Evaluation of Elite Wheat Germ Plasm for Resistance to Tan Spot.

Tan spot, caused by Pyrenophora tritici-repentis, is a serious foliar disease of wheat (Triticum aestivum) in North America. Control of tan spot through management practices and fungicide application is possible; however, the use of resistant varieties is the most effective and economical means of controlling tan spot. This study was conducted to determine the disease reaction of 126 elite hard red spring, white, and durum wheat varieties and advanced breeding lines collected from the northern Great Plains of the United States and Canada to individual races/toxins of P. tritici-repentis. Seedling evaluation of the 126 genotypes was done under controlled environmental conditions with virulent races 2, 3, and 5 of P. tritici-repentis and toxins Ptr ToxA and Ptr ToxB. Based on disease reactions, two resistant varieties and two advanced breeding lines adapted to the northern Great Plains were found to be resistant to all the races and insensitive to the toxins tested. Additionally, six genetically diverse lines/varieties were identified to be resistant to tan spot; however, these sources may not be well adapted to the northern Great Plains. These results suggest that the wheat germ plasm contains a broad genetic base for resistance to the most prevalent races of P. tritici-repentis in North America, and the resistant sources identified in this study may be utilized in wheat breeding programs to develop tan spot resistant varieties.

Detection of QTL linked to Fusarium head blight resistance in Sumai 3-derived North Dakota bread wheat lines.

During the past decade Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe has resulted in severe grain yield and quality losses of wheat (Triticum aestivum L.) in the Northern Great Plains of the U.S. Given the complexity of breeding for FHB resistance, molecular markers associated with this trait will be valuable in accelerating efforts to breed resistant cultivars. The objective of this study was to identify molecular markers linked to quantitative trait loci (QTL) for FHB resistance in wheat using a set of lines obtained by several cycles of crossing to North Dakota adapted genotypes, which derived their resistance from cv. Sumai 3. Microsatellite markers spanning the wheat genome were used to screen parents and derived lines. Polymorphisms for parental alleles were compared to disease scores for Type II resistance. The probability of linkage between markers and introgressed resistance genes was calculated using a binomial probability formula based on the assumption that a molecular marker at a specific distance from the introgressed gene, in a near-isogenic line (NIL), will carry the donor-parent allele as a function of the distance between marker and gene and the number of backcrosses/selfs performed in deriving the NIL. Microsatellite loci Xgwm533 and Xgwm274 were significantly associated with QTL for FHB resistance.

Physical location of a HSP70 gene homologue on the centromere of chromosome 1B of wheat ( Triticum aestivum L.).

Cereal centromeres consist of a complex organization of repetitive DNA sequences. Several repetitive DNA sequences are common amongst members of the Triticeae family, and others are unique to particular species. The organization of these repetitive elements and the abundance of other types of DNA sequences in cereal centromeres are largely unknown. In this study, we have used wheat-rye translocation lines to physically map 1BL.1RS centromeric breakpoints and molecular probes to obtain further information on the nature of other types of centromeric DNA sequences. Our results, using the rye-specific centromeric sequence, pAWRC.1, indicate that 1BL.1RS contains a small portion of the centromere from 1R of rye. Further studies used molecular markers to identify centromeric segments on wheat group-1 chromosomes. Selected RFLP markers, clustered around the centromere of wheat homoeologous group-1S chromosomes, were chosen as probes during Southern hybridization. One marker, PSR161, identified a small 1BS segment in all 1BL.1RS lines. This segment maps proximal to pAWRC.1 in 1BL.1RS and on the centromere of 1B. Sequence analysis of PSR161 showed high homology to HSP70 genes and Northern hybridization showed that this gene is constitutively expressed in leaf tissue and induced by heat shock and light stimuli. The significance of this work with respect to centromere organization and the possible significance of this HSP70 gene homologue are discussed.

Identification of 'Amigo' and 'Kavkaz' translocations in Ohio soft red winter wheats (Triticum aestivum L.).

One cultivar ('GR876') and two advanced Ohio soft red winter wheat lines ('OH413' and 'OH414'), with 'Kavkaz' in their pedigrees, were examined for the presence of the 'Kavkaz,' 1RS/1BL rye/wheat chromosome translocation. Another advanced line ('OH416'), with 'Amigo' in its pedigree, was examined for the presence of the 'Amigo,' 1RS/1AL translocation. Only two satellited chromosomes were observed in most mitotic root-tip cells from 'GR876,' 'OH413,' and 'OH414,' compared to four in most cells from 'OH416.' Heteromorphic bivalents were observed in most PMCs from hybrids produced by crossing 'GR876,' 'OH413,' and 'OH414' as females to 'Chinese Spring.' No heteromorphic bivalents were observed in PMCs from 'OH416' x 'Chinese Spring' hybrids. When 'GR876' and the Ohio lines were hybridized with 'Chinese Spring' dimonotelosomic-1B, telosomic trivalents, consisting of the short- and longarm telosomes paired with chromosome 1B, were only observed in PMCs from 43-chromosome hybrids involving 'OH416.' The long-arm telosome paired with the translocation chromosome, while the short-arm telosome remained unpaired in all other 43-chromosome hybrids. Separation of gliadin proteins from 'GR876' and the Ohio lines by PAGE revealed that secalin bands for 'GR876,' 'OH413,' and 'OH414,' migrated similarly to the secalins for 'Kavkaz.' Bands for 'OH416,' identified as possible secalins, migrated similarly to those for 'Amigo.' Cultivar 'GR876' and advanced Ohio soft red winter wheat lines 'OH413' and 'OH414' carry the 'Kavkaz' translocation, while 'OH416' carries the 'Amigo' translocation.