Transfer And Utilization Of Powdery Mildew Resistance Translocation Of 6RS·6AL

Wheat powdery mildew,caused by the fungus Blumeria graminis f.sp.tritici,can reduce its yield and quality.The application of resistance genes in wheat varieties is a safe and economical way to control powdery mildew.The new powdery mildew resistance gene Pm56 located in the sub-telomeric region of chromosome arm 6RS.It showed stronger resistance to powdery mildew than Pm20 both under field and greenhouse conditions,thus useful in resistance breeding.In our previous study,a 6RS·6AL translocation line HM812-41 harboring this gene has been generated within a genetic background of landrace.To evaluate the application value in wheat breeding using the 6RS·6AL translocation chromosome and HM812-41,we carried out the following works:distinguishing the centromere structure of the 6RS·6AL translocation,evaluating its genetic stability during hybridization and improving its agronomic traits using the"double top-cross"strategy.The main results are as follows:?1?The centromere structure of 6RS·6AL was analyzed by fluorescence in situ hybridization?FISH?using probes CCS1 and pAWRC.1.The probe CCS1 hybridizes to the centromeric regions of both wheat and rye chromosomes,while the probe for pAWRC.1 hybridizes specifically to the centromeric region of rye.The result showed the CCS1 signal extends the whole length of the centromere of 6RS·6AL,with no pAWRC.1signal detected,meaning that the centromeric region is derived from wheat 6A.Two6RS·6AL the translocation chromosomes paired into rod divalent at the metaphase I during meiosis in HM812-41.?2?The pollen viability were determined using iodine/potassium iodide?I₂-KI?solution staining.The mean ratio of viable pollens for 6RS·6AL translocation line HM812-41 was 94.1%,there were no significant differences compare to both Chinese Spring?CS;93.0%?and D-2-3-4?95.2%?.It indicated the 6RS·6AL translocation chromosome had no effects on the vigor of the male gamete.HM812-41 was crossed with CS and Kaixian-luohanmai as male and female.The molecular marker KU.962 specific for6RS was used track the 6RS·6AL translocation.The proportion of hybrids F₁ with KU.962were 99.74%,indicating the translocation chromosome 6RS·6AL can stably transmit to offsprings both through male and female gametes.?3?HM812-41 respectively crossed to common wheat varieties Shumai 580,Shumai830 and Shumai 969.The hybrids F₁ with 6RS·6AL/6A double monosomic karyotype confirmed by molecular cytology were backcrossed with CS as male and female.The proportions of offsprings included specific marker for 6RS crossing were both about a half of all despite as male or female.It indicated the chromosomes 6RS·6AL and 6A behaved like one single gene.The mean transmission frequency of 6RS·6AL was high both through female gametes?48.8%?and male gametes?47.4%?.?4?Fourty-one plants that derived from crossing between 6RS·6AL/6A double monosome and CS and harbored the target band for specific marker KU.962 were analyzed by genomic in situ hybridization.All of them contained one complete 6RS·6AL translocation chromosome.It indicated the 6RS·6AL translocation was very stable even under a heterozygous background.We thus can ignore the risk that 6RS·6AL was broke again during in the process of breeding application.?5?The results from F₂ population derived from"double top-cross"process suggested the 6RS·6AL translocation didn't linked to genes showing disadvantage to main agronomic traits,including plant height,spike length and spikelet number.All plants with 6RS·6AL translocation showed stably resistance to powdery mildew.The agronomic traits of HM812-41 can be largely improved through"double top crossing"strategy.