Molecular cytogenetic and agronomic characterization of advanced generations of wheat x triticale hybrids resistant to Diuraphis noxia (Mordvilko): application of GISH and microsatellite markers.

The PI 386148 triticale from Russia is among the highest resistant line to the Russian wheat aphid (RWA) (Diuraphis noxia (Mordvilko)). This triticale line was used as the male parent in crosses with Lamar wheat (Triticum aestivum L.). The F1 plants were backcrossed to Lamar wheat. The progenies were tested for RWA biotype 1 reaction for at least eight backcross and selfing generations. Five lines from these selections were identified for their resistance to the RWA and their seeds were increased for agronomic and other characterizations. Molecular and cytological analyses of these lines were performed using genomic in situ hybridization and rye chromosome-specific microsatellites markers. Three lines were cytologically stable and carried a pair of rye (Secale strictum (C. Presl) C. Presl) chromosomes as disomic addition lines of 1R. One line was unstable and showed a moderate level of mixoploidy with monosomic additions of 1R. Duplication of rye chromosome 1R was also identified. No wheat-rye chromosome interchange was detected, suggesting little homology between S. strictum and T. aestivum chromosomes. Specific microsatellite primers were used to identify the rye chromosomes present in each line. One rye chromosome, 1R, from the donor species contains genes for RWA resistance. Grain yield and test weight of three of the lines were similar to some adapted released wheat varieties under stress conditions.

Evaluation of Resistance of Winter Wheat to Fusarium acuminatum by Inoculation of Seedling Roots with Single, Germinated Macroconidia.

Fusarium acuminatum is one of the causal agents of dryland root rot of winter wheat in Colorado. The effect of F. acuminatum seedling root infection, recorded at heading, on winter wheat cultivars Sandy and CO84 was investigated in the greenhouse. Winter wheat seeds were surface disinfested, germinated, and vernalized. Vernalized seedling roots were inoculated by placing a single, germinated macroconidium of F. acuminatum on the largest root. Inoculated and non-inoculated vernalized seedlings were transplanted to pots and half the plants subjected to water stress. Inoculated plants had significantly lower survival rates and, at maturity, lower relative leaf water content, fewer tillers, shorter plant height, and higher cell ion leakage than non-inoculated plants. Wheat cultivars differed significantly for most traits studied. CO84 was susceptible whereas Sandy was more tolerant of the pathogen, particularly under water stress conditions. These results suggest that relative leaf water content, cell ion leakage, and to some extent seedling survival may be useful attributes for evaluation of resistance to the root rot pathogen.

Detection of a 2.6 kb single/low copy DNA sequence on chromosomes of wheat (Triticum aestivum) and rye (Secale cereale) by fluorescence in situ hybridization.

A fluorescence in situ hybridization procedure was developed to detect a 2.6 kb single/low copy DNA sequence on chromosomes of wheat (Triticum aestivum) and rye (Secale cereale). The probe, pTtksuI26, was from the wheat genomic library generated at Kansas State University and was labeled with Bio-11-dUTP by nick translation. The signal was amplified by a protocol of avidin-FITC (fluorescein isothiocyanate), biotinylated goat anti-avidin antibody, avidin-FITC. Two rye chromosomes and several wheat chromosomes showed the hybridization sites. The multiple sites in wheat are probably the result of the homoeologous nature of the three genomes in wheat. The ability to detect the hybridization signal of a small single/low copy DNA sequence is a very important step towards the physical mapping of plant genomes. This procedure might also be useful for studying the genomic relationship among wheat relative species.

An optimized fluorescence in situ hybridization procedure for detecting rye chromosomes in wheat.

In situ hybridization with an interspersed repeat clone from rye, pSc119, was shown to be useful for detecting rye chromosomes introduced into wheat. However, since pSc119 also shows strong hybridization to a few sites in certain wheat chromosomes, small rye chromosome segments added to wheat may be difficult to detect. In this study, detection of rye chromosomes present in triticale and triticale X wheat hybrids was accomplished with the use of a subfragment from pSc119 (pSc119.1) whose sequence is dispersed throughout the rye chromosomes and only weakly cross-hybridizes to a few telomeric and centromeric regions of wheat. The in situ hybridization conditions were optimized to readily distinguish rye chromosomes from wheat chromosomes without the need for intensive analysis of hybridization patterns. Rye chromosomes were readily detected using fluorescence in situ hybridization. Fluorescence detection provided increased sensitivity over enzymatic detection and allowed signals to be amplified with repeated use of biotinylated anti-avidin antibody and avidin-FITC. Detection of rye chromatin was further optimized by doubling the probe concentration. Finally, double exposure photography of the same cell with two different filters provided another means to further increase the contrast between rye and wheat chromosomes.