«Andean roots and tubers: Ahipa, arracacha, maca and yacon M. Hermann and J. Heller, editors Promoting the conservation and use of underutilized and ...»
12 Ecology The habitat of P. ahipa is known from cultivation only, in cool tropical/subtropical valleys, where it appears to be well adapted to an altitudinal range of 1800-2600 m asl, though the crop was also recorded at +3000 m as1 in sloping north-facing fields (fully exposed to the sun). The region of cultivation is located along the border between the warm (‘tierra templada’) and cold tropics (‘tierra fria’). The average temperature within the region is between 16 and 18°C where the climatic conditions are extremely dependent on the time of day. The temperature oscillates between a minimum of 0°C to a maximum of 30-35°C. As the average annual precipitation rate is 400-700 mm, occurring within 4-6 months, the remainder being the dry season, the climate is semiarid. Farmers reported that the cultivation period has a duration of 5-10 months, depending on the length and intensity of the rainy season. The P. ahipa plant will tolerate long dry spells, but an additional water supply is essential to increase tuber yield. Cultivation is predominantly carried out along loamy riverbanks, although sloping hillsides with loamy soil may in some cases be used. A well-drained soil type with pH=6-8 will meet the edaphic requirements of the crop (Ørting et al. 1996).
12.1 Photothermal neutrality (daylength sensitivity) A view generally held is that yam beans are short-day plants, i.e. that flowering and tuber production will only take place under decreasing daylength. However, field studies and observations and experiments conducted under greenhouse conditions have demonstrated the existence of genotypes with reduced or practically absent photothermal sensitivity.
Pachyrhizus ahipa has been grown continuously for a number of years in the greenhouses at RVAU, Denmark. Seeds have been planted in virtually all months of the year. During both short-day and long-day periods, the P. ahipa accessions have been observed to have the most rapid flower initiation among the Pachyvhizus species, i.e. from 87 days (in plants with determinate growth habit) to 140 (in indeterminate plants) days after sowing regardless of the season (Ørting 1996a). Furthermore, the tuber growth does not appear to be influenced by variations in daylength; hence this species may be regarded as daylength-neutral and neutral lines may be bred from interspecific hybrids involving the species.
According to Prof. I.F.M. Válio (pers. comm.), Dr M. de Fatima Ferrine has studied the daylength sensitivity in four to five accessions under different light and temperature regimes at UNICAMP, Brazil; however, the results from these experiments have yet to be published.
12.2 Climatic and edaphic requirements Physiological studies of the response to drought in Pachyvhizus have been carried out under field conditions in Senegal (Annerose and Diouf 1994) and under greenhouse conditions in France (Vieira da Silva, pers. comm.).
The studies in Senegal demonstrated P. erosus as being a good drought-avoider, i.e. able to reduce respiration and metabolic processes during drought spells, and 52 Ahipa (Pachyrhizus ahipa (Wedd.) Parodi) P. ahipa as being a drought-tolerant species, i.e. able to continue respiration and metabolism during drought spells. The latest trials, designed as pot trials, were aimed at studying the developmental competition between the reproductive organs (flower, legume and seed) and the storage organ (tuberous root) under the influence of drought.
The experiments, using P. ahipa, include four different treatments: (1) reproductive pruning and water stress, (2) reproductive pruning without water stress, (3) no reproductive pruning with water stress, and (4) no reproductive pruning without water stress. The results indicate that the reproductive pruning has no influence on the physiological response to drought, i.e. no influence on respiration or metabolic processes (Annerose and Diouf 1997; Diouf et al. 1997; Orthen and von Willert 1997).
The experiments studying the drought tolerance of the accessions of P. ahipa based on the correlation of leaf polar lipids and fatty acid composition on the cell membrane resistance to osmotic stress demonstrated the considerable variation in response to drought of these three accessions (AC102, AC521 and AC524) and the comparatively high drought tolerance in comparison with other tropical leguminous crops (Vieira da Silva 1995).
