«Andean roots and tubers: Ahipa, arracacha, maca and yacon M. Hermann and J. Heller, editors Promoting the conservation and use of underutilized and ...»
Today the principal germplasm collections are located with the individual partners linked within the Yam Bean Project. A complete collection is kept at Research Division, Ministry of Agriculture and Forestry, Tonga (South Pacific) where all accessions have been rejuvenated at regular intervals, and a core collection is kept at the Botanical Section, Royal Veterinary and Agricultural University, Copenhagen, Denmark. All available passport data are included in the germplasm list available from the authors. The completion of a comprehensive catalogue, which is to include experimental data on each accession from the field trials conducted pantropically, is currently in progress. This will be a valuable tool when selecting genotypes for introduction to new regions.
The largest collection kept by any institution not associated with the Yam Bean Project is kept at the Southern Regional Plant Introduction Station, USDA-ARS in Georgia, USA, although this institution does not store any P. ahipa accessions.
9.1 Availability of data on individual accessions Generally the available data on individual accessions is limited to the origin (although a number of accessions kept at different institutions are of unknown origin) with little or no geographic, climatic, edaphic, ecological and agronomic data. This has been one of the major constraints when evaluating accessions obtained from existing germplasm collections. Furthermore, it is difficult to assess the influence of the multiplication, i.e. selection, method used for seed production in the place of origin when comparing the performance of different landraces, e.g. Ørting et al. (1996) found that Bolivian farmers use very different criteria when selecting plants for seed production (see Section 2.2). The methods used are quite unlike the method commonly used in P. erosus where a special plot is cultivated for seed production only.
Promoting the conservation and use of underutilized and neglected crops. 21. 41 An effort to collect as much information as possible on the cultivation practices associated with each accession has been made on the field collections conducted by colleagues within the Yam Bean Project (Ørting 1996b; Ørting et al. 1996; Sørensen et al. 1997). To facilitate the field observations, a comprehensive questionnaire was developed, targeting a uniform data-set of information that enables statistical comparisons (Ørting et al. 1996).
9.2 Gaps in existing collections Among the known gaps in the existing germplasm collections the lack of any wild P. ahipa material is probably the most widely recognized. If the report by Ing. Agr.
J. Rea from Bolivia (pers. comm.) concerning the recent collection of such material can be further substantiated, and the material be made available for taxonomic and agronomic research, this would provide valuable information on the phylogeny of this species and be of considerable interest to present and future breeding programmes.
From what little is known of the extant landraces of the Tarija Province, Bolivia as well as those from the Argentinian provinces of Salta and Jujuy (so far only two accessions known to originate in this southernmost part of the distribution area are included in the germplasm collection), these landraces are morphologically distinct in their short bushy growth habit and earliness and have been identified as being highly efficient plants when considering the three most important quantitative traits: (1) tuberous root growth – high, (2) growth of the aboveground vegetative parts – determinate and erect/bushy, and (3) reproductive shoot formation – limited. A survey of these landraces is clearly of high priority. As previously mentioned no record is known to the authors of any extant P. ahipa landraces in Peru. However, according to Dr C. Arbizu (pers. comm.), P. ahipa may still be found in cultivation in the Tarapoto area and perhaps further south in the Cuzco, Apurimac and Juni Provinces, Peru, i.e. areas where the traditional cultivation systems as well as climatic and edaphic conditions resemble the main production areas in Bolivia. Material from these regions may well be extremely attractive for breeding, because this material would fill the gap between the Bolivian P. ahipa genotypes and the Chuin cultivar group ( P. tuberosus ) from the Ucayali river (see Sørensen et al. 1997). The last group is of extreme value to the yam bean germplasm, as it is suitable for cooking (used like manioc) owing to its high dry matter/starch content. Therefore, within the regions mentioned above a high dry matter genotype of P. ahipa may exist.
9.3 Conservation of the species (ex situ, in situ, on-farm) At present only ex situ conservation techniques are being used to preserve the germplasm collected. Indirectly, in situ conservation of wild population of P. ferrugineus, P. panamensis and P. tuberosus is used because populations belonging to these three species are located in national parks and forestry reserves and are thus in no imminent danger of becoming extinct.
