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FAIR-CT98-4297 AHIPA: Exploring the Potential of a Sustainable Crop as an Alternative Non-Food Source |
Introduction
The two-year study performed on ahipa (Pachyrhizus ahipa (Wedd.) Parodi) and its potential as alternative crop to other traditional sources of raw materials (proteins, starch, sugar, oil) shows it might be an interesting option for extensive agriculture in Europe after some selection and breeding. This tuberous-root producing legume would fit in sustainable and ecological agriculture schemes, as it can be cultivated without using contaminating chemicals (fertilisers or pesticides). Thus, ahipa might be a valuable resource for an agricultural system which would integrate the production of raw materials for industry (root starch and sugar, seed oil) and by-products (seed proteins, biomass for fodder). This crop would also have a lower environmental impact, since as it is capable of symbiotic N2 fixation it has a reduced requirement for fertilisers and pesticides).
Activities
The work was arranged in a series of tasks as follows.
Task 1. Potential of P. ahipa as a sustainable crop.
The effect of different environments (different locations in Portugal and Spain) and cultivation practices (reproductive pruning, irrigation) on ahipa root yield and composition was assessed, providing values for making comparisons with traditional crops. The main limitations of the crop, which should be addressed in breeding programmes (since available germplasm has undergone only a low level of breeding are related with adaptation to local conditions and present management practices. Thus, the selection and breeding for higher seedling growth rate (to improve competitiveness with weeds by rapid inter-row covering and water use efficiency), nematode resistance, and low pod setting (in order to reduce fruit-root competition) are required steps for making this crop a real alternative for European agriculture. In spite of using material with an apparent low genetic improvement, tuber yield reached approximately 50 ton/ha in some instances after reproductive pruning in unfertilised soils. This provides support for its potential as a competitive crop with a low input requirement.
Reproductive pruning, either by hand or by chemical treatment, greatly increased root yield by preventing diversion of photosynthates and nutrients to alternative sinks (pods). However, the accession (AC230) did not require reproductive pruning to reach good root yield (32.9-42.5 ton/ha). This indicates that proper selection schemes could provide cultivars with no requirement for manpower or chemical treatment to increase root yield. Variation in tuber composition, mainly sugar and starch, was observed but more experiments are required to determine genetic and environmental components of variation.
When plants are left to flower, seed production can reach levels similar to other of legumes such as French bean. The seeds are an important product in some accessions, as the amount of protein and oil content of seeds make them similar in quality to other legume crops, and they could be a source of nutrients for the fodder industry. Variation in the concentration of L-canavanine, a non-protein amino acid with potential toxicity, was observed among the accessions studied, and some breeding is required to lower its concentration.
Multiplication of 6 accessions and one interspecific hybrid began before the starting date of the project (greenhouse) and enough seeds were produced for the planned first year trials except for the hybrids (no seeds produced). Sowing greenhouse-generated seeds for further multiplication in Spain led to the successful production of enough seeds for the second year yield trials. Meanwhile, relevant agronomic information was obtained from ahipa in the field: characterisation of accessions in terms of their genotypic differences in dry matter partitioning into roots or fruits (pods), sensitivity to pests and climate, etc. Thus, there were genotypes with low pod production but high root yield per plant (AC203 and AC230), while in other genotypes fruit formation was a sink for photosynthates (AC102, AC521, AC524 and AC526) diverted from roots resulting in lower root yield when plants were not reproductively pruned. However, in studies with lines of accessions AC 102 and AC229, no genotypic correlation was obtained between root and pod growth. Yield estimate for accession AC203 in early planting and without reproductive pruning reached 53 ton/ha, yield value closed to traditional industrial crops like sugar beet (54 ton/ha).
High soil temperatures at planting affected seed germination and emergence. Preliminary germination tests performed under controlled conditions at different temperatures showed that optimum temperature for germination was 30° C, while at lower or higher temperatures germination rate was reduced.
