«Andean roots and tubers: Ahipa, arracacha, maca and yacon M. Hermann and J. Heller, editors Promoting the conservation and use of underutilized and ...»
(1991) recommend, for the cerrado latosols (poor in P and K), 600 kg/ha of compound fertilizers (N-P-K = 4-14-8) and an additional 20 kg/ha of borax every second year. However, Mesquita-Filho et al. (1996), who investigated the effects of borax fertilization on loamy latosols, found that borax dressings of 60 kg/ha (in a range of 0-90 kg/ha) gave the highest arracacha yields. With nitrogen supplies higher than those indicated above, arracacha produces exuberant foliage, harvest indices drop and crop duration is prolonged.
4.5.3 Harvest Root bulking is notoriously late in arracacha. Therefore, the crop is harvested, in general, not earlier than 10 months after planting, especially if unrooted propagules were used. Farmers, however, are compensated for the inconvenience of long crop duration by the possibility of leaving the crop in the ground for later harvest, either to profit from rising prices or to take advantage of seasonally changing availability of family labour. Typically, harvest takes place after 12 months but can be delayed up to 16 months after planting. Harvesting begins with completely pulling up the plants with the roots. The roots are easily broken away from the plant and the remaining crown is divided into rootstock (mostly for feed) and cormels. Often the entire crowns are left in a heap for a few days or weeks until needed for the preparation of propagules. To maintain a given area of arracacha, only one cormel per harvested plant is needed and the remaining aerial plant mass is used for feed or left to rot.
A continuous range of yields from 3 to 63 t/ha has been reported in a collection of Ecuadorean germplasm (Nieto 1993), but it is not clear how much of this variation is genetic. Yield figures usually include the storage roots as the only marketable product, but because of the highly variable dry matter partitioning of the plant, the total of roots and rootstocks would be a more appropriate measure for the capacity of the plant to build up starchy dry matter. For example, in varietal trials in the Sabana de Bogota comprising nine varieties, average yields of 20.1±4.2 t/ha were reported, of which only 3.22±1.78 t/ha were storage roots and the remainder were rootstocks (calculated from data in Higuita 1969). As will be seen in Section 5, the chemical composition of the rootstock is very similar to that of the storage root and could therefore have potential for processing.
In general, root yields are below 20 t/ha and reflect growth under residual nutrient availability. According to a nation-wide survey conducted by Santos (1993), average yields in Brazil are 8 t/ha. Where adequate care is provided to the crop through irrigation, fertilization and the use of appropriate propagules, arracacha Promoting the conservation and use of underutilized and neglected crops. 21. 113 yields are well above the national average (20 t/ha), even in the arid cerrado uplands of Goiás (1000 m altitude, 16° S), hitherto considered unsuitable for arracacha culture (Santos 1993).
4.5.4 Pests and diseases Arracacha is generally regarded as a robust crop with few disease or pest problems if it is appropriately rotated. But insects, bacteria and fungi can cause significant damage.
According to my field observations, acari (Tetranychus urticue) harm the crop frequently and are the most widespread and serious arracacha pest (Normanha and Silva 1963; Higuita 1969; Fornazier 1996). A beetle pest locally called 'chisa' is increasingly limiting arracacha culture in Tolima, Colombia (Mr J. Rivera Varón, 1996, pers. comm.; Sánchez and Vásquez 1996). 'Chisa' larvae mine the root and up to 40% of yield losses are reported. They belong to several genera of the subfamily Melolonthinae of the Scarabaeidae (Cyclocephala, Ancognata, Phyllophaga, Serica, Macroductylus, Plectris, Issonychus, Anomala ). Sánchez and Vásquez (1996) claim that excessive use of pesticides occurs in Colombia to combat the pest. Other minor pests in Brazil include the moth Agrotis ipsilon and the mining larvae of the beetle Conotrachelus cristatus (Fornazier 1996). In Brazil, nematodes of genus Meloidogyne have become a problem, but they can be controlled readily by long rotations (Santos et al. 1991; Ventura and Costa 1996).
Among bacteria, Erwinia species are widely considered to be the most harmful to storage roots both in the field and in the store (Ventura and Costa 1996). Erwinia occurs especially at high temperatures. It infects the plant systemically and the disease is thus distributed via the propagules (Reyes 1970; Camino and Díaz 1972;
Zapata and Pardo 1974).
A number of fungi attack different plant organs of arracacha. The most important disease in Brazil, especially in conditions of high soil moisture, is Sclerotinia sclerotiorum. It causes the plant and roots to rot and may lead to total crop losses.
