An adult plant stripe rust resistance gene maps on chromosome 7A of Australian wheat cultivar Axe

Sr65: a widely effective gene for stem rust resistance in wheat

KEY MESSAGE

Sr65 in chromosome 1A of Indian wheat landrace Hango-2 is a potentially useful all-stage resistance gene that currently protects wheat from stem rust in Australia, India, Africa and Europe. Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), threatened global wheat production with the appearance of widely virulent races that included TTKSK and TTRTF. Indian landrace Hango-2 showed resistance to Pgt races in India and Australia. Screening of a Hango-2/Avocet 'S' (AvS) recombinant inbred line population identified two stem rust resistance genes, a novel gene (temporarily named as SrH2) from Hango-2 and Sr26 from AvS. A mapping population segregating for SrH2 alone was developed from two recombinant lines. SrH2 was mapped on the short arm of chromosome 1A, where it was flanked by KASP markers KASP_7944 (proximal) and KASP_12147 (distal). SrH2 was delimited to an interval of 1.8-2.3 Mb on chromosome arm 1AS. The failure to detect candidate genes through MutRenSeq and comparative genomic analysis with the pan-genome dataset indicated the necessity to generate a Hango-2 specific assembly for detecting the gene sequence linked with SrH2 resistance. MutRenSeq however enabled identification of SrH2-linked KASP marker sunCS_265. Markers KASP_12147 and sunCS_265 showed 92% and 85% polymorphism among an Australian cereal cultivar diversity panel and can be used for marker-assisted selection of SrH2 in breeding programs. The effectiveness of SrH2 against Pgt races from Europe, Africa, India, and Australia makes it a valuable resource for breeding stem rust-resistant wheat cultivars. Since no wheat-derived gene was previously located in chromosome arm 1AS, SrH2 represents a new locus and named as SR65.

Mapping and validation of a novel major QTL for resistance to stripe rust in four wheat populations derived from landrace Qishanmai

Wheat yield has been constrained by stripe rust disease globally. A wheat landrace (Qishanmai, QSM) consistently showed lower stripe rust severities in multiple year studies than susceptible check varieties including Suwon11 (SW) at the adult plant stage. To detect QTL for reducing the severity in QSM, 1218 recombinant inbred lines (RILs) were developed from SW × QSM. QTL detection was conducted firstly using 112 RILs selected for similarity in pheno-morphological characters. The 112 RILs were assessed for stripe rust severity at the 2nd leaf, 6th leaf and flag leaf stages under field and greenhouse conditions, and genotyping was done primarily with a single nucleotide polymorphism (SNP) array. On the basis of these phenotypic and genotypic data, a major QTL (QYr.cau-1DL) was detected on chromosome 1D at the 6th leaf and flag leaf stages. Further mapping was conducted by genotyping 1218 RILs using new simple sequence repeat (SSR) markers, which were developed by referring to the sequences of the wheat line Chinese Spring (IWGSC RefSeq v1.0). QYr.cau-1DL was mapped within a 0.5 cM (5.2 Mb) interval delimited by the SSR markers 1D-320.58 and 1D-325.79. These markers were applied to select for QYr.cau-1DL by screening F₂ or BC₄F₂ plants of the wheat crosses RL6058 × QSM, Lantian10 × QSM and Yannong21 × QSM. F_2:3 or BC₄F_2:3 families derived from the selected plants were assessed for stripe rust resistance in the fields of two locations and in a greenhouse. Wheat plants carrying the resistant marker haplotype in homozygous state for QYr.cau-1DL showed lower stripe rust severities (by 44% to 48%) than plants lacking this QTL. The trial of RL6058 (a carrier of Yr18) × QSM also indicated that QYr.cau-1DL had larger effect than Yr18 on reducing severity; they acted synergistically, yielding an elevated level of stripe rust resistance.

Physiological specialization of Puccinia triticina and genome-wide association mapping provide insights into the genetics of wheat leaf rust resistance in Iran

Leaf rust caused by Puccinia triticina Erikss. (Pt) is the most widely distributed and important wheat disease worldwide. The objective of the present study was to determine the frequency of Iranian Pt races, their virulence to key resistance genes and map quantitative trait loci (QTL) for resistance to different Pt races from 185 globally diverse wheat genotypes using a genome-wide association study (GWAS) approach. The virulence pattern of the 33 Pt isolates from various wheat-growing areas of Iran on 55 wheat differentials showed that the FKTPS and FKTTS were relatively frequent pathotypes among the 18 identified races. The weighted average frequency of virulence on the resistance genes Lrb, Lr3bg, Lr14b, Lr16, Lr24, Lr3ka, Lr11 and Lr20 were high (> 90%). However, low virulence on the resistant genes Lr2a, Lr9, Lr19, Lr25, Lr28 and Lr29 indicates that these genes are still effective against the pathogen population in Iran at present. GWAS on a panel of 185 wheat genotypes against 10 Pt races resulted into 62 significant marker-trait associations (MTAs) belonged to 34 quantitative trait loci (QTL) across 16 chromosomes. Among them, 10 QTLs on chromosomes 1A, 1B, 3B, 3D, 4A, 6D, 7A and 7D were identified as potential novel QTLs, of which four QTLs (QLr.iau-3B-2, QLr.iau-7A-2, QLr.iau-7A-3 and QLr.iau-7D-2) are more interesting, as they are associated with resistance to two or more Pt races. The known and novel QTLs associated with different Pt races found here, can be used in future wheat breeding programs to recombine different loci for durable resistance against leaf rust races.

