Adapting Tropical Forages to Low-Fertility Soils

Tropical forages growing in low-fertility acid soils usually increase the amount of dry matter partitioned to roots at the expense of shoot growth, but substantially different adaptive attributes to such soils have been found, both between and within species. By possessing the C4 pathway of photosynthesis, grasses are more efficient than legumes in using N, Ca, and P, whereas legume roots are more efficient in extracting nutrients from low-fertility soils. Phosphorus uptake efficiency (mg of P uptake in shoot biomass per unit root length) of the legume Arachis pintoi is several times higher than that of the grass Brachiaria dictyoneura. But the grass’s P use-efficiency (g of forage produced per g of total P uptake from soil) is markedly higher than that of the legume. The superior ability of legume roots to acquire P from different inorganic and organic P sources was associated with higher levels of inorganic P in roots. For Al resistance, the grass Brachiaria shows considerable variation. For example, B. decumbens cv. Basilisk is much more resistant to Al toxicity than are other Brachiaria species. A rapid and reliable screening procedure was developed, based on findings from physiological studies, to identify Al-resistant genotypes and improve the efficiency of CIAT’s on-going Brachiaria breeding program. The use of such screening methods will help breeders develop superior genotypes that combine several desirable traits to improve pasture productivity and combat pasture degradation

The Role of Endophytic Fungi in \u3ci\u3eBrachiaria\u3c/i\u3e, a Tropical Forage Grass

In temperate zones, endophytic fungi are widely used as biological protection agents for forage and turf grasses. They form nonpathogenic and intercellular associations with grasses and sedges, completing their entire life cycle within the plants’ aerial parts. Our surveys and studies confirmed that various endophytic fungi, including Acremonium spp., also inhabit native savanna grasses and introduced tropical forage grasses. We are now determining the potentially symbiotic relationships between these fungi and C4 tropical forages, specifically between the endophyte A. implicatum and Brachiaria grasses. We treated half of a group of genetically identical clones of Brachiaria with fungicide to generate endophyte-free plants. So far, we have found that, under severe water stress, endophyte-infected plants of B. arrecta CIAT 16845 maintained better leaf expansion and produced significantly more leaf biomass than did clean plants. We also found that the endophyte protects B. brizantha from pathogenic fungi such as Drechslera sp. (causal agent of leaf spot), the grass showing fewer and smaller lesions than did endophyte-free plants. The endophyte also inhibits the growth of Rhizoctonia solani (causal agent of foliar blight in Brachiaria) and Pyricularia oryzae (causal agent of rice blast). It may even protect Brachiaria from pests such as the aphid Rhopalosiphum maidis. However, several years of research has shown that, in infected temperate grasses, endophytes reduce livestock productivity. Whether this is true for tropical forage grasses such as Brachiaria is not yet known, although what little evidence exists suggests that endophytes may cause various health disorders in livestock

A comparative study on plant growth and root plasticity responses of two Brachiaria forage grasses grown in nutrient solution at low and high phosphorus supply

Brachiaria forage grasses are widely used for livestock production in the tropics. Signalgrass (Brachiaria decumbens cv. Basilisk, CIAT 606) is better adapted to low phosphorus (P) soils than ruzigrass (B. ruziziensis cv. Kennedy, CIAT 654), but the physiological basis of differences in low-P adaptation is unknown. We characterized morphological and physiological responses of signalgrass and ruzigrass to low P supply by growing both grasses for 30days in nutrient solution with two levels of P supply using the hydroxyapatite pouch system. Ruzigrass produced more biomass at both levels of P supply whilst signalgrass appears to be a slower-growing grass. Both grasses increased biomass allocation to roots and had higher root acid phosphatase and phytase activities at low P supply. At low P supply, ruzigrass showed greater morphological plasticity as its leaf mass density and lateral root fraction increased. For signalgrass, morphological traits that are not responsive to variation in P supply might confer long-term ecological advantages contributing to its superior field persistence: greater shoot tissue mass density (dry matter content) might lower nutrient requirements while maintenance of lateral root growth might be important for nutrient acquisition in patchy soils. Physiological plasticity in nutrient partitioning between root classes was also evident for signalgrass as main roots had higher nutrient concentrations at high P supply. Our results highlight the importance of analyzing morphological and physiological trait profiles and determining the role of phenotypic plasticity to characterize differences in low-P adaptation between Brachiaria genotype

Factors Influencing Current and Future Prospects for Intensive Dairy Production in Rwanda

Intensive mixed crop-dairy systems dominate smallholder agriculture in Rwanda. However, factors that influence the intensification and crop-dairy integration in Rwanda have not been examined. The objective of this study was to determine factors that are influencing the current and future prospects for intensification and mixed crop-dairy production systems in Rwanda

Agronomic and Nutritional Characteristics of Selected \u3cem\u3eBrachiaria\u3c/em\u3e Hybrids and Varieties Harvested at Three Stages of Growth

Shortage of quality feed is a persistent livestock productivity constraint and it is accentuated by climate variability and increased unpredictability of precipitation in many areas in Sub-Saharan Africa. Improved Brachiaria genotypes are some of the interventions that can improve feed security and contribute to the global climate change mitigation efforts

Phenotyping common beans for adaptation to drought: protocol for field evaluation

This protocol was provided for the identification of phenotypic differences in drought resistance in common beans (Phaseolus vulgaris L.). It is available in both PDF and photo gallery format with the aim of providing visiting students and researchers with a consultation document they can use to answer questions about our in-house methodologies

Adaptive Responses of \u3cem\u3eBrachiaria\u3c/em\u3e Grasses to Hypoxia Stress

It is likely that oxygen shortage in waterlogged soils is the most limiting factor for plant growth, restricting root aerobic respiration and ATP production (Vartapetian and Jackson 1997). When oxygen becomes limiting for oxidative phosphorylation, plant cells depend on alternative metabolic pathways to produce ATP (Rocha et al. 2010). The induction of fermentative metabolism is considered of adaptive value to maintain ATP production under oxygen-limited conditions. Ethanol is the main end product of fermentation metabolism in plants. Alcohol dehydrogenase (ADH) is a key enzyme in ethanolic fermentation. Roots can sustain aerobic respiration under oxygen deficiency if aerenchyma is present. Aerenchyma commonly refers to tissue containing air-filled spaces that provide oxygen un-der oxygen-limited conditions (Colmer and Voesenek 2009). The main objective of the present study was to determine morpho-physiological adaptive responses of seven Brachiaria genotypes to hypoxia stress