«Andean roots and tubers: Ahipa, arracacha, maca and yacon M. Hermann and J. Heller, editors Promoting the conservation and use of underutilized and ...»
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M a c a (Lepidium meyenii Walp.) Carlos F. Quirós Department of Vegetable Crops University of California Davis, CA 95616, USA and
1 Species classification The Cruciferae (Brassicaceae) family contains many important crop plants and comprises approximately 3000 species. According to Rehm and Espig (1991), crops
of economic importance are:
starch plant - maca (Lepidium meyenii) oilseeds - rapeseed (Brassica napus) and crambe (Crambe abyssinica) vegetables-cauliflower, common cabbage, Brussels sprouts, etc. (Brassica olevacea var. botrytis, var. capitata, var. gemmifera); Chinese cabbage (B. rapa subsp.
chinensis); garden rocket (Eruca vesicaria subsp. sativa); watercress (Nasturtium officinale); radish (Raphanus sativus); garden cress (Lepidium sativum) spices - mustard (Brassica nigra, Brassica juncea and Sinapis alpa) fodder - fodder kale (Brassica spp.), fodder radish (Raphanus sativus).
The species in the Brassicaceae are classified in three large cosmopolitan sections — Dileptium, Monoploca and Lepidium — and three minor sections restricted to the Old World — Lepia, Lepiocardamon, Cardamon (Thellung 1906; Mummenhoff et al.
The genus Lepidum belongs to tribe Lepidieae and section Monoploca of the Brassicaceae family (Thellung 1906) and consists of approximately 175 species (Mummenhoff et al. 1992) being the largest genus in the Brassicaceae (Hewson 1982).
Maca (Lepidium meyenii Walp. in Nov. Act. Nat. Leopold. Carol. 19, Suppl. 1 (1843)
249) is the only species cultivated as a starch crop. In the genus three other species
are cultivated (Hanelt 1986; Mabberley 1993):
1. the garden cress or land cress (Lepidium sativum L.) is grown worldwide and is used at the cotyledon or seedling stage as a salad component
2. dittander (L. latifolium L.) was a cultivated salad plant of the Ancient Greeks and is used as a medicinal plant in the Canary Islands to alleviate renal lithiasis.
According to studies of Navarro et al. (1994), this species has diuretic action
3. poor man’s-pepper (L. virginicum L.) is used as a leafy vegetable (weed in maize) by the Tarahumara Indians in Mexico.
The taxonomic status of maca, the Andean cultivated species of Lepidium, has been questioned by Chacón (1990), who proposed to change its name L. meyenii Walp.
to L. peruvianum Chacón sp. nov., based on morphological observations and comparative analysis of herbarium specimens in Germany and the USA.
Additionally, the original collections of L. meyenii were done outside the present range of distribution of maca, namely Puno in Peru. Although it is believed that in Inca times maca was cultivated in Puno, there is no evidence of this crop being cultivated there at the present time (M. Holle, pers. comm.). Later, other accessions collected in Bolivia and Argentina were also classified as L. meyenii. After superficial morphological inspection, however, no resemblance to maca can be seen in these early herbarium specimens, which in many cases are not in optimal shape. Therefore the species name change seems justifiable, although further taxonomic research is required to solve this problem.
176 Maca (Lepidium meyenii Walp.)
Common names of the species are (National Research Council 1989):
English: maca, Peruvian ginseng Quechua and Spanish: maca, maka, maca-maca, maino, ayak chichira, ayak willku.
At least seven wild species of Lepidium, including the cultivated one, have been reported in Peru by Brako and Zarucchi (1993) from the departments of Ancash to Puno. In addition, other Andean species have been collected in Ecuador, Bolivia and Argentina (M. Hermann, pers. comm.). Practically nothing is known about the origin of these species and even less about their possible relationship to maca. Although maca is an octoploid, the Andean wild species of Lepidium surveyed so far include both tetraploid and octoploids (Quirós et al. unpublished). A survey of approximately 30 different cultivars of maca and 21 wild species from Ecuador, Peru and Bolivia, with Randomly Amplified Polymorphic DNA (RAPD) and Restriction Fragment Length Polymorphism (RFLP) markers for rDNA, cruciferins, napins and a self-incompatibility sequence (Kianian and Quirós 1991), disclosed very low polymorphism among cultivars. Phylogenetic distances calculated on the basis of 75 RAPD markers indicate that none of the wild species so far screened is closely related to maca (Quirós et al., unpublished). Tentatively three wild species could be identified by one of us (CFQ) when comparing them with herbarium specimens at the UC Berkeley Jepson herbarium, Berlin-Dahlem Herbarium in Germany, Museo de Historia Natural Javier Prado in Lima and Cesar Vargas Herbarium at the Universidad del Cusco. The species’ identities in the collection were confirmed by Dr I. Al-Shahbaz at the Missouri Botanical Garden. These species are L.
bipinnatifidum Desvaux, L. kalenbornii C.L. Hitchcock and L. chichicara Desvaux.
Tetraploid and octoploid forms were found for L. bipinnatifidum and L. chichicara.
Lepidium kalenbornii consisted only of tetraploid accessions. In 1996 we collected in the departments of Cusco and Apurimac at 3600 to 3950 m asl and found the same wild species. No cultivated maca was detected in this region.
Promoting the conservation and use of underutilized and neglected crops. 21.
2 Botanical description and reproductive biology The maca plant is a rosette of frilly leaves with an enlarged fleshy underground organ formed by the taproot and the lower part of the hypocotyl (Leon 1964; Tello et al. 1992).