Identification and molecular mapping of YrBm for adult plan resistance to stripe rust in Chinese wheat landrace Baimangmai

A new adult plan resistance gene YrBm for potentially durable resistance to stripe rust was mapped on wheat chromosome arm 4BL in landrace Baimangmai. SSR markers closely flanking YrBm were developed and validated for use in marker-assisted selection. The wheat stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst) frequently acquires new virulences and rapidly adapts to environmental stress. New virulences in Pst populations can cause previously resistant varieties to become susceptible. If those varieties were widely grown, consequent epidemics can lead to yield losses. Identification and deployment of genes for durable resistance are preferred method for disease control. The Chinese winter wheat landrace Baimangmai showed a high level of adult plant resistance (APR) to stripe rust in a germplasm evaluation trial at Langfang in Hebei province in 2006 and has continued to confer high resistance over the following 15 years in field nurseries in Hebei, Sichuan and Gansu. A recombinant inbred line population of 200 F₁₀ lines developed from a cross of Baimangmai and a susceptible genotype segregated for APR at a single locus on chromosome 4BL; the resistance allele was designated YrBm. Allelism tests of known Yr genes on chromosome 4B and unique closely flanking marker alleles Xgpw7272₁₈₉ and Xwmc652₁₆₄ among a panel of Chinese wheat varieties indicated that YrBm was located at a new locus. Moreover, those markers can be used for marker-assisted selection in breeding for stripe rust resistance.

Genome-Wide QTL Mapping for Stripe Rust Resistance in Winter Wheat Pindong 34 Using a 90K SNP Array

Winter wheat cultivar Pindong 34 has both adult-plant resistance (APR) and all-stage resistance (ASR) to stripe rust, which is caused by Puccinia striiformis f. sp. tritici (Pst). To map the quantitative trait loci (QTL) for stripe rust resistance, an F_6-10 recombinant inbred line (RIL) population from a cross of Mingxian 169 × Pingdong 34 was phenotyped for stripe rust response over multiple years in fields under natural infection conditions and with selected Pst races under controlled greenhouse conditions, and genotyping was performed with a 90K single nucleotide polymorphism (SNP) array chip. Inclusive composite interval mapping (ICIM) identified 12 APR resistance QTLs and 3 ASR resistance QTLs. Among the 12 APR resistance QTLs, QYrpd.swust-1BL (explaining 9.24-13.33% of the phenotypic variation), QYrpd.swust-3AL.1 (11.41-14.80%), QYrpd.swust-3AL.2 (11.55-16.10%), QYrpd.swust-6BL (9.39-12.78%), QYrpd.swust-6DL (9.52-16.36%), QYrpd.swust-7AL (9.09-17.0%), and QYrpd.swust-7DL (8.87-11.38%) were more abundant than in the five tested environments and QYrpd.swust-1AS (11.05-12.72%), QYrpd.swust-1DL (9.81-13.05%), QYrpd.swust-2BL.1 (9.69-10.57%), QYrpd.swust-2BL.2 (10.36-12.97%), and QYrpd.swust-2BL.3 (9.54-13.15%) were significant in some of the tests. The three ASR resistance QTLs QYrpd.swust-2AS (9.69-13.58%), QYrpd.swust-2BL.4 (9.49-12.07%), and QYrpd.swust-7AS (16.16%) were detected based on the reactions in the seedlings tested with the CYR34 Pst race. Among the 15 QTLs detected in Pindong 34, the ASR resistance gene QYrpd.swust-7AS mapped on the short arm of chromosome 7A was likely similar to the previously reported QTL Yr61 in the region. The QTLs identified in the present study and their closely linked molecular markers could be useful for developing wheat cultivars with durable resistance to stripe rust.

Molecular cytogenetics and development of St-chromosome-specific molecular markers of novel stripe rust resistant wheat-Thinopyrum intermedium and wheat-Thinopyrum ponticum substitution lines

BACKGROUND

Owing to their excellent resistance to abiotic and biotic stress, Thinopyrum intermedium (2n = 6x = 42, JJJ^sJ^sStSt) and Th. ponticum (2n = 10x = 70) are both widely utilized in wheat germplasm innovation programs. Disomic substitution lines (DSLs) carrying one pair of alien chromosomes are valuable bridge materials for transmission of novel genes, fluorescence in situ hybridization (FISH) karyotype construction and specific molecular marker development.

RESULTS

Six wheat-Thinopyrum DSLs derived from crosses between Abbondanza nullisomic lines (2n = 40) and two octoploid Trititrigia lines (2n = 8x = 56), were characterized by sequential FISH-genome in situ hybridization (GISH), multicolor GISH (mc-GISH), and an analysis of the wheat 15 K SNP array combined with molecular marker selection. ES-9 (DS2St (2A)) and ES-10 (DS3St (3D)) are wheat-Th. ponticum DSLs, while ES-23 (DS2St (2A)), ES-24 (DS3St (3D)), ES-25(DS2St (2B)), and ES-26 (DS2St (2D)) are wheat-Th. intermedium DSLs. ES-9, ES-23, ES-25 and ES-26 conferred high thousand-kernel weight and stripe rust resistance at adult stages, while ES-10 and ES-24 were highly resistant to stripe rust at all stages. Furthermore, cytological analysis showed that the alien chromosomes belonging to the same homoeologous group (2 or 3) derived from different donors carried the same FISH karyotype and could form a bivalent. Based on specific-locus amplified fragment sequencing (SLAF-seq), two 2St-chromosome-specific markers (PTH-005 and PTH-013) and two 3St-chromosome-specific markers (PTH-113 and PTH-135) were developed.

CONCLUSIONS

The six wheat-Thinopyrum DSLs conferring stripe rust resistance can be used as bridging parents for transmission of valuable resistance genes. The utility of PTH-113 and PTH-135 in a BC1F2 population showed that the newly developed markers could be useful tools for efficient identification of St chromosomes in a common wheat background.