Physical mapping of a new powdery mildew resistance locus from Thinopyrum ponticum chromosome 4AgS

Establishment of a set of St-group wheat-Thinopyrum ponticum derivative lines conferring resistance to powdery mildew

Thinopyrum ponticum (2n = 10x = 70, EeEeEbEbExExStStStSt), a wild relative of common wheat (Triticum aestivum L., 2n = 6x = 42), possesses extensive genetic diversity. The primary objective of this study was to develop and evaluate alien derivatives carrying the St-chromosome from Th. ponticum, aiming to improve wheat disease resistance and agronomic traits. In this study, a set of St-chromosome alien derivatives was developed from Th. ponticum. Chromosomal compositions, karyotypes and homoeologous group affiliations of seven derivatives were characterized using genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH), multicolor GISH (mc-GISH), and liquid chip analysis. Resistance assessments showed that the 4St and 7St derivatives exhibited strong resistance to the E09 isolate at the seedling stage and to naturally occurring pathogen mixtures in the field at the heading stage. The 7St derivative line, based on agronomic trait evaluations, is considered an ideal bridging material for breeding, with a reduction in plant height to 71.3 cm, while thousand-kernel weight and kernel length increased to 41 g and 0.77 cm, respectively. Specific markers for the St-homoeologous groups were developed through genome sequencing, achieving a development efficiency of 47.5%. This study provides a theoretical and technical basis for applying Th. ponticum genetic resources to improve wheat resistance and agronomic performance.

A new leaf pubescence gene, Hl1th , introgressed into bread wheat from Thinopyrum ponticum and its phenotypic manifestation under homoeologous chromosomal substitutions

Blue-grain lines were created on the basis of the spring bread wheat variety Saratovskaya 29 (S29) with chromosome 4B or 4D replaced with chromosome 4Th from Thinopyrum ponticum. The leaf pubescence of the two lines differs from S29 and from each other. In this work, we studied the effect of these substitutions on the manifestation of this trait. To quantify pubescence, the LHDetect2 program was used to determine trichome length and number on the leaf fold microphotographs. The key gene Hl1 on chromosome 4B and another unidentified gene with a weak effect determine the leaf pubescence of the recipient S29. Their interaction leads to the formation of trichomes of up to 300 microns in length. Replacement of both copies of chromosome 4B with two copies of wheatgrass chromosome 4Th modifies leaf pubescence in line S29_4Th(4B) so that the leaf pubescence characteristic of S29 becomes more sparse, and trichomes of up to 600- 700 μm in length are formed. Additionally, we described modification of pubescence in the substitution line S29_4Th(4D) where chromosome 4D that does not carry any pubescence gene was replaced. Under this substitution, trichomes of up to 400 μm in length were formed and the average length of trichomes on the underside of the leaf was reduced. The replacement of the Hl1 gene in the lines was also confirmed by the allelic state of the linked microsatellite marker Xgwm538. Thus, as a result of the studies, a new leaf pubescence gene introgressed from Th. ponticum into bread wheat was identified. We designated it as Hl1th. For the purpose of selection, we propose to use the unlicensed informative microsatellite markers Xgwm538 and Xgwm165, allowing chromosomes 4A, 4B, 4D and 4Th to be distinguished.

Exploitation of the genetic potential of Thinopyrum and Agropyron genera to protect wheat from diseases and environmental stresses

Common wheat is one of the most important food crops in the world. Grain harvests can be increased by reducing losses from diseases and environmental stresses. The tertiary gene pool, including Thinopyrum spp., is a valuable resource for increasing genetic diversity and wheat resistance to fungal diseases and abiotic stresses. Distant hybridization between wheat and Thinopyrum spp. began in the 1920s in Russia, and later continued in different countries. The main results were obtained using the species Th. ponticum and Th. intermedium. Additionally, introgression material was created based on Th. elongatum, Th. bessarabicum, Th. junceiforme, Agropyron cristatum. The results of introgression for resistance to diseases (leaf, stem, and stripe rusts; powdery mildew; Fusarium head blight; and Septoria blotch) and abiotic stresses (drought, extreme temperatures, and salinity) to wheat was reviewed. Approaches to improving the agronomic properties of introgression breeding material (the use of irradiation, ph-mutants and compensating Robertsonian translocations) were described. The experience of long-term use in the world of a number of genes from the tertiary gene pool in protecting wheat from leaf and stem rust was observed. Th. ponticum is a nonhost for Puccinia triticina (Ptr) and P. graminis f. sp. tritici (Pgt) and suppresses the development of rust fungi on the plant surface. Wheat samples with the tall wheatgrass genes Lr19, Lr38, Sr24, Sr25 and Sr26 showed defence mechanisms similar to nonhosts resistance. Their influence led to disruption of the development of surface infection structures and fungal death when trying to penetrate the stomata (prehaustorial resistance or stomatal immunity). Obviously, a change in the chemical properties of fungal surface structures of races virulent to Lr19, Lr24, Sr24, Sr25, and Sr26 leads to a decrease in their adaptability to the environment. This possibly determined the durable resistance of cultivars to leaf and stem rusts in different regions. Alien genes with a similar effect are of interest for breeding cultivars with durable resistance to rust diseases and engineering crops with the help of molecular technologies.

