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Sperling, C.R. and S.R. King. 1990. Andean tuber crops: Worldwide potential. p. 428-435. In: J. Janick and J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.

Andean Tuber Crops: Worldwide Potential

Calvin R. Sperling and Steven R. King

  1. INTRODUCTION
    1. The Andean Crop Complex
    2. Description
    3. Pre-history
    4. Current Distribution
  2. AGRICULTURAL REQUIREMENTS
    1. Environment and Habitat
    2. Cultural Practices
    3. Cropping Cycle
    4. Diseases
    5. Yields
  3. NUTRITIONAL VALUE
    1. Comparative Nutritional Value
    2. Secondary Compounds
  4. GERMPLASM
    1. International Collections
    2. Diversity
  5. POTENTIAL
  6. SUMMARY
  7. REFERENCES
  8. Table 1
  9. Table 2
  10. Fig. 1
  11. Fig. 2
  12. Fig. 3
  13. Fig. 4
  14. Fig. 5
  15. Fig. 6
  16. Fig. 7
  17. Fig. 8
  18. Fig. 9
  19. Fig. 10
  20. Fig. 11

INTRODUCTION

The Andean region of South America is one of the eight centers of diversity of cultivated plants described by Vavilov (1951) and has recently become recognized as an important area for minor-crop development and germplasm conservation (IBPGR 1982). There is also strong evidence that the southern Peruvian Andes is one of the four areas of the world where the independent invention of agriculture took place (Hawkes 1983).

The potato has been the subject of international crop development and is now commonly grown throughout the world. There are, however, many other important food crops that were domesticated in the Andes but that are poorly known scientifically. The subject of this paper is three of these crops: Ullucus tuberosus Caldas (Basellaceae, Fig. 1, 2); Oxalis tuberosa Mol. (Oxalidaceae, Fig. 3, 4); and Tropaeolum tuberosum R. & P. (Tropaeolaceae, Fig. 5, 6). Each of these crops is a potential new crop for other areas of the world.

The Andean Crop Complex

Numerous other root and tuber crops have been domesticated in the Andes; Arracacia xanthorriza Bancr. (Apiaceae), Canna edulis Ker-Gawl. (Cannaceae), Lepidium meyenii Walp. (Brassicaceae), Mirabilis expanse R & P (Nyctaginaceae) and Polymnia sonchifolia Poepp. & Endl. (Asteraceae). No discussion of Andean crop resources would be complete without mentioning the global potential of these and other crops that are part of the agricultural heritage of the Andean region. Other important crops include the high protein pseudograins, Chenopodium quinoa Willd. (Chenopodiaceae), C. pallidicaule Heller, and a high protein legume, Lupinus mutabilis Sweet (Fabaceae). As a group, these tuber, grain legume and other crops have been among the primary food sources in the highland Andean region for centuries. A National Academy of Sciences report on Andean crops has presented general information on these and other crops (NRC 1989).

Description

These herbaceous crops are all annually propagated for their starchy tubers. Tubers are produced below ground on axillary stolons which enlarge to form terminal tubers. Ullucus tuberosus, ("Ullucu" or "lisas"), produces smooth spherical tubers 2-10 cm across or curved and elongate to 25 cm long. Oxalis tuberosus ("Oca") and Tropaeolum tuberosum ("Mashua" or "Añu") despite being in different botanical families bear many morphological similarities. Both produce elongate tubers slightly roughened from the enlarged scale leaves.

Pre-history

Sources for dating the presence and importance of Andean tubers include illustrations on wooden vessels (keros), ceramic urns, and sculptures. Images of Oxalis tuberosa and Ullucus tuberosus have been documented on keros from the early post-conquest era in Southern Peru (Vargas 1981). A "pacheco" urn dated to 950 (before present) BP from the central Peruvian highlands is decorated with paintings of all three of these tubers (Yacovleff and Herrera 1934, Sperling 1987). Botanical material from several coastal Peruvian archaeological sites has also been identified as containing starch grains, vessels and xylem elements of all three of the crops discussed in this paper (Martins 1976). Evidence of Oxalis tuberosa and Ullucus tuberosus dating to ±4,250-4,050 BP has been recorded in the dry coastal dessert of Peru (Martins 1976). One highland archaeological site, Tres Ventanas at 3,925 m has yielded material of Ullucus tuberosus reputed to be from a time period 10,000 years BP (Engel 1970).

Current Distribution

These three crops are cultivated in the Andean region from Venezuela to Argentina (Fig. 7). Outside of the Andean region Oxalis tuberosa is cultivated commercially in Mexico and New Zealand (Fig. 8). Compared to potatoes, which are now cultivated in 130 countries around the world, these tubers are essentially still unknown outside of the Andean region. The crop characteristics that have, up to now, caused this limited distribution will be examined below.

