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Review of the Pachyrhizus tuberosus (Lam.) Spreng. cultivar groups in PeruIsabel Oré Balbin Marten Sørensen Lars Peter Kvist Octavio Delgado Vasquez
Particularly in tropical parts of the world, a number of vegetable, even fruit-like, species of root and tuber crops exist, many of which remain little known outside their native areas. Due to a general lack of agro-economic interest, the traditional cultivation methods have not improved and conservation measures have not been taken, implying that many landraces are in danger of extinction. However, traditional crops often have favourable characteristics that may help mitigate the world food and environmental crisis, including being productive in areas unsuitable for major crops, integrating well in agricultural systems appropriate to marginal areas, being reliable sources of food even in climatically adverse years, and contributing to nutritionally more diverse diets.
Of some 9000 species belonging to the Fabaceae or Papilionaceae family, at least 25 species are cultivated in various parts of the world for consumption of the roots (Vietmeyer 1986). Among the most important of these is the genus Pachyrhizus DC. (Grum 1990; Sørensen 1996), with three cultivated species: Pachyrhizus erosus (L.) Urban widely cultivated in Mexico and Central America and introduced elsewhere; P. ahipa (Wedd.) Parodi limited to a small area at mid-elevations in Bolivia (Ørting et al. 1996); and P. tuberosus (Lam.) Spreng., originally widely distributed in South American lowland tropical and premontane forest (Sørensen 1990). Pachyrhizus also include two wild species: P. ferrugineus (Piper) Sørensen and P. panamensis Clausen (Sørensen 1988).
In concordance with the statement above, the focus of the present study, Pachyrhizus tuberosus, has received little agro-economic attention since first the reliable record (Tessmann 1928). The species enriches the soil and provides more protein (ca 10% of the dry matter) than well-known tropical root vegetables like manioc (Manihot esculenta Crantz), sweet potato (Ipomoea batatas (L.) Lam.) or yams (Dioscorea spp.). Like these, it provides high yields of edible tuberous roots per hectare (Sørensen 1996), but, in contrast to them, P. tuberosus is propagated by seed and can therefore be multiplied on a large scale and is easy to transplant to other areas. Also, non-marketable roots and the foliage can be used as fodder for domesticated animals. Due to the Rhizobium-Bradyrhizobium-facilitatednitrogen fixation and the content of the natural insecticide rotenone in the seeds (Sørensen 1996), Pachyrhizus tuberosus constitutes an interesting option in organic agriculture, also as cover crop to improve soil conditions and for weed or erosion control. The extraction of rotenone could be converted into a crop by-product, useful to fight thrips (e.g. Frankliniella spp.), aphids (Aphis spp., Brevicoryne spp. and Oregma spp.) and whitefly larvae (Orosius spp.) (Sørensen 1988). Furthermore, there is a potential possibility of using the high quality oil from the seeds (Sales 1985; Grüneberg et al. 1999). Finally, successful hybridization between P. tuberosus and P. ahipa landraces already has resulted in plants with favourable characteristics (Grüneberg et al. 2003).
Currently, P. tuberosus may be restricted to western tropical South America, with the greatest diversity in Peru and Ecuador, where at least 11 distinct landraces are found, assigned to four cultivar groups: the Jíquima (coastal Ecuador), the Ashipa (widespread in the western Amazon basin), the Chuin (along Peruvian rivers), and the Yushpe (very local in Peru). The present work describes the status of P. tuberosus, particularly in Peru, taking advantage of fieldwork initiated in 1993 and the available literature. The purpose is to make national and international agricultural research institutions aware of the many potentials of this traditional crop. The urgency for surveying P. tuberosus cultivation has repeatedly been confirmed through fieldwork in Ecuador and Peru, which has revealed that in many areas more than 90% of the farmers have lost the crop during the last decade (Sørensen et al. 1997a; Sørensen 2004), and particularly the Chuin and the Yushpe are endangered. These two cultivar groups are grown on flood plains inundated for 4–6 months annually. Unusually early and high floods may have become more common during the last decades (Gentry and Lopez-Parodi 1980), inundating the plants before farmers can harvest seed for next season’s propagation; most recently, unusually early and high floods occurred in 1994 and 1999, in both years causing many farmers too lose their Chuin.
