RESUMO
The gene Yr5 in wheat has generally been known to confer resistance to Puccinia striiformis f. sp. tritici races worldwide. However, a few reports indicated that some isolates of the stripe rust pathogen were virulent on the wheat genotypes with Yr5 in India, Australia, and China (Nagarajan 1986; Wellings and McIntosh 1990; Zhang et al. 2020). In April 2020, a stripe rust infection was observed on Triticum spelta 'Album' (TSA), the Yr5 donor, provided by Turkey Seed Gene Bank in a wheat breeding field at the experimental station of Akdeniz University in the Antalya province of Turkey. The sample was tested on the seedlings of the Yr single-gene lines in the Avocet S (AvS) background including Yr5 near-isogenic line (AvSYr5NIL), TSA, and susceptible bread wheat variety 'Morocco' according to the procedure reported by Wan et al. (2014), and found to be highly virulent on Morocco with infection type (IT) 9 and virulent on AvSYr5NIL and TSA with IT 7. To confirm this novel finding, single-pustule isolates derived from this sample were obtained from TSA and re-tested on the differentials and TSA. The Yr5-virulent isolate yielded similar infection types on these plants further verifying previous results. The single-pustule isolates were determined to be avirulent (Avr) (IT 0 to 6) on AvSYr1NIL, AvSYr8NIL, AvSYr9NIL, AvSYr10NIL, AvSYr32NIL, and AvSYr43NIL and virulent (Vr) (IT 7 to 9) on AvSYr5NIL, AvSYr6NIL, AvSYr7NIL, AvSYr17NIL, AvSYr24NIL, AvSYr27NIL, AvSYr44NIL, AvSYrSpNIL, and TSA. The isolates were identified as a new race and temporarily named TRVR20-5 based on its Avr/Vr pattern. Furthermore, to confirm the presence of Yr5, the genomic DNA of fresh leaves of AvSYr5NIL and TSA used in the virulence testing were isolated using NucleoSpin Plant II (Macherey-Nagel, Germany) according to the manufacturer's procedure. The genomic DNA samples were amplified with the primers STS-7 (5'-GTACAATTCACCTAGAGT-3') and STS-8 (5'-GCAAGTTTTCTCCCTATT-3') (Chen et al. 2003) using a thermal cycler (T-100, BioRad, USA), and the resulting PCR products were digested with DpnII and visualized on an agarose gel. AvSYr5NIL and TSA had the fragment linked to the resistance allele (308 bp) whereas AvS and Morocco had the fragment linked to the susceptible allele (181 bp). Thus, both wheat genotypes were confirmed to carry Yr5, and the new Pst race virulent to Yr5 was confirmed. To the best of our knowledge, this is the first report of a Pst race virulent to Yr5 in Turkey, where stripe rust epidemics have occured in 2 out of every 5 years with 1-5% crop losses in over 25% of the wheat growing areas (Chen 2020). In a nutshell, monitoring the Pst races virulent to Yr5 with a potential to cause devastating epidemics worldwide is crucial due to the fact that international wheat breeding programs have been using Yr5 to develop wheat cultivars with resistance to stripe rust.
RESUMO
Bread wheat (Triticum aestivum L.) gene pool was analyzed with 117 microsatellite markers scattered throughout A, B, and D genomes. Ninety microsatellite markers were giving 1620 polymorphic alleles in 55 different bread wheat genotypes. These genotypes were found to be divided into three subgroups based on Bayesian model and Principal component analysis. The highest polymorphism information content value for the markers resides on A genome was estimated for wmc262 marker located on 4A chromosome with the polymorphism information content value of 0.960. The highest polymorphism information content value (0.954) among the markers known to be located on B genome was realized for wmc44 marker located on 1B chromosome. The highest polymorphism information content value for the markers specific to D genome was found in gwm174 marker located on 5D chromosome with the polymorphism information content value of 0.948. The presence of linkage disequilibrium between 81 pairwise SSR markers reside on the same chromosome was tested and very limited linkage disequilibrium was observed. The results confirmed that the most distant genotype pairs were as follows Ceyhan-99-Behoth 6, Gerek 79-Douma 40989, and Karahan-99-Douma 48114.