Ahipa (Pachyrhizus ahipa (Wedd.) Parodi) Alternative in situ methods of conserving rare and endangered landraces are rapidly becoming apparent when surveying the status of the still extant landraces.
In the case of the Andean P. ahipa, the two surveys of the Bolivian and Argentinean P. ahipa conducted in April-June 1994 and in May-June 1996 recorded the present status of P. ahipa in cultivation, examined the infraspecific variation and conserved as many extant local landraces as possible (Ørting 1996b; Ørting et al. 1996).
During the 9 weeks of the first survey some 16 localities were visited, 24 farmers were interviewed and 17 new accessions (15 P. ahipa and 2 P. tuberosus) were collected. The second survey included visits to some 14 localities, 23 farmers were interviewed and 12 new accessions were collected. This proves that landraces are still to be found, but what transpired from the interviews and which calls for urgent initiatives was that only 65% of the farmers intended to continue to cultivate this crop.
When considering in situ /on-farm methods to conserve these endangered landraces, such efforts could well become successful for P. ahipa, especially if the authorities responsible for the agricultural policies were to promote the marketing of P. ahipa tubers. The present knowledge and interest is very limited.
9.4 Use of germplasm in research/breeding/crop improvement programmes In principle all accessions included in the Yam Bean Project collection of germplasm have been or will be morphologically described and evaluated for agronomic and breeding potential. This process obviously depends on the seed quantity available, i.e. successful multiplication of small samples. The results from field trials using some 50 accessions including all species have been published (Grum et al. 1991b, 1994, 1997).
In the course of the field trials traits such as tuber shape, tuber yield, protein content of the tubers and required vegetation period have been evaluated. In addition to the field experiment conducted in several tropical countries, three series of P. ahipa field trials have been successfully carried out under Mediterranean conditions for three consecutive seasons in northeast Portugal (Prof. J. Vieira da Silva, pers. comm.). Special tuber quality evaluation programmes involving P. ahipa have been initiated in Germany, focusing on dry matter content, protein, starch and sugar contents and composition under greenhouse conditions (pers. observ.).
Furthermore, initial hybridization experiments were conducted in order to examine the interspecific compatibility of the three cultivated species – P. erosus, P. ahipa and P. tuberosus (Grum 1994; Heredia G. 1994; Sørensen 1989, 1991; Sørensen et al. 1993).
The production of fertile interspecific hybrids from all combinations (including reciprocal crosses) is possible, although patience and numerous pollinated flowers are needed for hybrid seed formation. This has been demonstrated repeatedly in hybridization experiments with all Pachyrhizus species (Grum 1994; Heredia G. 1994;
Sørensen 1989, 1991; Sørensen et al. 1993). These experiments are not only of interest in phylogenetic studies, but interspecific hybrids must be regarded as being of Promoting the conservation and use of underutilized and neglected crops. 21. 43 considerable importance in breeding, because the entire Pachyrhizus genepool may in this way be used in a breeding programme.
Field trials evaluating the initial interspecific hybrids have been in progress since
1989. The interspecific hybrid production has been carried out as one-way crosses, e.g. P. erosus x ahipa (Fig. 7), P. erosus x tuberosus and P. tuberosus x ahipa, as well as three-way crosses, e.g. P. tuberosus x ( P. erosus x ahipa ). Material of these experimental hybrids is now approaching non-segregating generations (F6 or later). The selected lines are regarded as being extremely agronomically and commercially interesting according to information from Ing. Agr. A. Heredia Z. (pers. comm.). This material may be released to producers in 1-2 years. The new 'cultivars' of P. erosus x ahipa origin will possess several traits originating in either species, e.g. the tuber quality of P. erosus combined with the erect, determinate growth habit and earliness found in P. ahipa (Fig. 7).
In breeding research the hybrids will be of importance when estimating the range of genetic parameters and the base of negative secondary effects within wide crosses in pre-breeding material.
