«Andean roots and tubers: Ahipa, arracacha, maca and yacon M. Hermann and J. Heller, editors Promoting the conservation and use of underutilized and ...»
8.2 Arracacha in genebanks Efforts to collect arracacha germplasm date back to the early 1970s when both Peruvian institutions, aided financially by the Interamerican Institute for Cooperation in Agriculture (IICA), established arracacha field collections. In 1977, the first of eight international congresses on Andean crops was held and subsequently other field genebanks of arracacha and other Andean root crops were started in the Andean countries, particularly in Peru. The ‘lost decade’ of the 1980s brought civil strife to Peru, and much of what had been collected was lost owing to political instability, the lack of financial resources and even terrorist threats to genebank curators (Dr C. Arbizu, 1989, pers. comm.). Also, the funding of international agencies was channeled mostly to collecting, but little incentive for follow-up activities, especially for the maintenance and characterization, was provided. Ironically, germplasm scientists in the region generally derive more prestige from the size of their holdings than from a small but well-curated collection.
Inflated collections and lacking financial resources proved thus to be a fatal combination that caused some of the loss that occurred. The only two collections 158 Arracacha (Arracacia xanthorrhiza Bancroft) that have essentially kept their holdings are in Quito (INIAP) and Cajamarca (University). Unfortunately, collecting missions during recent decades did not yield herbarium material. This is a source of particular regret when germplasm collections were lost. Informative germplasm catalogues with good location data are available for Peru (Arbizu and Robles 1986) and Ecuador (Tapia et al. 1996).
Table 7 provides an overview on current collections as they have been reported in genebank catalogues or other documents. A total of about 700 clonal accessions of arracacha are currently available from genebanks. Ecuador, northern Peru and parts of southern Peru have been comparatively well covered by collecting missions, but there are no significant collections from Bolivia, Colombia and Venezuela.
Table 7. Reported germplasm holdings of arracacha
Most collections are well documented in terms of passport data, but from the available genebank documentation the status of characterization and evaluation is unclear except for the INIAP holdings in Quito. Yield or other plant performance data from this collection, however, are not very meaningful as they come from a field genebank at 3050 m altitude, where arracacha is poorly adapted. Even by conservative estimates, INIAP’s arracacha collection is highly redundant, with 57% duplicated accessions (Mazón 1993). Based on a study involving the analysis of 75 polymorphic RAPD markers, Blas et al. (1997) estimated the clonal duplication of CIP’s arracacha collection to be 51%. We must assume that other collections have similar degrees of duplication, although there are few data to support this.
The arracacha collection of the International Potato Center is an opportunity collection assembled during multi-tuber crop missions to Chile, Colombia, Bolivia and Peru. It is not the result of systematic explorations of the arracacha genepool.
EMBRAPA-CNPH in Brazil currently holds some 2000 clones, of which 35 have been identified as promising material for distribution within Brazil. All this material was selected from self-set seed progeny of the only commercial Brazilian clone (see Section 8.4). In addition, CNPH conserves 11 Ecuadorean accessions donated from INIAP some years ago.
CATIE in Costa Rica had for some time a collection of 6 accessions, but it appears to have been lost because of poor adaptation to the tropical climate of Turrialba (600 m altitude, approx. 10° N) (Mr J.A. Morera, 1996, pers. comm.).
8.3 Conservation strategies The foregoing section illustrates the effort of many institutions in the Andean countries to preserve the genetic heritage of their countries, but it also shows the infant stage of the conservation of arracacha genetic resources. Mere amassing of materials with little regard for geographical representation or conservation needs is typical for any germplasm collection in its early stages and is a product of our ignorance of the structure and geographical distribution of crop genepools. Even the best-researched collections of global crops are plagued by this syndrome to some extent.
Arracacha, however, is a minor crop and only minor resources can justifiably be allocated to the preservation of its genepool. Also, the clonal diversity in a vegetatively propagated crop is a finite quantity and increasing collecting efforts inevitably result in diminished increments of captured diversity in analogy to the economic law of diminishing returns. It follows then that clonal comprehensiveness of arracacha collections should not be the aim but rather ‘lean’ collections that encapsulate a maximum of diversity in a minimum number of accessions.
The first step to achieve this is to identify clonal duplicates by the use of a number of conventional and molecular techniques, which have become available. The wealth of information that is gained in this process can be used to enhance our understanding of variation in the genepool and gaps in collections, geographic or otherwise, can be identified and targeted.
Arracacha (Arracacia xanthorrhiza Bancroft) In my experience, the clonal conservation of arracacha is cumbersome and prone to losses. To meet the crop’s ecological requirements in the Andes, field collections often have to be located far away from genebank headquarters, where they are difficult and costly to monitor. Although protocols for tissue culture storage of arracacha have now become available (Landázuri 1996), their application cannot always be recommended, as tissue culture laboratories are very vulnerable to the withdrawal of external funding necessary to sustain them. Where institutions have shown a capability to preserve field collections over many years, tissue culture undoubtedly becomes a valuable adjunct to increasing germplasm safety.
In addition to clonal collections, arracacha germplasm should increasingly be stored as sexually reproduced seed. The crop has retained the ability to produce seed and research should be undertaken to better understand the factors that induce flowering. From evidence presented in Section 4.3.1, drought stress and vernalization would appear to be factors involved and research is needed to elucidate the effectiveness of such treatments.
8.4 Crop constraints and breeding Plant breeding is all too often seen by its practitioners as the panacea for overcoming crop constraints. This approach tends to overlook productivity gains from improved cultivation, particularly from applying standard horticultural techniques to arracacha (transplanting, sanitation of planting stocks, improved post-harvest handling). The potential of horticultural intensification probably exceeds the benefits to be had from breeding arracacha with the limited resources available for a minor crop. Also, breeding requires a clear understanding of crop constraints, whether they are related to factors that limit production or consumption. In the absence of meaningful germplasm evaluations and consumer statistics, such an understanding is not available for most arracacha-producing areas.
