Oxalis tuberosa
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Oxalis tuberosa is a perennial herbaceous plant that overwinters as underground stem tubers. These tubers are known as uqa in Quechua,<ref>Teofilo Laime Ajacopa, Diccionario Bilingüe Iskay simipi yuyayk'ancha, La Paz, 2007 (Quechua-Spanish dictionary)</ref> oca in Spanish, yams in New Zealand and several other alternative names. The plant was brought into cultivation in the central and southern Andes for its tubers, which are used as a root vegetable. The plant is not known in the wild, but populations of wild Oxalis species that bear smaller tubers are known from four areas of the central Andean region.<ref name="Bradbury">Template:Cite journal</ref> Oca was introduced to Europe in 1830 as a competitor to the potato, and to New Zealand as early as 1860.
In New Zealand, oca has become a popular table vegetable and is called yams (although not a true yam). It is available in various colors, including yellow, orange, pink, apricot, and traditional red.<ref name="National">Template:Cite book</ref>
Cultural significance
Grown primarily by Quechua and Aymara farmers, oca has been a staple of rural Andean diets for centuries.<ref name="cipotato">Template:Cite web</ref> Of all Andean root and tuber crops, oca is currently second only to potato in area planted within the Central Andean region.<ref name="National" /> Oca is essential to local food security because of its role in crop rotations and its high nutritional content.
Diversity
Andean farmers, including the indigenous Quechua and Aymara people, cultivate numerous varieties of oca.<ref>Template:Cite web</ref> Oca diversity may be described with respect to morphological characters, local cultivar names, or molecular markers.
Morphological characters
Oca morphotypes are distinguished by foliar, floral, fruit, stem, and tuber characteristics, as described in the International Plant Genetic Resources Institute's document on oca descriptors.<ref name="IPGRI">IPGRI-CIP. 2001. Descriptores de oca. IPGRI, Rome, Italy; CIP, Lima, Peru.</ref> The morphological diversity of oca tubers, in particular, is astounding. Tubers range from 25 to 150 mm in length by 25 mm in width;<ref>Template:Cite journal</ref> skin and flesh color may be white, cream, yellow, orange, pink, red, and/or purple and distributed in range of patterns.<ref name="IPGRI" /> Template:Anchor
Local cultivar names
Oca-growing communities often name varieties based primarily on tuber morphology<ref name="TerrazasValdivia">Template:Cite journal</ref> and secondarily on flavor.<ref name="Bradbury" /> For example, common names may include ushpa negra (black ash) or puka panti (red Cosmos peucedanifolius). Great inconsistency of nomenclature has been reported within and among communities.<ref name="Ramirez">Template:Cite journal</ref> Template:Anchor
Molecular markers
Numerous studies have additionally described oca diversity through molecular approaches to study protein and genetic variation. Molecular markers, such as allozymes (e.g., del Río, 1999<ref name="delrio">Template:Cite thesis</ref>) and inter-simple sequence repeats (e.g., Pissard et al., 2006<ref name="PissardGhislainBertin">Template:Cite journal</ref>), show oca diversity to be low relative to other crops, probably because of its vegetative mode of propagation. While genetic differentiation corresponds well with folk classification,<ref name="DarwinHarvest">Template:Cite book</ref> cluster analyses indicate that folk cultivars are not perfect clones, but rather genetically heterogeneous groupings.<ref name="PissardGhislainBertin" /><ref name="DarwinHarvest" />
Edibility
Oca is cultivated primarily for its edible stem tuber, but the leaves and young shoots can also be eaten as a green vegetable. Mature stems can be used similarly to rhubarb.<ref>Template:Cite web</ref> Andean communities have various methods to process and prepare tubers, and in Mexico oca is eaten raw with salt, lemon, and hot pepper.<ref name="National" /> The flavor is often slightly tangy, but there is a considerable degree of flavor difference between varieties, and some are not acidic.<ref>Template:Cite web</ref> Texture ranges from crunchy (like a carrot) when raw or undercooked, to starchy or mealy when fully cooked.
