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«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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The amounts of essential amino acids in extracted (crude) protein the Mexican yam bean according to Evans et al. (1977) are listed in Table 3 in relation to the recommended values of the FAO/WHO (1989). As may be seen from the essential amino acid index (EAA) the chemical score of all amino acids exceeds the recommended values with the exception of the two amino acids, methionine and cysteine, where the EAA index is 1. These two amino acid contents are generally regarded as being limited in legumes.

Nevertheless, more precise information about the EAA values and range for the Andean yam bean is important. In particular, further evaluations of the ratio between crude protein and small peptides with different genotypes are urgently needed, especially as this ratio is presently regarded as poor (Evans et al. 1977).

In addition to the interesting and valuable protein content, the tuber is very rich in carbohydrates, which provides energy. The range of the starch content is between 45 and 55% and of the sugar between 8 and 24% (pers. observ.), whereas the lipid content is below 1% (Dr A. Borcherding, pers. comm.). Despite the lack of digestibility experiments it appears from the biochemical composition that the P. ahipa tubers have a very good nutritional composition. Nevertheless, the protein and energy concentration may be classified as being medium because of the high moisture content in the tuber — the major constraint of P. ahipa, if the crop is to be readily accepted by consumers used to the traditional starchy root crops outside its present distribution.

Ahipa (Pachyrhizus ahipa (Wedd.) Parodi) Table 3. Amino acid composition of Mexican Yam Bean (P. erosus) according to Evans et al. (1977) in comparison with the recommended FAO/WHO values (FAO/WHO 1989)

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4.4 Industrial and other aspects In addition to the recent advances in the evaluation of the Andean yam bean as a new vegetable crop in Europe, the evaluation of the P. ahipa tuber as a renewable resource crop has become of interest. This is mainly because of the high starch content and the high proportional amount of amylopectin (see above). Therefore, the Andean yam bean starch would represent a nearly perfect raw material for the starch industry.

However, the suitability of the P. ahipa starch for the industry will depend on several additional factors such as the extractability of the starch, the diameter of the starch particles/grains and their distribution. Examinations of these starch characteristics are in progress at the Georg-August University Göttingen.

The industrial use of the protein content of the tubers may also be of commercial interest. The protein market is of high economic interest to the European Union as Europe has to import several million tonnes of soyabean (Glycine max (L.) Merr.) protein each year. Also, the total tuber protein yield per hectare of P. ahipa exceeds that of soyabean seed protein. However, 80% of the protein is water-soluble and not extractable within a pH range of 2-10. This characteristic may be an advantage to the food industry (Dr A. Borcherding, pers. comm.).

Of further interest is the sugar and fibre content of the P. ahipa tuber, although the use of either component seems only to be worthwhile provided both the starch and protein contents can be used. The potential exploitation of the saccharose content is mainly of interest as a by-product. Regarding the P. ahipa tuber fibre the mechanics Promoting the conservation and use of underutilized and neglected crops. 21. 31 Table 4. Comparison of starch yields of indigenous (European) starch crops (yield potentials in classic crop areas) and P. ahipa

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of the fibre within a thermoplastic matrix were compared in a preliminary survey with flax (Linum usitatissimum L.) and ramie (Boehmeria nivea (L.) Gaudich.). Even though the results were unclear, it will be worthwhile to investigate this possibility in the future (Dr Bader, pers. comm.) To demonstrate the attractive possible uses of the Andean yam bean in the nonfood sector the authors have calculated the starch yield per hectare in comparison with the yields of other starch-producing crops on the basis of P. ahipa field experiments in Portugal (Table 4).

Ahipa (Pachyrhizus ahipa (Wedd.) Parodi) 5 Uses The tuber is used as a vegetable, as mentioned earlier. It is locally considered as being a fruit rather than a vegetable, hence it is marketed by the street or market vendors selling fruits and not vendors of vegetables, according to Ørting et al. (1996).

It is consumed raw like an apple, in various dishes or as juice.