A thorough bibliographic search was carried out to identify potential locations of P. tuberosus, with subsequent fieldwork in the Peruvian departments of Loreto, Ucayali, San Martín, Huánuco, Junín and Madre de Díos (and M. Hermann collected in Cusco in 1991–92 (pers. comm.)). The field surveys were particularly intensive in areas close to the Ucayali and Marañon rivers, where the Chuin and Yushpe landraces are found. Numerous communities were visited in order to locate and register the species, and to inquire of local farmers regarding their uses and cultivation of P. tuberosus. Herbarium material and germplasm were collected, and semi-structured interviews with individual farmers were conducted. A standardized numerical questionnaire was used to record observations and information regarding traditional agricultural systems and utilization, and to register local names.
According to Sørensen (1990) and León (1987), P. tuberosus is a herbaceous climbing plant with autogamous sexual reproduction (2–4% cross-pollination). It is the largest species in the genus, and while the trailing or climbing genotypes can attain up to 10 m in length with moderately branched, trailing or climbing stems, the bushy erect genotypes reach 1–1.5 m. The trifoliate leaves are ternate, large, abundant and dark, have entire to slightly dentate margins, and the terminal leaflet vary from being subentire to deeply trilobate. The petioles are 40–208 mm long, with pubescent pulvini and linear-lanceolate stipules. One inflorescence develops per leaf axil, with thick, cylindrical, 10 to 25 cm-long peduncles having lateral branches with 7–33 flowers. The petals are usually pubescent, but glabrous specimens occur. The colour of the flower is white or light to dark bluish violet. The pods have reddish, irritant hair, and being 13–19 cm long and 14–23 mm wide are the largest in the genus. The seeds are either rounded kidney-shaped, or flat, almost square, being ca. 10 × 15 mm and 9 × 12 mm, respectively. Both kinds of seeds may have orange, reddish or black coats, and in addition, kidney-shaped seeds may be white to cream with black dots, and square seeds claret-coloured or cream-coloured with brown dots. The tuberous roots are either mono-tuberous extending vertically into the soil, or multi-tubered, spreading laterally from the main stem; they are carrot or sausage shaped, long, round or irregular, up to 30 cm long and 25 cm wide. Their flesh is crunchy, succulent, white or yellow, sometimes with a touch of purple. The morphological characterization of the genetic variation of the P. tuberosus accessions stored in the Pachyrhzus germplasm collection at CATIE, Costa Rica, is presented in Tapia and Sørensen (2003).
In Peru, the cultivar groups Ashipa, Yushpe, and Chuin occur, represented by three, one and five individual cultivars or landraces, respectively. An overview of the characteristics of the three cultivar groups is presented in Table 2.
White Ashipa cultivar group (Ashipa blanca)
Yellow Ashipa cultivar group (Ashipa amarilla)
Ashipa cultivar group (San Martín)
Yushpe cultivar group
Chuin cultivar group
Chuin cultivars with high root dry matter content
Yellow Pitichuin (Chuin amarillo)
Purple Pitichuin (Chuin morado)
Chuin cultivars with low root dry matter content
Purple Cocotichuin (Cocotichuin morado)
Characterization of cultivation sites
Pachyrhizus tuberosus is cultivated in the Amazon region of Peru on both terra firma soils (high, non-inundated areas) and alluvial soil (low in generally annually inundated areas). It appears from Figure 2 that Ashipa and Chuin/Yushpe are mainly grown on terra firma and alluvial areas, respectively.
