area.
Study traditional yacon farming systems as models of organic management.
Experiment with yacon in agroforestry systems and polycultures.
Evaluation of the aerial parts as forage.
Development and evaluation of post-harvest technologies, particularly for small farmers.
Development and evaluation of different processing technologies.
Development of standardized techniques for quantitative estimation of oligofructans.
Biochemical and nutritional/medicinal studies Evaluation of the medicinal properties of the leaves.
Promoting the conservation and use of underutilized and neglected crops. 21. 239 References Arbizu, C. and E. Robles. 1986. La colección de raíces y tubérculos andinos de la Universidad de Huamanga. V Congreso International de Sistemas Agropecuarios Andinos. Anales - INIPA - UNA - Puno.
Asami, T., M. Kubota, K. Minamisawa and T. Tsukihashi. 1989. Chemical composition of yacon, a new root crop from the Andean Highlands. Jpn. J. Soil Sci. Plant Nutr.
Asami, T., K. Minamisawa, T. Tsuchiya, K. Kano, I. Hori, T. Ohyama, M. Kubota and T.
Tsukihashi. 1991. Fluctuations of oligofructan contents in tubers of yacon (Polymnia sonchifolia) during growth and storage. Jpn. J. Soil Sci. Plant Nutr. 62:621-627.
Barrantes del Aguila, F. 1988. Enfermedades de cultivos andinos en Ayacucho, Peru. IV Congreso Internacional de Cultivos Andinos. Memorias INIAP-Quito.
Barrantes, F. and G. De La Cruz. 1988. Caracterización de la epidermis foliar en cultivos andinos. IV Congreso International de Cultivos Andinos. Memorias INIAP-Quito.
Blake, S.F. 1917. Polymnia uvedalia and its varieties. Rhodora 19:46-48.
Blake, S.F. 1930. Notes on certain type specimens of American Asteraceae in European herbaria. Contrib. to the US Nat. Herbarium 26:227-263.
Brako, L. and J.L. Zarucchi. 1993. Catalogue of the flowering plant and gymnosperms of Peru. Monographs in Systematic Botany from the Missouri Botanical Garden 45:1XI:1-1286.
Brucher, H. 1989. Useful Plants of Neotropical Origin. Springer Verlag, Heidelberg, Berlin New York.
Cabrera, A. L. 1978. Flora de la Provincia de Jujuy, X. Compositae. INTA, Buenos Aires.
Calvino, M. 1940. A new plant Polymnia edulis for forage or alcohol. Industria Saccharifera Italiana (Genova) 33:95-98.
Cárdenas, M. 1969. Manual de plantas económicas de Bolivia. Editorial Los Amigos del Libro. Cochabamba, Bolivia.
Castillo, R., C. Nieto and E. Peralta. 1988. El germoplasma de cultivos andinos en Ecuador.
VI Congreso Latinoamericano de Cultivos Andinos. Memorias INIAP-Quito, Ecuador.
Chaquilla, G. 1997. Obtención de azucar a partir de yacon (Polymnia sonchifolia) y su potencial. IX Congreso Internacional de Cultivos Andinos. Cusco, Perú.
Cobo, B.  1890-1895. Historia del Nuevo Mundo. Ed. Marcos Jiménez de la Espada.
4 vol. Sociedad de Bibliófilos Andaluces, Sevilla.
De Candolle, A.P. 1836. Prodromus Systematis Naturalis Regni Vegetabilis. Vol 5.
Treuttel et Würz, Paris.
De la Cruz G. and J. Jiménez. 1997. Conservación y micropropagación in vitro de Polymnia sonchifolia Poeppig & Endl. IX Congreso internacional de cultivos andinos. Cusco, Perú.
De la Cruz, G. 1995. Informes sobre yacón conservado en invernadero. In Memorias RTADebouck, D.G. and D. Libreros Ferla. 1995. Neotropical montane forests: A fragile home of genetic resources of wild relatives of New World crops. Pp. 561-577 in Biodiversity and Conservation of Neotropical Montane Forests, Proceedings of a Symposium, New York Botanical Garden, 21-26 June 1993 (S.P. Churchill, H. Balslev, E. Forero and J.L. Luteyn, eds.). New York Botanical Garden, New York.
Endt, D. 1992. Growing yacon leaflet. Landsendt, New Zealand.
Estrella, J.E. and J.E. Lazarte. 1994. In vitro propagation of jicama (Polymnia sonchifolia Poppig & Endlicher): a neglected Andean crop. HortSci. 29(4):331.