Macroscopic and Microscopic Phenotyping Using Diverse Yellow Rust Races Increased the Resolution of Seedling and Adult Plant Resistance in Wheat Breeding Lines

We characterized yellow rust (YR) resistance in sixteen winter wheat breeding lines using three different pathogen races and macroscopic and microscopic phenotyping in lab and greenhouse. Three rust races were used on seedlings and two races on fifth and flag leaf growth stages. The wheat lines were previously characterized to possess none or different quantitative trait loci for YR resistance in field trials. At the seedling stage, twelve lines showed race-specific seedling resistance whereas four lines gave strong seedling resistance to all three races. Seven of eight lines with QTL.1B showed strong seedling resistance against the two races also used at fifth and flag leaves. Microscopic phenotyping of line NOS50906215 (QTL.1B) showed small fungal colonies stopped within 3 dpi associated with extensive hypersensitive response (HR). The lines NOS51014910 and NOS51014911 (QTL.3D alone) showed strong adult plant resistance (APR) from the fifth leaf stage. The lines NOS70140801 and NOS70140808 (QTL.3D + 7B) showed strong APR to one race but partial resistance to the other race at all growth stages. Microscopic phenotyping of line NOS70140801 (QTL.3D + 7B) showed more fungal growth and less HR against the race revealing strong APR compared to the one revealing partial resistance. Line NOS51010312 (QTL.7B alone) showed strong APR response against both races whereas line NOS51010313 (QTL.7B) was susceptible. A partial APR response was observed on line NOS51005019 (no QTLs reported). In conclusion, the approach of combining macroscopic and microscopic phenotyping and diverse pathogen races facilitates the identification of multiple and diverse seedling and adult plant resistance responses to yellow rust in wheat.