Pods required a long time attached to plants for seed to reach full maturity. In the field, pods must be collected before they reached maturity in the autumn to avoid rotting (beginning of the rainy season in the Mediterranean region). After harvest, the immature pods can be dried in glasshouses (2-3 months) or forced-air ovens (30-35° C, 4-7 days) to get mature dried seeds. A variable amount of pods (depending on the drying rate) decay by fungal attack (Sclerotinia spp.) and no viable seeds are recovered. Soybean threshing machinery can be adapted with good results for obtaining clean seed when pods are dry.
One main feature that has to be improved in ahipa is germination vigour and traits related to a rapid seedling establishment. In spite of high germination rates in Petri dishes, low seedling populations are obtained in the field, mostly related with low vigour and defective (?) embryos (epicotyls with damaged first leaf pair), early chlorosis in first leaf pair (unknown origin), etc. Maturating the seeds in planta might solve some of these problems. Low seed vigour, and probably an inherent low growth rate, delays plant establishment and row covering, making the crop very sensitive to weed competition. Special efforts should be put into increasing seedling growth rate either by searching for other accessions in the areas of origin or selecting the available accessions for these specific traits (early germination, high vigour, etc). Low temperature (15-20° C) inhibited ahipa seed germination and early sowing would benefit from search on germplasm for increased germination rates at low temperature.
Accessions AC521 and AC102 gave the highest yields (50.9 and 51.7 ton/ha respectively) at Alvalade, when fruit setting was avoided by flower pruning. However, when pruning was not made, yield was greatly reduced. One accession (AC230) reached good yield without reproductive pruning (42.5 ton/ha), in agreement with results of the previous year in Spain, when accessions AC203 and AC230 showed low fruit production and high root yield. Reducing irrigation to supply the 50% of water requirements (ETc-based calculations) reduced productivity in approximately 50%. Root yield was lower at Coruche, and the best producing accessions were AC102 and AC229 (36.4 and 44.6 ton/ha) but a similar trend in yield was observed at both sites (Alvalade and Coruche) when plants were pruned or irrigation was reduced. No statistical difference among accession was observed for sugar content (Brix), but reduced irrigation led to a significant increase in sugar content.
The main trial for yield comparison among accessions in Coria del Rio (Spain), designed to test five accessions (three high flowering and two low flowering vaneti6s) without flower pruning was spoiled by nematode attack. Results from a trial in cooler region (Sabiote, Jaen) performed with accessions AC230 and AC521 showed low root growth, probably as consequence of a short season with adequate temperatures for ahipa.
The rhizobia inoculation trial performed with accession AC521 in Las Torres provided valuable data of root and seed productivity of ahipa for late sowing (12th June) without reproductive pruning. The yield of roots reached 15 ton/ha whereas fruit production was 23 ton/ha with a dry seed yield of 1.2 ton/ha.
Very low levels of insect damage were observed during the two-year trials, and the attack of whiteflies (Bemisia spp.) because of the proximity of infested cotton fields partially affected the crop and no insecticidal treatment was applied. However, nematodes can have devastating effects and previous analysis of nematode population in soils should be carried out before planting. Fungal diseases had certain importance after harvesting, when pods and tuberous roots were infected with Sclerotinia spp. because of high humidity and relatively low temperatures during storage.
Task 2. Ecophysiological studies of P. ahipa.
Ecophysiological studies performed on accessions subjected to drought and heat stress during growth showed genotypic variation in physiological parameters linked to crop yield. Some constrains to plant growth have been identified (limitations by high temperature, nutrient deficiency and toxicity). The tolerance to insects (as indicated above) contrasted to the extreme sensitivity to nematodes (Meloidogyne hapla). Reducing irrigation in 50% of normal requirements calculated by ETc led to a significant yield reduction (close to 50%). Probably, this was due to the low water-holding capacity of soils, which were mostly sandy soils. However, soils with higher clay content (and water retention capacity) may restrict root growth by physical impedance or increase root rot diseases. The reduction in irrigation (50% of ETc) reduced yield in all accessions but some differences in relative reduction in growth among genotypes were observed. The reduction by low irrigation was higher in sandy soils of Coruche because of the lower water holding capacity than in soils of Alvalade.
