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Genotypic Variation for Root Trait Morphology in a White Clover Mapping Population Grown in Sand

^a Pastoral Genomics, AgResearch Ltd., Grasslands Research Centre, Private Bag 11008, Palmerston North, New Zealand
^b Pastoral Genomics, AgResearch Ltd., Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand
^c Pastoral Genomics, ViaLactia Biosciences (NZ) Ltd., Auckland, New Zealand

^* Corresponding author (zulfi.jahufer{at}agresearch.co.nz).

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 significant (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 identified. 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 identified. 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 identification of root trait quantitative trait loci.

Abbreviations: BLUP, Best Linear Unbiased Predictor • MP, mapping population • QTL, quantitative trait loci • RD, root dry weight • RF, number of root forks • RF/RL, root forks per unit length • RL, root length • RS, root surface area • RT, number of root tips per plant • RT/RL, root tips per unit root length • RV, root volume

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Received for publication March 21, 2007.