Terra firma areas constitute more or less hilly landscapes, which tend to be well-drained in spite of torrential rains, but poor in nutrients and unsuited for permanent intensive cultivation. Alluvial areas are flat, only slightly undulating, and are formed by silting sediments carried by white-water rivers mostly descending from the Andean slopes. Many alluvial soils remain influenced by active river dynamics constantly reforming the landscape, and are flooded by white-water rivers from short periods up to seven months annually. As a consequence, forests cover the floodplain landscape, at different stages of active succession, and the soils are young and fairly fertile, implying that many local communities exploit flood plains for agriculture. Encarnación (1995) and Kvist and Nebel (2001) describe the flood plain habitats and their uses.
Peruvian P. tuberosus is mostly cultivated in flood plain habitats, namely: (1) sandy beaches (playa), submerged for about six months annually, coinciding with low and high water levels in rivers, and only covered with temporary annual herbs and semi-aquatic species. Sandy beaches are well drained and have fairly fertile soils; (2) clayish beaches (barrial) that are also inundated for up to six months annually and only with annual vegetation, but have soil formed by finer particles, with intermediate draining abilities, and with many plant nutrients; and (3) levees, both low and high level (restinga), that are the alluvial deposits of white-water rivers that may flood for 1–3 months annually (low level) or for less than one month or irregularly (high level). Levees are naturally covered with forest, and their floristic composition and biomass depend on their age. Lower-level levees have intermediate draining capacity and are fairly fertile, while higher levees tend to have more compact soils, with fewer nutrients.
Based on field surveys and interviews with 74 informants, the principal characteristics and cultivation practices of P. tuberosus are summarized in Table 3, and the associated crop species appear in Table 4. Overall Ashipa tends to be combined with other crops or grown in complex home gardens, while Chuin is generally cultivated in monoculture, but occasionally in association with other crops.
Due to its long cultivation cycle (ca. 12 months), Ashipa can only be cultivated on terra firma and the upper, rarely or never flooded, flood-plain levees (Figure 2). Ashipa is often cultivated integrated with one or several other crops, particularly manioc, maize or banana, which serve as trellise for the Ashipa. Particularly in San Martín department, Ashipa occurs cultivated in small home gardens, together with various fruit trees and numerous medicinal plants, in this case using shrubs and trees as live stakes. Some authors consider this method an imitation of the layered rain forest and refer to it as ‘farm forest’ or ‘orchard forest’ (De Jong 2001). In general, very few Ashipa plants are found per field or farmer; more than four plants were rarely recorded, and only a single farmer from Lamas, San Martín, had up to 100 plants on his farm. In contrast to all monotuberous landraces, the multi tuberous Ashipas are frequently cultivated as a perennial crop, removing only single tuberous root branches while leaving the remaining roots attached to the plant.
The Chuin cultivars were exclusively recorded from alluvial soils, particularly sandy and clayish beaches and on lower levees (Figure 2). On beaches, farmers typically grow 30–40 individuals in mono-cultural plantings (Figure 3), next to the equally mono-cultural plantings of cowpea (Vigna unguiculata (L.) Walp. ssp. unguiculata), groundnut (Arachis hypogaea L.) or rice (Oryza sativa L.). Their rapid development—four months for roots and six months for seeds—facilitate their cultivation on beaches. In contrast, on low-level levees, Chuin cultivars are mostly grown associated with other crops, particularly maize. Chuins are not cultivated on upper levees or terra firma soils. According to Delgado et al. (unpubl. data), based on field trials at Iquitos, the reason is that the growth of Chuin depends on fairly loose, relatively well-drained, soils. On high sandbanks and terra firma soils, growth is very slow, taking up to eight months to develop seeds and small roots, suggesting that compact soils inhibit development (Ore Balbin et al. 2005).