AGRICULTURAL REQUIREMENTS

As with most tuber crops, all three Andean tuber crops discussed here are propagated vegetatively. Whole tubers are selected from storage for annual planting. No effort is made to select larger or more vigorous appearing tubers. In fact, smaller tubers are preferred for planting in Peru as they are less valuable for food.

As these tuber crops have been vegetatively propagated from thousands of years there has been little selection pressure for sexual seed production, a common pattern in most vegetative crops. Seed production is uncommon in two of these tubers. Ullucus tuberosus and Oxalis tuberosa. Ullucus tuberosus was long thought to be have been a completely sterile plant. However, fruit production has recently been independently documented (Rousi et al. 1986, 1988; Sperling 1987) and germination has been observed for some true seed (Rousi et al. 1988). True viable seed has only recently been documented in Oxalis tuberosa (Gibbs et al. 1978) while Tropaeolum tuberosum is known to occasionally produce fruits with viable seed (J. Rea pers. commun.).

Environment and Habitat

All three tuber crops are adapted to high Andean altitudes of 2,400-4,000 m (4,200) where introduced Old World crops are not well adapted. The few other crops found at the upper attitudinal limits of agriculture in the Andes are bitter potatoes, (Solanum spp.) "maca" (Lepidium meyenii) and barley. The high altitude Andean ecosystem is typified by steep terrain, strong winds, shallow soil and bare rock surfaces with high water run-off. Low minimum temperatures and large ranges in diurnal temperatures impose severe stress on plants.

Cultural Practices

Cultural practices for all three tubers are similar to potatoes. Planting is done in rows or hills 80-100 cm apart with plants spaced 40-60 cm apart in the rows (Rea 1975). Most planting and harvest is by hand, with mechanization rare or unknown. Monoculture predominates, but interplanting of several tuber species in one field is common. In many instances Andean farmers will allow a mixture containing two or three tuber crops to be planted in one field. Often this mixture consists of several different clones of each species. Such mixed fields may later be sorted into tuber types during harvest or before cooking. Mixed planting with legumes or grain crops is occasionally practiced.

Cropping Cycle

The length of cropping cycle is quite variable from the northern to southern Andes. In Colombia, planting takes place from March to August followed by harvest 180-360 days later. In Equador, planting starts in December in some areas and may continue until July depending on local climate. In Peru, tubers are most commonly planted in November and harvested in June. Irrigation is practiced in some areas. The variation in cropping cycle reflects not only the different climatic and day length regimes of the Andes, but also the variation between different clones of each species.

All three crops are short day length plants. Ullucus tuberosus requires 11-13.5 hours of day length for stolon formation and tuberization (Razumov 1931; Sperling 1987). Tubers fail to form under longer days. In each species tubers are borne on axillary stolons produced below, or rarely above ground which are positively geotropic and enlarge into terminal tubers underground.

Diseases

Andean farmers report that few pests or diseases bother these crops. However, viruses can be a problem as in many clonally propagated crops. Ullucus tuberosus may contain complexes of three or four viruses. These viruses are identified as a potevirus (PMV/U, a tobamovirus (TMV/U) a polyvirus, (Ullucus mosaic virus, UMV), and a newly recognized comovirus (Ullucus virus C) (Brunt et al. 1982b). All four viruses have been experimentally eliminated from Ullucus tuberosus using meristem-tip culture and chemotherapy (Stone 1982). Eliminating viruses dramatically increases plant vigor and yield (Stone 1982). Further research on this topic is needed. Material exchanged internationally will have to be disease free.

Yields

Yields vary with the cultural method but are similar for all three species with Ullucus tuberosus and Oxalis tuberosa producing about 7-10 tons/hectare. In Peru, Ullucus tuberosus and Oxalis tuberosa are each planted on 15,000 hectares annually (King 1987). Annual production figures are difficult to determine as much of the crop is cultivated in small fields in remote areas.

Nearly all production is for fresh market consumption. Traditional dishes, especially soups and stews are prepared from all three tubers. Ullucus tuberosus has a smooth, somewhat mucilaginous taste, similar to okra and makes excellent soups. Oxalis tuberosa, has a sweet acid flavor. A very small portion of the Ullucus tuberosus crop is canned and exported to major cities of the United States (see Fig. 9). One of the important factors for people within and outside the Andean region is the nutritional value of the crops.

NUTRITIONAL VALUE

Nutritional analysis of these tubers has shown that there is great variation in both the quantity and quality of protein within and between cultivars of the three species (King and Gershoff 1987). Clearly much variability exists in the protein content of these species. Recently conducted amino acid profiles of these three species has revealed that they contain a good balance of essential amino acids, with the limiting amino acids being valine and tryptophan (King 1988).

