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Rheological Hardness Index for Assessing Hardness of Hexaploids and Durums

¹European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (present address), formerly CSIRO Plant Industry, Black Mountain Laboratories, Canberra ACT 2601, Australia. ²Agricultural Institute, Centre for Agricultural Research, Hungarian Academy of Sciences, Brunszvik u. 2., Martonvásár 2462, Hungary. ³NSW Department of Primary Industries, Tamworth Agricultural Institute, 4 Marsden Park Road, Calala, NSW 2340, Australia. ⁴Department of Plant Physiology and Molecular Plant Biology, Eötvös Loránd University, Pázmány P 1/C, Budapest 1117, Hungary. ⁵CSIRO Mathematical and Information Sciences, North Road, ANU Campus, Acton ACT, P.O. Box 664, Canberra, ACT 2601, Australia. ⁶Corresponding author. Phone: +61 2 6216 7260. Fax: +61 2 6216 7111. E-mail: Bob.Anderssen@csiro.au

Kernel hardness of cereal grains is a fundamental phenotype, and various protocols for its characterization have been proposed. Although, from different perspectives, each has proved useful, these methods do not directly address the rheological (fracturing) response of a grain when subjected to compression. Such information is hidden in the individual crush response profiles (iCRPs) obtained by measuring the response of individual grains to crushing on an SKCS 4100 device. Here, the appropriateness and utility of rheological phenotypes, based on single-kernel measurements, are demonstrated by proposing and validating a new wheat grain hardness phenotype, the rheological hardness index (RHI). It is defined in terms of the rheological phenotype phases (RPPs) of the averaged CRPs (aCRPs) obtained by averaging a large number of iCRPs. The utility of RHI is illustrated by showing how it provides improved insight about the differences in brittleness and compactness of grains from different wheat varieties. This investigation highlights the opportunity that the RPP of the aCRPs represent for obtaining specific quantitative phenotypes for the study of hardness in cereal grains. In particular, successful plant breeding relies on segregating a breeding population into appropriate end-use categories, for which RHI has a potential role to play.