The photosynthetic activity and stomatal conductance of ahipa leaves decreased along the growth cycle and differences in stotamal conductance among accessions were recorded at same sampling dates. Drought treatment led to a reduction in stomatal conductance but no differences in leaf water potential between treatments (50% and 100% ETc) were recorded. There were differences in response of gas exchange and water potential to drought stress between the field sites included in the study (Alvalade and Coruche) probably because of differences in soils properties (water holding capacity) and climate (air humidity). Very high air temperature and low relative humidity, as recorded in July and August in Spain, might reduce photosynthetic activity of ahipa by inducing para-heliotropic movements and stomatal closure. In fact, comparative studies performed with ahipa and species of tropical origin (P. erosus and P. tuberosus) have shown differential patterns of behaviour in stomatal conductance and photosynthesis between early morning and midday measurements. Differences in photosynthetic capacity (that is the photosynthetic potential with light, C02 and humidity at saturation) were observed among some accessions and they were related to differences in photosystem II activity.
Studies of the effect of drought on six different accessions under controlled conditions led to the conclusion that ahipa showed some water stress tolerance as only severe stress treatments (when leaf relative water contents were below 70%) affected photosynthetic machinery. No differences were observed among accessions for measured parameters (photosynthetic 02 evolution, chlorophyll fluorescence). However, differences in sensitivity to drought among accessions were recorded when studying leaf membranes integrity and membrane lipid composition and content. Significant changes in galactolipids were induced by drought. Some phospholipids increased their concentrations in AC524 in response to drought but the concentrations slightly changed in AC 1 02.
Membrane damage was increased by the combined effect of heat and drought stress. Ultrastructural studies revealed disorganisation in cell plastids (chloroplasts, mitochondria) because of damaged membranes, and the cytoplasm reflected a strong reduction in ribosomes. Results obtained from the studies on heat and drought stress effects on membranes reflected differential sensitivity between accessions, and these results are particularly important as might be used for germplasm evaluation and selection in breeding programmes for drought and heat stress tolerance.
Day length certainly affected plant growth and dry matter distribution, as well as other morphological traits (like internode length): short-day treatment led to higher root dry matter accumulation than long-day treatment. Long-day treatment increased flower shedding. These results showing s significant day length effect on ahipa are in agreement with studies carried out with other accessions, and modify preliminary statements about neutral reaction to day length variation.
The nutrient uptake and accumulation studies performed during growth of ahipa under field conditions showed that pod shells and seeds are main recipients for P, and limitation in root P uptake jointly with P redistribution from leaves to fruits could probably restrict plant growth. This is suggested by critical leaf P levels recorded at some growth stages. Roots and pod-shells were main sinks for plant K, and the concentration of K in leaves showed it was ranging deficiency levels (or clearly deficient) in most dates. Deficiency of P and K would certainly affect root yield because of the implication of both nutrients in carbohydrate synthesis and translocation.
Leaf nutrient concentration studies performed on leaf samples from different sites in Portugal and Spain showed some soils were limiting nutrient uptake either by their low concentration in the soils or physico-chemical conditions reducing nutrient solubility and availability.
Thus, uptake of P and Zn would be restricted in some soils, whereas Cu would be at limiting concentrations for optimum growth in other soils. High Ca concentration in soils might affect P availability and even produce toxicity symptoms leaves at some growth stages.
Plant nutrition studies carried out throughout the crop cycle pointed out to phosphorus and potassium as main limiting factors in the calcareous soils of SW Spain. Leaf analyses of ahipa grown in different field experiments of Portugal and Spain revealed critical levels for some macro (mainly P and K) and micronutrients (Zn, Cu). High leaf Ca concentration, at an apparent toxic level, was found in leaves from plants grown in SW Spain, and jointly with the decreasing leaf K concentration by translocation might have limiting root growth and carbohydrate accumulation.
Task 3. Germplasm characterisation.
