Turakulov

Stripe rust, caused by Puccinia striiformis (Ps), is a destructive disease affecting various crops worldwide, including wheat, barley, rye, triticale, and certain graminaceous hosts. Recently, clonal lineages of Ps on wheat have been reported in Uzbekistan, a Central Asian country. However, it is still unclear how these clonal lineages persist throughout the year and whether they are exclusive to wheat or can also infect other hosts. To better understand, we conducted surveillance in various locations of Uzbekistan (Jizzakh, Qashqadaryo, Samarkand, and Sirdaryo) in 2024. Site selection of barley and wild barley fields was done based on their proximity to infected wheat fields. Our results showed low genetic distance (F _ST ) among the wheat, barley, and wild barley Ps populations. The wheat Ps population showed the lowest genotypic diversity (Simpson’s diversity = 0.46) while high genotypic diversity was found in barley (0.87) and wild barley (0.96). Most multilocus genotypes that were found in barley and wild barley were confined to their respective hosts except MLG-2, which was predominant on wheat but also infected barley and its wild relatives. MLG-2/MLG34 was also responsible for 2023 epidemic in all wheat-growing regions of Uzbekistan and showed temporal maintenance during the 2024 cropping year. This lineage may have resulted from hybridization between P. striiformis f. sp. tritici and P. striiformis f. sp. hordei although the source of parental lineages is still unknown, which requires further investigation. Monitoring the migration patterns of this lineage and estimating its pathogenic impact on overcoming different resistant genes is essential as it has the potential to cause epidemics in both wheat and barley.

In this study, molecular markers were employed to determine the resistance of wheat varieties to yellow rust. Resistant isogenic lines of Avocet were crossed with high-yielding varieties, and the resulting backcross generations were evaluated both phenotypically and genotypically. The research findings confirmed that SSR markers Xpsp3000 and Barc008 are closel linked to the resistance genes Yr10 and Yr15, respectively. These results demonstrated that the application of marker-assisted selection (MAS) technology in the breeding process is an effective approach for developing new varieties resistant to yellow rust.

The fungal pathogen Puccinia striiformis f. sp. tritici, which causes yellow rust disease, poses a significant economic threat to wheat production not only in Uzbekistan but also globally, leading to substantial reductions in grain yield. This study aimed to develop yellow rust-resistance wheat lines by introgressing Yr10 and Yr15 genes into high-yielding cultivar Grom using the marker-assisted backcrossing (MABC) method. Grom was crossed with donor genotypes Yr10/6*Avocet S and Yr15/6*Avocet S, resulting in the development of F₁ generations. In the following years, the F₁ hybrids were advanced to the BC₂F₁ and BC₂F₂ generations using the MABC approach. Foreground and background selection using microsatellite markers (Xpsp3000 and Barc008) were employed to identify homozygous Yr10- and Yr15-containing genotypes. The resulting BC₂F₂ lines, designated as Grom-Yr10 and Grom-Yr15, retained key agronomic traits of the recurrent parent cv. Grom, such as spike length (13.0–11.9 cm) and spike weight (3.23–2.92 g). Under artificial infection conditions, the selected lines showed complete resistance to yellow rust (infection type 0). The most promising BC₂F₂ plants were subsequently advanced to homozygous BC₂F₃ lines harboring the introgressed resistance genes through marker-assisted selection. This study demonstrates the effectiveness of integrating molecular marker-assisted selection with conventional breeding methods to enhance disease resistance while preserving high-yielding traits. The newly developed lines offer valuable material for future wheat improvement and contribute to sustainable agriculture and food security.

Puccinia striiformis f. sp. tritici (Pst) is a destructive pathogen that causes wheat stripe rust worldwide. Understanding the population structure and dynamic of pathogen spread is critical to fight against this disease. Limited information is available for the population genetic structure of Pst in Uzbekistan, Central Asia. In this study, we carried out surveillance from nine different regions (Andijan, Fergana, Jizzakh, Kashkadarya, Namangan, Samarkand, Sirdaryo, Surkhandarya, and Tashkent) of Uzbekistan to fill this gap. A total of 255 isolates were collected, which were genotyped using 17 polymorphic simple sequence repeat markers. The DAPC analysis results showed no population subdivision in these sample-collected regions except Surkhandarya. Multilocus genotype (MLG) analysis, F_ST, and Nei’s genetic distance results indicated a clonal population (rBarD ≤ 0.12) and merely three MLGs accounting for 70% of the overall population. MLG-34 was predominant in all regions of Uzbekistan, followed by MLG-36 and MLG-42. Low genotypic diversity was observed in Andijan, Fergana, Jizzakh, Kashkadarya, Namangan, Sirdaryo, and Tashkent (0.56 to 0.76), compared with Samarkand (0.82) and Surkhandarya (0.97). No virulence against Yr5, Yr15, YrSp, and Yr26 was found, while resistance was overcome against Yr1, Yr2, Yr6, Yr9, Yr17, and Yr44 genes (virulence frequency ≥75%). Comparative study results of Uzbekistan with the previous Himalayan population showed divergence from China and Pakistan populations. Further studies need to be conducted in a worldwide context to understand migration patterns; for that purpose, collaborative work is essential because of the Pst long-distance migration capability.

Glomerella leaf spot (GLS), caused by the fungus Colletotrichum fructicola, is one of the most devastating apple diseases. Our previous study reported that the GLS resistance locus was defined on the chromosome 15 region. Here, we further found a single-nucleotide polymorphism (SNP) site (SNP_7309212) in the GLS resistance that was able to distinguish resistant cultivars (lines) from susceptible ones. On the basis of the SNP site, we cloned a TNL gene from the GLS resistant locus and named it MdTNL1 (NCBI Accession Number: ON402514). This gene contains a toll/interleukin-1 receptor transmembrane domain (TIR), nucleotide-binding sites (NBS), and leucine-rich repeat (LRR) domain. Subcellular location indicated that MdTNL1 was expressed in the nucleus and cell membrane. Ectopic overexpression of MdTNL1 in Nicotiana benthamiana caused cell death. We further demonstrated allelic polymorphisms in MdTNL1. It is noteworthy that NBS and LRR domains of the MdTNL1 protein serve as the repository for generating allelic diversity. Quantitative real-time PCR (qRT-PCR) assay revealed that MdTNL1 was highly expressed in resistant apple cultivar ‘Fuji’ after inoculation with C. fructicola, whereas susceptible cultivar ‘Golden Delicious’ exhibited low expression after inoculation. Over-expression of MdTNL1-1 in susceptible apple fruits and leaves improved disease resistance, while in ‘Orin’ calli, silencing the MdTNL1-1 gene conversely decreased GLS resistance. In conclusion, we identified a GLS associated with SNP_7309212 and demonstrated that a TIR-NBS-LRR gene MdTNL1-1 positively regulates GLS resistance in apple.