Characterization of New Wheat-Thinopyrum intermedium Derivative Lines with Superior Genes for Stripe Rust and Powdery Mildew Resistance

The wild species Thinopyrum intermedium (genome JJJSJSStSt) serves as a valuable germplasm resource providing novel diseases resistance and agronomically important genes for wheat improvement. Two wheat-Th. intermedium partial amphiploids, TAI7045 (2n = 56) and 78784 (2n = 56), exhibit high resistance to stripe rust and powdery mildew, and their chromosome constitutions have been characterized. With the aim to transfer novel resistance genes from Th. intermedium, the crosses of common wheat line MY11 with TAI7045 and 78784 were produced, and their individual F2-F5 progenies were characterized using sequential non-denaturing fluorescence in situ hybridization (ND-FISH) and molecular markers. We identified a set of wheat-Th. intermedium addition lines, involving the chromosomes 1St-JS, 2St, 2St-JS, 3St, 4J, 4St, 5St, 5J.St, 6JS.J, and 7JS. Above all, the stable wheat-Th. intermedium small segmental translocation lines with chromosomes 4DS.4DL-4StL-4DL-4JL and 4DS.4DL-4StL-4DL were selected. Combining data from specific marker amplification and resistance evaluation, we mapped the gene(s) for resistance to powdery mildew and stripe rust in the 233.56-329.88 Mb region of the long arm of the 4St chromosome from the reference Th. intermedium genome. The new wheat-Th. intermedium introgressions will be used as novel germplasm for breeding purposes.

Development and identification of a novel wheat-Thinopyrum ponticum disomic substitution line DS5Ag(5D) with new genes conferring resistance to powdery mildew and leaf rust

BACKGROUND

Powdery mildew (caused by Blumeria graminis f. sp. tritici (Bgt)) and leaf rust (caused by Puccinia triticina (Pt)) are prevalent diseases in wheat (Triticum aestivum L.) production. Thinopyrum ponticum (2n = 10x = 70, EeEeEbEbExExStStStSt) contains genes that confer high levels of resistance to these diseases.

RESULTS

An elite wheat-Th. ponticum disomic substitution line, DS5Ag(5D), was developed in the Bainong Aikang 58 (AK58) background. The line was assessed using genomic in situ hybridization (GISH), oligo-nucleotide probe multiplex (ONPM) fluorescence in situ hybridization (FISH), and molecular markers. Twenty eight chromosome-specific molecular markers were identified for the alien chromosome, and 22 of them were co-dominant. Additionally, SNP markers from the wheat 660 K SNP chip were utilized to confirm chromosome identification and they provide molecular tools for tagging the chromosome in concern. The substitution line demonstrated high levels of resistance to powdery mildew throughout its growth period and to leaf rust at the adult stage. Based on the resistance evaluation of five F5 populations between the substitution lines and wheat genotypes with different levels of sensitivity to the two diseases. Results showed that the resistance genes located on 5Ag confered stable resistance against both diseases across different backgrounds. Resistance spectrum analysis combined with diagnostic marker detection of known resistance genes of Th. ponticum revealed that 5Ag contained two novel genes, Pm5Ag and Lr5Ag, which conferred resistance to powdery mildew and leaf rust, respectively.

CONCLUSIONS

In this study, a novel wheat-Th. ponticum disomic substitution line DS5Ag(5D) was successfully developed. The Th. ponticum chromosome 5Ag contain new resistance genes for powdery mildew and leaf rust. Chromosomic-specific molecular markers were generated and they can be used to track the 5Ag chromosome fragments. Consequently, this study provides new elite germplasm resources and molecular markers to facilitate the breeding of wheat varieties that is resistant to powdery mildew and leaf rust.

Chromosomal mapping of a major genetic locus from Agropyron cristatum chromosome 6P that influences grain number and spikelet number in wheat

KEY MESSAGE

A novel locus on Agropyron cristatum chromosome 6P that increases grain number and spikelet number was identified in wheat-A. cristatum derivatives and across 3 years. Agropyron cristatum (2n = 4x = 28, PPPP), which has the characteristics of high yield with multiple flowers and spikelets, is a promising gene donor for wheat high-yield improvement. Identifying the genetic loci and genes that regulate yield could elucidate the genetic variations in yield-related traits and provide novel gene sources and insights for high-yield wheat breeding. In this study, cytological analysis and molecular marker analysis revealed that del10a and del31a were wheat-A. cristatum chromosome 6P deletion lines. Notably, del10a carried a segment of the full 6PS and 6PL bin (1-13), while del31a carried a segment of the full 6PS and 6PL bin (1-8). The agronomic characterization and genetic population analysis confirmed that the 6PL bin (9-13) brought about an increase in grain number per spike (average increase of 10.43 grains) and spikelet number per spike (average increase of 3.67) over the three growing seasons. Furthermore, through resequencing, a multiple grain number locus was mapped to the physical interval of 593.03-713.89 Mb on chromosome 6P of A. cristatum Z559. The RNA-seq analysis revealed the expression of 537 genes in the del10a young spike tissue, with the annotation indicating that 16 of these genes were associated with grain number and spikelet number. Finally, a total of ten A. cristatum-specific molecular markers were developed for this interval. In summary, this study presents novel genetic material that is useful for high-yield wheat breeding initiatives to meet the challenge of global food security through enhanced agricultural production.