Preliminary studies in the field showed an important intra-accession variation for traits like shoot and root growth, seedling vigour and number of flowers and pods, whereas no variation in time to flowering was observed when a limited number of accessions were planted on different dates. Few accessions showed plants with indeterminate growth, and some accessions (provided by Dr W. Griineberg) did not produce pods. From the material used for seed production during first year, it clearly appeared that some accessions (AC203 and AC230) were able to produce bigger roots and less seeds than other accessions (AC 1 02, AC229, AC52 1, AC524, AC526) which produced smaller roots and more seeds.
The study of available germplasm for determination of phenological indexes under controlled conditions showed that accessions reached the V4-stage (i.e. third trifoliate leaf) almost simultaneously, but great variation was observed for R6- and R7-stages (first flower and first pod respectively). The leaf length:width ratio showed some variation among the studied accessions. Two groups could be differentiated by using this descriptor: accessions from most northern areas in Bolivia generally presented lower values in leaf length:width ratio than accessions from Southernmost areas.
Some accessions showed greater tuber yield under controlled conditions when flowers were removed. Initiation of tuberisation was apparently not linked to flowering events, as deduced from the fact that early or late flowering accessions (e.g. AC526 and AC270S respectively) reached the lowest tuber weight at harvest. However, in one accession (AC230) root growth was reduced when flowers were plucked out.
All accessions studied in the greenhouse trial produced more than a single tuber, although there was an important variation among genotypes in the relative dry matter partitioning to main and secondary tubers. The dry matter content of tubers averaged 23.7% among accessions, fluctuating from 18% to 33%. No association was found between root size and root dry matter content considering all accessions, and similar conclusion was obtained from a single accession cultivated under field conditions (AC521, Las Torres 2000). Counting of pods and pod-chambers showed that this parameter could be used to describe variation among accessions. Measurement of length of internodes did not provide data showing great variation in this parameter, although some variation among accessions was recorded for the minimum internode length.
Pollen studies indicated that all accessions produced flowers with great variation in pollen fertility, and that reproductive pruning induced an increased production of flowers with low pollen fertility.
Short-day treatment induced early flowering in most accessions, but one accession (AC270S) appeared as the most sensitive to short-day treatment. No effect of day length of tuberisation was recorded, but the effect was obviously recorded in the amount of biomass partitioned to fruits.
Studies of biomass partitioning during crop growth showed major increases in root growth from the fifth month after planting and no main differences were observed between accessions. Indications of root growth restriction at decreasing temperature in the autumn was observed, apparently associated with the reduction in leaf photosynthetic rates. However, more data are required for a complete assessment of low temperature restriction to photosynthetic activity and growth.
Task 4. Selection of Rhizobium spp. strains for effective N2 fixation in P. ahipa accessions.
From a lyophilised collection of Rhizobium and Bradyrhizobium spp strains from different Pachyrhizus species, some strains formed nodules in ahipa (AC521). These nodule-forming rhizobia were subcultured and their N2 fixation efficiency tested under greenhouse conditions. Some strains were efficient N2 fixers in symbiotic association with accession AC521: the shoot dry weight of plants fed with mineral N (non-inoculated, +N control) did not differ with shoot dry weight from plants inoculated with strains PAC48 and PAC51. In the second year, additional strains recovered from liophilised cultures tested under controlled conditions were not as efficient in N2 fixation as strains characterised the previous year. Biochemical and physiological studies on rhizobia strains are being carried at present to fully characterise the microsymbionts.
In field trials performed during the first year, no native soil rhizobia were able to nodulate ahipa, and a good response to inoculation in low N soils might be expected. Inoculation with a commercial inoculant (Nitragin Spec 1) resulted in an erratic modulation in soils although it formed good nodular mass in perlite/vermiculite or sand substrates. Therefore, some soils constraints or the extreme high soil temperatures recorded after sowing might have affected rhizobial viability and, might explain the poor modulation obtained under field conditions.