12.3 Impact on environment The beneficial effects on the environment – mainly as a result of the biological nitrogen fixation (see Section 4.1) – must be considered as surpassing the negative effects. Hence, a list of the beneficial effects will include the following characteristics and their effect: highIy efficient nitrogen fixation – increased vigour among the neighbouring plants (especially so on poorer soils); good drought tolerance-provide high-protein forage for livestock and other herbivores; erosion control – though not as aggressive as the Pueraria spp. the Packyrhizus spp. will effectively reduce soil erosion. The negative effects are: seed propagated – the crop may easily (be) spread into the wild vegetation bordering fields cultivated for seed production;
rotenone/rotenoid content – the poisonous seeds may cause problems in livestock foraging on escaped plants among the wild vegetation, and as the seeds may be used to poison fish this poses a risk in areas where unauthorized use of such methods may disturb the ecological balance; vigorous growth – although as mentioned, the Packyrkizus spp. are not as aggressive as some of the Pueraria spp., a few of the P. tuberosus genotypes are very large, strong vines and they may upset a fragile indigenous flora; legume – several of the species have been found to become infected by different viruses and escaped plants may therefore serve as hosts for such diseases;
tuber/root crop – in areas suffering from heavy infestation by nematodes, escaped plants may serve to maintain a high level of infestation, also some insect pests, e.g.
Diabrotica spp., may find refuge on escaped plants.
Careful quarantine measurements should be implemented when introducing the crop to new regions in order to minimize the risk of introducing diseases (especially those possibly seedborne) and, more importantly, bean weevils (= bruchids) specific to Packyrkizus which do not at present occur in any of the areas outside the Neotropics.
Promoting the conservation and use of underutilized and neglected crops. 21. 53 13 Agronomy
13.1 Propagation of the crop Packyrhizus ahipa is always propagated by seed and seeds are sold in the markets (Fig. 9a).
Ørting et al. (1996) report that two different methods are used when selecting plants for seed production: (1) the grower will select the healthiest and most vigorous looking plants and leave these without reproductive pruning to produce seeds, or (2) leave the first developed legume/pods on all plants and remove all subsequently produced.
Seeding rates of 21-105 kg/ha have been recorded, but general rates are 40-65 kg/ha. Again, factors like preferred tuber size, soil fertility and obviously seed weight play a major role when determining the rates (Ørting et al. 1996).
13.2 Crop husbandry Ahipa is generally grown as a monocrop, but may in some instances be intercropped with maize (Zen mays L.). Crop rotation is always practised and P. ahipa is cultivated prior to maize/potato, maize/tomato (Lycopersicon esculentum Miller nom. cons.), maize/oca (Oxalis tuberosa Molina), groundnut or manioc. Planting distances vary from 20-60 cm between rows and 6-25 cm between plants within rows, i.e. 6-83 plants/m (Fig. 9b). In areas with high precipitation rates during the growth period or when the crop is flood-irrigated, it is planted on ridges to increase the drainage, a practice which is generally necessary in the Andean region. As part of the land preparation, the soil is loosened to a depth of 15-25 cm using a hoe, and thoroughly cleaned from weeds and stones. There are no reports of later weeding, but the practice of reproductive pruning is regarded as being of considerable importance. This manual operation was reported as being conducted once or twice in order to obtain the optimal tuber size (Ørting et al. 1996) (Fig. 9c).
13.3 Field trials The various experiments conducted within the Yam Bean Project have succeeded in demonstrating the potential of P. ahipa with regard to both its immediate utilization as a high-yielding tuber/root crop with high contents of sugar and protein for subtropical regions, and its use in interspecific hybrid combinations with the other two cultivated species in the development of early, photothermally neutral and bushy-type cultivars. In trials carried out in Portugal by the French partner in the project the astonishing potential of the Andean yam bean (= P. ahipa) under Mediterranean conditions was observed -yields of 54t/ha with up to 24% dry matter were achieved, and crude protein percentages of 9.6 to 11.1 (DM).
The various trials have been/are carried out at different altitudes and cover a wide range of soil and climatic conditions. Both high-rainfall and semi-arid regions are included.
54 Ahipa (Pachyrhizus ahipa (Wedd.) Parodi)
Fig. 9. a. Selling seeds by the head/hat (‘por la cabeza’). Accession number: AC203; origin:
Bolivia, Prov. Loaiza, Azambo near Luribay. Harvested 1993. The farmer, Sr. Luis Masí has bought the seeds from his uncle Sr. Luis Palo in Anquinoma. Collected by: Bo Ørting, Wolfgang
Grüneberg and Jonas Ørting. Date: 19th April 1994. Seed colour: dull black. Approx. altitude:
2500 m asl. Photo, B. Ørting.
b. Accession number: AC205; origin: Bolivia, Prov. Ayopaya, Sanchu Panpa near Machaca.