Rotation is recommended to combat the disease. Other fungi damaging the roots in the field and during storage include Sclerotium rolfsii, Fusarium sp., Phoma sp. and Rhizopus sp. (Normanha and Silva 1963; Ventura and Costa 1996). Leaf spot diseases in arracacha are caused by Septoria sp., Cercospora sp. and Xanthomonas campestris pv.
arracaciae (Ventura and Costa 1996).
Several arracacha viruses and their features have been described (Jones and Kenten 1978, 1981; Kenten and Jones 1979), but it is not clear how they affect plant performance and yield. No degeneration of arracacha seed stocks has been observed as it occurs in the case of virus-infested potatoes. To date, five viruses infecting arracacha are known: AVA (arracacha virus A, nepovirus), AVB (arracacha virus B, nepovirus), the potyvirus AP-1, the carlavirus AV-3 and PBRV/A, a recently found variant of the potato black ring spot virus. PBRV/A was found to infect a range of potato cultivars (Lizárraga et al. 1994). Recently, simple and multiple virus infections were found in a sample of 40 plants belonging to 10 Ecuadorean arracacha accessions.
Arracacha (Arracacia xanthorrhiza Bancroft) Only 23% of the plants were free of the five arracacha viruses tested. AP-1 and AVwere found in 53 and 38% of the plants, respectively (Mr L.M. Duque, 1996, pers.
comm.). These two viruses also accounted for most of the infections found in a sample of Peruvian arracacha accessions (Lizárraga 1997).
4.5.5 Post-harvest For a root, arracacha must be considered highly perishable and this constrains the commercial exploitation of the crop. Within a few days after harvest, and before the roots actually start to deteriorate, they develop brown spots, lose their brilliance and become unattractive in market displays. Also, large roots frequently crack at harvest even when carefully handled. The marketable life of arracacha at 25°C extends barely a week, the main cause for deterioration being rapid weight loss and subsequent rotting (Czyhrinciw and Jaffé 1951; Thompson 1980). Thompson observed that roots, at 18.5°C and 69% relative humidity, had lost 10.6% weight in 7 days. Under these conditions infections with Rhizopus, Penicillium, Aspergillum, Nigrospora, Mucor and Syncephulastrum occurred after 4 days. Arracacha is much more susceptible than carrot to mechanical damage which causes soft lesions and subsequent infections with opportunistic parasites (Henz 1995).
Deterioration, however, can be delayed over several weeks, either by reducing storage temperatures (3°C or 12°C; Czyhrinciw and Jaffé 1951), or, more economically, by measures that prevent root desiccation. A promising approach involves the application of plastic wrappings to individual roots. Using PVC cling or shrink films, Thompson reports a reduction of daily weight loss rate to less than 1 g/kg compared with about 17 g/kg for unwrapped roots. Likewise, Casali et al.
(1988) found minimal weight loss (1%) of roots “stored in polyethylene film” during 90 days at 5°C.
Leaving arracacha roots unwashed has also proved to enhance shelf-life (Thompson 1980; Câmara 1984b), but markets usually require washed roots. In this context, it is interesting to note that the Sibundoy Indians in Colombia used to bury harvested arracachas to keep them fresh for up to three weeks (Bristol 1988). Washing itself does not cause deterioration but rather the small wounds inflicted on the root surface during handling. These provide entry points for bacteria (Henz 1995). In Brazil, the most common post-harvest diseases are caused by the bacterium Erwinia and by the fungus Rhizopus (Henz 1995). Revetti (1967) reports doubled shelf-life after gamma-irradiation of arracacha.
Arracacha plant crowns discarded at harvest and often left near fields may survive for several months and this demonstrates that the storability of these parts is much better than that of the storage roots, despite the fact that they closely resemble the roots in chemical composition.
4.6 Crop ecology No experimental data on the ecological requirements of crop growth of arracacha are available, but a number of conclusions can be drawn from the analysis of Promoting the conservation and use of underutilized and neglected crops. 21.
temperature and rainfall patterns at arracacha-growing sites, which display enormously varying ecological conditions (Fig. 13). Altitudes range from 900 m (coastal Peru) to 3300 m (Peru, Bolivia) and annual rainfall varies from 0-30 mm (coastal Peru) to 5000 mm (Sibundoy, southern Colombia). Near the equator, arracacha is grown in the diurnal climate of tropical highlands, usually above 2000 m altitude. Farther away from the equator, such as in the subtropical climates of southern Brazil (not south of 26° S) the seasonal variation of temperature (and daylength) is much more pronounced and the crop is confined to lower altitudes where mean daily minimum temperatures during the cold season are above 5°C.