Use categories
Oca is fairly high in oxalates, concentrated in the skin.<ref name="Albihn">Template:Cite journal</ref> Significant variation in oxalate concentration exists among varieties, and this variation distinguishes two oca use-categories recognized by Andean farmers.<ref name="Bradbury" />
One use category, sour oca, contains cultivars with high oxalic acid levels.<ref name="Bradbury" /> Farmers process these tubers to form a usable storage product called khaya in Quechua.<ref name="DarwinHarvest" /> Tubers are first soaked in water for approximately one month to prepare khaya. Then they are left outside during hot, sunny days and cold, freezing nights until they become completely dehydrated.<ref>Template:Cite journal</ref><ref name="DarwinHarvest" /> This process is similar to the preparation of chuñu from bitter potatoes. Cultivars in this use category are referred to in Quechua and Aymara as khaya (name of the dried, processed product) or p'usqu (sour/fermented),<ref name="DarwinHarvest" /> and in Aymara as luk’i.<ref name="Bradbury" />
The other use category, sweet oca, contains cultivars with lower oxalic acid levels.<ref name="Bradbury" /> The traditional Andean preparation methods for this use category are also geared towards reducing the oxalate level of the harvested vegetable, but without dehydration. This is done by exposure to sunlight, which decreases the organic acid content and increases the oca's sweet taste. The concentration of oxalates is also reduced in the dehydrated product called khaya (similar to chuño).<ref>Template:Cite journal</ref>
| nutrient per 100 g |
fresh | dried |
|---|---|---|
| Energy | Template:Convert | Template:Convert |
| Water (g) | 84.1 | 15.3 |
| Protein (g) | 1.0 | 4.3 |
| Carbohydrates (g) | 13.3 | 75.4 |
| Ash (g) | 1.0 | 3.9 |
| Calcium (mg) | 2 | 52 |
| Phosphorus (mg) | 36 | 171 |
| Iron (mg) | 1.6 | 9.9 |
| Retinol (μg) | 1 | 0 |
| Riboflavin (mg) | 0.13 | 0.08 |
| Niacin (mg) | 0.43 | 0.85 |
| Vitamin C (mg) | 38.4 | 2.4 |
Once exposed to sunlight, oca can be boiled, baked, or fried. In the Andes it is used in stews and soups, served like potatoes, or can be served as a sweet. Cultivars in this category are referred to in Quechua as wayk'u (boiling), misk'i (sweet/delicious) and in Aymara as q'ini.<ref name="Bradbury" />
Sour oca and sweet oca form distinct genetic clusters based on AFLP data.<ref name="EmshwillerTheim">Template:Cite journal</ref> This suggests the possibility of distinct evolutionary histories for each use-category.
Nutrition
Oca is a source of carbohydrates, dietary minerals, and protein.<ref name="Hermann">Template:Cite thesis</ref><ref name="King">Template:Cite journal</ref> Cultivars vary substantially in nutritional content.<ref name="King" />
Cultivation
Oca is one of the important staple crops of the Andean highlands due to its easy propagation and tolerance for poor soil, high altitude, and harsh climates.<ref name="National" />
Distribution
Oca is planted in the Andean region from Venezuela to Argentina,<ref name="Sperling">Template:Cite book</ref> from 2800 to 4100 meters above sea level.<ref name="DarwinHarvest" /> Its highest abundance and most extraordinary diversity are in central Peru and northern Bolivia, the probable area of its domestication.<ref name="ArbizuTapia">Arbizu, C., and Tapia, M. 1992. Tubérculos andinos. In Cultivos marginados: otra perspectiva de 1492. Edited by J.E. Hernández Bermajo and S. León. FAO, Rome, Italy. pp. 147–161.</ref>
Climate requirements
Oca needs a long growing season and is day length dependent, forming tubers when the day length shortens in autumn (around March in the Andes). In addition, oca requires climates with average temperatures of approximately 10 to 12 °C (ranging between 4 and 17 °C) and average precipitation of 700 to 885 millimeters per year.<ref name="Gonzales">Template:Cite book</ref>
Oca requires short days to form tubers. Outside the tropics, it will not begin to form tubers until approximately the autumn equinox. The plant will die before producing tubers if frosts occur too soon after the autumn equinox.<ref name="National" />
Soil requirements
Oca grows with very low production inputs, generally on plots of marginal soil quality, and tolerates acidities between about pH 5.3 and 7.8.<ref name="National" /> In traditional Andean cropping systems, it is often planted after potato and therefore benefits from persisting nutrients applied to, or leftover from, the potato crop.<ref name="Gonzales" />
Propagation
Oca is usually propagated vegetatively by planting whole tubers.