Farmer: Sr. Luis Orellano. Collected by: Bo Ørting, Wolfgang Grüneberg and Jonas Ørting.
Date: 30th April & 1st May 1994. Pods harvested April 1994 from seeds sown September 1993.
Seed colour: mauve. Approx. altitude: 2250 m asl. Photo, B. Ørting.
c. Harvested tubers from plants, accession AC102, with (right) and without (left) reproductive pruning; cultivated at the DRATOM experimental station near Mirandela, Tras-os-Montes, Portugal. Photo, J. Vieira da Silva.
Promoting the conservation and use of underutilized and neglected crops. 21. 55 Ahipa has been tested in field trials in Tonga, Mexico and Portugal. These are the first trials reporting yield size under different climatic conditions (Table 5). In Tonga the species has been tested during three growth seasons and the yield averaged between 3 and 22 t/ha depending on whether the flowers were removed or not and with plant populations ranging from 38 095 to 111 111 plants/ha. The first trials involving this species conducted in Mexico were flood-irrigated, with removal of fertile shoots and a plant population of 38 095. The yield was between 16 and 20 t/ha. The plant density was increased to 110 000 plants/ha in subsequent trials, resulting in a marked yield increase (see Section 13.7). The experiments in Tonga have shown P. ahipa as having one of the highest dry matter contents recorded among the cultivated Pachyrhizus species as much as 20% or higher (see also Section 4.3).
This amount compares favourably with the traditional African tuber crops like cassava and yams (Dioscorea spp.). Hence, the possibility exists for breeding new high-yielding ‘yam bean’ cultivars which are more like the better-known tuber crops with a higher dry matter content.
Additional information concerning the layout and results from the field trials is reported in Grum et al. (1994), Heredia G. (1994) and Morera (1994).
The field trials conducted in Mexico, Tonga and Portugal have yielded quite different results (see Table 5). The tuber quality varies according to climatic conditions, i.e. faster growth and lower dry matter in warm climates and short growth seasons. The very high dry matter contents recorded in the trials in Portugal demonstrate the possibility of utilizing P. ahipa tubers in processed and non-food products (see Section 4.4) There are very few studies available on the quality aspects of forage hay of P. ahipa.
The recent field experiment conducted in Mexico by Castellanos et al. (1997) reports
the following yields and nitrogen contents of P. ahipa aboveground parts:
• accession number AC102: 1.7 t/ha dry matter with 55.1 kg N/ha in reproductively pruned plants, and 5.8 t/ha with 147.7 kg N/ha in unpruned plants
• accession number AC521: 1.8 t/ha dry matter with 62.8 kg N/ha in reproductively pruned plants, and 5.9 t/ha dry matter with 129.8 kg N/ha in unpruned plants.
These results demonstrate that the nitrogen concentration as a percentage in the aboveground parts increases as a result of reproductive pruning although forage yield decreases, i.e. from 3.24-3.49% in pruned plants to 2.20-2.54% in unpruned plants. Also, the total amount of nitrogen fixed (kg/ha, tuber + aboveground parts) did not differ significantly between the pruned and unpruned plants, in P. ahipa – 68.7-74.3 kg N/ha for pruned plants and 58.4-79.7 kg N/ha for unpruned plants (see also Section 4.1).
Table 5. Results from P.
ahipa field trials in Tonga, Mexico and Portugal †
13.4 Diseases and pests Although diseases and pests are listed below according to observations made in the three cultivated species, there is little doubt that the majority of both the diseases, regardless of the disease-inflicting organism, and the insect pests will in fact be common to all three species. Thus the differences recorded are due to geographic, climatic, ecological, and edaphic conditions rather than specificity. This has been confirmed in field trials in Tonga, Costa Rica, Ecuador and Thailand when cultivating all five species in one location, e.g. Bean Common Mosaic Virus (BCMV) will infect all three cultivated species and will also – although with some delay due to the prominent hairiness of all vegetative parts which has some repelling effect on the aphid vectors – successfully infect the wild species P. panamensis. Only the other wild species P. ferrugineus appears to possess some resistance or tolerance to this virus.
When introduced to other areas for evaluation, most insect pests normally associated with the other species will attack P. ahipa. However, in Bolivia the local producers did not identify any leaf-damaging insect pests as being of importance when cultivating the crop (Ørting et al. 1996).