Comparative analysis of Fusarium crown rot resistance in synthetic hexaploid wheats and their parental genotypes.

BACKGROUND: Fusarium crown rot (FCR) is a chronic disease of cereals worldwide. Compared with tetraploid wheat, hexaploid wheat is more resistant to FCR infection. The underlying reasons for the differences are still not clear. In this study, we compared FCR responses of 10 synthetic hexaploid wheats (SHWs) and their tetraploid and diploid parents. We then performed transcriptome analysis to uncover the molecular mechanism of FCR on these SHWs and their parents. RESULTS: We observed higher levels of FCR resistance in the SHWs compared with their tetraploid parents. The transcriptome analysis suggested that multiple defense pathways responsive to FCR infection were upregulated in the SHWs. Notably, phenylalanine ammonia lyase (PAL) genes, involved in lignin and salicylic acid (SA) biosynthesis, exhibited a higher level of expression to FCR infection in the SHWs. Physiological and biochemical analysis validated that PAL activity and SA and lignin contents of the stem bases were higher in SHWs than in their tetraploid parents. CONCLUSION: Overall, these findings imply that improved FCR resistance in SHWs compared with their tetraploid parents is probably related to higher levels of response on PAL-mediated lignin and SA biosynthesis pathways.

Identification of a suppressor for the wheat stripe rust resistance gene Yr81 in Chinese wheat landrace Dahongpao.

KEY MESSAGE: Combined with BSE-Seq analysis and multiple genetic populations, three genes involved in stripe rust resistance were identified in Chinese wheat landrace Dahongpao, including a novel suppressor on 2BS. Dahongpao (DHP), a landrace of hexaploid wheat in China, exhibits a high degree of stripe rust resistance in the field for many years. In this study, bulked segregant analysis coupled with exome capture sequencing (BSE-Seq) was used to identify genes encoding stripe rust resistance in multiple genetic populations from the cross between DHP and a susceptible hexaploid Australian cultivar, Avocet S (AvS). The most effective QTL in DHP was Yr18, explaining up to 53.08% of phenotypic variance in the F2:3 families. To identify additional genes, secondary mapping populations SP1 and SP2 were produced by crossing AvS with two resistant lines derived from F2:3 families lacking Yr18. An all-stage resistance gene, Yr.DHP-6AS, was identified via BSE-Seq analysis of SP1. Combined the recombinant plants from both SP1 and SP2, Yr.DHP-6AS was located between KP6A_1.66 and KP6A_8.18, corresponding to the same region as Yr81. In addition, secondary mapping populations SP3 and SP4 were developed by selfing a segregating line from F2:3 families lacking Yr18. A novel suppressor gene on chromosome 2BS was identified from DHP for effectively suppressing the resistance of Yr.DHP-6AS in the SP3 and SP4. As a result, the wheat lines carrying both Yr18 and Yr.DHP-6AS show higher level of stripe rust resistance than DHP, providing an effective and simple combination for developing new wheat cultivars with ASR and APR genes. Further, the newly developed KASP markers, KP6A_1.99 and KP6A_5.22, will facilitate the application of Yr.DHP-6AS in wheat breeding via marker-assisted selection.

Exome Sequencing from Bulked Segregant Analysis Identifies a Gene for All-Stage Resistance to Stripe Rust on Chromosome 1AL in Chinese Wheat Landrace 'Xiaohemai'.

Stripe rust caused by Puccinia striiformis f. sp. tritici is one of the most destructive diseases of wheat. Identifying novel resistance genes applicable for developing disease-resistant cultivars is important for the sustainable control of wheat stripe rust. Chinese wheat landrace 'Xiaohemai' ('XHM') is an elite germplasm line with all-stage resistance (ASR) effective against predominant Chinese P. striiformis f. sp. tritici races. In this study, we performed a bulked segregant analysis coupled with exome capture sequencing (BSE-seq) to identify a candidate genomic region strongly associated with stripe rust resistance on chromosome 1AL in 173 F2:3 lines derived from the cross 'XHM' × 'Avocet S'. The gene, designated as YrXH-1AL, was validated by a conventional quantitative trait locus analysis using newly developed Kompetitive allele-specific PCR (KASP) markers, explaining up to 48.50% of the phenotypic variance. By testing a secondary mapping population comprising 144 lines from the same cross at the seedling stage with prevalent P. striiformis f. sp. tritici race CYR34, YrXH-1AL was identified as a single Mendelian factor in a 1.5-cM interval flanked by KASP markers KP1A_484.33 and KP1A_490.09. This region corresponded to a 5.76-Mb genomic interval on 'Chinese Spring' chromosome 1AL. Furthermore, two cosegregating KASP markers showed high polymorphisms among 130 Chinese wheat cultivars and could be used for marker-assisted selection. Because no other Yr genes for ASR that originated from common wheat have been detected on chromosome 1AL, YrXH-1AL is likely a novel gene that can be incorporated into modern breeding materials to develop wheat cultivars with enhanced stripe rust resistance.

Molecular Mapping and Analysis of an Excellent Quantitative Trait Loci Conferring Adult-Plant Resistance to Stripe Rust in Chinese Wheat Landrace Gaoxianguangtoumai.

