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Pachyrhizus Ahipa
Pachyrhizus ahipa (pachy=thick, rhizus=root), also called the Andean bean is a tuberous root producing legume, which is mainly distributed in the Andean region. Page text.

History
Archaeological evidence suggests, that Pachyrhizus Ahipa was widely distributed about 2000 years ago. Page text. The first mentioning of Ahipa was in connection with the Indian cultures in the Andes, more precisely in the Salta and Jujuy provinces of Argentina.Page text. Indications of the Pachyrhizus species in general were also made at the southern coast of Peru, in the Nasca culture. The origin of the Ahipa plants is most likely in the “ceja de montañas” Andean region. Today it is still in use in small native communities in Bolivia and Northern Argentina. The crop was never widely distributed which could have to do with the very specific climatic adaptions Ahipa exhibits. Another reason could be the acquisition of Latin America by the Spanish and Portuguese conquest, which had the general policy to destroy the traditional Andean agricultural systems. The local marketing of the Andean bean during the religious festival “Corpus Cristi” indicates a relationship with ancient religious uses. Today, the production is restricted to a few local villages and farmers.

Biology
P.Ahipa is one of a few Fabaceae and predominantly self-pollinating. It is a perennial plant. Page text.

The Andean bean is a perennial plant and can grow in erect, semi-erect and in twining forms. The erect species can get 15-40 cm tall, the semi-erect one about 30-60 cm and the twining forms 60-200 cm long. P.Ahipa plants are herbaceous and lignified depending on the genotype. They do not show a lateral axis.

The leaves are trifoliate leaves with stipules or pinnately arranged leaflets with caduceus stipels. The flowers, which grow on short stalks, are white blossoms or of a pale lavender colour. They show a tubular calyx and a papilionaceous corolla. Generally the flowers exhibit an internally curved stigma in close contact with the anthers. This habitus is very unfavourable in connection with the pollination behaviour of insects, as those are not able to pollinate the flowers very effectively. Additionally, the pollen fertility is often not very high. It differs between 45-100%. The flowering pattern is not consistent. Per season 100 – 800 flowers per plant can be produced. P. Ahipa is a short-day plant. Therefore, the flowering will take place under decreasing day length.

The pods are 13-17 cm long and up to 16 mm wide.

The seeds are black, lilac, maroon or black and white mottled. They are round, kidney shaped and about 0.8-1 cm long. The seed production differs from plant to plant and lies between 20-100 per plant. The thousand grain weight is around 300 g.

Every plant shows a single swollen root, which thins out toward both ends. The roots are about 15 cm long and usually weight about 500-800 g. The yellow skin of the root encloses a white pulp, which is interwoven with a soft fiber.

Sowing
Before sowing, the soil has to be loosened to a depth of 15-25 cm using a hoe. Further, the soil has to be thoroughly cleaned from weeds and stones. In Bolivia P.Ahipa is normally sown between August and October, depending on the rainy season. The seeding rate is between 40 and 65 kg/ha. In determining the rate, preferred traits such as tuber size play an important role. Further soil fertility and seed weight have to be taken into account. The planting distance is 20-60 cm between rows and 6-25 cm between plants in the same row. Therefore about 6-83 plants/m2 are possible. P.Ahipa is planted on ridges, when it is flood irrigated, which is mostly the case in the Andean region.

Cultivation
The cultivation period is between 5-10 months. 87-140 days after sowing the first flowers appear. Those flowers have to be removed manually, a process called reproductive pruning. This means, that the flowers, as well as the young pods are removed. Therefore the tuberous roots remain the main sink for photosynthates and nutrients. The yield improves drastically. Reproductive pruning is very labour intensive and has to be done once or twice a season. Mature pods normally show themselves in April till June. At about nine months, the roots are tuberized and the aerial part is completely dry. P. Ahipa is normally sown in a pure culture and can be intercropped with maize. In a crop rotation, P. Ahipa is sown prior to maize/potato, maize/tomato, maize/oca, groundnut or manioc.