The Shipibo Amerindians sow Chuin in May, shortly after the retreating water has exposed the beaches, and harvest fresh roots for consumption about four months, later in August. At the same time, they replant the upper parts of the tubers for vegetative propagation, now with trellises supporting the individual plants, in order to induce the formation of many branches, thus increasing seed production. Finally, seeds are harvested before the beaches are inundated again in December and January, and the seed stored for sowing after the flooding.
Information regarding ‘Yushpe’ comes from a single farmer cultivating it on a low, sandy levee. Yushpe was grown at the base of a grapefruit tree, surrounded by fruit and medicinal species. Tuberous roots were harvested after six months and seeds after 7–8 months.
The only field management traditionally carried out by the woodland farmers in Peru is manual weeding every 15–20 days. Several agronomic experiments, particularly with the Central American P. erosus and the Andean P. ahipa have shown that the reproductive pruning usually carried out with these species may double their production of roots (Heredia-Zepeda 1996; Sørensen et al. 1997b). In Tonga (South Pacific), recent field experiments involving P. tuberosus have yielded similar results (Nielsen et al. 1999). However, this practice was not recorded with any of the P. tuberosus cultivars grown in Peru.
Regarding control of pests and diseases, only occasional manual elimination was observed. At the same time, a Lamas Quechua farmer apparently used Ashipa as a pest barrier for other crops, planting Ashipa along the border of his farm. Specific pests affecting Pachyrhizus include (1) Diabrotica sp., a beetle known as papaso, well known for damaging the leaves of P. tuberosus and other crops. Heavily perforated leaves as well as Diabrotica beetles were frequently observed during farm visits, but the leaf damage does not apparently hamper the plants significantly, as root growth and pod development appeared normal (pers. obs.); (2) a species of Orthopthera known as grillo, said by farmers to cut the stems of recently germinated seedlings, causing them to wither and die, although its overall impact also seems relatively low (pers. obs.); and (3) the bruchids Caryedes icamae Guerin-Meneville and Acanthoscelides taboga Johnson, which destroy stored seeds, and may constitute a serious threat to propagation, especially in areas where few farmers save seeds for the next growing season.
Farmers judge Pachyrhizus plants to be ready for harvest when the pods turn yellow, and the expanding tubers lift the soil around the plant. Tubers are not allowed to become exposed, as exposure causes them to photosynthesize and thus decrease root quality. Tubers can be conserved for about a month in the soil, and, after harvest, unwashed roots can be stored in a dark place for about another month. During the storage period, the sugar concentration increase, making the tubers sweeter. Another conservation method practised in floodplain communities is to grate the harvested roots to a kind of dough, which is buried before the inundation and excavated after the water recedes, subsequently providing basic food as flour during the lean months until the newly established crops start to produce.
Chuin, and maybe also Yushpe, is specifically adapted to the lower parts of the flood plain environment, characterized by short growing seasons between floods, and unstable, temporary beaches. This human selection for short cropping cycle and adaptation for cultivation on alluvial seasonally flooded fields is unique to the Chuin as a root crop, as is evident from the frequency of cereal crops in numerous cultures using flood irrigation, i.e. the relative absence of cereals in this habitat in America may not reflect the situation when the Europeans arrived, as hypothesised by Clement who, in addition to Zea mays L., mentions two native cereals that may have been cultivated at that time (1999a,b).
Our field-work has documented the advanced genetic erosion of virtually all P. tuberosus cultivars. Yushpe and Cocotichuin may be nearly extinct, and the more common Ashipa and Pitichuin cultivars are much scarcer than a few decades ago. The acculturation process implies that mostly older and relatively traditional farmers maintain these crops, implying that cultivation will decrease even faster as they stop cultivating. The occurrence of occasional early floods that prevent the production of the next season’s seeds will probably also further accelerate this disappearance of Chuin compared with Ashipa. However, even the Ashipa cultivars are now rare everywhere, except in parts of the San Martín department, e.g. around the small town Jepelacio at 1000 m a.s.l. In the case of Ashipa, it is also a problem that the markets for this crop are limited, as urban populations are no longer familiar with the product, making it even more difficult for the few remaining producers to sell their produce.