In the main field trial for testing symbiotic N2 fixation of different strains performed at Las Torres during year 2000, no modulation was recorded in spite of the high number of viable cells in the inocula (108 cells/g inoculant). A new trial was performed in the year 2001 to study the variables, which might have affected modulation in 2000. Two main questions need to be answered: how heat and/or desiccation affect the rhizobia strain viability and ahipa ability to initiate or develop nodules. Analysis of inoculated ahipa seedlings showed a very high concentration of amide (asparagine) in the roots that could explain the delay in the infection by rhizobia and nodule initiation processes. High soil temperatures recorded after sowing might have affected rhizobia survival on seeds. However, more data are required for providing evidence of main factors involved in modulation failure of ahipa under field conditions.
Good modulation was observed in the field trial run at La Corregidora (Sabiote, Ja6n) with accessions AC230 and AC521, but no quantification of N2 fixation was carried out because of not including control treatments (no inoculation treatment). Greenhouse experiments performed with two ahipa accessions and three rhizobial strains showed plant genotype x rhizobia strain interaction for some symbiotic parameters.
Task 5. Yield of raw materials (proteins, starch, sugars, oil) in P. ahipa accessions.
The analysis for root and seed carbohydrates (sugar, starch), nitrogen compounds (proteins, amino acids) and lipids was performed in different accessions, and some variation (genotypic?) was detected among the available collection of ahipa germplasm. Protein content in roots of ahipa was lower than expected according to other, however seed concentration of protein was high (28%). Seeds also showed a high content in oil (21%), at similar levels as it is found in other legumes like soybean. The concentration of starch in ahipa roots was approximately 50%, lower than the concentration found in potato (65-80%), but with different properties. The nonprotein aminoacid L-canavanine was found in seeds but not in tuberous roots of ahipa plants grown under different environments (field trials, greenhouse).
The N concentration in seeds (4.0-5.0%) led to calculated protein contents from 25.2-31.4%, higher than in French bean seeds (22.1%) but lower than in soybean seeds (40.3%). The concentration of starch and sugar varied from 2.1-4.8% and 9.6-10.8% respectively. Future analyses on seeds from different accessions will be carried over. The concentration of oil in seeds ranged from 20-22%, providing similar values than soybean. Analysis of seed composition on different accessions during the second year could not be performed as only a reduced amount of seeds was recovered from the field plot at La Hampa.
Tuberous roots showed a high water content, between 79% and 84%. Variation in the dry matter content between accessions was observed but more studies are required to determine environmental and developmental factors affecting dry matter accumulation. The concentration of N in roots in different accessions was lower than expected from previous reports for different Pachyrhizus species and varied from 0.20% to 0.56%. The concentration of amino acids in roots was quite high, ranging from 0.48 to 1.09 mg/ml root juice. The concentration of starch in roots of different accessions ranged between 38.0 to 54.4% while the concentration of sugars ranged from 28.2 to 47.8%. The effect of pruning on tuber composition remains to be studied. As in other industrial crops, root composition might be affected by management practices (irrigation, fertilisation), climatic conditions, etc. Reduction in irrigation led to an increase in sugar concentration in roots (Brix degrees).
In the second year, analysis of root composition in different accessions was carried out only in two accessions (AC 102 and AC52 1), as they were the only two accessions from which healthy roots were recovered from field plots. Analysis of roots from accession AC521 harvested in Las Torres provided similar values as those obtained the previous year, with starch and sugar contents of approximately 56 and 30% respectively. Analysis of roots from AC102 was performed by a local sugar beet extracting industry, indicating for ahipa roots a lower content in sucrose than in sugar beet but higher content in reducing sugars, whereas other industrial parameters (related with the sugar purification process) were similar.
The concentration of free amino acids in roots showed some differences between genotypes, with most accessions accumulating asparagine and glutamate mainly. In seeds, the main components of the free amino acid pool were aspartate, glutamate, histidine and canavanine, with significant variation among accessions in the concentration of canavariine.
The study of roots from N2-fixing and N03-fed plants showed significant differences in the accumulation of free amino acids, with N2-fixing plant roots showing a lower amino acid concentration than roots from N03-fed plants. Roots from field grown plants showed a lower amino acid concentration than those from greenhouse grown plants. Asparagine was the dominant amide accumulated in roots from either N2-fixing or N03- fed plants. None of the roots (grown in greenhouse or field) showed L-canavanine accumulation.