Environmental conditions
P. Ahipa can mainly be found in cool tropical and subtropical valleys, on sun-facing slopes, on the border between the warm and cold tropics. The average temperature in this region is 16-18 °C, although the climatic conditions are extremely dependant on the time of day. The precipitation lies between 400-700 mm, occurring within 4-6 months, with the rest being the dry season. Therefore the climate is semi-arid. P.Ahipa grows on a height of 1800 – 3000 meters above sea level. Cultivation is mainly carried out along loamy riverbanks. At a pinch, it can also be grown on loamy hillsides. P. Ahipa favours pH conditions from 6-8 and well-drained soil types.

P.Ahipa plants can tolerate long dry spells. Anyway, to increase tuber yield, an additional water supply is essential.

Nutrient Needs
P. Ahipas nutrient needs are versatile. At the time of harvest, seeds show high nitrogen (N) contents. Anyway, a lot of N remains in leaves, providing a N-rich straw which can be used for animal feeding or as fertilizer, given that the plant material is incorporated into the soil. In one season, 67 kg N/ha were taken up by roots and seeds. This N is mainly provided by the inoculation with efficient bacteria strains. The P.Ahipa plant is therefore able to form an efficient symbiosis with nitrogen fixing bacteria, such as Rhizobium and Bradyrhizobium. Because of that, P. Ahipa is able to fix 58-80 kg nitrogen per hectare and therefore does not need any further supply via nitrogen fertilizer. A further positive aspect is that if the vegetative aboveground parts are left in the field, a substantial amount of the fixated nitrogen is returned to the soil. This can be seen in the soil enrichment of about 12-80 kg N/ha. The enrichment is very important if a sustainable land-use system is desired. During nodulation, an increased phosphorus (P) supply is advantageous, because this way the nodulation can be improved. Further it promotes the root and seed yield in P.Ahipa plants. The final recipients of P are the pod shells, as well as the seeds. In total, about 7-9.6 kg P/ha were extracted from the soil. At harvest, the highest potassium (K) contents can be found in pod shells, as well as in the roots. The removal of K at harvest was about 20.2 kg K/ha. Page text.

Disease
P.Ahipa plants are not very susceptible to pests. Anyway, nematodes such as Meloidogyne sp. can pose a serious problem. Further, some of the bean weevil species can be harmful to P.Ahipa. The most serious viral disease is the bean common mosaic virus (BCMV). Yields can be reduced up to 30% if infected by this virus. If a general irrigation management is lacking, rot is also likely to appear.

Harvest
The tubers of P. Ahipa are harvested, as soon as the tubers show a marketable weight, depending on consumer’s preferences. Mostly the preferred weight lies minimally at about 0.4 kg. The tubers are mostly harvested using a hoe. Harvest duration lies between 10 and 30 days. The vegetative top is often left on the field to later incorporate it into the fields. If the tubers are not needed at the moment, they can even be left in the soil until needed. Only the plant tops have to be cut off. The yields of the different organs differ a lot. It is about 28-53 tonnes/ha for the tuberous roots, 18-36 tonnes/ha for the fruits and 1.3-2.7 tonnes/ha for the dry seeds.

Post-Harvest
The optimal storage temperature for tubers lies between 12.5 and 17.5 °C. The storage however, changes the ratio of starch and sugar in the direction of sweeter tubers. This characteristic is valued by most consumers. There are even farmers, who leave their tubers in a sunny place, before marketing them. Due to a high moisture content, the P.Ahipa tubers may shrivel and lose condition. The storage and transportation methods therefore have to be improved. Another solution to fight the shrivelling could pose a thicker epidermis.Page text. It is important, to avoid a damage to the tuber while harvesting. This has one main reason. If the tubers are damaged, they are getting very susceptible to attacks by fungi, mainly by Rhizobus stolonifer, Cladosporium sp. as well as Penicillin sp.. An attack of one of those fungi leads to textural changes, decay and internal browning when stored at low temperatures and high relative humidity (>80%). The seed storage is problematic. Under humid conditions, the germination rapidly decreases. This is challenging, because the climate in tropics is very humid in the rainy season.