The Chinese wheat landrace "Gaoxianguangtoumai" (GX) has exhibited a high level of adult-plant resistance (APR) to stripe rust in the field for more than a decade. To reveal the genetic background for APR to stripe rust in GX, a set of 249 F6:8 (F6, F7, and F8) recombinant inbred lines (RILs) was developed from a cross between GX and the susceptible cultivar "Taichung 29." The parents and RILs were evaluated for disease severity at the adult-plant stage in the field by artificial inoculation with the currently predominant Chinese Puccinia striiformis f. sp. tritici races during three cropping seasons and genotyped using the Wheat 55K single-nucleotide polymorphism (SNP) array to construct a genetic map with 1,871 SNP markers finally. Two stable APR quantitative trait loci (QTL), QYr.GX-2AS and QYr.GX-7DS in GX, were detected on chromosomes 2AS and 7DS, which explained 15.5-27.0% and 11.5-13.5% of the total phenotypic variation, respectively. Compared with published Yr genes and QTL, QYr.GX-7DS and Yr18 may be the same, whereas QYr.GX-2AS is likely to be novel. Haplotype analysis revealed that QYr.GX-2AS is likely to be rare which presents in 5.3% of the 325 surveyed Chinese wheat landraces. By analyzing a heterogeneous inbred family (HIF) population from a residual heterozygous plant in an F8 generation of RIL, QYr.GX-2AS was further flanked by KP2A_36.85 and KP2A_38.22 with a physical distance of about 1.37Mb and co-segregated with the KP2A_37.09. Furthermore, three tightly linked Kompetitive allele-specific PCR (KASP) markers were highly polymorphic among 109 Chinese wheat cultivars. The results of this study can be used in wheat breeding for improving resistance to stripe rust.

A Stable Quantitative Trait Locus on Chromosome 5BL Combined with Yr18 Conferring High-Level Adult Plant Resistance to Stripe Rust in Chinese Wheat Landrace Anyuehong.

Chinese wheat landrace Anyuehong (AYH) has displayed high levels of stable adult plant resistance (APR) to stripe rust for >15 years. To identify quantitative trait loci (QTLs) for stripe rust resistance in AYH, a set of 110 recombinant inbred lines (RILs) was developed from a cross between AYH and susceptible cultivar Taichung 29. The parents and RILs were evaluated for final disease severity (FDS) in six field tests with a mixture of predominant Puccinia striiformis f. sp. tritici races at the adult plant stage and genotyped via the wheat 55K single-nucleotide polymorphism (SNP) array to construct a genetic map with 1,143 SNP markers. Three QTLs, designated as QYr.AYH-1AS, QYr.AYH-5BL, and QYr.AYH-7DS, were mapped on chromosome 1AS, 5BL, and 7DS, respectively. RILs combining three QTLs showed significantly lower FDS compared with the lines in other combinations. Of them, QYr.AYH-5BL and QYr.AYH-7DS were stably detected in all environments, explaining 13.6 to 21.4% and 17.6 to 33.6% of phenotypic variation, respectively. Compared with previous studies, QYr.AYH-5BL may be a new QTL, whereas QYr.AYH-7DS may be Yr18. Haplotype analysis revealed that QYr.AYH-5BL is probably present in 6.2% of the 323 surveyed Chinese wheat landraces. The kompetitive allele specific PCR (KASP) markers for QYr.AYH-5BL were developed by the linked SNP markers to successfully confirm the effects of the QTL in a validation population derived from a residual heterozygous line and were further assessed in 38 Chinese wheat landraces and 92 cultivars. Our results indicated that QYr.AYH-5BL with linked KASP markers has potential value for marker-assisted selection to improve stripe rust resistance in breeding programs.

Genome-Wide Association Analysis of Stable Stripe Rust Resistance Loci in a Chinese Wheat Landrace Panel Using the 660K SNP Array.

Stripe rust (caused by Puccinia striiformis f. sp. tritici) is one of the most severe diseases affecting wheat production. The disease is best controlled by developing and growing resistant cultivars. Chinese wheat (Triticum aestivum) landraces have excellent resistance to stripe rust. The objectives of this study were to identify wheat landraces with stable resistance and map quantitative trait loci (QTL) for resistance to stripe rust from 271 Chinese wheat landraces using a genome-wide association study (GWAS) approach. The landraces were phenotyped for stripe rust responses at the seedling stage with two predominant Chinese races of P. striiformis f. sp. tritici in a greenhouse and the adult-plant stage in four field environments and genotyped using the 660K wheat single-nucleotide polymorphism (SNP) array. Thirteen landraces with stable resistance were identified, and 17 QTL, including eight associated to all-stage resistance and nine to adult-plant resistance, were mapped on chromosomes 1A, 1B, 2A, 2D, 3A, 3B, 5A, 5B, 6D, and 7A. These QTL explained 6.06-16.46% of the phenotypic variation. Five of the QTL, QYrCL.sicau-3AL, QYrCL.sicau-3B.4, QYrCL.sicau-3B.5, QYrCL.sicau-5AL.1 and QYrCL.sicau-7AL, were likely new. Five Kompetitive allele specific PCR (KASP) markers for four of the QTL were converted from the significant SNP markers. The identified wheat landraces with stable resistance to stripe rust, significant QTL, and KASP markers should be useful for breeding wheat cultivars with durable resistance to stripe rust.