The bread wheat genome harbors a high content of repetitive DNA, which is amenable to detection and characterization using fluorescence in situ hybridization (FISH) karyotyping.  An integrated genetic map was derived from a recombinant inbred population bred from a cross between a synthetic hexaploid wheat and a commercial Chinese bread wheat cultivar, based on 28 variable FISH sites and >150 000 single nucleotide polymorphism (SNP) loci.  The majority (20/28) of the variable FISH sites were physically located within a chromosomal region consistent with the genetic location inferred from that of their co-segregating SNP loci.  The eight exceptions reflected the presence of either a translocation (1R/1B, 1A/7A) or a presumptive intra-chromosomal inversion (4A).  For eight out of the nine FISH sites detected on the Chinese Spring (CS) karyotype, there was a good match with the reference genome sequence, indicating that the most recent assembly has dealt well with the problem of placing tandem repeats.  The integrated genetic map produced for wheat is informative as to the location of blocks of tandemly repeated DNA and can aid in improving the quality of the genome sequence assembly in regions surrounding these blocks.

 

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a serious disease in bread wheat (Triticum aestivum L.).  Identification and use of adult plant resistance (APR) resources are important for stripe rust resistance breeding.  Bread wheat line C33 is an exotic germplasm that has shown stable APR to stripe rust for more than 10 years in Sichuan Province of China.  Here, 183 recombinant inbred lines (RILs) derived from the cross between C33 and a susceptible line X440 were genotyped with diversity arrays technology (DArT) markers to identify resistance quantitative trait locus (QTL).  Field trials were conducted in five years at Chengdu and Xindu of Sichuan Province, using maximum disease severity (MDS) as stripe rust reaction phenotypes.  A total of four quantitative trait loci (QTLs) were detected, respectively designed as QYr.saas-3AS, QYr.saas-5AL, QYr.saas-5BL, and QYr.saas-7DS, explaining 4.14–15.21% of the phenotypic variances.  QYr.saas-5BL and QYr.saas-7DS were contributed by C33.  However, the level for stripe rust resistance contributed by them was not strong as C33, suggesting the presence of other unidentified QTLs in C33.  QYr.saas-7DS corresponded to Yr18 and QYr.saas-5BL remains to be formally named.  The RIL lines carrying combinations QYr.saas-5AL, QYr.saas-5BL, and QYr.saas-7DS showed comparability resistance with C33.  The present study provides resources to pyramid diverse genes into locally adapted elite germplasm to improve the stripe rust resistance of bread wheat.