It is with these reservations that I turn to plant breeding as a means of increasing arracacha’s competitiveness with other crops. The two single most important issues emerging in discussions with growers, extensionists and users are long crop duration and limited post-harvest life. Even when arracacha propagules are pre-cultured (to facilitate rooting and crop establishment), the crop needs 7-8 months from transplanting to harvest (see Section 4.5.1). This limits the crop’s diffusion in two ways. First, entrepreneur farmers aware of the significance of the opportunity cost of land and factor productivity give preference to other vegetables with shorter durations. Second, arracacha does not fit into the tight cropping cycles of densely populated areas, nor can it be expected to expand into more temperate climates unless more precocious cultivars are available (see Section 4.6). Unfortunately, the evidence points to limited variability of crop duration in the cultivated genepool and it is likely that only a combination of genetic improvement or selection with improved crop management will produce the desired results.
There are no data on the extent of genetic variation of root perishability in arracacha collections, but the ubiquity of the problem would suggest that possibilities Promoting the conservation and use of underutilized and neglected crops. 21. 161 of selecting or breeding cultivars with dramatically improved shelf-life are low.
Again, the potential of improved post-harvest handling (see Section 4.5.5) should not be overlooked.
Arracacha root characteristics are the subject of regional or even local preferences (for details see Section 2). It seems that preferences for yellow and intensely flavoured roots in Brazil and for white and weakly flavoured roots in other countries or regions are ingrained in local culinary customs and these need to be taken into account in breeding programmes. On the other hand, no singular cultivar is likely to satisfy the needs of different market segments. For example, some processing companies are mainly concerned about intense and evenly distributed root pigmentation while others place emphasis on high dry matter contents and strong aroma. Yet for direct consumption, weakly flavoured roots may appeal to consumers who find the strong umbelliferous aroma undesirable.
As outlined in Section 4.5.4, arracacha is affected by a number of parasitic organisms but there is no single disease or pest known to limit production across growing areas. Even if the area devoted to arracacha was to expand significantly, it would remain comparatively small and long rotations, known to control diseases and pests, would remain an effective option for phytosanitary control. Therefore, pests and diseases rank low in overall priorities and they should not unnecessarily compound the complexity of breeding programmes.
The breeder also will have to struggle with the practical problems involved in cross-pollinating arracacha. The plant has tiny flowers (see Section 4.2.2), and magnifying aids are necessary to emasculate them. Also the scarcity of pollen makes pollinations a tedious task, and hardly more than 20-50 manual pollinations can be done per hour. Moreover, a fruit develops only a maximum of 2 seeds.
The narrow variation found in the arracacha genepool would have to be widened by the use of wild Arracacia species. These, however, are presently too little known and no germplasm collections are available.
To my knowledge there is only one arracacha breeding programme. It was started in 1987 at EMBRAPA-CNPH in Brasilia and motivated by the need to breed cultivars with adaptations to different environments. All Brazilian arracacha is derived from one clone, but researchers noted that this cultivar releases much useful diversity when reproduced from sexual seed (Dr F.F. Santos, 1992, pers. comm.). Since the plant does not, or rarely so, set seed under the hot and dry conditions of Brasilia, self-set seed has been collected every year between November and January from farmers’ fields in the cooler states of Paraná, Santa Catarina and Minas Gerais. The established seedlings are transplanted into the field and the first screening takes place at plant maturity after a lo-month crop duration. The only genotypes retained are those that show superior vigour and have strong yellow root pigmentation similar or more intense to the commercial clone and cylindrical roots which are preferred for packing. Of many thousand genotypes thus evaluated (2000-20 000 per year) only some 50-100 are further evaluated for agronomic performance, nematode resistance, post-harvest behaviour and reduced crop duration. Only about 162 Arracacha (Arracacia xanthorrhiza Bancroft) 10% of the genotypes will survive this (second) screening cycle and eventually 5-10 new genotypes are added to the collection as advanced materials ready for multilocation trials. However, other materials that are of no immediate interest to Brazil, such as white genotypes, also are retained, or others with exceptional yields, pigmentations, etc. As a result, CNPH has accumulated a collection of 2000 clones including 35 promising accessions, the latter for cultivation in Brazil.
Giordano et al. (1995) report significantly increased yields of several new clones which are distributed to a wide range of environments across Brazil. Also, clones with somewhat reduced crop duration but otherwise similar characteristics to the traditional clone have been identified and are being tested in multilocation trials (Dr F.F. Santos, 1995, pers. comm.).
8.5 Research needs As with so many other minor crops, there is a plethora of possible research questions surrounding arracacha. Previous chapters have highlighted a number of issues that could be approached in only a speculative fashion because of the dearth of data.
Among the most under-investigated topics is certainly the biosystematic relationships of arracacha to its closely related wild relatives. If the ancestry of arracacha could be solved, then an interesting model for the domestication of a unique umbelliferous plant would be at hand.
In the context of this monograph, the following research needs have been identified to back-up the conservation effort: studies of the factors inducing flowering, better understanding of the breeding system, germplasm conservation by sexual seed and the sanitation of planting stocks.
From a production viewpoint, two issues appear to be of utmost importance.
First, how can the crop duration be reduced and what role would a crop model play in achieving this goal? Second, the storage life of the root needs to be improved, by either genetic improvement or better storage technologies.
Finally, processing research and development of new products will be instrumental in promoting this crop for urban consumption. Pilot trials should explore the potential to introduce arracacha outside Latin America.
8.6 Crop prospects In closing this monograph, one might ask what the future will bring for arracacha.