Task 6. Characterisation of tuber and seed proteins and starch.
The characterisation of root and seed starch and proteins was performed; showing that ahipa root is not a realistic source of proteins for industrial use. Results from analyses performed in six ahipa accessions showed 4.8-8.4% protein (dry matter, calculation based on Kjeldahl N). Ahipa starch is somewhat unusual when compared to other legume starches in that it has a relatively low amylose content. Ahipa starch could find specific food applications, e.g. to minimise amylose solubilisation and retrogradation after processing.
Tissue printing of tuber sections showed an even distribution of proteins throughout the whole tuber. The protein extraction from tubers corresponded to 93.1% of the crude salt-soluble fraction, but 30.8% was lost after dialysis, which is in agreement with the high soluble N concentration described above. The residue after salt extraction did not show clear protein bands on gels even after dialysis and freeze drying concentration. Therefore, protein purification was only carried out on the salt soluble fraction. Separation on basis of hydrophobicity with ammonium sulphate yielded three fractions, which were then analysed by SDS-PAGE. Main bands obtained after SDS- PAGE were further purified by ion exchange chromatography and 4 samples were then chosen for N-terminal amino acid sequencing to determine protein homology. The analysis of N-terminal sequences revealed that one fraction (protein C, 22kDa) had high homology (100%) with hevein protein (from rubber tree) and chitinases from bean leaves and Arabidopsis. The protein fraction E (25kDa) showed a high homology (99%) with two cysteine proteases (YBGI and YBG2) from P. erostis.
Five main protein bands, ranging from 17 to 66 kDa, were detected in samples from six ahipa accessions. The protein concentration in the roots (from Kjeldahl-N analysis) ranged from 4.8-8.4% (dry matter) or 1.3-2.3% (fresh weight). No protein bodies were visible in any of the samples.
All the seed proteins showed multiple protein bands after separation by SDS- PAGE, and different patterns of cross-reactivity were detected to three different antibodies (legumin, vicillin, convicillin polyclonal antibodies).
Starch granules from ahipa showed sizes ranging from 5 to 35 micron, with peaks at about 10 micron, and growth rings were observed by SEM after cracking. The amylose content varied between 11.6 to 16.8% dry weight, values lower than those found in cereal starches and legume starches (smooth-seeded pea) where the amylose content is above 25%. Analysis by X-ray diffraction showed starches from seeds and roots of ahipa AC521 and AC526 had an A-type diffraction pattern (similar to cereal starches) but accession AC230 showed a CA-type pattern. Samples from roots of the accessions AC 102, AC229 and AC524 gave different patterns, being either A-type or CA-type. Ion exchange chromatography of amylopectin derived-chains showed that chain lengths of the short chain fraction were intermediate between that found for an A-type starch (wheat) and a C- type pattern (smooth-seeded pea). However, it was not possible to accurately predict the crystalline form found (A, CA, C) simply from chain length distribution. The crystalline form of starch has an impact on the heat changes associated with gelatinisation. Differential scanning calorimetry trace of endothermic heat versus temperature for the gelatinisation was used to further characterise ahipa starch. The endothermic peak varied between starches from different ahipa accessions. Although many of the granular and molecular features of ahipa starch are consistent with the known properties of legume starches is somewhat unusual in that it has a relatively low amylosc content. This feature suggests that ahipa could find food applications where it was desired to minimise the effects of amylose solubilisation and retrogradation after processing.
Discussion
The project finished with a realistic knowledge of the yield potential of ahipa and the main products, which can be obtained by processing ahipa root and seeds. Field trials designed to test yield potential of different accessions in Portugal were successful, but only partially in Spain, where the main yield trial during the second year was spoiled by nematodes. In spite of that set-back, enough data from the previous year and other locations were collected and they are being processed at present to ascertain the adaptability of the crop to a diversity of soils, planting dates and weather conditions. The crop yield was found similar to an average value for a crop like sugar beet (i.e. 50 ton/ha) but higher than potato (20 ton/ha). The root production in ahipa was obtained in less time (6-7 months) than in sugar beet (8-9 months). Root dry matter content in ahipa (I 9-20%) was somewhat lower than sugar beet (22-26%) produced in the region (Andalusia, Southern Spain).
