Genetics and Resistance / Génétique et Résistance Genetic mapping and marker development for the leaf rust resistance gene Lr30 in wheat ( Triticum aestivum L.)

QTL Mapping for Leaf Rust Resistance in a Wheat Recombinant Inbred Line Population of Liang66-S/Hengmai28

Leaf rust (LR), caused by Puccinia triticina, is a major constraint to global wheat production. Identifying quantitative trait loci (QTLs), conferring adult-plant resistance (APR), and developing breeder-friendly markers are essential for durable disease control. In this study, a recombinant inbred line (RIL) population derived from Liang66-S × Hengmai28 was evaluated for leaf rust severity across four environments. Maximum disease severity (MDS) showed continuous variation and moderate to high correlations among environments, indicating polygenic inheritance. Five APR QTLs were mapped on chromosomes 2BL, 3BS, 3BL, 7BL and 7DL, explaining 4.5–9.8% of the phenotypic variance (PVE) with LOD scores of 2.9–7.9. Among these, QLr.DFI-2BL, QLr.DFI-3BS, and QLr.DFI-7BL correspond to previously reported APR loci, whereas QLr.DFI-3BL and QLr.DFI-7DL represent potentially novel loci. QLr.DFI-3BL was detected across all four environments, while QLr.DFI-3BS and QLr.DFI-7BL showed the highest R2 (7.7–8.5% and 8.4–9.8%). Multiple defense-related genes within the QTL intervals for LR were identified, including the putative NBS-LRR, the putative BTB/POZ-MATH, F-box, receptor-like kinase, polyphenol oxidase, calcium-dependent protein kinase, peroxidase, and ethylene-responsive transcription factors. Based on the flanking markers, five KASP markers were developed. K-LR-3BS (for QLr.DFI-3BS) and K-LR-7BL (for QLr.DFI-7BL) successfully genotyped a natural population with 120 accessions, with call rates of 100% and 94.2%, and showed significant association with reduced leaf rust severity. However, further validation in diverse genetic backgrounds and populations is required before they can be considered for routine marker-assisted selection. These results provide two KASP markers as promising markers that require further validation in diverse backgrounds and highlight QLr.DFI-3BS and QLr.DFI-7BL as promising targets for fine mapping and eventual cloning of APR genes in wheat.

Characterisation of advanced breeding lines for bacterial leaf blight resistance by morpho-molecular screening in rice (Oryza sativa L.)

Sixty advanced breeding lines of rice were evaluated for resistance to bacterial leaf blight (BLB) both phenotypically and genotypically at Regional Agricultural Research Station (RARS), Maruteru, Andhra Pradesh, India during kharif, 2023. Phenotypic screening was performed following the International Rice Research Institute (IRRI), standard evaluation system (SES) scale. Among the sixty entries, seven genotypes, 251-3-3-2, MS-1, NLR-163, NLR-164, NLR-945, CM-469 and BM-587, exhibited a highly resistant (HR) reaction with a score of 1, comparable to the resistant check RP Bio-226. Twenty-two lines expressed BLB severity of 13–25 % (score 5) and were categorised as moderately resistant (MR). Molecular profiling using gene-specific simple sequence repeats (SSR) markers revealed significant variation in resistance genedistribution. The presence of xa5, xa13, Xa21, Xa4 and Xa10 was detected in 9, 4, 23, 44 and 20 lines respectively. Two-gene combinations were identified in 20 genotypes, whereas 11 genotypes possessed three-gene combinations, highlighting the effectiveness of gene stacking for broad-spectrum BLB resistance. Notably, lines 251-3-3-2, MS-1, NLR-164, NLR-945 and BM-587 exhibited congruence between phenotypic resistance (score 1) and the presence of multiple resistance genes, indicating their potential as elite donors for BLB resistance introgression. Yield performance coupled with gene pyramiding further strengthened the value of several genotypes. The genotypes VP-R-157 (Xa4+xa13) recorded 22.3 g/plant, BM-588 (xa5+Xa21) yielded 21.2 g/plant, while CM-467 (Xa4+xa5+Xa10+Xa21) produced 25.1 g/plant. The genotypes CM-470, CM-446 and CM-449 yielded 26.3 g, 21.0 g and 21.5 g/plant respectively, each carrying the Xa4+xa5 gene combination. These genotypes hold substantial promise for direct varietal release or utilisation in hybridisation programs aimed at developing high-yielding, BLB-resistant rice cultivars.