Comparative Nutritional Value

In Table 1 the mean proximate nutritional value of these three crops and several other root and tuber crops utilized around the world are compared. These data show that Ullucus tuberosus compares favorably to Ipomea batatas (sweet potato), and Manihot esculenta (cassava) in protein content Oxalis tuberosa is nearly equal to Solanum tuberosum (potato) and is superior in caloric value to Dioscorea spp. (true yams). The nutritional value of these Andean tuber crops then is good when compared with staple root and tuber crops eaten around the world.

Secondary Compounds

Each of the three species has been found to contain low levels of secondary compounds. Ullucus tuberosus, contains saponin (Hegnauer 1964), Oxalis tuberosa contains oxalic acid (King 1988) and Tropaeolum tuberosum contains a mustard oil, p-methoxybenzyl isothiocyanate, which has been used in Andean ethnomedicine (Johns and Towers 1981). The compound of concern to human nutrition is oxalic acid. The level of oxalic acid in Andean, Mexican and New Zealand cultivars of Oxalis tuberosa has been shown to vary between 1.2 to 51.3 mg/100 gram fresh material (King 1988). Even at the higher levels the oxalic acid content does not pose a threat to human health unless a persons diet consisted of 100% Oxalis tuberosa. Potatoes contain 2-7 mg/100 g fresh weight of oxalic acid and spinach (Spinacia oleracea) contains 356 to 780 mg/100 g fresh material.

GERMPLASM

International Collections

In recent years there have been several germplasm collecting expeditions in Ecuador, Peru and Bolivia. Germplasm of all three of these species is now being stored and evaluated in germplasm banks in Ecuador and Peru (Fig. 10). The current number of accessions for each species is listed in Table 2.

The Ecuadorian germplasm collection is maintained and evaluated at the Instituto Nacional de Investigaciones Agropecuarias (INIAP), Santa Catalina research station. The largest number of germplasm accessions is in Peru, with a total of five ex-situ germplasm banks located in Cajamarca, Huancayo, Ayacucho, Cuzco and Puno. These five germplasm banks are coordinated through the Proyecto Investigacion de sistemas Agropecuarias Andinos (PISA). In Peru, there is also a collection of all three species at the University of San Marcos laboratory of genetic resources and biotechnology This duplicate collection from Peruvian germplasm banks is maintained in-vitro. The primary aim of this group is to eliminate viruses from the three species.

Finnish researchers at the University of Turku have also collected germplasm of Ullucus tuberosus in Ecuador, Peru and Bolivia which is being used for research on variation patterns in this species (Rousi et al. 1986). There are no other known germplasm banks for the two to three cultivars of Oxalis tuberosa cultivated in Mexico and New Zealand. Mexican farmers, with only limited genetic diversity available, have expressed interest in testing some of the numerous cultivars from the Andean zone.

Oxalis tuberosa is the most well represented of the crops, 1205 accessions being maintained in six germplasm banks in Ecuador and Peru (King 1988). The next largest in number of accessions is Ullucus tuberosus, followed by Tropaeolum tuberosum.

Diversity

The large number of germplasm accessions of these three species is likely to contain much duplication. Research on the biochemical differentiation of these accessions is being developed for application to the large number of accessions of Oxalis tuberosa (Stegemann et al. 1988).

There is, however, a high degree of intraspecific diversity within all three of these species and agronomic characterization of these cultivars is being conducted at germplasm banks in Ecuador and Peru. In addition, The International Board for Plant Genetic Resources (IBPGR) is currently supporting a scientist to assist in the efforts to distinguish genotypes and characterize the collections.

POTENTIAL

Traditionally all three crops have been confined to their naive Andean home. Attempts were made to introduce them into Europe during the early part of the 19th century but these were largely unsuccessful the plants remaining little more than curiosities. Recently, there has been an effort to select adapted clones for trial in other regions of the World. These efforts are aimed at increasing the crop options available to farmers, increasing diversity of food sources and developing crops for marginal growing regions. Suitable areas include high altitude regions in low latitudes and oceanic or insular climates with long cool growing seasons. Possibilities also exist for treating these tubers as winter crops in mild climates of the southern and northern hemispheres. The success of introduction efforts will depend partly on careful selection of germplasm adapted to specific environments. The requirement of short days for tuber formation may limit potential production areas. The existing variation of different clones in response to day length gives promise that new cultivars adapted to long days or day neutral clones might be selected. Currently, these tubers are under trial in Nepal for growing in the Himalayas. With limited protection Ullucus tuberosus can produce a crop of tubers at Turku, Finland.

