Root Physiological and Morphological Characteristics of 24 Rice Varieties Selected for Diverse Grain Mineral Composition.

Root physiological characteristics impact mineral availability, solubility and mobility in the soil and morphological and physiological characteristics impact mineral absorption/uptake from soil into the roots thus influencing grain mineral composition. Prior flooded and unflooded field trials conducted in 2007 and 2008 identified genotypes with extreme grain mineral compositions. Our hypothesis was that these extreme grain mineral compositions were sometimes due to differences in their root morphology and physiology. The two main objectives of this study were to 1) quantify root morphological and physiological characteristics of 23 genotypes selected for extreme grain mineral concentrations along with the US standard variety, Lemont and 2) identify distinct root traits associated with specific mineral concentrations in grain. Four replications of the genotypes were grown in sand culture medium until 3 weeks after planting under controlled conditions. At harvest, roots were thoroughly washed and digitally imaged by scanning so that root morphological traits could be quantified using WinRhizo Pro software (Regent Instruments, Canada). Root respiration was measured spectrophotometrically by treating roots with naphthylamine and quantifying naphthylamine oxidation. Although genotypes showed significant differences in roots (fresh and dry weights) and also shoots (leaf area, fresh and dry weight), no distinct traits were found to associate with specific mineral accumulation. We conclude that the root traits observed herein were not significant factors underlying individual mineral concentrations among these genotypes and we hypothesize that these differences may be more due to altered uptake mechanisms. Future studies will be conducted using F₂ progenies to better determine which root traits are associated with grain mineral accumulation segregating among specific biparental progeny.