No records on the use of the insecticidal properties or ethnobotanical uses of the plant are known to the authors, but during the interviews conducted in Bolivia by Ørting et al. (1996) it was repeatedly stated that the consumption of P. ahipa tubers is considered to have a cleansing effect upon the body, that it is beneficial to the lungs, and curative to infections of the air passage, i.e. coughs, etc. Ørting et al. (1996) did not encounter persons confirming the report by Cárdenas (1969) that P. ahipa tubers are considered curative for gout in Bolivia.

The economy of P. ahipa production in Bolivia was also studied by Ørting et al.

(1996). At the central markets in the major cities the price of P. ahipa per kilogram is comparable to the price of groundnuts (Arachis hypogæa L.) and potatoes (Solanum tuberosum L.) - 1994 prices: US$0.5-1.0. The price at the local markets is somewhat lower (US$0.25), the price obtained when selling to wholesalers varies (US$0.l5kg). The optimal price is obtained during May-June, while the lowest is from August-September, when the competition by fruits produced in Las Yungas is at its peak. Apparently the wholesalers make a gross profit of 50-100% when reselling to the retailers. The latter will then also increase the price by 50-100%. Even though the price per kilogram of P. ahipa tubers was higher than that of potatoes or cassava (Manihot esculenta Crantz), the profit per unit area for these or other tuber/root crops may exceed that of P. ahipa, but more importantly these other crops provide a continuous cash flow throughout the year in contrast to a short-season crop like P. ahipa. The market share of P. ahipa in both urban and rural areas is small and is steadily declining, possibly as a result of an increased demand for industrially produced soft drinks in combination with the labour-demanding practice of reproductive pruning.

The marketing of P. ahipa associated with the religious festival of 'Corpus Cristi' may indicate some linkage with ancient religious uses.

Promoting the conservation and use of underutilized and neglected crops. 21. 33 6 Genetic resources: range of diversity for major characteristics In 1985, when the Yam Bean Project was initiated, few seed samples and very little information about the yam bean species were available from the worlds various genebanks. Through different contacts some 20 samples of the Mexican yam bean (P. erosus) and two samples of the Andean species (P. ahipa) were procured, but there were virtually no details concerning the exact origin of this material, the cultivation practices involved or other relevant data. Thus, in order to make a comprehensive examination of the crop’s potential, a thorough recording of the natural and cultivated distribution of the genus, based on information available from herbarium specimens, had to be undertaken (Grum et al. 1991a; Sørensen et al. 1993).

Subsequently, a number of field collections were carried out and today approximately 200 sample groups, covering both wild and cultivated material, are available for the hybridization and evaluation experiments currently in progress.

In P. ahipa the recent analysis of infraspecific variation conducted by Ørting (1996a) under greenhouse conditions has clearly succeeded in demonstrating that what was previously regarded as a quite homogeneous taxon does in fact possess a wide range of morphological and physiological diversity Figures 3-6 show the variability in stem length, number of flowers produced by individual plants, pollen fertility and development stages. Both twining vines and genotypes with very short internodes having an erect bushy growth habit exist. Furthermore, both multituberous and monotuberous lines have been identified (though the monotuberous form appears to be dominant). Sørensen (1996, Table 2) gives an overview of the morphological variation of 27 characters in the five species.

Strikingly different abscission rates exist, and the number of flowers produced by the individual plant as well as the actual number of seeds produced per plant differ considerably. The yield of the 20 accessions so far analyzed also differs.

Field evaluations recently conducted in Tonga have served to further substantiate the diversity available within this species, as have the physiological droughttolerance studies conducted by Prof. Vieira da Silva (Univ. Paris VII) and Dr D.J.M.

Annerose (CERAAS, Senegal). The recent examination of photothermal sensitivity and the rotenone/rotenoid contents of the species, conducted by Prof. Válio and his associates, will certainly serve to increase the available information on the diversity of P. ahipa.

Ahipa (Pachyrhizus ahipa (Wedd.) Parodi)

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AC102 AC201 AC202 AC203 AC204 AC205 AC206 AC207L AC207S AC208 AC209 AC213 AC214 AC215 AC216 AC217 AC521 AC524 AC525 AC526 Fig. 3. Stem lengths of individual plants in 20 P. ahipa accessions (each bar represents one plant).