Genetic Background-Dependent Expression of Lr34, Lr67 and the Lr46-Associated Candidate Gene Lr46-Glu2 in Wheat (Triticum aestivum L.) Highlights Contrasting Transcriptional Responses Following Puccinia triticina Infection

Adult plant resistance (APR) is widely used in wheat breeding, but its behaviour across genetic backgrounds remains poorly understood. In this study, we analysed the expression of three APR loci (Lr34, Lr46, Lr67) following their introgression into elite winter wheat cultivars. BC2F1 populations derived from crosses between donor lines and commercial cultivars were evaluated under controlled infection with Puccinia triticina (Pt). Gene expression was assessed using RT-qPCR, and miRNA abundance was quantified by ddPCR at five time points (0–48 hours post-inoculation, hpi). Expression patterns differed markedly between genetic backgrounds, affecting both the magnitude and timing of gene activity. Lr34 and Lr67 showed the highest expression prior to inoculation, with no consistent or sustained induction following infection. In contrast, the candidate gene Lr46-Glu2 displayed a clear tendency towards early induction, with peak expression typically observed at 6–12 hours post-inoculation, although the amplitude of this response varied among genotypes. Levels of miRNA varied across genotypes and time points and did not consistently reflect mRNA expression. The results suggest that the expression of APR-associated loci is influenced by genetic background. Lr34 and Lr67 showed predominantly baseline-associated expression, whereas the Lr46-associated candidate gene Lr46-Glu2 displayed a more infection-responsive transcriptional profile following inoculation. These patterns are consistent with different transcriptional behaviours of the analysed genes but do not establish their functional contribution to resistance. Further phenotypic and functional validation will be required to determine the biological significance of these expression patterns.

Identification of stripe rust resistance loci in Gansu wheat landraces using genome-wide association analysis

Discovery and mapping of a new gene in wheat for race-specific adult plant resistance to Puccinia striiformis f. sp. tritici

Key message A non-durable adult plant stripe rust resistance gene in wheat was mapped to the distal region of chromosome 2DS and designated Yr88. Wheat stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most damaging fungal pathogens of wheat globally. Efforts to breed improved wheat cultivars have placed high priority on incorporating resistance to Pst. The resistances used are expressed at either all growth stages (all stage resistance; ASR) or at post-seedling growth stages (aka adult plant resistance; APR). Although APR has a reputation for being more durable than ASR examples have been documented of virulence for this type of resistance in the UK, Europe and in North America. Incursions of two genetically and pathogenically distinct pathotypes of Pst into Australia in 2017 and 2018 changed adult plant field stripe rust responses of many wheat cultivars grown in eastern Australia at that time. In some cases, changes in response could not be accounted for based on virulence on ASR genes, suggesting that the protective value of APR may have changed. This study reports the discovery of a new gene conferring race-specific APR to Pst pathotype 198 E16 A- J+ T+ 17+, a member of the internationally accepted multi-locus genotype (MLG) PstS13. The gene was mapped to the distal region of chromosome 2DS and designated Yr88. Evidence is provided for the presence of Yr88 in near isogenic genes carrying selected ASR and APR Yr genes, four Australian wheat cultivars (LRPB Hellfire, Sherriff CL Plus, Vixen, Wyalkatchem) plus the Mexican green revolution wheat cultivar Lerma Rojo 64 and the Pakistani wheat cultivar Moomal 2000.

Unlocking the potential of spring wheat genetic resources: uncovering resistance sources against leaf rust and yellow rust

Integrating high-throughput phenotyping with multiple complementary GWAS models reduces method-dependent bias and enables reliable identification of novel loci and elite germplasm for durable yellow and leaf rust resistance in wheat. The causal agents of yellow and leaf rust in wheat, Puccinia striiformis f. sp. tritici and Puccinia triticina, pose a serious threat to grain yield and quality worldwide. Growing durable resistant wheat cultivars is an effective protection measure contributing to sustainable agriculture. Many of the known resistance genes, however, have been overcome due to the high genetic diversity and adaptability of pathogen populations. Therefore, the present study aimed to identify novel loci associated with yellow rust and leaf rust in a genome-wide association study using 1984 spring wheat accessions from the German Federal ex situ Genebank. Phenotypic data obtained from a detached-leaf assay were combined with 90,283 genotyping-by-sequencing genome-wide markers. Six significant peak marker-trait associations were identified for yellow rust and leaf rust, respectively. These are located on chromosomes 1D, 2B, 3B, 4A, 4B, 4D, 5A, 6B, and 7D. Six candidate genes were identified close to the identified loci. These findings may be valuable for identifying and deploying genetic resources to broaden the genetic basis of resistance and safeguard durability of resistance against yellow and leaf rust.