Genetic Relationships, Phenotypic Diversity, and Disease Responses of Wheat Lines Used to Identify Races of the Common Bunt and Dwarf Bunt Pathogens

Summary

Common bunt (caused by Tilletia caries (DC.) Tul. & C. Tul. and Tilletia laevis J. G. Kühn) and dwarf bunt (caused by Tilletia controversa J. G. Kühn) are two important fungal diseases that can reduce yield and quality in wheat (Triticum sp.). The bunt differential lines are important genetic materials that have been used worldwide for decades to monitor virulence in various Tilletia populations and to identify resistance genes. However, there is limited information available regarding the genetic relationships among these bunt differential lines. The present study comprehensively evaluated these lines through molecular marker genotyping, greenhouse testing, and field nurseries. Seventeen wheat bunt differentials were assessed for dwarf bunt resistance in field trials over eight years (2016-2020, 2022, 2023 and 2024) in Logan, Utah, and in controlled greenhouse experiments for common bunt resistance over three years (2022-2024) in Aberdeen, Idaho. Significant variation among the differential lines was observed in responses to a composite bunt race inoculum. Lines carrying resistance genes Bt8, Bt11, Bt12, Bt13, and Btp consistently showed high level resistance to both common and dwarf bunt across all environments and years. Conversely, lines carrying Bt1, Bt2, Bt4, Bt6, and Bt7 were highly susceptible, with more severe responses observed for dwarf bunt. Bt9 and Bt10 showed more susceptibility to common bunt than dwarf bunt. To measure the genetic relationship among the differential lines, they were genotyped using a Wheat 90K Illumina SNP array. The cluster analysis results obtained did not reflect the resistance of the differential lines. Bt12, Bt13, and Btp were grouped in the same cluster, while Bt8 and Bt11 were grouped in two different clusters. This grouping corresponded to the geographic origin of the differential lines. These lines were also characterized for plant height, heading date, spike and seed feature in field and greenhouse experiments. The resistance profiles and genetic relationships of these differential lines will benefit future efforts to breed wheat cultivars with bunt resistance.