The characterization of genetic variation of plant-genetic resources is of high priority in strategic investigation efforts worldwide. This is due to the role that traditional crops and cultivars may have in the solution of present and future problems related to food security, e.g. adaptation to climatic changes and development of new alternatives by means of either traditional or biotechnological methods (Ayad et al. 1995). When compared to current major crops like manioc and banana, field observations in combination with field evaluations have clearly identified the P. tuberosus complex as a promising alternative for the Peruvian Amazon and lowland tropics in general. In addition, the Ashipa, Yushpe and Chuin cultivar groups show significant differences regarding both their adaptations and agricultural potentials, and the other Pachyrhizus species equally have their proper qualities.
The higher carbohydrate content make the Chuin cultivars particularly promising as they are consumed as staple foods, but contain much more protein than usual tropical staple food sources of starch. However, the existing Chuin cultivars are relatively demanding regarding soil texture and fertility, implying that larger-scale and more widespread cultivation would depend on the selective breeding of favourable characteristics from other Pachyrhizus species and cultivars capable of producing on the poorer soils dominating much of the tropics. Should this be successfully accomplished, the Chuin might indeed help to solve the world’s food crisis, particularly in reducing malnutrition in rural areas (Figure 4). Therefore, it is important to preserve intraspecific as well as the intrageneric variation, and to investigate the origin and development of the Pachyrhizus species, cultivar groups and landraces. Such studies and programmes should preferably also include wild ancestors and their genotypes, implying that it will be necessary to locate these ancestors.
Pachyrhizus tuberosus has attractive traits, including high yield per unit area, high protein content, nitrogen fixation ability, the potential provision of rotenone and good quality seed oil, and easy multiplication and transplantation by seeds. Yields up to 80 t/ha have been obtained with existing landraces, and between 120 and 145 t/ha for new cultivars of P. erosus in Mexico (Sørensen 1996), exceeding the average yields of other well known root and tuber crops, e.g. manioc with 9.95–15.8 t/ha (Alarcón and Dufour 2002; Albuquerque and Cardoso 1980), and the protein content is three to five times that of either manioc or sweet potato (Sørensen 1996). Furthermore, depending of the cultivar group, the tuberous roots can be eaten raw, prepared as juice or cooked as an attractive alternative to manioc (Peckolt 1922), and a number of derivate products can be produced, viz. fariña, masato, wine, spirit, vinegar, insecticide and others, both mentioned in this study and by PADA (1999). Finally, the nitrogen-fixation ability (Badillo and Castellanos 1998) also help to restore impoverished soils, making P. tuberosus a potentially important component of agrosystems on marginal and poor soils, i.e. where well known crops like manioc, maize or banana have low yields.
The largest variability in of Pachyrhizus tuberosus is found in the Peruvian Amazon, but various landraces are in imminent danger of extinction. To counter—or at least ameliorate—the consequences of this development, both scientific-agronomic and commercial attention and promotion are required. It is necessary to characterize and collect the existing plant genetic resources; to develop improved Pachyrhizus cultivars, e.g. by hybridization of existing cultivars and species, and to distribute these to farmers in Peru and elsewhere; and to develop new markets for Pachyrhizus products.
This work would not have been possible without the positive collaboration of numerous farmers in the Peruvian Amazon, who patiently shared with the authors their valuable knowledge regarding their crops and farming systems. The Peruvian Institute of Investigations of the Amazon (IIAP) and the National University of the Peruvian Amazon (UNAP) facilitated the work by providing scientific advice and logistic support. The Botanical Section, Department of Ecology, at the Royal Veterinary and Agricultural University in Denmark, is gratefully acknowledged for providing facilities during the analysis and writing of this document. Mrs Charlotte Schomacker efficiently translated the manuscript from Spanish. The study was financed by a grant from the DANIDA Council for Development Research.
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