Varietal differences in shoot and rooting parameters of pearl millet on sandy soils in Niger

Root parameters are important traits for the acquisition of nutrients and water under resource-limited conditions. In order to investigate the extent of varietal differences in rooting parameters in pearl millet, we compared a total of eight pearl millet varieties in two experiments (ridging and traditional sowing) over four years at the ICRISAT Sahelian Centre, Niger. We found substantial genotypic variation for root length density (RLD), root dry matter, and total root length (RL), but not for specific root length, depth of rooting, or partitioning of roots between topsoil and subsoil (>20 cm depth). RL showed a highly dynamic pattern over the growing season. RL and shoot dry matter were positively correlated over P supplies and contrasting levels of field productivity. The relationship between RL and grain yield as well as harvest index were less clear. The root fraction responded to variation in soil productivity, increasing from roughly 20% under high productivity to more than 40% at low productivity, but we found no evidence of varietal differences in this trait despite pronounced differences in maturity and plant stature. Identification of pearl millet varieties suited for growth under low input conditions in south-west Niger can potentially make use of existing genotypic variability in root parameters, but we suggest that, due to high variability for root traits, indirect selection for shoot parameters (e.g., number of stems) is more promising than direct selection for RLD or RL.