Fig. 7. Interspecific hybrid (F4), from original cross of EC032 (P. erosus from Mexico, State of Yucatan, Kantunil) x AC102. Grown at the CEBAJ experimental station near Celaya, State of Guanajuato, Mexico. Photo, E. Heredia G.
44 Ahipa (Pachyrhizus ahipa (Wedd.) Parodi) 10 Breeding As mentioned above, a wider variation of P. ahipa material has become available for plant breeding only recently. Four accessions only were available prior to 1994, in 1994 an additional 14 accessions were added, and finally in 1996 a further 12 accessions were included (Ørting 1996b; Ørting et al. 1996). Nonetheless, P. ahipa has gained a remarkable attraction for applied and theoretical aspects in plant breeding.
10.1 Strategy for the traditional and more advanced production areas In general a suitable breeding strategy depends mainly on the reproduction biology and the applicable sources of variation. For the reproduction biology, P. ahipa may be treated as a cloneable, annual self-pollinator as mentioned. However, for breeding and production it must be propagated sexually because the reproductive rate by cloning from tubers is low (1-2) compared with potatoes (10-15). Of course this rate is certainly higher if biotechnological propagation methods or cuttings are used.
Nevertheless, the possibility of plant propagation by seed in P. ahipa and the other Pachyrhizus species may be regarded as an advantage, to avoid transmission of virus and to avoid costly storage of propagation material. With regard to the applicable sources of variation, in P. ahipa all possibilities still exist. There is considerable variation between and within landraces. Also the use of the entire Pachyrhizus genepool via fertile hybrid production within and between species may be considered.
The work on all current breeding challenges is possible by selection between and within landraces or by selection between and within cross/hybrid progenies, apart from the fact that creation of genetic variation in P. erosus induced by radiation has been conducted in India (Nair 1989; Nair and Abraham 1985, 1989,1990).
The utilization of existing variation within and between landraces for selection has been carried out by positive mass selection, e.g. in Portugal and Mexico. These field experiments were conducted using the accessions AC201, AC524 and AC521.
Until 1992 only this material had been sufficiently multiplied to allow mass selection to be conducted.
From breeding experiments with the Mexican yam bean (= P. erosus ) it may be concluded that the mass selection procedure within landraces is very efficient, especially on traits like crop duration, pod-formation, tuber size and shape, yield and geographic adaptability. All known cultivars of P. erosus – Mexican, Indian or Far Eastern—are the result of mass selection without the induction of genetic variation via crosses.
The main emphasis is currently given to individual plant selection of landrace material by testing of single-plant progenies. These tests are carried out under greenhouse conditions and a series of field experiments, the latter coordinated by the Yam Bean Project. At present, this is undertaken with all presently available P. ahipa accessions, including the material collected in 1994 and 1996 (Ørting 1996b;
Ørting et al. 1996).
In spite of the high short-term selection response expected through the selection in landrace material, the target of this procedure is not to release superior material Promoting the conservation and use of underutilized and neglected crops. 21. 45 for agronomic production. The main target is to identify interesting parental lines for cross-breeding.
The introduction of new variation via crosses combined with selection of singleplant progenies that have been sufficiently multiplied to conduct enough pure line field tests is generally the backbone in any breeding programme in self-fertilizing species. In P. ahipa this has been undertaken with F5 and F6 derived-material of all pair crosses between accessions AC201, AC521 and AC524. This non-segregating material is currently being evaluated in field trials in Mexico and according to information by Ing. Agr. A. Heredia Z. (pers. comm.) this material may be released to producers in the near future.
The main emphasis in these experiments is given to the combination of superior characters, e.g. tuber shape and required growth period. To conduct this on a large scale, with accession material and with material that shows highly significant genetic distance, was until recently possible to a limited extent only. The limitations were (1) small botanical seed samples of two of the three accessions used as cross-breeding parents, and (2) different indications that the whole material originates from one region in south Bolivia. This situation changed owing to the mentioned Bolivian and Argentinean collecting trips, but no pure line material is presently available.