Lodging, the displacement of plants from the vertical position, is a critical issue in barley causing decreased yield, harvest difficulty, increased disease, and reduced grain quality. During cultivar development, lodging is commonly assessed by visual scoring which creates challenges for robust assessments due to the variability between selection environments, especially when no lodging is observed. The main objective of the study was to identify root and stem traits important for lodging resistance for future cultivar improvement. Since lodging is often caused by anchorage failure, there was an important focus on characterizing root system architecture, the shape and spatial arrangement of roots, in both lodging-resistant and lodging-prone cultivars. High-throughput root system assessments also provided opportunities to develop efficient methods to screen for lodging resistance and compare root system variation across diverse barley germplasm. The study incorporated six replicated field trials in Saskatoon and Rosthern to assess stem and root traits of 13 barley genotypes varying in lodging resistance. Stems were assessed for strength, diameter, and pushing resistance while root crowns were excavated to determine angle, spread, and depth. Field analyses revealed that reduced plant height and increased crown root angle were associated with lodging resistance. Root angle was positively correlated to horizontal spread of the root system – a trait previously associated with cereal lodging resistance. Image analysis of the root crowns identified solidity, the ratio of root area to convex area, as a trait associated with lodging whereby more spread-out root systems with wider angle and lower solidity were more lodging resistant. Measurement of stem pushing resistance as a lodging test yielded mixed results with an overall weak positive relationship to lodging. Innovative indoor root imaging of the 13 field-tested barley genotypes measured seminal root germination angle and root architectural traits of weeks-old seedlings in hydroponics and mature root systems in soil rhizoboxes. Of the 41 traits describing root architecture, and consistent with the field trial results, wider seminal and crown root angles and lower network solidity of seedlings were found to be associated with lodging resistance. Solidity was used to help train a decision tree model to predict lodging resistance in a set of 19 additional barley genotypes with some success; although more data is required to develop a robust model. To examine root diversity, an association mapping panel of 168 barley genotypes was assessed indoors for root system architecture traits. Screening of the panel revealed how root angle is distributed through western Canadian germplasm and has been inherited amongst genotypes with common pedigree. Preliminary genome-wide association analyses revealed genomic regions controlling angle and solidity. Overall, the identification of root angle and solidity as traits which can be used to assess lodging resistance is a significant step forward – the ability to measure these traits indoors using high-throughput root imaging creates an efficient screening tool to help breeders select for and improve lodging resistance. From a production perspective, the results indicate the best lodging resistant cultivars have reduced height, for lower wind leverage forces, with wider root angles for increased plant anchorage.

Extension Messages

• Barley varieties with shorter stature, wider crown root angle and a diffuse root system tend to be more resistant to lodging
• Root angle is established immediately after germination thus allowing breeders to select for this trait in an indoor environment with relative simplicity and high-throughput
• Identifying traits linked to lodging resistance through methods that are not dependent on conditions which promote field lodging will help breeders increase their ability to select and release improved lodging-tolerant varieties