WAGENINGEN AGRICULTURAL UNIVERSITY PAPERS 90-3 (1990) Observations on distribution, ecology and cultivation ofth e tuber-bearing legumegenu sPachyrhizus Rich ,e xDC . Marten S0rensen Department of Botany Royal Veterinary andAgricultural University Rolighedsvej 23 DK-1958 Frederiksberg C (Copenhagen) Denmark OUrVANGEM 2* mmo Wageningen mm Agricultural University ]\\u U^4M »IBUOTHEEÏg CÄMDBOUWUNIVEßSIIEQi WAGENINGEN CIP-dataKoninklijk e Bibliotheek, DenHaa g Sorensen,M . Observations on distributyion, ecology and cultivation of the tuber-bearing legumegenu sPachyrhizu s Rich,e xDC ./ M.S0rensen .- Wageningen :Agricultura l University. - 111.- (Wageningen Agricultural Universitypapers . ISSN0169-345 X; 90-3(1990) ) Withref . ISBN90-6754-168- 0 SISO632. 4UD C 633.49NUGI83 5 Subject headings:Pachyrhizu s/ tuber-bearin glegume . ISBN90-6754-168- 0 NUGI 835 © Agricultural UniversityWageningen ,Th eNetherlands ,1990 . No part of this publication, apart from abstract, bibliographic and brief quo­ tationsembodie di ncritica lreviews ,ma yb ereproduced , re-corded orpublishe d inan yfor mincludin gprint ,photocopy ,microform , elektronico relektromagne - ticrecor dwithou t written permission from thepublishe r Agricultural Universi­ ty,P.O.Bo x9101 ,670 0H BWageningen ,th eNetherlands . Printedi nth eNetherland sb yDrukkeri j Veenman B.V.,Wageninge n Abstract The distribution, ecology and cultivation of the genus Pachyrhizus is examined on the basis of herbarium taxonomie studies, field observations, growth experi­ ments under greenhouse condition and study of relevant literature. The great potential of the genus as a high-yielding tuber crop for tropical countries isconfirme d and specific areas in need of further study are indicated. Contents Introduction 1 Materials and methods 1 General remarks on the genus 2 Notes on the species 3 1. Pachyrhizus erosus (L.) Urban 3 2. Pachyrhizusferrugineus (Piper) Sorensen 6 3. Pachyrhizuspanamensis Clausen 7 4. Pachyrhizus tuberosus (Lam.) Spreng. 7 5. Pachyrhizus ahipa(Wedd. ) Parodi. 9 Biochemical studies of the genus 10 Pests and diseases 14 Growth experiments 16 Conclusions 25 Acknowledgements 26 Lists ofexsiccata e 27 References 36 Introduction The increase of the general agricultural interest in and knowledge of tuberous legumes during the past decade is very noticeable. This interest has previously been limited to a few research centres in India, Thailand and the Philippines. All these institutions (with one exception in Mexico) are situated outside the natural distribution area of the genus attributed with the highest production of leguminous tubers on a world basis; i.e. the genus Pachyrhizus - the yam beans. A number of countries in the third world has experienced dramatic changes in soil quality due to the application of intensified agricultural practices. This especially applies to areas whereth eus eo fartificia l fertilizer and chemical herbi­ cides and pesticides has increased in order to maintain the productivity level of high-yielding grain crops in monoculture. Thus, the interest in these poten­ tially very valuable crops has recently spread to several developing countries in the tropics. The genus Pachyrhizus has been the subject of acomprehensiv e biosystematic study carried out at the Department of Crop Science; The Institute of Botany, both at the Royal Veterinary & Agricultural University, Copenhagen and the Botanical Laboratory, University of Copenhagen. The objective ofthi s research project has been the examination of the potential of the genus as a high-yielding tuber crop through artificial hybridization and preliminary yield estimates (based on experiments carried out under greenhouse conditions). Materials and methods The examination of ecology and distribution of the different species is partly based on the study of herbarium material obtained from the following herbaria: AAU, ARIZ, BAA, BH, BM, BR, BRI, C, COL, CR, F, G, GB, INPA, K, L, LISU, MA, MICH, MO, NY, P, QCA, S, SI, SP, U, UC, US, VEN, and partly onow n observations obtained onfield trip sthroug h theneotropica l distri­ bution area of the genus. Furthermore, the germplasm collection, obtained through field collections and from various botanical and agricultural institu­ tions, forms the basis for the growth experiments (a detailed description of the materials and methods used in these growth experiments is given on page 16). The data on nutritional composition and chemical constituents have been com­ piled from literature and own findings. WageningenAgric. Univ.Papers 90-3 (1990) Generalremark s onth egenu s The 5 species(se eSorense n 1988)ar edistribute d from Central America to North and Central South America, see Fig. 1.I n pre-Columbian times the distribution probably extended further south into Argentina. No collections have been seen from Surinam and French Guyana, but the genus was reported to be cultivated in French Guyana by Bertoni (1910)). Therear esom edifficultie s indeterminin g theexten t ofth enatura l distribution of P. erosus and P. tuberosus, as these two species have