«Andean roots and tubers: Ahipa, arracacha, maca and yacon M. Hermann and J. Heller, editors Promoting the conservation and use of underutilized and ...»
Although production of maca is restricted primarily to the central Andes of Peru, it can be grown successfully in other parts of the world. Field experiments in Davis, California indicate that this crop can be grown during the winter in this area as an annual crop if irrigation is available throughout its whole life cycle. At Davis, 4 to 6-week-old seedlings transplanted in the field at the middle of September initiated hypocotyl development in 6-8 weeks. At this time of the year daylength is approximately 10 hours and mean soil temperature approximately 12°C. The ‘hypocotyls’ reached a maximum size of 35-50 mm in diameter 7 months after transplanting, when daylength was over 13 hours and mean soil temperature was approximately 20°C. By the middle of March, at the end of the rainy season, irrigation water was supplied as needed. Floral stems developed at this stage at the base of the stem, reaching anthesis and fruit-setting 8-9 months after sowing the seed.
Therefore, most of the plants completed their seed-to-seed cycle in 10-11 months.
Experiments on photoperiod response in growth chambers demonstrate that maca does not require short days for general development, hypocotyl enlargement or flowering. Hypocotyl enlargement takes place at similar rates under either short (12 hours) or long days (14 hours) (Fig. 10). Similarly, flowering takes place independently of daylength and without need of a vernalization period (Quirós et al. 1996). It is unknown, however, whether vernalization will promote more profuse and coordinated flowering in this species. From the results of these experiments, maca can be considered photoperiod-neutral and can be grown as an annual or biennial species, depending of water availability and optimal temperatures. Low temperatures and water availability during the growing season seem to be more important than daylength in the development of the maca plant. Therefore, with adequate water supply to the plants and cool temperatures, in situ as well as ex situ germplasm conservation activities can be carried out for maca without much impediment. Maca may be grown outside its native habitat, the Andean highlands of Junín, and therefore its range of adaptation is not as narrow as previously believed (Tello et al. 1992).
Maca (Lepidium meyenii Walp.)
Fig. 10. ‘Hypocotyl’ width (mm) based on four accessions, five plants per accession grown under long (light line) and short day (dark line) conditions for 29-32 weeks at two temperature regimes.
A: 18°C maximum and 8°C minimum temperatures; B: 22°C maximum and 12°C minimum temperatures. Error bars are shown at each point (Quirós et al. 1996).
Promoting the conservation and use of underutilized and neglected crops. 21. 191 8 Agronomy Maca is sown in small plots in empty grazing fields by broadcasting the seeds still containing floral debris mixed with soil. In the Junín area sowings with seed stored for 4 years are common. However, the viability of these seeds may be only 50%.
One kilogram of seed with 15 kg of soil is used for high-density planting or 1 kg of seed and 25 kg of soil for low density. Then sheep are released to the field to trample the seed. This will result in 700 000-400 000 plants/ha depending on the sowing density used. Sowing takes place from September to October starting at the initiation of the rainy season, usually in the morning to avoid winds. The soil is well prepared, with clods broken up, and is fertilized with sheep manure. Often the plants are thinned out 2 months after sowing to obtain uniform and larger hypocotyls.
Weeds, if present in the field, are removed by hand. The seed is commercialized as charpu, which is the amount of seed and floral debris mix contained in an l8-cm diameter dish (Tello et al. 1992). The pastures lie fallow for as many as 10 years before maca is again planted in the same plot. This is because maca seems to exhaust the soil by extracting nitrogen and other nutrients (Tello et al. 1992). Also, fallow plots will result in less incidence of weeds, pathogens and pests when the crop is produced.
The main pests and diseases, which are just a few, include a root borer called gorgojo de los Andes (Premotrypes spp.) and a leaf fungus causing mildew (Peronospora parasitica). Other fungal pathogens causing diseases present in the area are Fusarium graminium and Rhizoctonia solani (Tello et al. 1992; Aliaga-Cárdenas 1995).
The hypocotyls are harvested from May to July when they are at their maximum size, about 5 cm in diameter (Leon 1964; Tello et al. 1992). At this time, most of the leaves in the plants are still growing, without showing signs of senescence. A local hand hoe called a cashu is used for digging the plants one by one (Fig. 11). The curved Fig. 11. Utilization of a cashu for maca harvesting in Junín.