These parts of the plant swell during growth, forming a storage organ resembling a turnip. For simplicity, we will call this organ ‘hypocotyl’, which is the economic product of maca (Fig. 1). The foliage forms a mat, growing in close contact with the ground. The leaves exhibit dimorphism, being larger in the vegetative phase and reduced in the reproductive cycle (Tello et al. 1992). The ‘hypocotyls’ display a variety of colours from purple to cream and yellow (Leon 1964) (Fig. 2). This species is an octoploid with 2n=8x=64 chromosomes (Quirós et al. 1996), considering that the basic genomic number of Lepidieae is x=8 (Fig. 3). Its meiosis is normal, with the chromosomes associating predominantly as bivalents. This type of association
Fig. 5. Generative branch bearing mature siliques.
Promoting the conservation and use of underutilized and neglected crops. 21. 179 indicates that maca is a disomic polyploid. Polyploidy is a common event among the species in the tribe Lepidieae to which maca belongs (Darlington and Wylie 1945).
Most of the pollen collected from the flowers is fertile, as measured by pollen stainability. Consistent with other cruciferous species, pollen grains are trinucleated.
Maca is an annual crop completing its life cycle within a year when climatic conditions are favourable (Quirós et al. 1996). However, often maca considered a biennial plant (Tello et al. 1992) because it has a vegetative cycle followed by a reproductive phase. Furthermore, in the Junín area maca is grown as a biennial by holding the ‘hypocotyls’ underground during the dry season. However, during favourable years, when there is enough moisture in the soil and an absence of killing frosts, plants left in the field complete their life cycle within a year. The vegetative phase includes the expansion and growth of the ‘hypocotyl’ and root. These organs are fully enlarged approximately 7 months after planting. At this time the plants initiate their reproductive phase. Often the first floral buds will appear in a small cluster at the centre of the rosette (Fig. 4), or as solitary flowers in some of the leaf axils, announcing the initiation of the generative shoots, the main reproductive structures. Only a few of the first flowers will produce fruit. Almost at the same time, at the base of the plant, radially and under the leaves, generative shoots will rapidly grow, producing secondary branches. These will generate most of the seed of the plant. Approximately 20 primary generative branches are produced per plant, and each of these will produce approximately 13 secondary branches (AliagaCárdenas 1995). The generative branches will produce profuse flowering racemes for the next 3 months. Each secondary branch will yield racemes with 50-70 flowers each. Therefore, a primary branch will bear close to 1000 flowers. Fruits will set in most of these flowers throughout this period, maturing in approximately 5 weeks (Fig. 5). At this time, the fruits will initiate dehiscence and the mature seed will be released. During the long period of flowering, it is possible to observe both fruits and flowers in the generative branches.
Fig. 6. Maca seed.
180 Maca (Lepidium meyenii Walp.) Approximately 85% of the fruits will bear seeds. Apparently seeds do not have dormancy, germinating in 5-7 days at 25°C and good moisture conditions. A single plant of maca produces approximately 14 g of seeds. One gram contains approximately 1600 seeds. Seeds are small, measuring 2 mm in length, and are light tan to brown in colour (Fig. 6) (Aliaga-Cárdenas 1995).
The flowers of maca are inconspicuous and arranged in axillar racemes. They have four erect, concave sepals, and four small white petals. The ovary is oval and bicarpelar with a short style, which develops into a dehiscent silique of two locules, carrying one seed per locule. Only two stamens (Fig. 7a), or seldom three (Fig. 7b), with well-developed anthers are present in the flowers. A variable number of rudimentary stamens consisting only of filaments is also present (Fig. 7a). The normal number of functional stamens in the family Brassicaceae is six, four larger than the other two. However, androeceum variation reflected in number of complete stamens is a common feature of the genus Lepidium (Thellung 1906). Small nectaries at the base of the stamens are also present. It is unknown, however, whether these are functional. Aliaga-Cárdenas (1995) found that maca is primarily an autogamous species. Pollination is initiated 4-5 days after the flower bud is first visible to the naked eye, and continues for another 3 days. The anthers and petals wither for the next 2 days while the ovary starts to enlarge initiating fruit development. Part of the anthesis takes place while the flower is still closed, thus indicating that the maca flowers are partially cleistogamous. Further evidence of autogamy is provided by spontaneous fruit-setting of flowering plants in growth chambers, where insects were excluded (Quirós et al. 1996). In Junín, the native area of maca production, no insect pollinators working the flowers were observed. Only sporadic visitation by two or three species of Dipterae which landed in the leaves and flowers have been seen (Quirós, unpublished).
In the field at Davis, California, only a few syrphid flies were observed visiting the foliage and seldom the flowers. Plants grown from different accessions are morphologically alike, with a few exceptions. All these observations suggest that maca reproduces predominantly by self-pollination.
Promoting the conservation and use of underutilized and neglected crops. 21.
3 Origin and geographical distribution
3.1 Origin The genus Lepidium is widely distributed throughout the world in all continents except Antarctica. The genus probably originates in the Mediterranean basin where most of the diploid species are found (Thellung 1906; Mummenhoff et al. 1992). Little is known about the time of origin of the genus and the mechanisms responsible for its worldwide distribution. However, most of the existing evidence indicates that long-distance dispersal during the late Tertiary or Quaternary, rather than continental drift, was responsible for the colonization of these species to the Americas and Australia. This seems to be the prevalent mechanism of distribution of other genera in the family such as Capsella and Cardamine (Mummenhoff et al. 1992).
Common genetic features observed in the immigrant species of Lepidium are autogamy and polyploidy, which helps their establishment in new habitats.