Production of true seed will be necessary for breeding. Given the occurrence of occasional fruit production in each of these species the probability of identifying mechanisms for seed failure is likely Cytological studies of Ullucus tuberosus indicate that abnormal meiosis resulting in incomplete microsporocyte formation may account for the rarity of seed formation (Sperling 1987).

Additional exploration and germplasm collection should be undertaken, particularly at the southernmost portion of cultivation where clones adapted to longer day are more likely to be found. Exploration should occur in Argentina and Chile as the Andean tuber complex is reported from the island of Chilöe. In order to investigate seed biology, accessions should be obtained for each wild progenitor, especially for Ullucus tuberosus Caldas subsp. aborigineus (Brücher) Sperling (Fig. 11).

The Andean potato was originally adapted to the same environment and had the same day length requirements as these three tubers. Given the success of the potato, there is a strong possibility of successfully introducing these three tubers in new growing regions.

SUMMARY

These three Andean tuber crops have been cultivated in the Andean region for centuries and they continue to be an important food crop in Colombia, Ecuador, Peru and Bolivia today. They are a good source of nutrition and have strong aesthetic appeal due to their wide degree of variation in form and color. A large degree of the diversity of these species has been collected and is available for research and breeding. One of the species, Oxalis tuberosa, has spread to Mexico and New Zealand where it is marketed and consumed in numerous dishes. Another, Ullucus tuberosus, is now canned in Peru and exported to many major United States cities.

Much research remains to be done. Germplasm with traits to overcome day length sensitivity needs to be sought through exploration in the southern extremes of it cultivated range. Wild forms which produce true sexual seed should also be sought for breeding programs. Simple methods for eliminating viruses need to be established and viral free material made available to agronomists and breeders worldwide.

There is great potential for introducing these crops as new crops for other areas of the world. The increased acceptance of new food products, continually expanding demands of the United States produce markets and increased agricultural interest in alternative crops suggests a greater demand and market for these new crops. Finally, with increased international research attention the production and use of these crops in their native Andean range could also be improved, providing much needed food for increasing Andean populations.

REFERENCES

Table 1. Comparative proximate nutritional values for Andean Oxalis tuberosa, Tropaeolum tuberosum, Ullucus tuberosus and other major crops (per 100 g fresh weight edible portion).

Species Protein (g) Moisture (%) Fat (g) Ash (g) Crude fiber (g) Carbohydrate (g) Calories (kcal)
Dioscorea spp. (Yam) 2.2 72.0 0.2 1.0 4.1 24.2 72.0
Ipomea batatas (Sweet potato) 1.4 70.2 0.4 0.8 2.5 27.4 116.0
Manihot esculenta (Cassava) 1.1 62.6 0.3 0.9 5.2 35.2 145.0
Oxalis tuberosa (Oca)z 0.9 79.0 0.2 0.4 0.8 18.5 79.7
Solanum tuberosum (Potato) 2.1 78.0 0.1 1.0 2.1 18.5 80.0
Tropaeolum tuberosum (Mashua)z 1.5 87.0 0.1 0.5 0.8 9.7 45.7
Ullucus tuberosus (Ullucu)z 1.9 85.6 0.1 0.6 0.7 10.9 52.5
zThe data presented for these species are mean values from Colombia, Peru and Bolivia. Values for other crops are from Woolfe (1987).

Table 2. Germplasm accessions in Andean gene banks.

No. accessions
Species Ecuadorz Peruy
Oxalis tuberosa 135 1050
Tropaeolum tuberosum 49 233
Ullucus tuberosus 156 255
zFrom Castillo, et al. 1988.
yFrom Tapia and Mateo, in press.

Fig. 1. Ullucus tuberosus in Tulcan, Ecuador. Plant habit.

Fig. 2. Ullucus tuberosus in Ayacucho, Peru. Variation in tuber morphology.

Fig. 3. Oxalis tuberosa with flowers, Chinchero, Peru.

Fig. 4. Tuber variation of Oxalis tuberosa from market in Pasto, Colombia.

Fig. 5. Commercial field of Tropaeolum tuberosum during harvest near Tunja, Colombia.

Fig. 6. Tuber variation in Tropaeolum tuberosum in Chinchero, Peru.

Fig. 7. Distribution map of the three species in the Andean zone.

Fig. 8. New Zealand Yam, Oxalis tuberosa, for sale in wholesale market in Auckland, New Zealand.

Fig. 9. Imported Ullucus tuberosus, sold in New York markets and several other U.S. cites.

Fig. 10. Ex-situ germplasm bank of the three species in Puno, Peru.

Fig. 11. Wild Ullucus tuberosus subsp. aborigineus in Sorata, Bolivia.

Last update September 4, 1997 by aw