Molecular Mapping of a Stripe Rust Resistance Gene YrH9020a Transferred from Psathyrostachys huashanica Keng on Wheat Chromosome 6D

Stripe rust （yellow rust）, caused by Puccinia striiformis f. sp. tritici （Pst）, is one of the most devastating diseases of wheat throughout the world. H9020-1-6-8-3 is a translocation line originally developed from interspeciifc hybridization between wheat line 7182 and Psathyrostachys huashanica Keng and is resistant to most Pst races in China. To identify the resistance gene（s） in the translocation line, H9020-1-6-8-3 was crossed with susceptible cultivar Mingxian 169, and seedlings of the parents, F1, F2, F3, and BC1 generations were tested with prevalent Chinese Pst race CYR32 under controlled greenhouse conditions. The results indicated that there is a single dominant gene, temporarily designated as YrH9020a, conferring resistance to CYR32. The resistance gene was mapped by the F2 population from Mingxian 169/H9020-1-6-8-3. It was linked to six microsatellite markers, including Xbarc196, Xbarc202, Xbarc96, Xgpw4372, Xbarc21, and Xgdm141, lfanked by Xbarc96 and Xbarc202 with at 4.5 and 8.3 cM, respectively. Based on the chromosomal locations of these markers and the test of Chinese Spring （CS） nullitetrasomic and ditelosomic lines, the gene was assigned to chromosome 6D. According to the origin and the chromosomal location, YrH9020a might be a new resistance gene to stripe rust. The lfanking markers linked to YrH9020a could be useful for marker-assisted selection in breeding programs.

Analysis of Genetic Diversity in Natural Populations of Psathyrostachys huashanica Keng Using Microsatellite (SSR) Markers

Psathyrostachys huashanica Keng is endemic to China and only distributed in Huashan Mountain in Shaanxi Province, China. In this study, 15 P. huashanica populations consisting of 450 individuals sampled across their main distribution were investigated by using the simple sequence repeats （SSRs） markers. A total of 184 alleles were detected on 24 SSR loci, and the number of alleles on each locus ranged from 2 to15, with an average of 7.667. The total gene diversity （HT= 0.683） and the coefficient of population differentiation （GST = 0.125） showed that P. huashanica had a relatively high level of genetic variation, and the genetic variation was mainly distributed within the populations. The gene flow among the populations of P. huashanica （Nm = 1.750） was much less than that of the common anemophytes （Nm = 5.24）. Correlation analysis demonstrated that the number of alleles as well as genetic diversity of the five populations of Huangpu valley decreased along with the increase of altitudes, but the correlation was not significant. Implications of these results for future P. huashanica collection, evaluation and conservation were discussed.

Identification of genetic locus with resistance to take-all in the wheat-Psathyrostachys huashanica Keng introgression line H148

Take-all is a devastating soil-borne disease of wheat(Triticum aestivum L.).Cultivating resistant line is an important measure to control this disease.Psathyrostachys huashanica Keng is a valuable germplasm resource with high resistance to take-all.This study reported on a wheat-/R huashanica introgression line H148 with improved take-all resistance compared with its susceptible parent 7182.To elucidate the genetic mechanism of resistance in H148,the F_(2)genetic segregating population of H148×XN585 was constructed.The mixed genetic model analysis showed that the take-all resistance was controlled by two major genes with additive,dominant and epistasis effects.Bulked segregant analysis combined with wheat axiom 660K genotyping array analysis showed the polymorphic SNPs with take-all resistance from P.huashanica alien introgression were mainly distributed on the chromosome 2A.Genotyping of the F_(2)population using the KASP marker mapped a major QTL in an interval of 68.8-70.1 Mb on 2AS.Sixty-two genes were found in the target interval of the Chinese Spring reference genome sequence.According to the functional annotation of genes,two protein genes that can improve the systematic resistance of plant roots were predicted as candidate genes.The development of wheat-P.huashanica introgression line H148 and the resistant QTL mapping information are expected to provide some valuable references for the fine mapping of disease-resistance gene and development of take-all resistant varieties through molecular marker-assisted selection.