Keywords: Genetics, gravitropism, phosphorus, roots, transcriptome.

Summary:
Sufficient phosphorus (P) is essential for plant growth and reproduction. It is acquired by plant roots from the soil solution as inorganic phosphate ions, denoted here as P. The low concentration and slow diffusion of P in the soil solution force plant roots to forage for P, and the ability of crops to grow and yield well on soils with little available P is often related to the volume of soil explored by their root systems. In particular, increased topsoil foraging, the production of long root hairs and the proliferation of lateral roots in P-rich patches facilitate P acquisition and are associated with increased agricultural productivity on infertile soils. There is considerable genetic variation both between and within crop species in all these root traits. This variation can be harnessed for breeding crops with improved P acquisition, growth and yield on soils with little plant available P. In addition, the genetic events leading to the development of root systems specialised for P acquisition are being elucidated and appear to be common to many plant species. Genes regulating root development might be manipulated to improve P acquisition by crops.

P J White, D J Greenwood and J P Hammond, Warwick HRI, University of Warwick, Wellesbourne, Warwick CV35 9EF, UK.
M R Broadley, School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough LE12 5RD, UK.

28 pages, 4 figures, 116 references.