Production Of Secondary Recombination Line Of Wheat-Dasypyrum Villosa Harbouring Gene Pm21

Wheat-Dasypyrum villosa 6VS.6AL translocation（T6VS.6AL）harboring the gene Pm21 has made a great contribution to powdery mildew resistance breeding in China.The frequency of 6VS.6AL translocation in southwest wheat varieties is relatively high,but the origin and the exact form of these translocations are still unclear.Moreover,T6VS.6AL has a relatively lower transmission frequency through male gametes and a negative effect on tiller number and plant height.Generating 6VS/6AS recombinants with smaller chromosome segments introduced into common wheat might further promote the utilization of gene Pm21 in the breeding program.Therefore,this study analyzed the origin and the existing forms of 6VS.6AL chromosome in southwest wheat variety using the 55K SNP genotyping data of 165 Sichuan wheat varieties（lines）.A set of primary translocation of 6VS/6AS induced by ph1b were generated.Subsequently,a number of secondary translocation lines harboring Pm21 gene were generated by using the primary translocation lines.The main findings are as follows:1.Based on the genotypying data of 55K SNP,25（15.4%）out of 162 Sichuan wheat varieties contained T6VS.6AL.Haplotype analysis based on the recombination breakpoint of the 25 varieties showed that all of the 25 varieties contain centric translocations.Line92R178 was proposed as the original donor of the 6VS.6AL translocation in these varieties based on the pedigree analysis.2.Sixteen primary translocation lines of 6VS/6AS were indicated by the genotyping results of 6VS/6AS terminal（telomere and centromeric）specific KASP markers C_V/C_Aand T_V/T_A.By in situ hybridization,twelve of them were further ensured with 6AS-6VS.6AL configuration（named as C＿6VS/6AS＿AV type）and four of them were in 6VS-6AS.6AL configuration（named as C＿6VS/6AS＿VA type）.3.Secondary recombinant in 6AS-6VS-6AS.6AL configuration containing Pm21 was generated by crossing primary recombinants 6VS-6AS.6AL with 6AS-6VS.6AL.Based on the Chinese Spring reference genome,the crossover points of secondary recombinant were located within 53.1-53.8 Mb and 90.7-92.2 Mb of chromosome 6A.The inserted 6VS fragment size was about 36.9-39.1 Mb.Therefore,the secondary recombinant had a much smaller 6VS chromatin than the primary recombinants.4.Molecular cytological identification also detected extensive recombination among wheat endogenous homoeologs in the ph1b background,which was undesirable for genetic stabilization andr wheat breeding.It is necessary to eliminate endogenous recombinants as soon as possible.A proposed solution to reduce endogenous recombination was to preserve the ph1b mutant line in a heterozygous condition and reduce the selfing times during the development of ph1b-mediated wheat-alien recombination.