Promoting the conservation and use of underutilized and neglected crops. 21. 35

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Fig. 5. Pollen fertility (%) of individual plants in 20 P. ahipa accessions (each bar represents one plant).

Promoting the conservation and use of underutilized and neglected crops. 21. 37

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7 Geographical distribution of important traits in the entire genepool The initial analysis of existing genetic variation within the 31 accessions available demonstrated the presence of highly significant differences in growth habit. It furthermore became apparent that this trait follows a geographical distribution from north to south with the strongest vine-like genotypes to the north near La Paz in Bolivia and the smallest, bushy landraces to the South in the provinces of Chuquisaca and Tarija, Bolivia and in the provinces of Jujuy and Salta, Argentina (Fig. 2). The considerable difference in flower/seed production recorded between the different accessions may well be the result of differences in the agronomic selection pressure, i.e. the short bushy landraces produced fewer than 100 flowers and fewer than 20 seeds per plant and had pollen fertility percentages of less than 45% whereas several accessions from the La Paz area produced more than 800 flowers and more than 100 seeds per plant and had practically 100% fertile pollen (see Figs. 4 and 5). The abscission rate also varied significantly as did the pollen fertility percentages (Ørting 1996a, Table 3).

Promoting the conservation and use of underutilized and neglected crops. 21. 39 8 Importance of wild relatives as a source of diversity If the high disease and pest resistance observed in P. ferrugineus, recorded in multiplication plots in Tonga, Ecuador and Costa Rica, can be successfully transferred to the cultivars this would be of obvious agronomic interest. However, although interspecific hybridization experiments have been attempted repeatedly in both Costa Rica and Tonga, so far all combinations involving this species have been unsuccessful. The ecological association of P. ferrugineus with soil types low in available phosphorus may also be of potential breeding interest (see Manu et al. 1996), as could the evergreen habit.

The interspecific hybridization experiments have, as mentioned in Section 2.2, primarily involved cross-breeding between the three cultivated species P. erosus, P. ahipa and P. tuberosus. But the wild populations belonging to P. erosus from either the Department of Huehuetenango, Guatemala or from the Province of Guanacaste, Costa Rica and the wild species P. panamensis also have been used in interspecific crosses. The objective of the experiments is the transfer of the strigose pubescence of the vegetative parts and subcoriaceous leaf type to high-yielding genotypes that are susceptible to insect damage and/or which may need improved drought tolerance in order to increase the climatic adaptability. The strigose pubescence has been successfully transferred and, among the resulting hybrids, genotypes with high yield potential have been identified (Dr P.E. Nielsen, pers. comm.).

Until actual analyses of the variability in the rotenone content of the two wild species as well as the wild populations of the cultivated species have been concluded, it can only be theorised whether some genotypes among these groups may possess sufficiently high levels of rotenone to make the extraction of seeds from interspecific hybrids involving these genotypes and P. ahipa commercially interesting.

Ahipa (Pachyrhizus ahipa (Wedd.) Parodi) 9 Institutions holding germplasm collections A comprehensive list of the institutions holding Pachyrhizus ahipa germplasm (and Pachyrhizus germplasm in general) is given in Appendix I. Seed samples of especially P. erosus landraces have been made available from a large number of institutions to the partners within the Yam Bean Project. The viability of the received germplasm (all species) varied from 0 to 100%. Pachyrhiztus seeds lose viability within one year if insufficiently dried and not kept under cool conditions. Yam bean has orthodox seed storage behaviour. A moisture content of less than 10% (5% is preferable) if the seeds are to be stored for prolonged periods and a temperature below 5°C is recommended.

Of the Pachyrhizus material registered with institutions holding germplasm collections as listed by IBPGR (1981), 98% represent one species only: P. erosus (some accessions may have been registered as belonging to other species, and misidentifications are common).

Very few of the institutions involved have the financial means, interest and knowledge necessary to implement an efficient rejuvenation programme. Hence, a number of the recorded accessions – stored with institutions not part of the Yam Bean Project – are no longer viable and only if complete passport data have been filed will the individual records be of interest.

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