Mapping Of An All-stage Stripe Rust Resistance Gene YrCf75 In Wheat Cultivar Changfeng 75

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici（Pst）,is one of the most serious diseases on wheat in the world.Breeding and planting disease-resistant varieties is the most economical,effective and environmentally friendly measure to control stripe rust.Changfeng 75,breeding by Shaanxi Changfeng Seed Industry Co.,Ltd,is a new wheat variety with high resistance to stripe rust..In the previous study,our lab group also found that it has high resistance（IT=0-1）to Chinese predominat Pst races CYR32,CYR33 and CYR34.Combined bulk segregation analysis（BSA）with Wheat 660K SNP chip array and RNA-Seq（BSR-Seq）,the KASP markers were developed to map the stripe rust resistance genes in Changfeng 75.The main results are showed as follows:1.At the seedling stage,the F₁,F₂,F_2:3generations of Mingxian 169/Changfeng 75 and their parents were inoculated with Pst race CYR34.the results showed that Changfeng 75was resistance（IT=0-1）,whereas Mingxian 169 was susceptible（IT=8-9）,and F₁generation were susceptible too.For the 458 individual plants of Mingxian 169/Changfeng 75 F₂generation,117 were resistant and 341 susceptible,and the segregation ratio was consistent with the 1R:3S ratio（χ²=0.07,P=0.79）;Among 148 F_2:3generation lines,36 lines were homozygous resistant,:71 segregation,and 41 homozygous susceptible,which also conformed to the segregation ratio of 1:2:1（χ²=0.58,P=0.75）.To further verify the genetic law of resistance to stripe rust in Changfeng 75,Another Mingxian 169/Changfeng 75 F₂generation including 950 individual plants were also inoculated with Pst race CYR34,and the results indicated that 244 plants showed disease resistance and 706 were susceptible,which also conformed to the 1R:3S segregation ratio.The above results indicated that the seedling resistance of Changfeng 75 to CYR34 was controlled by a pair of recessive gene,tentatively named as YrCf75.2.The 148 F₂individual plants which have obtained F_2:3generation families were used to construct the mapping population.The resistant DNA bulk and susceptible DNA bulk were constructed by randomly selecting 10 extremely resistant individual plants and 10extremely susceptible individual plants,respectively.Then Changfeng 75,Mingxian 169,resistant bulk and susceptible bulk were genotyped by wheat 660K SNP array,.The results showed that the number of polymorphic SNPs on chromosome 2A was the largest,and the SNP distribution frequency was the highest in the range of 550-780 Mb.Therefore,YrCf75was probably located on wheat chromosome 2A.In addition,10 homozygous resistant families and 10 homozygous susceptible families of Mingxian 169/Changfeng 75 hybrid F_2:3generation were used to construct resistance and susceptible pools,respectively,and these bulks and two parents were used for for BSR-Seq.The results showed that the frequency of SNP distribution in the interval of 0-100 Mb and 550-780 Mb on the wheat chromosome 2A was the highest,which further indicated that YrCf75 may be located on the wheat chromosome 2A.3.The polymorphic SNPs on chromosome 2A obtained by wheat 660K SNP array and BSR-Seq were converted into KASP markers,and 148 individual plants of Mingxian169/Changfeng 75 F₂generation were detected by BSA method.The results showed that there were 31 pairs of KASP markers were linked to the target gene YrCf75,and YrCf75 is located on the wheat 2AL chromosome.SSR markers located on the chromosome 2AL were further used to encrypt the target gene region.Finally,31 pairs of KASP markers and 1pair of SSR markers are linked to YrCf75.And the two closely linked flanking markers were AX-1110060462 and AX-111004763,with genetic distances of 1.2 c M and 2.7 c M,respectively.Disease resistance,molecular testing and pedigree analysis indicated that YrCf75 is probably a novel gene different from the officially named stripe rust resistance genes（Yr1 and Yr32）on chromosome 2AL.4.Candidate gene analysis was performed in the 61 Mb interval（577-638 Mb）of the closely linked flanking markers of YrCf75,the results showed that this interval contains LRR receptor kinase,hydroxycinnamoyl transferase,calmodulin-binding receptor-like cytoplasmic kinase,F-box protein,calmodulin-binding transcriptional activator,ABC transporter G Family members,etc.All of these have been pointed out in the relevant literature to directly or indirectly participate in plant disease resistance activities.It is preliminarily speculated that one of them may be a candidate gene of YrCf75,and more research is needed to further confirm the function of these candidate genes.