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

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

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