For a detailed cost analysis, more data are required, as with present data higher input in manpower for ahipa (manual weeding at initial stages) would compensate for inputs into herbicide and insecticide treatments in sugar-beet and potato production. Important points to consider are the low (if any) fertilisation requirement for ahipa, and the environmental benefits of avoiding insecticides and high N fertilisation rates traditionally used for crops like potato. Because of the sensitivity to nematodes it is necessary to obtain resistant lines.
Flower pruning, either by hand or by chemical treatment, greatly improved root yield. However, some accessions clearly showed high root weight without reproductive pruning. In view of the present results, accessions AC203 and plant material bearing similar characteristics would be more suitable for cultivation, showing increased profitability by reducing manpower and chemical costs of treatments required for reproductive pruning.
The protein content of ahipa roots (3-5% crude protein) is within the range of potato (3-6%) and sweet potato (1-10%), and is sufficiently high to contribute significantly to its nutritional properties but not high enough for it to be grown as a protein crop. Seed protein characterisation showed some similarities with other legume seed proteins, indicating that it could be an interesting crop for the fodder industry if anti-nutritional compounds (like L-canavanine, rotenone) are removed or accessions containing low concentration are used (variation in L-canavanine content in accessions were available). Seed and tuber starches presented differential properties when compared with starches from cereals and legumes, basically a relatively low amylose content, which could be appropriate for specific uses such as food applications where solubilisation and retrogradation of starch has to be avoided.
Ahipa appears to be competitive as a multipurpose crop because of low input requirement and low environmental impact, but not entirely in terms of its present yield and lack of know-how as already established for traditional crops. However, it deserves attention as a strategic new crop that requires some work invested in breeding to boost its potential as producer of raw products for feed or industrial uses. Similarly, considering the increasing importance in Asia and North America of ahipa as horticultural crop with good nutritional, ahipa might find its niche in the green horticulture market, as a relative novelty that might increase farmer incomes.
Ecophysiological studies on different accessions showed some degree of tolerance to heat and drought stress conditions. Physiological and biochemical traits related to plant tolerance to abiotic stress (heat, drought) was identified and they could be useful for breeding programmes. Low water availability greatly inhibited plant growth and tuber yield. However, more studies need to be carried out in soils with higher water-holding capacity than those soils used in the reported experiments. The study of germplasm under controlled and field conditions revealed the existence of some variability in time to flowering, pod setting and tuberisation in response to the photoperiodic and/or thermoperiodic treatments. This information is essential for any breeding attempts or further field trials including accessions from different geographical areas. If broadening the collection of germplasm were possible, studies should be carried out to identify accessions with low temperature tolerance for early sowing and high initial growth rate in order to improve agronomic performance (increased water use efficiency and competitiveness with weeds).
Nitrogen fixation of ahipa inoculated with selected strains under field conditions could not be tested as nodulation failed. At present, a new trial is being carried out to study limiting conditions (soil temperature and dessication, phosphorus availability), affecting either rhizobia survival or plant capacity for nodule initiation and development. Under greenhouse conditions, root yield and composition of N2-fixing and N fertilised plants showed differences, which should be studied in detail in the field. The plant mineral nutrition studies performed in Portugal and Spain showed the main crop requirements for root and seed production, and the constraints to ahipa growth derived from soil physico-chemical properties (soil texture, pH, K and Ca availability, etc.).
Discussion
If successful the search for ahipa accessions with higher initial growth rate, reduced flowering, nematode resistance and cold tolerance could improve its cultivation and product quality and yield. Symbiotic nitrogen fixation should be improved by searching for appropriate rhizobia strains able to nodulate ahipa in a wide range of environmental conditions. The identification of potential users of raw products (sugar and starch from roots, seed proteins) is being carried out by contacting Innovation Relay Centres (e.g. Food technology Institutes) and local Agriculture authorities.
© Copyright 2006 Policy Statements
Updated
by CPL Press
3 July, 2007
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