GOBIERNO DE LA CIUDAD DE BUENOS AIRES

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

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

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.