Our research published in Crop Science journal

Genotypic Variation for Root Trait Morphology in a White Clover Mapping Population Grown in Sand
M. Z. Z. Jahufer, S. N. Nichols, J. R. Crush, Li Ouyang, A. Dunn, J. L. Ford,
D. A. Care, A. G. Griffiths, C. S. Jones, C. G. Jones, and D. R. Woodfield
Crop Sci. (2008) 48:487–494
doi: 10.2135/cropsci2007.03.016

Abstract:
A study of 386 white clover (Trifolium repens L.) mapping population F1 progeny was conducted to quantify the type and magnitude of genotypic variation for a range of root morphology traits. Clones of each of the 386 white clover progeny were grown in sand. There were signifi - cant (P < 0.05) genotypic variance components and repeatability estimates for all the root traits examined. Progeny genotypes with high expression of key traits, including number of root tips and number of root forks were identifi ed. These types may improve phosphate uptake as their highly branched roots will explore a large volume of soil per unit root weight. A strong positive phenotypic and genotypic correlation between several root traits was identifi ed. This suggests an opportunity for indirect selection. For example, selection for high root fork number, a trait that is relatively less complicated to measure, should result in the concurrent increase in expression of the following root traits: surface area, number of tips, volume, and dry weight. Comparison of results from the sand-based trial with an earlier trial using hydroponic conditions, with clones of the same 386 progeny, showed similar correlations exist among the root traits in both systems. The progeny genotype-by-trait Best Linear Unbiased Predictor matrix generated from the sand study is currently being used for the identifi cation of root trait quantitative trait loci.