Efficiency of a Seedling Phenotyping Strategy to Support European Wheat Breeding Focusing on Leaf Rust Resistance

SIMPLE SUMMARY: Leaf rust resistance is of high importance for the European wheat production in order to avoid yield and quality losses. Modern breeding is aiming to maximize the selection gain within a short time period. To realize a successful resistance breeding, detailed knowledge about the genetic architecture of leaf rust resistance, as well as a precise and fast phenotyping strategy, are necessary. The examination of detached leaf assays of juvenile plants inoculated under controlled conditions and phenotyped by a robotic-based, high-throughput system is a promising approach in this respect. Known leaf rust resistance genes showing qualitative or quantitative effects and their expression starts at different developmental stages of wheat. Therefore, this study validated the transferability of results from detached leaf assays to the field and assessed the benefits of this phenotyping strategy to support leaf rust resistance breeding. Phenotyping detached leaves of wheat seedlings by using an automated, high-throughput methodology is a valuable tool to improve leaf rust resistance. ABSTRACT: Leaf rust resistance is of high importance for a sustainable European wheat production. The expression of known resistance genes starts at different developmental stages of wheat. Breeding for resistance can be supported by a fast, precise, and resource-saving phenotyping. The examination of detached leaf assays of juvenile plants inoculated under controlled conditions and phenotyped by a robotic- and computer-based, high-throughput system is a promising approach in this respect. Within this study, the validation of the phenotyping workflow was conducted based on a winter wheat set derived from Central Europe and examined at different plant developmental stages. Moderate Pearson correlations of 0.38–0.45 comparing leaf rust resistance of juvenile and adult plants were calculated and may be mainly due to different environmental conditions. Specially, the infection under controlled conditions was limited by the application of a single rust race at only one time point. Our results suggest that the diversification with respect to the applied rust race spectrum is promising to increase the consistency of detached leaf assays and the transferability of its results to the field.