been cultivated for a very long period, and have been introduced to a great number of areas. It may, however, be deduced that in isolated areas where the species show little or no morphological variation the occurrence may be the result of a single introduc­ tion. E.g. P. erosus in the Yucatan peninsula, where the history of this crop incultivatio n dates back at least onemillennium , and where there are no records ofundoubtedl y wild material. Undoubtedly wild material of P. erosus is available from Guatemala and Costa Rica, where it was collected by the author in 1985. Its wild origin is con­ firmed by the small size of the seeds, legumes and tubers, and in Costa Rica by the absence of records of P. erosus ever having been cultivated (except for a few recent introductions through agricultural institutions). Clausen (1945) claimed tohav esee non ecollectio n from Costa Rica,marke d ascultivated . How­ ever, this specimen has also been examined by the present author, and from theinformatio n given onth elabe li tbecome seviden t that thisparticula r material was introduced from Mexico for cultivation at the agricultural experiment station atTurrialb a (confirmed byDr .J . Leon, CATIE,Turrialba ,pers .comm.) . The altitudinal range of the genus is from coastal plains to Central Mexican and Andean valleys.P. ahipareache s 2.000m a.s.l. ,P.ferrugineus and P. tubero­ susar e restricted to tropical lowlands, P.panamensis occurs in coastal lowlands, and P. erosusrange s from 0-1.750m a.s.l. in Central and coastal Mexico. The habitat ranges from seasonally dry areas with open bush vegetation to dense humid tropical rain forest. The variation in annual mean precipitation rate isfro m 250-500 mm (in the Yucatan peninsula and coastal regions of Ecua­ dor) to over 1.500m m (Central America and the Amazon region). Cultivation practices vary considerably; on larger scale P. erosus is normally cultivated as a monocrop, on smaller scale P. erosusi s often intercropped with Zea mays, thusprovidin g aroo t crop aswel la sa grai n crop.Thi styp eo f cultiva­ tion alsoha sa beneficial effect on soil fertility because of the symbiotic, nitrogen fixating Rhizobium bacteria. Studies carried out at the Botanical Laboratory, University of Copenhagen, proved that plants (P. erosus) grown with the sym­ biotic bacteria to be superior in yield to plants grown without bacteria, but with artificial nitrogen fertilizer (unpubl. manus.). P. tuberosus is grown in shifting cultivation byth e Indians ofth e Amazon region (Brücher 1977an d Duke 1981). Bertoni (1913) reported that the Indians at the Parana river (Paraguay) used an extract of P. tuberosus leaves as an insecticide. P. ahipa is now grown in 2 WageningenAgric. Univ.Papers 90-3 (1990) monoculture in the high lying valleys of Bolivia and Peru, and was formerly also cultivated in the northern provinces of Jujuy and Salta, Argentina (Parodi 1935, Burkart 1952). In agreement with Pinto Cortés (1973), Zinsou (1987a & b and 1988) and Pauli (1988)i tha sbee nobserve d byth epresen t author that maximal tuber devel­ opment is achieved under short day conditions, i.e. an 11-12hou r photoperiod induces flowering aswel la stube r initiation. Tuber initiation isinduce d 4-6wee k after sowing regardless of length of photoperiod. Albeit, daylengths exceeding 12hour swil lencourag e vegetative growth and reduce tuber development. Addi­ tional increase in tuber development may be obtained by the removal of fertile shoots P. erosus as reported by Arguelles (1979), Noda & Kerr (1983) and Zepeda(1985). The considerable number of chemical investigations of the various parts of the plants (with very few exceptions all the material studied has been obtained from onespecie sonly :P. erosus) ca n conveniently beseparate d intotw o subjects: nutritional and insecticidal, i.e. tubers and seeds/pods respectively. The findings ofth e research published prior to thecompletio n ofth epresen t paper are treated in a later paragraph. Notes on the species 1.Pachyrhizu serosu s(L. ) Urban Morphology: A herbaceous vine, with great variation in the outline of the leaf­ lets, from dentate to palmate. The species is defined by the lack of hairs on the petals, the number of flowers (4-11) per lateral inflorescence axes and the length of the inflorescence, 8-45 cm. Furthermore, morphological characters of the legumes (pods), qualitative as well as quantitative, are used to separate the species. The size, 6-13 cm x 8-17 mm, the reduction of the strigose hairs at maturity and the colour, pale brown to olive-green/brown are characters spe­ cific to the legume of P. erosus. A number of seed characters are also specific, the colour being olive-green, brown or reddish brown, and the shape is flat, square to rounded. Distribution: Known in the wild state from the following areas:Th e Mexican states of Jalisco, Guanajuato, San Louis Potosi, Michoacan, Morelos, Puebla, Guerrero, Oaxaca, Vera Cruz and Chiapas. Central and Western Guatemala, El Salvador, Western Honduras, Western Nicaragua and Northwestern Costa Rica;(figur e 1.).