Objective Approach for Phenotyping Solid, Semi-Solid, and Hollow Stems in Wheat

Plant host resistance to the Wheat Stem Sawfly in wheat (Triticum aestivum L.) has proven to be the most effective method to combat the effects of the insect. Currently, breeding for solid stemmed and semi-solid stemmed wheat shows the most control of wheat stem sawfly. The current method to assess stem solidness is a visual rating scale of one (hollow) to five (solid). To approach this objectively, a Stem Solidness Rating (StSR) was created by imaging internode segments and measuring the inside and outside diameters of the segment. Data collected was used to determine that the top internode, alone, can accurately phenotype a line as solid, semi-solid, or hollow. Additionally, results show that a sample size of n=3 top internodes is adequate to make a stem solidness classification. Assessment must be conducted twice throughout the growing season to identify semi-solid stems. It was determined that sampling prior to Feekes 9 and after Feekes 10.5 allows for capture of an early solid rating and a later hollow rating for cultivars expressing the semi-solid trait. Advisor: P. Stephen Baenzige