Commercial Aspects
The sometimes dwarf like habit makes P. Ahipa well suited for large-scale commercial cultivation. P.Ahipa is on one hand grown for home consumption on the other hand, half of its production is sold on the local markets. There is no international trade in P. Ahipa.

Roots
The carbohydrate-rich roots can be eaten raw and provide calories and vitamin K and C, as well as potassium to the diet.Page text. Normally they are eaten fresh, almost like a fruit. In some raw cases, it is also prepared as a juice. The roots taste sweet and are crisp like an apple and are an attractive addition to green salads. They can be boiled and even after cooking, they retain their crunchy texture. Ahipa tubers are even considered to have a cleansing effect on the body. It is supposed to cure infections of the throat and the air passage.

Its dry matter ranges from 15-30%.

Further the tuber contains 48-54% starch, which consists of 96-99.9% amylopectin. This is a very high value and especially interesting for food processing, where low solubilisation and retrogradation are important. Because of the high starch and amylopectin content, Ahipa is a good material for the starch industry. Further the suitability of th Andean bean depends on other factors such as extractability of the starch, the diameter of the starch granules or particles and their distribution. After nine months, the starch granules are very homogenously distributed in the tuber. There is a high percentage of granules, which show the same size of about 12-18 μm diameter. This indicates that the tuber growth is completed.

P.Ahipa can produce 19-28% sugars in its root.

The protein content lies between 8 and 18%. The protein content is of interest as well. Mainly, because the European market is economically highly interested in the protein import, mostly as feed for cattle. Further the protein content may be interesting for the food industry, because about 80% of the protein is water soluble and not extractable within a pH range of 2-10.

The lipid content is very low and lies below 1%.

Altogether the tuber shows a very good nutritional composition. However, because the tuber contains a lot of water, the protein and energy concentration may be rated as being medium.

Seeds
The seeds of the Andean bean contain high protein concentrations. As an adaption to insect predators, Ahipa plants accumulated canavanine in its seeds. This is highly toxic to some insects and can pose a big problem in the livestock foraging, especially if the Ahipa plants escaped into the wild vegetation. The oil of the seeds has special properties such as high palmitic acid and γ-tocopherol concentrations as well as few linolenic acids. These aspects are of interest in the food industry.

Breeding
There are several breeding aims which are important in P.Ahipa, apart from it being used as a vegetable crop, a basic food crop or a possible industrial crop. Those traits are mainly the reduction of the growth period and a reduced pod formation. This is especially important, because this way, the reproductive pruning could be avoided. Therefore a lot of time and money could be saved.

P.Ahipa plants have to be propagated sexually, because the reproductive rate by cloning from tubers is very low. The propagation by seed is very advantageous. This is mainly, because this way a transmission of viruses can be avoided and the storage of the propagation material is pretty cheap.

There have been interspecific hybridization experiments among all the Pachyrhizus species. The traits of the Andean bean, which are most interesting are tuber quality, growth habit as well as the earliness. The results of the breeding between the different species showed especially good performing hybrid lines with regard to high tuber yield as well as wide adaptability. Nevertheless, negative secondary effects, such as reduced seed set and reduced germination rates, have been observed.

Prospects
P.Ahipa should be used by a higher variability of farmers for several reasons:
 * It shows a very good adaptability to climatic and edaphic ranges
 * The nutritious composition of the protein/starch content is very well balanced, additionally, the taste is good
 * It shows good post-harvest and storage characteristics
 * The nitrogen fixation as well as a little demand for fuel wood in the preparation of food are favourable for the environment