Maca (Lepidium meyenii Walp.) blade of this tool avoids damage to the roots. Estimated yields of fresh hypocotyls are 14.7 t/ha and 4.4 t/ha of dried hypocotyls with a harvest index of approximately 0.77 (Tello et al. 1992). After harvesting, the whole plants are dried during the day under the sun for 10-15 days, and covered during the night to avoid rain and frost damage. The leaves are left on the plant during drying because the local farmers believe that this will result in sweeter roots. After drying, the leaves are removed and the hypocotyls are taken to the market or stored dry in layers of less than 10 cm thick in well-ventilated sheds protected from the rain. Some of the freshly harvested plants are replanted for seed production during the following spring when the first Fig. 12. Maca production biennial cycle in Junin coordinated with rainy season (redrawn from Tello et al. 1992).
Promoting the conservation and use of underutilized and neglected crops. 21. 193 rains appear (Tello et al. 1992). For this purpose, the whole plants are stored in pits covered with soil for approximately 45 days to allow root regrowth and initiation of generative shoots. This practice results in the loss of many plants due to rotting of the foliage. After this period, when the generative shoots are about to appear, the hypocotyls are dug out and transplanted 0.6-0.7 cm apart in empty sheep stables where plenty of manure is available in the soil. Therefore, maca is handled as a biennial crop because of water limitation in the region. Each cycle, vegetative and reproductive, is coordinated with the beginning of the rainy season in the central Andes, as illustrated in Fig. 12. After approximately 4 months the whole plants are lifted, when the siliques begin to turn yellow before dehiscence to avoid seed shattering. The plants are then dried and the seed is thrashed by rubbing the dry inflorescences with both hands (Tello et al. 1992).
194 Maca (Lepidium meyenii Walp.) 9 Limitations, research needs and prospects
9.1 Limitations The main limiting factors of maca production are availability of good-quality seed, adequate weed control, acid soils in the present area of cultivation and post-harvest handling. Seed is often sufficient for planting only small plots, sincelarge quantities are hard or impossible to find from a single source. The presence of floral debris and soil mixed with the seed makes it difficult to know how much actual seed is really available. Other limitations are lack of information on soil management practices as well as weed, insect and disease control.
9.2 Research needs Better seed-cleaning methods must be adopted.
The seed bulked from many plants of different characteristics makes it impossible to determine the root colours that will be obtained in the crop. This makes necessary the systematic selection of plants of different traits to generate cultivars possessing predictable traits. Simple breeding and selection schemes along with good seed-production practices will rapidly solve this limitation.
Effective practices for weed control are necessary to increase yields.
Soil acidity could be solved by application of amendments to increase the pH.
Little research has been done on this problem, whose solution could result in substantial yield increases (Quirós et al. 1996). At the present time, it is possible that maca is not being grown to its full potential because of the lack of optimal soil in the production areas.
The current practice of drying the plants after harvesting needs improvement.
Often it results in losses of 30-50% of the harvest due to rotting caused by overheating of foliage still present in the plants. Research is necessary to determine the optimal practices for root drying to minimize losses.
9.3 Prospects Maca is one of a few crops that can be grown at high altitudes. It has gained great popularity as a nutritious food and its reputed medicinal properties open up the opportunity to grow it on a larger scale in the highlands of the Andean region. Its amenability for processing in a large number of products, including health supplements, makes this crop quite attractive for regions where other crops cannot be grown. Further, the unmet demand of maca at the present time provides the challenge to expand the area dedicated to this crop and to work toward the solutions of its present limitations.
Promoting the conservation and use of underutilized and neglected crops. 21. 195 Acknowledgements We are indebted to M. Holle and Francisco Delgado de la Flor for supporting research on maca, to Vincent D’Antonio and Francisco Jarrín and Judith Toledo for technical assistance, to Michael Hermann for supplying seeds of some of the wild species and to Dr I. Al-Shahbaz for species identification. Research was supported in part by a grant from the Consortium for the Sustainable Development of the Andean Ecoregion at the International Potato Center (CIP-COTESU).
The International Plant Genetic Resources Institute would like to thank Prof.
Timothy Johns for his critical review of the manuscript.
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Yacon Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson Alfredo Grau Laboratorio de Investigaciones Ecológicas de las Yungas (LIEY) Universidad Nacional de Tucumán Yerba Buena, Tucumán, Argentina and
Contents 1 Introduction 2 Vernacular names 3 Taxonomy
3.1 The genus
3.2 The species
3.3 The other Smallanthus species
3.4 Relationships between species 4 Species description
4.1 Botanical/morphological description
4.2 Reproductive biology