Development and characterization of a new wheat-rye T6BS.6BL-6RL^Ku small segment translocation with powdery mildew resistance and potential breeding value

Rye (Secale cereale L.) contains numerous disease resistance genes that can be utilized for wheat (Triticum aestivum) improvement. For example, rye chromosome 6 carries powdery mildew resistance genes. Wheat-rye 6R translocation lines are highly useful, but more wheat-rye 6R translocation lines with potential breeding value are needed. In this study, we identified a new wheat-rye T6BS.6BL-6RL^Ku translocation chromosome, conferring powdery mildew resistance, from the progeny of the irradiated wheat-rye 6RL^Ku ditelosomic addition line. Genotyping using the wheat GBW16K array and specific markers revealed that approximately 104.03 Mb of the distal segment of 6RL^Ku replaced approximately 6.1 Mb of the distal segment of the long arm of 6B (6BL) to form the translocation chromosome. Oligo-FISH painting indicated that the 104.03 Mb segment of 6RL^Ku is homologous to homoeologous group 7 chromosomes. Using wheat cultivars Chuanmai 62 (CM62) and Chuannong 32 (CN32) as backcross parents, we transferred the T6BS.6BL-6RL^Ku chromosome into the two wheat backgrounds. We selected two translocation lines: CM62-6RL and CN32-6RL. Genotyping analysis indicated that the CM62-6RL and CN32-6RL genomes are highly similar to those of CM62 and CN32, respectively. The grains of CM62-6RL were shriveled, whereas those of CN32-6RL were full. The effect of the T6BS.6BL-6RL^Ku chromosome on grain width also depended on the genetic background of the wheat. The improved grain lengths of both CM62-6RL and CN32-6RL contributed to the improvement in their thousand-kernel weight. The translocation chromosome had no negative effects on other important agronomic traits. These findings highlight the potential breeding value of the wheat-rye 6R translocation chromosome T6BS.6BL-6RL^Ku. The compensation mechanisms of this translocation chromosome in different wheat backgrounds deserve further study.