Propagation by seed is possible but is rarely used in practice.<ref name="National" /> Sexual propagation is complicated by several factors. First, like many other species in the genus Oxalis, oca flowers exhibit tristylous heterostyly and are consequently subject to auto-incompatibility.<ref name="Carrion">Template:Cite journal</ref> Furthermore, on the rare occasion that oca plants do produce fruit, their loculicidal capsules dehisce spontaneously, making it difficult to harvest seed.<ref name="Carrion" /> Oca flowers are pollinated by insects (e.g., genera Apis, Megachile, and Bombus).<ref name="Carrion" />
Cropping factors
Oca tuber seeds are planted in the Andes in August or September and harvested from April to June.<ref name="Gonzales" /> The first flowers bloom around three to four months after planting, and the tubers also begin to form.<ref name="Carrion" /> Between planting and harvesting, the oca crop requires little tending, except for a couple of weedings and hillings.<ref name="Gonzales" />
Oca is a component of traditional crop rotations and is usually planted in a field directly after the potato harvest. A standard sequence in this rotation system may be one year of potato, one year of oca, one year of oats or faba beans, and two to four years fallow.<ref name="Gonzales" /> Within this system, q’allpa is a Quechua term that signifies soil previously cultivated and prepared for the planting of a new crop.<ref name="Gonzales" />
The cultural practice is similar to potatoes. Planting is done in rows or hills 80–100 cm apart, with plants spaced 40–60 cm apart in the rows.<ref>Template:Cite book</ref> Monoculture predominates, but interplanting with several other tuber species, including mashua and olluco, in one field is common in Andean production. Often, this intercropping consists of several different varieties of each species. Such mixed fields may later be sorted into tuber types during harvest or before cooking.<ref name="National" />
Yields
Yields vary with the cultural method. Annals from Andean countries report about 7-10 tonnes per hectare of O. tuberosa production. However, with adequate inputs and virus-free propagation material, oca production can range from 35 to 55 tonnes per hectare.<ref name="National" /><ref name="Sperling" />
Limitations
Pests and diseases limit the production of oca. Crops in the Andes are often infected with viruses, causing chronic yield depression. Adequate techniques to remove viruses have to be applied before the varieties can be used outside the Andean region.<ref name="National" /> Cultivation is also constrained by the Andean potato weevil (Premnotrypes spp), ulluco weevil (Cylydrorhinus spp), and oca weevil, the identification of which remains uncertain (possibly Adioristidius, Mycrotrypes, or Premnotrypes). These weevils often destroy entire crops. Further notable pests are nematodes.<ref name="Sperling" />
As already mentioned, both day-length restrictions and the presence of oxalates can also be considered limiting factors. Scientists work with specific breeding, selection, and virus-cleaning programs for these purposes.<ref name="National" />
Conservation efforts
Several ongoing ex situ and in situ conservation projects currently focus on the preservation of O. tuberosa diversity.<ref>Template:Cite web</ref> The International Potato Center (CIP) in Peru has several hundred accessions of oca collected from regions in Bolivia, Argentina, and Peru to help ensure and maintain diversity. There are further efforts to collect accession of oca in regions where habitat destruction and pests threaten the diversity of wild oca accessions.
Alternative names
- Apilla in Bolivia
- Apiña in Bolivia and Peru
- Batata-baroa or mandioquinha (literally, 'little mandioca') in Brazil, a name shared with the unrelated arracacha
- Cuiba or quiba in Venezuela<ref name="CadimaFuentes">Template:Cite book</ref>
- Hibia or cubio in Colombia
- Macachin or miquichi in Venezuela<ref name="CadimaFuentes" />
- Papa extranjera in Mexico<ref name="CadimaFuentes" />
- Huasisai, qua or ibi in Peru,
- Truffette acide in France<ref>Template:Cite book</ref>
- Yam in New Zealand,<ref name="Albihn" /> where the Dioscorea vegetables known elsewhere as yams are uncommon
See also
References
Further reading
External links
- Oca in Lost Crops of the Incas
- NewCROP page on oca
- Andean root and tuber crops at the International Potato Center
- Oca, ulluco, and mashua at the International Potato Center
- Oxalis tuberosa at Plants for a Future