Because frost kills the plant, plantations at high altitudes in southern Brazil (1000 m) are at risk in the three coldest months of the year. If cultivars with reduced crop duration became available, arracacha could possibly be cultivated in the 7-8 frostfree months of many climates at higher latitudes and altitudes. It is not clear why the plant is not cultivated in the tropical lowlands, but there is some evidence from Florida that arracacha does not produce storage roots in hot and wet environments (Hodge 1954). On the other hand, I have recently seen well-developed arracacha plantings with precocious storage root bulking in the hot, albeit semi-arid, conditions
of the upper São Francisco valley (northern Minas Gerais, Brazil; locality:
Mocambinho, 14°55’ S, 43°57’ W, 450 m altitude; mean daily minimum (maximum) temperatures: 15-20 (30-33)°C). It remains to be seen whether arracacha can be cropped sustainably in the hot tropics where pests and diseases, particularly bacteria afflicting storage roots, are often more of a problem than in cooler environments.
Mean monthly temperatures in arracacha-growing sites vary mostly between 15 and 20°C; they rarely exceed 20°C (see Fig. 13).
Although the formidable storage tissues of arracacha may confer some resistance against temporary drought, the plant thrives best when soil moisture is available throughout the cropping cycle. This may partly explain the widespread cultivation of arracacha in the humid Venezuelan and Colombian Andes with their bimodal rainfall patterns (see climate diagrams for Mérida, Bogotá and Pasto in Fig. 13). Also the rather wet conditions of Paraná, southern Brazil (exemplified by the diagram of Curitiba, Fig. 13), and of the Amazonian slopes of the Andes (no diagrams shown) allow its rain-fed cultivation with annual precipitations well over 1000 mm.
However, root yields can double in southern Brazil when supplementary irrigation is provided (Dr F.F. Santos, 1995, pers. comm.). At sites with pronounced dry seasons (usually with less than 1000 mm precipitation) or in arid environments, however, arracacha needs to be irrigated; examples include the inter-Andean valleys, which lie in the rain shade of the Eastern Cordillera (see diagrams for Ambato and Cochabamba in Fig. 13) and the oases of the Peruvian and Chilean coastal desert (for example Tacna; see Fig. 13).
In conclusion, arracacha is largely restricted to relatively cool, but frost-free, montane tropical environments; it thus resembles arabica coffee in ecological requirements although the latter crop might be somewhat less cold tolerant. It should be possible to crop arracacha where arabica coffee has been successfully grown.
116 Arracacha (Arracacia xanthorrhiza Bancroft)
Fig. 13. Climates of arracacha growing sites. The lines in each diagram provide mean monthly temperature and precipitation data; units on left and right vertical axes are 10°C and 20 mm precipitation, respectively. Arid periods are represented by dotted areas (when the precipitation goes below the temperature curve). Humid periods are indicated by hatched areas. Periods with monthly precipitation above 100 mm are in solid black and reduced in scale by 1 :10.
Altitude (m), yearly mean temperature (°C) and yearly mean precipitation (mm) are given on top of each diagram; numbers to lower left indicate (where available) the mean daily minimum temperature of the coldest month (Curitiba: 6.6°C) and the lowest temperature ever measured (Curitiba:
Numbers following the location name are years of meteorological observations. Source of diagrams: Walter and Lieth (1960).
Promoting the conservation and use of underutilized and neglected crops. 21. 117 Indeed, arracacha culture often provides an alternative for small producers abandoning coffee cultivation for lack of profit or because of phytosanitary problems (Colombia, Brazil).
Little else can be said about the crop ecology of arracacha, except perhaps that the susceptibility of its storage root formation to environmental conditions deserves further study. For example, storage root initiation and bulking of arracacha are retarded by conditions that induce lush foliage growth as observed in fields of high nitrogen availability or excessive irrigation (Dr F.F. Santos, 1995, pers. comm.).
Arracacha forms only minute storage roots in container culture as various trials under a variety of nutrient and temperature conditions in Quito greenhouses have shown. Clearly, this sets arracacha apart from other crop plants including sweetpotato, potato and the other species discussed in this volume, which readily form tubers or storage roots in pots.
Daylength effects on root formation of arracacha have not been reported yet.