Genetic Analysis Of The Stripe Rust Resistance Gene Yr81 And Its Suppressor Gene Derived From Wheat Landrace ’Dahongpao’

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici,is an important worldwide fungal disease affecting wheat production,particularly severe in China.The safest and most effective way to control stripe rust is to breed resistant varieties.However,in recent years,many resistant varieties have become susceptible due to the emergence of a new Pst race CYR34.Therefore,finding new effective sources of resistance is the key to breeding for disease resistance.Wheat landraces are valuable germplasm resources conserved by natural selection and human intervention,and are important genes source for improving stripe rust resistance in breeding.Previous study has shown that the wheat landrace Dahongpao（DHP）has stable adult plant resistance（APR）to the predominant Pst races and pathotypes in China.The genetic analysis and molecular mapping of DHP×Avocet S and the construction of its resistance gene mapping revealed that the main resistance locus controlling the resistance to stripe rust at the adult stage was located on the short arm of chromosome 7D,and confirmed that this locus was the Yr18 known resistance gene,which explained 30.78-53.08%of phenotypic variation.However,it was also found that a few single plants that did not carry Yr18were still highly resistant to stripe rust at the adult stage,suggesting that DHP also carries other known or unknown genes for resistance to stripe rust that have not been identified.Based on this,we constructed multiple secondary populations using resistant individuals without Yr18 and applied bulked segregant analysis combined with exome capture sequencing（BSE-Seq）to isolate and map the unidentified stripe rust resistance genes in DHP.The main results are as follows:1.Based on the F_2:3 lines derived from a cross between DHP and susceptible cultivar Avocet S（AvS）and using gene specific functional marker Lr34-KASP-E11 for Yr18 screening,we identified two individual plants（DHP49 and DHP87,IT≤3）without Yr18 but highly resistant to stripe rust for crossing with AvS,and constructed two secondary F₂ populations named SP1 and SP2,respectively.Phenotypic identification and genetic analysis showed that the resistance in SP1 population was controlled by an all-stage resistance gene.BSE-Seq analysis of SP1 population revealed a significant peak signal on the short arm of chromosome 6A,with most differential SNPs located in the0～7Mb physical region（Chinese Spring IWGSC Ref Seq v1.0）.By using KASP markers developed in this study and recombinant plants from SP1 and SP2 populations,the gene was mapped between KP6A＿1.66 and KP6A＿8.18 and co-segregated with seven KASP markers.The combined results of previous studies showed that this gene should be highly co-linear with the known all-stage resistance Yr81,which confirmed that the gene controlling the all-stage resistance to stripe rust in DHP is Yr81.2.The F_2:3 resistant segregating families were selected from a cross between DHP and susceptible cultivar AvS,and the segregating line DHP122,which did not carry Yr18and was phenotypically segregated,was used as a reference for constructing the secondary segregating populations SP3 and SP4 using the residual heterozygous line.Genetic analysis showed that besides being affected by Yr81,there might be another resistance suppressor locus affecting the expression of stripe rust resistance in SP3 and SP4 populations.The BSE-Seq and QTL analysis of SP3 population showed that this locus was located on the short arm of chromosome 2B,between KP2B＿146.01 and KP2B＿190.20,which explained 44.00%of the genetic variation,tentatively named as Yr.DHP-2BS.Genotype and phenotype analysis showed that when Yr.DHP-2BS was homozygous for DHP allele,it could effectively suppress the all-stage resistance conferred by Yr81.3.The analysis of the genetic effects of Yr18,Yr81 and Yr.DHP-2BS using F_2:3 and F₄populations constructed by crossing the DHP with the susceptible cultivar AvS showed that Yr81 and Yr.DHP-2BS were susceptible when carried together,confirming that Yr.DHP-2BS had a strong suppressive effect on the expression of resistance to Yr81,and Yr.DHP-2BS was also found to have a suppressive effect on Yr18.The convergent lines carrying Yr18 and Yr81 showed transgressive（DHP）stripe rust resistance,which can provide a simple and effective combination of resistance genes for breeding durable and highly resistant wheat varieties.Meanwhile,the newly developed KASP markers KP6A＿1.99 and KP6A＿5.22 were identified to facilitate the marker-assisted selection of Yr81.