Core Collection Approaches and Genetic Diversity in \u3ci\u3eFlemingia macrophylla\u3c/i\u3e

Core collections are a useful means to optimise the management, including conservation, of forage germplasm collections. Such optimisation is warranted in view of increasingly limited research resources. As there are several potential options to create core collections, a project is presented in which three approaches are compared: (i) based on germplasm origin information; (ii) genetic diversity assessment by agronomic characterisation/evaluation; and (iii) DNA markers. As example-species for the project, the tropical legume shrub Flemingia macrophylla is selected because of its particular multiple-use potential in smallholder production systems. An important diversity descriptor is the content of tannins influencing feed and litter quality of this species. Data will be analysed using multivariate statistics and GIS tools. The results from the core collection approach comparison are expected to be applicable also to other wild legumes

Potential Role of Native Bush in the Chaco for Mitigation of Dryland Salinity in Grassland

There is a zone of some 3.000.000 ha with an elevated dryland salinity risk in the Paraguayan Chaco due to a shallow saline ground water table. Evidence is shown of the crucial role native bush seems to play in keeping the water table at a low level and reducing therefore the risk of soil salinisation. In this paper a planned field experiment is outlined to define the tolerable level of deforestation and pasture establishment for a sylvopastoral production system in the Chacoan zone prone to dryland salinity

Amphicarpy in the Tropical Legume \u3ci\u3eCentrosema rotundifolium\u3c/i\u3e: A Research Project in Eastern Venezuela

Amphicarpy is a particular reproduction mechanism by which a plant can produce both above-ground and below-ground seeds and thus has the potential to contribute to an enhanced persistence of a plant population. It can be found in a range of tropical legumes, e.g. in several Centrosema species. The balance between above- and below-ground seed production is evidently influenced by environment and management factors but these influences are not well known. In the case of perennial tropical legumes, in addition to seed production shifts the allocation of resources affects also the production of tuberous roots as storage organs. A research project in El Tigre, Eastern Venezuela, investigates the extent to which resource allocation is influenced by five management (= environmental stress) factors: plant density, associated grass, fertilization, cutting intensity, and fire. The species chosen for this research is Centrosema rotundifolium, a perennial, moderately productive legume which because of its amphicarpy-based persistence and its adaptation to sandy and acid, low-fertility soils has a potential as pasture plant and for soil conservation on sandy savanna soils of the dry-subhumid tropic

Evaluation of \u3ci\u3eCentrosema rotundifolium\u3c/i\u3e for Sand-Soil Savannas in Eastern Venezuela

An evaluation of a collection of amphicarpic Centrosema rotundifolium showed considerable variability among the six accessions tested, regarding above- and below-ground seed production. Dry-season forage yields were very low but rainy-season yields reached acceptable levels. Contents of crude protein, P and Ca were intermediate to high (CP and P) or low (Ca). Three accessions are suggested for on-farm testing in association with grasses in order to explore the plant persistence implications of belowground seed production under practical conditions. Furthermore, the potential of this amphicarpic species for the conservation of sandy soils deserves attention

Utilized Metabolizable Energy and its Impacts on the Management of Grass Pastures in the Central Chaco of Paraguay

Animal production from sown pastures of Gatton Panic (Panicum maximum Jacq.) and Estrella (Cynodon nlemfuënsis Vand.) on a luvic Kastanozem in the Central Chaco of Paraguay (mean annual rainfall 850 mm) was measured over two years (Sep. 1992 to Nov. 1994). The pastures were grazed continuously by Brahman X Hereford steers at six stocking densities, ranging from 0.5 to 2.0 American Animal Units (1 AU = 454 kg) per hectare. Herbage availability, chemical composition (ME, XP, fibre) and cattle liveweight gains were measured at four weekly intervals. Building regression models for Utilized metabolizable energy (UME in GJ/ha) and ME requirements for maintenance (RM in GJ/ha) over stocking densities, the maximum energy conversion was obtained with 1.8 AU/ha. At this stocking density, 29 % of UME was transformed into liveweight gain. The calculated intersect of the UME and RM functions occured at a stocking density of 3.4 AU/ha when, theoretically, animals only maintain their body weight

Amphicarpic Legumes for Tropical Pasture Persistence

Amphicarpy, by which a plant produces underground seeds in addition to aerial fruits, is found in many plant families and in species of at least 15 legume genera. First studies on the tropical Centrosema rotundifolium and subtropical Macroptilium panduratum revealed for both species, besides their stoloniferous growth habit, two important mechanisms for survival under unfavorable conditions: (1) Underground meristems and reserve organs, and (2) regeneration from a soil seed reserve based on underground, aerial-flowering independent, seed production. Underground seed production was for both species particularly high on very sandy soils, but amphicarpy enables the plants to exhibit a plasticity response to unfavourable soil conditions by changing resource allocation from underground to above-ground reproduction. The latter, which seems to be influenced by cross-pollination and thus aids gene-recombination, favours spreading of plant populations whereas underground reproduction ensures population survival on-site. Preliminary information on the agronomic potential of both species is given and several research needs are highlighted

\u3cem\u3eCanavalia brasiliensis\u3c/em\u3e: A Multipurpose Legume for the Sub-Humid Tropics

Canavalia brasiliensis Mart. ex Benth. ( Brazilian jackbean ) is a weakly perennial, prostrate to twining herbaceous legume with a wide natural distribution in the New World tropics and subtropics. In comparison with C. ensiformis ( jackbean ), research reports on C. brasiliensis are scattered and restricted to studies done in Latin America. The species develops a dense and extensive, deep-reaching root system and subsequently tolerates a 5-6 month dry period. Based on studies that generally were done with only one genotype, it is adapted to a wide range of soils, including very acid, low-fertility soils. Its main use is as green manure, for fallow improvement and erosion control. Due to medium biomass decomposition, nutrient release of C. brasiliensis green manure has the potential to synchronise well with the nutrient demand of the succeeding crop and may lead to high N recovery rates. Whereas the high concentration, in Canavalia seeds, of antinutritive substances such as toxic amino acids (e.g., canavanin), lectins (e.g., concanavalin Br) and trypsin inhibitors, there is little information on the nutritive value of the herbage of this species (Schloen et al., 2004). In order to develop multipurpose legume germplasm for smallholder systems in the sub-humid tropics, we initiated a C. brasiliensis germplasm screening experiment and engaged with farmers in Central America to integrate this legume into local maize-bean production systems. First promising results are reported

Legume-Legume Complementary for Sustainable Pasture Development in the Tropics

The use of legume-legume mixtures to alleviate limitations of individual species in legume based technologies was investigated in subhumid Nigeria. The results indicate the potential of legume mixtures, through processes of complementation and compensation, to reduce the risk of legume establishment and survival and thus ensure sustainable legume yields and percentages. The implications for on-farm adoption of forage legumes are discussed